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REVIEW PAPER
Nutritional strategies for alleviating the detrimental effects of heat
stress in dairy cows: a review
Li Min
1,2
&Dagang Li
1,2
&Xiong Tong
1,2
&Xuemei Nan
3
&Diyun Ding
1,2
&Bin Xu
1,2
&Gang Wang
1,2
Received: 18 October 2018 / Revised: 29 March 2019 /Accepted: 5 June 2019
#ISB 2019
Abstract
Heat stress responses negatively impact production performance, milk quality, body temperature, and other parameters in dairy
cows. As global warming continues unabated, heat stress in dairy cows is likely to become more widespread in the future. To
address this challenge, researchers have evaluated a number of potentially available nutritional strategies, including dietary fat,
dietary fiber, dietary microbialadditives, minerals, vitamins, metal ion buffer, plant extracts, and other anti-stress additives. In this
paper, we discuss the evidence for the efficacy of these nutritional strategies aimed at alleviating the detrimental effects of heat
stress in dairy cows. It was comprised of the treatment (dosage and usage), animal information (lactation stage and number of
dairy cows), THI value (level of heat stress), duration of exposure, the changes of feed intake and milk yield (production
performance), the changes of milk protein and milk fat (milk quality), the changes of rectal temperature and respiration rate
(body temperature), other indices, and reference resources. The results of these studies are presented with statistical justification
in the tables. In total, the 49 kinds of dietary interventions derived from these eight types of nutritional strategies may provide an
appropriate means of mitigating heat stress on a particular dairy farm based on the explanation of the results.
Keywords Heat stress .Dairy cows .Nutritional strategies .Improvement
Abbreviations
AA Amino acids
ADF Acid detergent fiber
CP Crude protein
DCAD Dietary cation-anion difference
DIM Days in milk
ECM Energy-corrected milk
FCM Fat-corrected milk
HSP Heat shock protein
IL Interleukin
NDF Neutral detergent fiber
NEFA Non-esterified fatty acid
OM Organic matter
THI Temperature humidity index
TMR Total mixed ration
TNFαTumor necrosis factor α
Introduction
As global warming continues unabated, the prevalence of heat
stress in animals is projected to increase in terms of frequency,
duration, and severity (Min et al. 2017). Heat stress responses
are now regarded as an expensive problem in the animal hus-
bandry of many species around the world. In the dairy industry,
dairy cows are highly susceptible to heat stress (Bernabucci
et al. 2014). Heat stress responses negatively impact the body
temperature, health, and a variety of productivity traits of dairy
cow, including the increasing of rectal temperature and respira-
tion rate and the decreasing of feed intake, milk production,
milk quality, and reproductive performance (Atrian and
Shahryar 2012). Moreover, dairy cows can even succumb
Li Min and Dagang Li contributed equally to this work.
*Gang Wang
wanggang@gdaas.cn
1
State Key Laboratory of Livestock and Poultry Breeding, Institute of
Animal Science, Guangdong Academy of Agricultural Sciences,
Guangzhou 510640, People’sRepublicofChina
2
Guangdong Key Laboratory of Animal Breeding and Nutrition,
Institute of Animal Science, Guangdong Academy of Agricultural
Sciences, Guangzhou 510640, People’s Republic of China
3
State Key Laboratory of Animal Nutrition, Institute of Animal
Science, Chinese Academy of Agricultural Sciences,
Beijing 100193, People’sRepublicofChina
International Journal of Biometeorology
https://doi.org/10.1007/s00484-019-01744-8
during the hot summer, the number of deaths rising sharply with
the increasing of THI value (level of heat stress) (Vitali et al.
2009). Therefore, heat stress represents a significant financial
burden (St-Pierre et al. 2003) that may impede the further de-
velopment of the dairy industry. Thus, methods of effectively
alleviating the negative effects of heat stress that will also im-
prove production performance are urgently required.
At present, advances in genetic, managerial, and nutritional
strategies have been applied to mitigate the detrimental effects
of heat stress in dairy cows. It has traditionally been consid-
ered that cooling systems (shades, ventilation and spray, and
fans), assisted with nutritional strategies, are preferentially
recommended to be used in heat-stressed dairy cows. The
objective of this paper is to assess the efficacy of a range of
successful dietary manipulations (nutritional strategies) that
have been used in heat-stressed dairy cows in recent years
(Tables 1,2,3,4,5,6,7,and8). By considering a wide range
of such nutritional strategies, we aim to identify clues or per-
spectives that will enable the selection of the most appropriate
methodology for particular dairy farms to improve cow health
and productivity during heat stress.
Nutritional strategies to ameliorate heat
stress in dairy cows
Eight types of nutritional strategies are introduced in the fol-
lowing section, including dietary fat, dietary fiber, dietary mi-
crobial additives, minerals, vitamins, metal ion buffer, plant
extracts, and other anti-stress additives.
Dietary fat
During heat stress, a significant reduction in feed intake in
dairy cows results in negative energy balance, during which
energy intake cannot meet the requirement for lactation. The
traditional approach to this problem is the supplementation of
the diet with additional fat to ameliorate the energy deficit and
reduce thermogenesis (because fat generates less heat incre-
ment than dietary carbohydrate or protein) (Wang et al. 2010).
Specifically, a previous study reported that a supplement of
3% unprotected fat had been advocated for use during hot
summers (Drackley et al. 2003). Feeding of a higher energy
diet resulted in greater circulating NEFA concentrations,
reflecting a diminution in the energy deficit of heat-stressed
Holstein dairy cows. As a consequence, milk yield was sig-
nificantly increased from 28.5 to 30.4 kg/day, but milk fat
content was reduced (P< 0.05). Presumably, supplementation
with unprotected fat interfered with ruminal fermentation, de-
creasing the ruminal acetate to propionate ratio and therefore
milk fat synthesis. Thus, it may be preferable to use a form of
protected fat, such as saturated fatty acid, hydrogenated fish
fat, fatty acid calcium salts, or oil seeds.
Palmitic acid is a lipid form that is not fermented in the
rumen,andwhenthiswasfedtoearly Holstein lactation dairy
cows at approximately 450 g/cow/day during the summer
(Warntjes et al. 2008),milkyieldtendedtobehigher(36.69
versus 38.04 kg/day, P= 0.07) and milk true protein content
was significantly higher (1.08 versus 1.13 kg/day, P< 0.05).
This approach did increase the proportion of C16:0 in the milk
fatty acids, but the positive effects of this supplement on milk
production outweighed the negative effect on fatty acid com-
position of the milk. Subsequently, the effects of diet consisting
of supplemental saturated fatty acids (contained 1.3% C14:0,
54% C16:0, 34% C18:0, 8% C18:1, 1.2% C18:2, and 0.6%
other fatty acids) were evaluated in heat-stressed mid-lactation
Holstein dairy cows (Wang et al. 2010). The feeding of a 1.5%
saturated fatty acid supplement was associated with a reduction
in rectal temperature during the hottest part of the day (14:00 h),
an increase in milk yield from 26.4 to 28.6 kg/day, and im-
provements in milk composition with regard to fat, protein,
and lactose content (P< 0.05). A remarkable amount of meta-
bolic heat was saved by energetically replacing fermentable
carbohydrates with supplemental saturated fatty acids.
Hydrogenated fish fat is another type of dietary fat supple-
ment that is not degraded in the rumen and is used for dairy
cows in countries where fishmeal is produced. Dietary supple-
mentation with 200 g/cow/day hydrogenated fish fat in graz-
ing Holando Argentino dairy cows in summer produced a
significant increase in milk production from 23.9 to 26.4 l/
cow, as well as improvements in milk protein and fat content
(P< 0.05) (Gallardo et al. 2001). The authors concluded that
hydrogenated fish fat would be a good ingredient to sustain
high productivity in grazing dairy cows during heat stress.
Another alternative that had been tried was supplementa-
tion with 300 g/cow/day (1.5% of diet) calcium salts of fatty
acids, and although this had no effect on milk yield in heat-
stressed Israeli-Holstein dairy cows, the use of this method to
increase the energy density of dairy cow diet dramatically
enhanced milk protein and the efficiency of milk yield per
kg feed intake, while reducing metabolic heat production from
26.4 to 25.1 Mcal/day (P< 0.05) (Moallem et al. 2010). In
brief, it was effective at increasing metabolic and production
efficiency in heat-stressed dairy cows. Furthermore, Serbester
et al. (2005) found that feeding with 2.54% calcium salts of
fatty acids in the diet would increase 4% FCM and milk fat
yield (P< 0.05) of mid-lactation Holstein dairy cows during
summer. In addition to its effect on production variables in
heat-stressed dairy cows, supplementation with dietary fat
can enhance the immune responses of cows exposed to heat
stress. Another previous study demonstrated that fat supple-
mentation using 6.5% whole flaxseed during heat stress led to
higher titers of Ig G (P< 0.05) in Italian Friesian cows, sug-
gesting an improvement in humoral responses. Furthermore,
Int J Biometeorol
Table 1 The efficacy of dietary fat for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal
information
THI value Duration
of exposure
(days)
Feed
intake
Milk yield
(control value)
Milk
protein
Milk fat Rectal
temperature
Respiration
rate
Other indices References
3% unprotected fat 154 DIM (n=9)
and 167 DIM
(n=9)
Average 68 to 71 28 + 6.67% (28.5 kg/day) −5.43% +Circulating
NEFA
Drackley et al.
(2003)
450 g/cow/day
palmitic acid
Early lactation
(n= 324)
Ave ra ge 60 t o 84
a
35 + 3.68% (36.69 kg/day)* + 4.63% +C16:0 in milk
fatty acids
Warntjes et al.
(2008)
1.5% saturated
fatty acids
184 DIM
(n=48)
72.2 at 07:00 h, 84.3
at 14:00 h, and
76.6 at 22:00 h
63 + 7.69% (26.4 kg/day) + 18.96% + 5.08% −2.04% at
14:00 h
+Milk lactose
content
Wan g et al .
(2010)
200 g/cow/day
hydrogenated
fish fat
Mid-lactation
(n=32)
Ave ra ge 72 .9
(63.14 to 77.3)
63 + 10.5% (23.9 l/cow) + 11.2% + 10.0% Gallardo et al.
(2001)
300 g/cow/day
calcium salts of
fatty acids
158 DIM
(n=42)
Average 76.8 77 + 3.0% +Efficiency of
milk yield/feed
intake
−Metabolic heat
production
Moallem et al.
(2010)
2.54% calcium salts
of fatty acids
150 DIM
(n=8)
Average 69 to 80 21 + 17.1% + 4% FCM Serbester et al.
(2005)
6.5% whole flaxseed 100 DIM
(n=16)
Average above 72,
maximum
exceeded 88
84 +Ig G, −IL-10 Caroprese et al.
(2009)
Net energy for
lactation of
6.95 MJ/kg
169 DIM
(n=25)
Average74.5to82.6 45 −3.32% + 4.53% (26.5 kg/day)* + 23.3% −0.95% at
14:00 h
−7.30% at
14:00 h
+FCM and milk
energy
Yan e t a l .
(2016)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
a
THI was calculated using [0.8 × ambient temperature (°C)] + [(% relative humidity/100) × (ambient temperature −14.4)] + 46.4; *P≤0.1; +, significantly higher; −, significantly lower; blank space, no
significant difference
Int J Biometeorol
Table 2 The efficacy of dietary fiber for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal information THI value Duration
of exposure
(days)
Feed
intake
Milk yield
(control value)
Milk
protein
Milk fat Rectal
temperature
Respiration
rate
Other indices References
16.5% corn silage
component
replaced with
soy hulls
125 DIM (n= 42) Approximately
average 68 to 83
a
42 + 6.06% + 6.50% +In vitro OM and NDF
digestibilities, feed
intake per meal and meal
duration, 4% FCM, and
economically corrected
milk yield
Halachmi et al.
(2004)(36.3 kg/day)
28.9% dietary NDF Prepartum (3 weeks)
and postpartum (5
weeks) (n=30)
Average 77.7 to
86.8
56 + 26.5% + 10.3% +Calf birth weights and
4% FCM
Kanjanapruthipong
et al. (2010)(26.3 kg/day)
12% shredded beet
pulp instead of
corn silage
126 DIM (n=4) and
121 DIM (n=4)
Exceeded 68 for
19 h/day, 70 for
16 h/day, and 72
for 13 h/day
21 + 6.23% + 8.62% +Milk lactose content and
neutral detergent
insoluble CP, −Rumen
pH*, rumen concentration
of ammonia nitrogen and
milk concentration of urea
Naderi et al.
(2016)(38.5 kg/day)
TMR plus 27%
crushed corn
248.4 DIM (n= 24) 65.4 to 79.0 29 + 6.19% −14.0% −0.51% Gonzalez-Rivas
et al. (2018)(19.4 kg/day)(76% of the days
had average
exceeded 72)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
a
THI was calculated using [0.8 × ambient temperature (°C)] + [(% relative humidity/100) × (ambient temperature −14.4)] + 46.4; *P≤0.1; +, significantly higher; −, significantly lower; blank space, no
significant difference
Int J Biometeorol
Table 3 The efficacy of dietary microbial additives for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal
information
THI value Duration of
exposure
(days)
Feed
intake
Milk yield
(control
value)
Milk
protein
Milk fat Rectal
temperature
Respiration
rate
Other indices References
60 g/cow/day
yeast culture
105 DIM
(n=38)
NA, temperature
exceeded 32 °C
(51 days)
84 + ECM/feed intake Schingoethe
et al. (2004)
30 g/day yeast
culture
20 to 140
DIM
(n=723)
Average above 72,
maximum
above 81
Approximately
120
+ 2.84% + 2.52% +Milk lactose yield Bruno et al.
(2009)(42.2 kg/day)
240 g/day yeast
culture
204 DIM
(n=81)
Average 76.6 90 + 3.37% −0.77% at
14:30 h*
+Net energy balance
and feed efficiency
Zhu et al.
(2016)(68 to 86) (20.8 kg/day)
−Concentrations of
milk urea nitrogen
15 g/day yeast
culture
234 DIM
(n=32)
Average 72.7 35 −4.43% −0.74% at
15:00 h
−7.18% at
07:30 h,
−8.09% at
15:00 h
−Skin temperature Dias et al.
(2018)(exceeded 68 was
92.2%)
0.25 g/kg of live
yeast (10
10
cfu/g)
per feed intake
114 DIM
(n=42)
Average 69.4
(at morning) to
79.3 (at
afternoon)
91 + 2.49% + 4.13% + 7.08% + 4% FCM, milk lactose
concentration, and
feed efficiency
Moallem et al.
(2009)(36.3 kg/day)
4 g/day live yeast
(1.5 × 10
10
cfu/g)
145 DIM
(n=56)
Average above 79 35 + 5.30% +Apparent digestibility
of NDF
Dehghan-Banadaky
et al. (2013)
10 g/day live yeast
(25 × 10
10
cfu live
cells and 5 × 10
10
cfu dead cells)
207 DIM
(n=28)
Average 71.8 70 + 5.12% −14.3% + ECM, 4% FCM, and
milk lactose secretion
Salvati et al.
(2015)(25.4 kg/day)(60.5to85.1,
exceeded 68
was 75.6%)
1 g/kg zymosan 60 DIM
(n=40)
Average 74.8 to
86.2
28 + 6.77% + 16.3% −8.99% at 18:30 h +Serum Ig A, IL 2, and
TNF αand hepatic Bcl
2/Bax-αratio
Sun et al. (2018)
(29.4 kg/day)
−Hepatic expression of
HSP 70
400 g/day live bacterial inoculants
(4 × 10
9
cfu of a combination
of Lactobacillus acidophilus
and Propionibacterium
freudenreichii)
120 DIM
(n=60)
NA, average
temperature was
25.6 °C, with a
low
of 17.4 °C and a
high of 35.1 °C
70 + 7.57% + 6.90% + ECM, apparent
digestibilities of CP and
NDF
Boyd et al. (2011)
(31.7 kg/day)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
*P≤0.1; +, significantly higher; −, significantly lower; blank space, no significant difference; NA, not mentioned
Int J Biometeorol
Table 4 The efficacy of minerals for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal information THI value Duration
of
exposure
(days)
Feed
intake
Milk yield
(control value)
Milk
protein
Milk
fat
Rectal
temperature
Respiration
rate
Other indices References
4 g/day chelated
chromium yeast
120 to 130 DIM
(n=160)
Averaged 78.6 70 + 8.59% + 11.3% Al-Saiady et al. (2004)
(29.87 kg/day)
6mg/head/day
dietary
chromium
3 weeks prepartum
through 12 weeks
postpartum (n= 120)
Averaged 90 to 99 105 + 10.5% + 11.9% +Percentage of pregnant
in the first 28 days of
breeding, −body
weight loss
Soltan (2010)
(averaged 31.2 kg/day)
0.31 and 0.5 mg/kg
selenium
Mid-lactation (n= 40) Averaged 72.23 and
maximum 79.09
140 +Glutathione peroxidase
activity
Calamari et al. (2011)
278 mg/kg selenium
yeast
n= 24 Averaged 75.9
a
124 + 2.46% −Somatic cell count Oltramari et al. (2014)
35 mg/kg Zn
hydroxychloride
plus 40 mg/kg
Zn-Met complex
99.7 DIM
(n=72)
Average 77 84 +Gene expression of
E-cadherin in
mammary tissue*
Weng et al. (2018)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
a
THI was calculated using [0.8 × ambient temperature (°C)] + [(% relative humidity/100) × (ambient temperature −14.4)] + 46.4; *P≤0.1; +, significantly higher; −, significantly lower; blank space, no
significant difference
Int J Biometeorol
Table 5 The efficacy of vitamins for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal information THI value Duration of
exposure
(days)
Feed
intake
Milk yield
(control value)
Milk
protein
Milk
fat
Rectal
temperature
Respiration
rate
Other indices References
100,000 IU/cow/
day VA
Late gestation at
45 days before
calving (n= 30)
59 to 78
a
90 +Immune function
and reproductive
performance
De et al. (2014)
(minimum temperature
was 15.21 °C,
maximum was 27.93 °C)
12 g/day rumen-
protected
niacin
145 DIM (n= 12) Above 72 for 12 of 24 h/d 14 −0.44% −Vaginal temperature Zimbelman
et al. (2010)
12 g/day rumen-
protected
niacin
166 DIM (n= 427) All above 68 and above 80
from15to30 days
60 −Core body temperature
and vaginal temperature
Zimbelman
et al. (2013)
12 g/day rumen-
protected
niacin
95 DIM (n= 24) From 70 to 80 for 24 h 21 +Water intake Rungruang
et al. (2014)
19 g/day rumen-
protected
niacin
53 DIM (n= 137)
and 188 DIM
(n= 185)
From 60.5 to 81.0 for 24 h 56 −9.61% at
09:00 h
−Panting scores at 04:30,
09:00, and 20:30 h
Wrinkle et al.
(2012)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
a
THI was calculated using [0.8 × ambient temperature (°C)] + [(% relative humidity/100) × (ambient temperature −14.4)] + 46.4; +, significantly higher; −, significantly lower; blank space, no significant
difference
Int J Biometeorol
Table 6 The efficacy of metal ion buffer for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal information THI value Duration of
exposure (days)
Feed
intake
Milk yield
(control value)
Milk
protein
Milk fat Rectal
temperature
Respiration
rate
Other indices References
2.2% NaCl 27 to 96 DIM (n= 48),
32 to 160 DIM
(n= 48)
Above 78 during
34 to 50% of the
period
67 and 42 + 9.78% + 12.6% + 4% FCM, −milk
production, 4% FCM,
fat and protein in mild
heat stress
Granzin and
Gaughan
(2002)
DCAD of 50 mEq/100 g
ofdrymatterwith15or
17% dietary CP
255 DIM (n= 32) Averaged 81.3
(maximum) and
71.7 (minimum)
42 −11.5% + 11.1% +Serum total A A
concentrations*, essential
AA concentrations and
ratio of essential AA: total
AA
Wildman
et al.
(2007a)
(31.4 kg/day)
in 17%
dietary CP
DCAD of 58 mEq/100 g
of dry matter
188 DIM (n= 42) Averaged 75.6 56 −Blood urea nitrogen Wildman
et al.
(2007b)
(70.3 to 80.8)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
*P≤0.1; +, significantly higher; −, significantly lower; blank space, no significant difference
Int J Biometeorol
Table 7 The efficacy of plant extracts for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal
information
THI value Duration
ofexposure
(days)
Feed
intake
Milk yield (control
value)
Milk protein Milk fat Rectal
temperature
Respiration
rate
Other indices References
0.25 g/kg Radix
bupleuri extract
75 DIM
(n= 40)
Average 78.2 at
06:00 h, 79.7
at 14:00 h, and
78.3 at22:00 h
70 + 9.09% + 8.23% + 8.99% + 10.8% −0.51% −8.12% Pan et al.
(2014)(31.6 kg/day)
50/100 g/day
Chinese herbal
medicine mixture
comprised of 18
herbs
230 DIM
(n= 40)
Average 74.5 42 + 3.68/1.84%
(16.3 kg/day) in
day 14,
+ 10.7/13.2%
(15.9 kg/day) in
day 28,
+ 11.3/14.6%
(15.1 kg/day)
in day 42
+ 2.60/4.91% in
day 14,
+ 4.96/6.71%
in day 28,
+ 4.65/7.27%
in day 42
+ 16.2/20.3%
in
day 28, +
19.0/17.6%
in day 42
+Leukocyte and
lymphocyte counts in
peripheral blood,
immune function,
−apoptosis rate of the
lymphocytes, serum
Baxlevel,IL1,Bax
and Bak mRNA
expression
Shan et al.
(2018)(69.4 to 79)
0.25% of Ascophyllum
nodosum
supplementation
138 DIM
(n= 32)
Average 71.7 56 −Core body temperature
andrumpskin
temperature
Pompeu
et al.
(2011)
(63.5 to 81.7)
a
2.27 kg/day yeast
combined with
essential oil
187 DIM
(n= 36)
Average 79 70 +Digestibility of ADF,
−milk fat percentage
Boyd et al.
(2011)(72.1 to 84.0)
4 g/day citrus extracts 200 DIM
(n= 310)
Approximately
60 to 70 for
9h/day,
approximately
70 to 80 for
15 h/day
56 +Comfort level and
mammary health
Havlin and
Robinson
(2015)
15 g/day dietary
betaine
101 DIM
(n= 32)
Average 78.68 56 + 2.63% + 5.27% + 4.35% +Milk lactose, plasma
cortisol, glutathione
peroxidase, superoxide
dismutase,
and malondialdehyde
levels
Zhang et al.
(2014)(27.7 kg/day)
57 and 114 mg/kg
betaine of body
weight
101 DIM
(n= 24)
Above 68 for
17 h/day
31 +Serum insulin and
glucose levels, the
expressions of
HSP 27 and HSP70
in vitro at high dose of
dietary betaine
Hall et al.
(2016)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
a
THI was calculated using [0.8 × ambient temperature (°C)] + [(% relative humidity/100) × (ambient temperature −14.4)] + 46.4;+, significantly higher; −, significantly lower; blank space, no significant
difference
Int J Biometeorol
Table 8 The efficacy of other anti-stress additives for the alleviation of the detrimental effects of heat stress in dairy cows
Treatment Animal
information
THI value Duration of
exposure
(days)
Feed
intake
Milk yield
(control
value)
Milk
protein
Milk fat Rectal
temperature
Respiration
rate
Other indices References
450 mg/day
monensin
89 DIM
(n= 34)
Peaking at 82 for
2 h/day and grad-
ually declined un-
til 73
18 −13.1% −4.56% −4.30% + 1.31% at 06 :00 h,
+ 1.02% at
15:00 h, + 0.70%
at 18:00 h
+ 14.3% at
06:00 h,
+9.98%at
18:00 h
+Feed efficiency and
whole body glucose
rate of appearance per
unit of feed intake
Baumgard
et al.
(2011)
40 mg/kg
γ-aminobutyric
acid of dry matter
141 DIM
(n= 60)
Average 78.4 at
07:00 h, 80.2 at
14:00 h, and
78.7 at 22:00 h
70 + 7.08% + 6.39% + 4.58% + 10.1% −0.48% at 07:00 h,
−0.45% at
14:00 h, −0.43%
at 22:00 h
+Milk lactose Cheng et al.
(2014)(31.3 kg/day)
56 g/cow/day
immunomodulatory
in lactation
167 DIM
(n= 32)
Average 74.2 56 + 7.14%* +Final body condition
score and mean serum
insulin concentrations*,
−vaginal temperature
mostly and mean somatic
cell count
Leiva et al.
(2017)(above 68 for 633 h
within a total of
672 h)
56 g/cow/day
immunomodulatory
in lactation
91 DIM
(n= 30)
Above 68 for
17 h/day
21 + 8.77%* −14.0% −0.57% at
14:00 h
−7.28% at
14:00 h,
−15.1% at
18:00 h
+Plasma adrenocorticotropic
hormone
Hall et al.
(2018)
−Plasma cortisol during
acute heat stress
56 g/cow/day
immunomodulatory
during the dry period
The dry period
and early in
lactation
(n=36)
Above 68 Approximately
120
+12.8% −9.72% +Body weight Fabris et al.
(2017)(35.9 kg/day)
56 g/cow/day
immunomodulatory
during the dry period
Calves
(n= 16)
Average 77 Approximately
46
−3.29%* +Birth weight*, lymphocytes,
neutrophil function, acute
phase protein production,
red blood cell counts,
hematocrit, and hemoglobin
Skibiel et al.
(2017)(above 68 for the
entire period)
Rumen-protected capsule
consisted of minerals
and vitamins
21 days before
calving to
63 DIM
(n= 50)
Average 71.43 and
maximum 77.7
84 + 4.81% + 6.2% + 7.55% +Solid non-fat percen tage and cumula-
tive pregnancy
at fifth artificial insemination, −the
milk linear somatic cell count score
and days open (calving to concep-
tion)
Khorsandi
et al.
(2016)
(47.8 kg/day)*
0.13373 kg K
2
SO
4
,
0.02488 kg vitamin C,
0.021148 kg niacin, and
0.044784 kg
γ-aminobutyric acid
70 DIM
(n= 30)
Average 80 42 + 7.08% + 18.0% + 18.9% + ECM, -HSP 70, adrenoco rticotropic
hormone, and lactate dehydrogenase
in serum
Guo et al.
(2017)(above 75 for the
entire period)
(29.27 kg/day)
THI value below 68 belongs to no heat stress, range from 69 to 78 belongs to mild heat stress, range from 79 to 88 belongs to moderate heat stress, above 89 belongs to severe heat stress
*P≤0.1; +, significantly higher; −, significantly lower; blank space, no significant difference
Int J Biometeorol
IL-10 secretion was much lower in this study, suggesting that
flaxseed supplementation can assist cows in their immune
function by suppressing the secretion of Th2 cytokines in
hot environments (Caroprese et al. 2009). To sum up, fat sup-
plementations based on whole flaxseed would enhance im-
mune responses of dairy cows exposed to heat stress.
Twenty-five mid-lactation Holstein dairy cows were ran-
domly assigned to five groups (6.15, 6.36, 6.64, 6.95, and
7.36 MJ/kg) to determine the optimal dietary net energy for
lactation under heat stress condition (Yan et al. 2016). The
dietary net energy for lactation contents were adjusted by
changing the proportions of calcium fatty acid and other feed
ingredients. Results showed that feed intake decreased signif-
icantly with the elevated dietary net energy concentration
from 6.15 to 7.36 MJ/kg (P< 0.01). Milk fat content, FCM,
and milk energy were the highest (P< 0.05), and rectal tem-
perature and respiration rate at 14:00 h were the lowest
(P< 0.01) when the net energy concentration was 6.95 MJ/
kg, while milk yield tended to increase quadratically to
6.95 MJ/kg group (P= 0.08). On the basis of regression equa-
tion, the optimal dietary net energy for lactation in mid-
lactation dairy cows under heat stress might range from 6.83
to 6.92 MJ/kg (1.63 to 1.65 Mcal/kg) in this study.
Dietary fiber
Under conditions of heat stress, lactating dairy cows show
markedly lower feed intake and higher energy maintenance
requirements. A survival strategy to minimize the energy de-
ficiency is to increase energy input by replacing the TMR
roughage component with more readily digestible NDF of
non-roughage origin. High-quality dietary fiber tends to im-
prove feed digestibility and palatability and further increase
feed intake.
Halachmi et al. (2004) evaluated the effects of feeding be-
havior and productivity in heat-stressed Holstein dairy cows
when roughage NDF was replaced by soy hulls, which contain
readily digestible dietary fiber. In the experimental group, the
16.5% corn silage component was replaced with soy hulls,
reducing the roughage NDF from 18 to 12%, which was as-
sociated with a much higher in vitro OM and NDF digestibil-
ity (P< 0.05). Furthermore, feed intake per meal and meal
duration were significantly higher (P≤0.05). These feeding
behavior changes in heat-stressed dairy cows can effectively
increase the feeding times and ensure that TMR stay longer in
the feeding lane. The aforementioned changes also affected
production performance, with milk yield being raised from
36.3 to 38.5 kg/day, and milk fat content, 4% FCM, and eco-
nomically corrected milk yield being significantly higher in
heat-stressed dairy cows that were fed high-quality dietary
fiber (P= 0.05). In a subsequent study, cassava chips were
used to partly replace grass silage in heat-stressed dairy cows
(87.5% Holstein × 12.5% Sahiwal) for the 3 weeks before and
the 5 weeks after calving, so that dietary NDF values were
34.2%, 32.1%, and 28.9%, respectively (Kanjanapruthipong
et al. 2010). During the 3-week period before calving, feed
intake gradually increased (P< 0.01), which was accompa-
nied by a reduction in dietary NDF (10.2, 11.5, and 12.9 kg/
day, respectively). After parturition, calf birth weights, milk
yield, and 4% FCM were increased when the amount of
roughage NDF was decreased (P<0.05).
Beet pulp contains a high proportion of digestible NDF and
pectic substances, implying that it may increase nutrient intake
and thereby lead to an improvement of production perfor-
mance in dairy cows. To evaluate these possibilities, shredded
beet pulp was included in the diet of heat-stressed Holstein
dairy cows in place of corn silage (Naderi et al. 2016). The
dietary groups used in this study were as follows: 16% corn
silage, 8% corn silage and 8% beet pulp, 4% corn silage and
12% beet pulp, and 16% beet pulp. Substituting beet pulp for
corn silage increased the neutral detergent insoluble CP con-
tent of the diet, which tended to reduce mean rumen pH and
ruminal acetate and butyrate concentrations, while it increased
the ruminal propionate concentration. As a result, milk pro-
duction increased linearly (P= 0.03) (38.5, 39.3, 40.9, and
39.6 kg/day, respectively). Overall, substituting beet pulp for
corn silage at up to 12% in the diet of heat-stressed dairy cows
resulted in an optimal combination of higher milk yield, milk
protein, and milk lactose content (Naderi et al. 2016).
It is hypothesized that feeding slowly fermentable grains
would reduce the amount of heat released from fermentation
and digestion, which would ameliorate the physiological re-
sponses to heat stress and improve productivity in dairy cows
during the summer. Gonzalez-Rivas et al. (2018)established
that feeding TMR plus 27% crushed corn (a type of slowly
fermentable grain) to Holstein-Friesian dairy cows ameliorat-
ed the heat stress responses, as indicated by the improved milk
yield (19.4 versus 20.3 kg/day, P< 0.01) and lower rectal
temperature (39.1 versus 38.9 °C, P< 0.01), although there
was a decline in milk fat percentage (P<0.05).
Dietary microbial additives
Dietary microbial additives, such as yeast and yeast cultures,
have been widely used in dairy cows to increase feed intake
and feed efficiency, improve rumen fermentation and digest-
ibility, and ultimately increase milk production. Live yeast
might scavenge oxygen in the rumen to increase feed efficien-
cy. Yeast cultures might have growth factors produced by
Saccharomyces cerevisiae that improve lactation perfor-
mance. During summer, Holstein dairy cows were fed a diet
containing 60 g/cow/day Diamond V XP yeast culture (Cedar
Rapids, IA) (Schingoethe et al. 2004). As a result, feed effi-
ciency defined as ECM/feed intake was improved by 7% with
Int J Biometeorol
supplementing yeast culture in the diet of heat-stressed dairy
cows (P< 0.05). However, the resulting change in milk pro-
duction did not reach statistical significance in this study.
Therefore, to further investigate the effect of feeding a yeast
culture on heat stress, 723 Holstein dairy cows (20 to 140
DIM) were randomly assigned to a control diet or one con-
taining 30 g/day of a Saccharomyces cerevisiae yeast culture
during a period of heat stress (Bruno et al. 2009). The results
indicated that supplementation with a yeast culture improved
lactation performance in heat-stressed dairy cows, because
milk yield was increased from 42.2 to 43.4 kg/day and milk
protein and lactose yield were also higher (P< 0.05). Zhu
et al. (2016) found that the addition of Saccharomyces
cerevisiae fermentation products had dose-dependent positive
effects. Rectal temperature at 14:30 h tended to decrease lin-
early (P= 0.07) in Holstein dairy cows supplemented with
120 or 240 g/day yeast culture compared with control cows,
while milk yield increased linearly (P= 0.02) with higher
levels of supplementation (20.8, 21.3, and 21.5 kg/day, re-
spectively). Net energy balance increased linearly alongside,
while milk urea nitrogen decreased linearly with higher levels
of supplementation (P< 0.01). Therefore, feed efficiency
(milk yield/feed intake) was the highest in dairy cows fed a
diet supplemented with 240 g/day Saccharomyces cerevisiae
fermentation products. Furthermore, the supplement also im-
proved the feed efficiency and thermal comfort of dairy cows
in late lactation during the summer. The results revealed that
15 g/day yeast culture supplementation (Saccharomyces
cerevisiae) in heat-stressed Holstein dairy cows improved
feed efficiency by reducing feed intake (19.4 versus 20.3 kg/
day, P< 0.05) at similar milk yield and increased body heat
loss (P< 0.05) by reducing rectal temperature (15:00 h), skin
temperature, and respiration rate (07:30 h and 15:00 h) (Dias
et al. 2018).
In addition to yeast culture, live yeast is also reported to be
beneficial for dairy cows during the hot season. Moallem et al.
(2009) reported that the feeding of 0.25 g/kg of live yeast
(10
10
cfu/g) per feed intake increased daily dry matter intake
by 2.49% and increased milk yield from 36.3 to 37.8 kg/day
(P< 0.01). The 4% FCM, milk lactose concentration, milk fat
yield, and the feed efficiency of using dry matter to produce
4% FCM were also greater when live yeast was used to sup-
plement the diet of Israeli-Holstein dairy cows (P< 0.05).
Thus, it can be concluded that live yeast supplementation in
heat-stressed dairy cows increases feed intake and conse-
quently enhances their productivity and efficiency.
Nevertheless, no prominent improvement in milk production
and feed intake was observed in Holstein dairy cows fed with
4 g/day live yeast (1.5 × 10
10
cfu/g) during hot summer con-
ditions (Dehghan-Banadaky et al. 2013). Regardless, the
higher milk fat percentage and apparent digestibility of NDF
measured in this study (P< 0.05) suggests that feeding live
yeast may increase dietary cell wall digestibility and improve
milk composition (milk fat percentage) in heat-stressed dairy
cows. According to a recent study, a diet containing 10 g/day
live yeast (25 × 10
10
cfu live cells and 5 × 10
10
cfu dead cells)
increased milk production from 25.4 to 26.7 kg/day and also
increased ECM, 4% FCM, and milk lactose secretion of
Holstein dairy cows under heat stress (P≤0.05) (Salvati
et al. 2015). In addition, heat-stressed dairy cows consuming
yeast supplements had consistently lower respiratory rate
throughout the experiment (P=0.02).
Zymosan, which is extracted from yeast, has protective
effects against heat stress-induced immunosuppression and
apoptosis in Holstein dairy cows (Sun et al. 2018). For usage,
1 g/kg zymosan mixed into the TMR for heat-stressed dairy
cows increased feed intake (19.2 versus 20.5 kg/day, P<0.01)
and milk yield (from 29.4 to 34.2 kg/day, P<0.01),decreased
respiration rate at 18:30 h (P< 0.01), and also increased serum
Ig A, IL-2, and TNF-αconcentrations, as well as hepatic Bcl-
2/Bax-αratio, and decreased hepatic HSP70 expression
(P< 0.05), suggesting the amelioration of immune and stress
responses.
With the exception of yeast and yeast cultures, the addition
of 400 g/day live bacterial inoculants (4 × 10
9
cfu of a combi-
nation of Lactobacillus acidophilus and Propionibacterium
freudenreichii) improved milk yield (31.7 versus 34.1 kg/
day, P< 0.01), milk protein yield, and ECM (P< 0.05) for
Holstein dairy cows subjected to heat stress (Boyd et al.
2011). Furthermore, improvement in the apparent digestibility
of CP and NDF (P< 0.05) was observed after heat-stressed
dairy cows were fed this supplement.
Minerals
Minerals play an important role in maintaining normal phys-
iological functions in animals. However, heat stress responses
are thought to increase mineral loss as well as body fluid loss
by excretion in dairy cows. Hence, limiting changes in body
mineral balance by adding a trace mineral supplement to the
diet might alleviate the adverse effects of such a loss in heat-
stressed dairy cows.
Chromium (Cr) is widely used physiologically in a number
of oxidation states. The addition of 4 g/day chelated Cr yeast
to the diet increased feed intake and milk yield in heat-stressed
Holstein dairy cows from 19.56 to 21.24 kg/day and 29.87 to
33.24 kg/day (P< 0.01), respectively (Al-Saiady et al. 2004).
As further support for this phenomenon, 120 Holstein dairy
cows were used to assess the effects of dietary Cr supplemen-
tation (6 mg/head/day) on their production and reproductive
performance during heat stress (Soltan 2010). They were fed a
Cr-supplemented diet for 15 weeks, commencing 3 weeks
before calving, which resulted in better retention of body
weight and improved feed intake, such that their energy bal-
ance deficit after calving was ameliorated. In addition, Cr
Int J Biometeorol
supplementation markedly increased milk yield (P≤0.05), by
6.7%, 12.3%, and 16.5%, at 4, 8, and 12 weeks postpartum,
respectively. A trend towards an improvement in reproductive
performance was also observed, in the form of a higher rate of
conception during the first 28 days of breeding.
Selenium (Se) reduces the adverse impact of heat stress on
redox balance and metabolism, resulting in improved immune
function, milk quality, and dairy cow health (Sejian et al.
2012). It is worth noting that significant decreases in plasma
selenoprotein P, which contains most of the Se, occur in heat-
stressed dairy cows (Min et al. 2016). Diet supplementation
with Se can significantly raise plasma selenoprotein P and Se
concentrations (Hill et al. 2012), which might be a potential
mechanism to protect dairy cows against heat stress. Indeed,
the metabolic responses to heat stress can be partially amelio-
rated by feeding dietary Se to Italian Friesian dairy cows, as
evidenced by an increase in glutathione peroxidase activity in
whole blood (P< 0.01), implying an improvement in the an-
tioxidant system (Calamari et al. 2011). In a subsequent study,
the effects of organic (278 mg/kg Se yeast) and inorganic
(0.617 mg/kg sodium selenite) sources of Se in the diet of
heat-stressed dairy cows (Holstein-Friesian and Brown
Swiss) were evaluated with regard to milk production and
quality, mammary gland health, and physiological indicators
(Oltramari et al. 2014). Dairy cows that consumed organic Se
produced a higher percentage of milk fat and had a lower
somatic cell count (P= 0.01), suggesting that organic Se im-
proves milk quality and mammary gland health during heat
stress. Interestingly, although respiratory rate was lower in
cows fed with the inorganic Se, hair coat temperature was
lower in those fed with the organic Se (P<0.05).
Zinc (Zn) is an essential micronutrient that has been sug-
gested to improve the epithelial integrity of pigs under heat
stress condition (Sanz Fernandez et al. 2014). According to a
recent study, heat-stressed Holstein dairy cows fed with
35 mg/kg Zn hydroxychloride plus 40 mg/kg Zn-Met com-
plex tended to show higher levels of E-cadherin expression in
mammary tissue (P= 0.09), suggesting an improvement in the
integrity of the mammary epithelium (Weng et al. 2018).
Vitamins
Vitamins function as enzyme cofactors (coenzymes), partici-
pate in a variety of metabolic pathways as catalysts, and are
essential for the normal growth and development of a multi-
cellular organism. It is possible that the addition of vitamin
supplements to the diet of dairy cows might also contribute to
the relief of the negative effects of heat stress.
In an in vitro experiment, oocytes incubated at 41.0 °C, to
represent heat stress, were less likely to develop to the blasto-
cyst stage and generated fewer nuclei (Lawrence et al. 2004).
However, 5 μM retinol (vitamin A; VA) ameliorated the heat
stress-induced defects in the development of bovine oocytes
to the blastocyst stage. Following this up, pregnant dairy cows
(Karan-Fries, Tharparkar × Holstein-Friesian) in late gestation
that were kept in a semi-arid tropical environment were sup-
plemented with 100,000 IU/cow/day VA, which caused sig-
nificant increases in indicators of immune function, including
the phagocytic activity of blood neutrophils and plasma IL-8
concentration (P< 0.05). In addition, milk somatic cell count
was reduced and indices of reproductive performance (days
open and the number of services required per conception)
improved (De et al. 2014). As mentioned above, VA supple-
mentation around the peripartum period could boost the im-
munity and improve the reproductive performance of heat-
stressed dairy cows.
It has generally been assumed that heat stress causes oxi-
dative stress, which is accompanied by a reduction in the
plasma concentration of vitamin C (VC, an antioxidative vi-
tamin). Padilla et al. (2006) demonstrated that heat stress was
associatedwith a lower plasma VC concentration (P=0.04)in
lactating Holstein cows, implying that endogenous VC pro-
duction may be insufficient. However, it remained unclear
whether hypovitaminosis C adversely affected the productiv-
ity and health of lactating cows and thus whether dietary sup-
plementation with VC may be beneficial for lactating cows in
hot weather. More studies are necessary to investigate these
possibilities.
Niacin (vitamin B
3
) supplementation increases resistance
to heat stress by inducing greater cutaneous vasodilatation and
blood flow (Di et al. 1997). The greater cutaneous vasodilata-
tion after niacin supplementation is caused by prostaglandin D
produced by epidermal Langerhans cells, which acted on vas-
cular endothelial prostaglandin D2 receptors (Maciejewski-
Lenoir et al. 2006; Cheng et al. 2006). The increase in blood
flow after niacin supplementation is associated with an in-
crease in the sweating rate and evaporative heat loss from
the skin surface (Di et al. 1997). When rumen-protected niacin
was fed to Holstein cows (12 g/day), there was a small but
detectable reduction in the rectal and vaginal temperature dur-
ing heat stress compared with the control cows (Zimbelman
et al. 2010). A subsequent study of a large number of Holstein
dairy cows (n= 427) found that their core body and vaginal
temperature were moderately lower when they ingested 12 g/
day rumen-protected niacin (P< 0.05), whereas milk produc-
tion and milk components were inconsistently affected over
the whole trial period (Zimbelman et al. 2013). However,
another study of Holstein dairy cows exposed to moderate
heat stress in Arizona showed that 12 g/day rumen-protected
niacin did not improve thermotolerance but increased water
intake (P< 0.03) (Rungruang et al. 2014). To further evaluate
the effects of niacin on the body temperature of dairy cows
during heat stress, Wrinkle et al. (2012) conducted experi-
ments in early (53 DIM, n= 137) and mid-lactation Holstein
dairy cows (188 DIM, n= 185) and found that their respiration
Int J Biometeorol
rate was lower at 09:00 h (P= 0.02) and their panting scores
were lower at 04:30, 09:00, and 20:30 h (P≤0.01), after con-
sumption of niacin. Interestingly, supplementation with
rumen-protected niacin reduced the milk fat proportion in ear-
ly lactation, but increased it in mid-lactation, dairy cows.
These inconsistent effects on milk fat were analogous to those
identified by Zimbelman et al. (2013). Differences in milk fat
responses in early and mid-lactation cows are most likely trig-
gered by reduced plasma triglyceride production. Although a
reduction in plasma triglyceride production was also observed
in the mid-lactation cows, they produced less milk but con-
sumed a similar amount of dry matter. Dietary fat intake most
likely compensated for the reduced de novo synthesis
(Wrinkle et al. 2012).
Metal ion buffer
During heat stress, additional dietary Na
+
and K
+
(in the form
of a metal ion buffer) are required to compensate for a reduc-
tion in feed intake (when animals fail to meet the minimum
daily intake of Na
+
and K
+
) and losses due to greater sweating
in heat-stressed dairy cows (Sanchez et al. 1994). Another
rationale for increasing dietary metal ion buffer is to increase
urine Na
+
and K
+
excretion. Increases in these excretions are
coordinated to increases in bicarbonate ion excretion caused
by respiratory alkalosis when lactating cows are under heat
stress (West et al. 1991).
Forty-eight Holstein-Friesian dairy cows (27–96 DIM)
kept in a humid sub-tropical environment were allocated to
one of four groups that were fed diet supplemented with NaCl
at concentrations of 0, 1.1%, 2.2%, or 3.3% during summer in
experiment one (Maximum THI was ≥78 during 50% of the
experimental period) (Granzin and Gaughan 2002). These re-
sulted in significantly higher 4% FCM, fat, and protein in
cows fed with 2.2% NaCl than in the other groups
(P< 0.05). However, counter-intuitively, milk yield, 4%
FCM, fat, and protein were lower (P< 0.05) in cows (32–
160 DIM, n= 48) fed with 2.2% NaCl in experiment two
(Maximum THI was ≥78 during 34% of the experimental
period). Thus, the success of NaCl supplementation may de-
pend on the degree of heat stress being experienced. The ben-
eficial effect might be more noticeable in warm, humid con-
ditions (maximum THI was ≥78 during 50% of the experi-
mental period) than in milder conditions (maximum THI was
≥78 during 34% of the experimental period).
Dietary cation-anion difference (DCAD), calculated using
Na
+
,K
+
,andCl
−
concentrations, has a significant effect on
productivity and health status by influencing acid base bal-
ance (Hu and Murphy 2004). Wildman et al. (2007a)reported
that a DCAD of 50 mEq/100 g of dry matter in the diet of
Holstein dairy cows during heat stress would improve AA
availability for protein synthesis (serum total AA
concentrations (P< 0.1), essential AA concentrations, and
the ratio of essential AA: total AA (P< 0.05) were all higher)
because additional AA becomes available that would other-
wise be used for the maintenance of acid base balance. A
higher DCAD also reduced blood urea nitrogen in heat-
stressed Holstein dairy cows (P< 0.01), suggesting the possi-
bility that it enhanced microbial ammonia utilization for pro-
tein synthesis and ruminal N metabolism or utilization
(Wildman et al. 2007b).
Plant extracts
In recent years, significant research has focused on the use of
dietary plant extracts that have nutritional and medicinal value
to improve dairy cow production. Particular plant extracts
may have the potential to ameliorate the negative effects of
heat stress in dairy cows.
Radix bupleuri is widely known as an oriental folk medi-
cine, to which a number of pharmacological effects have been
ascribed, including diaphoretic, antipyretic, and immunomod-
ulatory effects (Ashour and Wink 2011). Pan et al. (2014)
assessed the effects of Radix bupleuri extract supplementation
(0, 0.25, 0.5, or 1.0 g/kg of the basal diet) on body temperature
and production variables in heat-stressed Holstein dairy cows.
During the experiment, average respiratory rate (65.6, 60.3,
and 67.4 versus 71.4 breaths/min) and rectal temperature
(39.1, 39.0, and 39.1 versus 39.3 °C) were significantly lower
(P< 0.01), and feed intake (22.8, 21.6, and 22.1 versus
20.9 kg/day, P< 0.05) and milk production (34.2, 33.4, and
32.4 versus 31.6 kg/day, P< 0.01) were significantly higher,
milk protein and fat yield were also improved (P<0.05) at
doses of 0.25, 0.50, and 1.0 g/kg. Taken together, the addition
of just 0.25 g/kg Radix bupleuri extract to the diet could
maximum mitigate the negative effects of heat stress on body
temperature and production in dairy cows. The significant
decrease in body temperature following Radix bupleuri ex-
tract supplementation may be due to the increasing of vasodi-
lation, which facilitates heat transfer to the skin via evapora-
tion. The improvement in milk production was probably not
only due to the increased feed intake, but also to the direct
mitigating effect of heat stress responses (decreased body tem-
perature), which provides more energy for production rather
than for homeothermy (Pan et al. 2014).
A fermented mixture of Chinese herbal medicines compris-
ing 18 herbs (including Radix rehmanniae preparata,Fructus
crataegi,Semen raphani,Radix et rhizoma rhei,Unguis sus
domestica,Radix astragali,Radix Codonopsis,Radix
angelicae sinensis,Rhizoma atractylodis,Pericarpium citri
reticulatae,Radix glycyrrhizae,Rhizoma chuanxiong,Herba
cistanches,Radix ophiopogonis,Radix paeoniae alba,
Cacumen platycladi,Artemisia capillaris thumb,and
Fructus gardeniae) had also been tested for its effects on
Int J Biometeorol
productivity and immune function in heat-stressed Holstein
dairy cows (Shan et al. 2018). The data clearly confirmed that
milk yield (16.3, 16.9, and 16.6 kg/day, respectively, in day 14
of the trial, 15.9, 17.6, and 18.0 kg/day, respectively, in day 28
of the trial, 15.1, 16.8, and 17.3 kg/day, respectively, in day 42
of the trial), milk fat, and protein content were greater
(P< 0.05) in 50 or 100 g/day of the mixture, when compared
with the group that did not receive the supplement. In addi-
tion, leukocyte and lymphocyte counts in peripheral blood
were higher and the lymphocyte apoptosis rate was lower
(P< 0.05). Serological and gene expression effects were also
observed, suggesting that the supplement could improve im-
mune function in heat-stressed dairy cows: serum concentra-
tions of Ig G, IL-2, IL-6, and Bcl-2 and mRNA expression
levels of IL-2, Bcl-2, and Bcl-xl were higher (P<0.05),while
serum Bax and mRNA expression levels of IL-1, Bax and Bak
were lower in the 100 g/day group (P< 0.05). Moreover, some
of these measurements were also significantly affected by
adding 50 g/day to the diet. The fermented mixture of
Chinese herbal medicines promoted milk production and im-
mune function in heat-stressed dairy cows.
A new product derived from Ascophyllum nodosum had
also been evaluated for its effectiveness in alleviating heat
stress in Holstein dairy cows (Pompeu et al. 2011). The inclu-
sion of 0.25% Ascophyllum nodosum in the diet had no effect
on milk production and reduced feed intake only in some
instances. However, the increases in core body and rump skin
temperature were less (P< 0.05) than in control animals as the
ambient temperature increased. Boyd et al. (2011)investigat-
ed the effect of a combination of yeast and another plant ex-
tract, consisting of essential oils derived from capsicum,
cinnamaldehyde, and eugenol, on milk production and the
apparent production efficiency of Holstein dairy cows during
a hot summer. Although they did not identify any differences
in body temperature and production parameters between the
treatment groups, the digestibility of ADF was improved
(P< 0.01), despite a reduction in milk fat percentage
(P< 0.01). Thus, additional researches are needed to examine
the potential role of Ascophyllum nodosum and essential oil
supplementation in heat-stressed dairy cows.
Citrus extracts contain a large amount of VC and have
beneficial effects on rumen fermentation (Benchaar and
Calsamiglia 2008). As described above, dairy cows demon-
strated VC deficiency in their plasma during heat stress
(Padilla et al. 2006). Therefore, the feeding of supplemental
citrus extracts might be beneficial in replacing the depleted
VC and improving production in heat-stressed dairy cows.
Havlin and Robinson (2015) reported that inclusion of citrus
extracts at 4 g/cow/day in the diet led to a higher proportion of
Holstein cows lying down rather than standing (P< 0.01),
suggesting an improvement in comfort level. In addition, this
level of supplementation improved mammary health, as indi-
cated by lower somatic cell count (P<0.05).
Methionine is frequently one of the most limiting AAs in
dairy cows, which is of benefit for milk protein synthesis
(Rulquin et al. 2006). In addition, the dietary supply of betaine
affects the methionine requirements of dairy cows (Davidson
et al. 2008). Heat stress potentially results in a decline in milk
protein, and with these facts in mind, Zhang et al. (2014)
determined whether supplying betaine to Holstein dairy cows
could overcome the effects of heat stress. Feeding 15 g/day
dietary betaine to heat-stressed dairy cows for 8 weeks in-
creased feed intake from 22.76 to 23.36 kg/day, milk produc-
tion from 27.70 to 29.16 kg/day, and also increased milk lac-
tose and milkprotein (P<0.05). Moreover, antioxidant capac-
ity was improved based on the increasing of plasma cortisol,
glutathione peroxidase, superoxide dismutase, and
malondialdehyde levels (P< 0.05). However, another study
reported slightly lower efficacy of dietary betaine supplemen-
tation (Hall et al. 2016). No differences were found between
cows that had consumed betaine supplements (57 or
114 mg/kg betaine) and the control group with regard to milk
production and composition during heat stress. Nevertheless,
serum insulin and glucose levels were higher (P< 0.05) in
heat-stressed dairy cows, the HSP 27 and HSP 70 expression
were higher (P< 0.05) in bovine mammary epithelial cells
treated with a high dose of dietary betaine in vitro. The over-
expression of HSP 27 and HSP 70 in bovine mammary epi-
thelial cells would be beneficial to protect against hyperther-
mia in heat-stressed dairy cows (Min et al. 2015).
Other anti-stress additives
Monensin is a well-described rumen modifier, which can aug-
ment the rumen production of propionate, the predominant
gluconeogenic precursor in dairy cows (Ipharraguerre and
Clark 2003; Duffield et al. 2008). Monensin increases feed
efficiency in lactating ruminants based on the increasing of
carbon conservation during fermentation (Schelling 1984).
Based on these results, Baumgard et al. (2011)hypothesized
that monensin supplementation in Holstein dairy cows would
increase gluconeogenesis and glucose homeostatic parame-
ters, which would ameliorate heat stress responses. Actually,
dairy cows fed with 450 mg/cow/day monensin consumed
less feed intake (1.59 kg/day), which led to a higher feed
efficiency (7%), and had a higher whole body glucose rate
of appearance per unit of feed intake (10%) (P<0.01), but
produced the same amount of milk. It is worth noting that
the negative effects of monensin supplementation were in-
creased in rectal temperature (at 06:00 h, 15:00 h, and
18:00 h) and respiration rate (at 06:00 h and 18:00 h) and
decreased in milk protein and fat levels in heat-stressed dairy
cows (P< 0.05). Overall, feeding monensin appears to be of
limited value and is associated with some adverse effects in
heat-stressed dairy cows.
Int J Biometeorol
γ-Aminobutyric acid is an inhibitory neurotransmitter that
regulates body temperature (Quéva et al. 2003)andinhibits
heat production (Dimicco and Zaretsky 2007). γ-
Aminobutyric acid directly inhibits cold-sensitive neurons,
central or systemic administration of γ-aminobutyric acid
and its agonists result in hypothermia, whereas its antagonists
produce hyperthermia (Sanna et al. 1995;Ishiwataetal.
2005). A clinical research has indicated that a single oral ad-
ministration of γ-aminobutyric acid induced a decrease in
body core temperature and total heat production in a hot en-
vironment in humans (Miyazawa 2012). In addition, γ-
aminobutyric acid would stimulate feed intake (Wang et al.
2013), the injecting of γ-aminobutyric acid agonist into the
lateral ventricles increased the feed intake of satiated ruminant
(Seoane et al. 1984). It is co-expressed with the neuropeptide
Y to promote feed intake (Pu et al. 1999) and plays a positive
effect on gastric acid secretion (Piqueras and Martinez 2004).
As aforementioned, γ-aminobutyric acid supplementation
might improve feed intake and reduce heat production, which
would resultin better performance in heat-stressed dairy cows.
An experiment was performed to assess the effects of rumen-
protected γ-aminobutyric acid (0, 40, 80, or 120 mg/kg of dry
matter) on productivity in heat-stressed Holstein dairy cows
(Cheng et al. 2014). The results showed that γ-aminobutyric
acid supplementation dramatically lowered rectal temperature
at 07:00, 14:00, and 22:00 h and resulted in higher feed intake
and milk production. It also improved milk composition as
indicators by milk fat yield, milk protein, and lactose concen-
trations (P< 0.05). The peak values were reached at a dose of
40 mg/kg (Cheng et al. 2014). Thus, feeding γ-aminobutyric
acid to dairy cows during heat stress could alleviate heat stress
by reducing rectal temperature and improve feed intake, milk
production, and milk composition.
Several studies have been conducted regarding the thermo-
regulatory abilities of the immunomodulatory feed ingredient
Omnigen-AF (consisting of a mixture of silicon dioxide, cal-
cium aluminosilicate, sodium aluminosilicate, brewers
dehydrated yeast, mineral oil, calcium carbonate, rice hulls,
niacin supplement, biotin, D-calcium pantothenate, vitamin
B
12
supplement, choline chloride, thiamine mononitrate, pyr-
idoxine hydrochloride, riboflavin-5-phosphate, and folic acid)
in heat-stressed dairy cows (Hall et al. 2018; Skibiel et al.
2017; Leiva et al. 2017; Fabris et al. 2017). Before the exper-
iment proper started, the on-dairy phase of Omnigen-AF sup-
plementation or control diet was conducted to demonstrate
differences in markers of homeostatic signals between these
two groups (Wu et al. 2017). Thirty-two lactating Holstein ×
Gir cows were assigned to either receive (n= 16) this supple-
ment at 56 g/cow daily or not (n= 16) under heat stress con-
ditions (Leiva et al. 2017). Dairy cows supplemented with
Omnigen-AF showed reduced vaginal temperature through-
out most of the experiment (P< 0.05) and showed a lower
mean somatic cell count (P= 0.01). Mean feed intake (by
7%, P= 0.1), final body condition score (by 11%, P=0.01),
and mean serum insulin concentrations (P< 0.1) were also
increased after Omnigen-AF supplementation. In the other
studies, a treatment × environment interaction was identified
in lactating Holstein cows fed Omnigen-AF, which showed a
lower rectal temperature (at 14:00 h, P<0.01)andrespiratory
rate (at 14:00 h and 18:00 h, P≤0.05) and higher feed intake
(by 8.77%, P< 0.1) than in the control group during heat
stress (Hall et al. 2018). Furthermore, this study revealed that
feeding Omnigen-AF reduced plasma cortisol during acute
heat stress and increased basal plasma adrenocorticotropic
hormone levels, perhaps indicating that Omnigen-AF altered
pituitary or adrenal responses to factors controlling cortisol
secretion and regulated the hypothalamic-pituitary-adrenal ax-
is (Hall et al. 2018). Supplementation with this immunomod-
ulatory substance during the dry period might also be able to
overcome the negative effects of heat stress and improve sub-
sequent performance in cows (Fabris et al. 2017). Cows given
56 g/day Omnigen-AF had higher body weight during the dry
period than the control group (P< 0.01) and subsequently
produced more milk (35.9 versus 40.5 kg/day, P<0.05).
The decrease of respiration rate (P< 0.01) also happened in
this process. Simultaneously, the addition of Omnigen-AF to a
maternal diet during late gestation would improve postnatal
calf growth and immune competence under heat stress condi-
tions (Skibiel et al. 2017). Calves born from Omnigen-AF-
supplemented Holstein cows tended to have lower rectal tem-
perature and be heavier at birth than those born from non-
supplemented dams (P≤0.1). In addition, they possessed a
more responsive immune system through stimulated lympho-
cytes at birth and increased neutrophil function, acute phase
protein production, red blood cell counts, hematocrit, and he-
moglobin. Together, these results suggest that adding
Omnigen-AF to the diet of heat-stressed cows during late
gestation would improve postnatal calf growth and immune
competence (Skibiel et al. 2017).
A sustained-release multi-trace element and vitamin was
estimated for its efficacy in alleviating the negative effects of
heat stress on lactation and reproductive performance of
Holstein dairy cows (Khorsandi et al. 2016). The sustained-
release multi-trace element and vitamin supplement consisted
of minerals (16.2 g Cu, 0.251 g Se, 0.236 g Co, 0.497 g I,
8.28 g Mn, and 13.32 g Zn) and vitamins (545.6 × 10
3
IU of
vitamin A, 109.1 × 10
6
IU of vitamin D
3
, and 1092 IU of
vitamin E). The results revealed that dairy cows supplemented
with this supplement had higher milk fat, protein, and solid
non-fat percentage (P< 0.05), and that it tended to result in
higher milk yield (47.8 versus 50.1 kg/day, P= 0.07) than
controls. The supplementation significantly reduced the milk
linear somatic cell count (P= 0.01), suggesting a positive im-
pact on udder health. The number of days open (calving to
conception) was shortened and the cumulative incidence of
pregnancy at the fifth artificial insemination was higher in
Int J Biometeorol
supplemented cows. Thus, supererogatory supplementation
with minerals and vitamins had positive effects on production
and reproductive performance in heat-stressed dairy cows.
Another sustained-release supplement containing niacin,
K
2
SO
4
, vitamin C, and γ-aminobutyric acid was fed to heat-
stressed dairy cows (Guo et al. 2017). During summer, 30
dairy cows were fed a diet with or without 0.13373 kg
K
2
SO
4
, 0.02488 kg vitamin C, 0.021148 kg niacin, and
0.044784 kg γ-aminobutyric acid per cow. As a result, feed
intake (20.34 versus 21.78 kg/day), milk yield (29.27 versus
34.53 kg/day), milk protein yield, and ECM were higher in the
supplemented group than in the control group (P<0.05).For
the serological indicators, the supplemented group had lower
levels of HSP 70, adrenocorticotropic hormone, and lactate
dehydrogenase than the control group. Thus, this mixture
may have the potential to ameliorate heat stress-induced im-
pairments in lactation performance and other physiological
variables in dairy cows.
Conclusions
We have summarized the effects of eight types of nutritional
strategies for heat-stressed dairy cows, which are listed in
Tab les 1,2,3,4,5,6,7,and8. The tables show the treatment
(dosage and usage), animal information (lactation stage and
number of dairy cows), THI value (level of heat stress), dura-
tion of exposure, the changes of feed intake and milk yield
(production performance), the changes of milk protein and
milk fat (milk quality), the changes of rectal temperature and
respiration rate (body temperature), other indices, and refer-
ence resources.
In general, the most striking predicament of heat-stressed
dairy cows is the pronounced reduction in milk production.
Concerning this issue, a number of nutritional strategies sum-
marized in this paper are capable of significantly increasing
milk production (by > 5%) in heat-stressed dairy cows: 3%
unprotected fat, 1.5% saturated fatty acid, 200 g/cow/day hy-
drogenated fish fat, replacement of 16.5% corn silage with soy
hulls, inclusion of 28.9% dietary NDF by the addition of cas-
sava chips, the use of 12% shredded beet pulp instead of corn
silage, the feeding of TMR plus 27% crushed corn, 10 g/day
live yeast (25 × 10
10
cfu live cells and 5 × 10
10
cfu dead cells),
1 g/kg zymosan, 400 g/day live bacterial inoculants (4 ×
10
9
cfu of a combination of Lactobacillus acidophilus and
Propionibacterium freudenreichii), 4 g/day chelated Cr yeast,
6 mg/head/day dietary Cr, 0.25 g/kg Radix bupleuri extract,
100 g/day of a Chinese herbal medicine mixture containing 18
herbs, 15 g/day dietary betaine, 40 mg/kg γ-aminobutyric
acid, 56 g/cow daily immunomodulatory substance during
the dry period, or a mixture of 0.13373 kg K
2
SO
4
,
0.02488 kg VC, 0.021148 kg niacin, and 0.044784 kg γ-
aminobutyric acid.
It is hypothesized that supplementation with vitamins or
metal ion buffer may play an auxiliary function in heat-
stressed dairy cows, such as the amelioration of defects in
immune function, reproductive performance, heat dissipation,
water intake, energy balance, mammary health, and N utiliza-
tion. In summary, eight types of nutritional strategies
consisting ofa total of 49 kinds of dietary interventions should
provide clues or perspectives for the selection of an appropri-
ate methodology for particular dairy farms to mitigate heat
stress in their stock.
Acknowledgments This study was supported by the Guangdong
Innovation Project of Scientific Research Institutions
(2014B070706014) and the Natural Science Foundation of Guangdong
Province (2018A030313002).
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
interest.
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