Prepared by

Prof. Dr. Ahlam A. El Shewy Dairy Science Department

Food Industry and Nutrition Research Division

National Research Centre, Egypt

Climate

change

Introduction

Actually, climate change

term is new unlike heat

stress term; however,

it has made the problem

of heat stress worsen

Heat stress effect on dairy

cows could be briefly

illustrated as follows:

Nowadays,

climate change

is unequivocal

due to

1- continuous increasing in temperatures of global air and ocean

2- melting of snow and ice

3- rising global sea level

Heat stress a condition that occurs when

an animal cannot dissipate an adequate quantity of heat, whether it is produced or absorbed by the body, to maintain body thermal balance. This may cause physiological and behavioral responses, leading to physiological disorders that negatively affect the productive and reproductive performance of farm animals

Can be simply defined as

(West, 2003; Nardone et al., 2010)

Genetic factors affecting dairy cows sensitivity to heat stress

Colored cows

Phenotype effect Cows with thick skin have more sensitivity than that

with thin skin

Cows with dark color skin have less sensitivity than

that with light color .

High number of sweat glands per skin unit area, points

out low sensitivity to heat stress and vice versa

Species effect Under hot climatic conditions, the genetic

adaptation of Bos indicus cattle allows

them to have a lower respiration rate and a

lower rectal temperature than Bos taurus

cattle

Bos indicus (Indian or zebu) are humped cattle

Bos taurus are cattle in Europe and in some parts of Africa

Humped

cattle

Behavioral responses in

heat -stressed cows

Low appetite

High panting

Low movement

A

B

C

A

B

C

Temperature humidity index

(THI)

is

Different equations have been suggested for THI calculation . One of them is:

THI = (1.8 × T + 32) − (0.55 − 0.0055 × RH) × (1.8 × T − 26) where T = temperature (°C) and RH = relative humidity (%).

(Kelly and Bond, 1971)

Heat stress levels vary by differences among indices, geographic regions, and authors

a bioclimatic index that has been used to evaluate the

degree of heat stress in dairy

cattle

72< THI <79 mild stress 80<THI <90 moderate stress THI > 90 severe stress

(Armstrong , 1994)

79 ≤ THI ≤ 83 dangerous stress THI ≥ 84 emergency stress

(Huhnke et al. 2001)

68 < THI < 74 moderate stress THI ≥ 75 drastic stress

(De Rensis et al.,2015)

However, categorical THI values are considered as a

rough indicator of heat stress level.

0

10

20

30

40

50

60

70

80

90

day time

night time

THI

THI during spring

and summer

spring summer

Day time (10:00 h to 17:00 h),

night time (17:20 h to 09:40 h)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Loss

es

nu

mb

er

winter spring summer autumn

THI values of 80 and

70 were the maximum

and minimum THI,

respectively, above

which the number of

deaths in dairy farms

starts to increase.

Maximum and

minimum THI values

of 87 and 77 were the

upper critical THI

above which the risk of

death for dairy cows

becomes maximum.

Seasonal pattern of mortality in dairy cows (Italian bovine)

Average of losses number during 6- years (2002- 2007)

Biological indicators in heat –stressed

dairy cows

Effect of season on some parameters in

Holstein cows

Not only, body temperature (vaginal

or rectal) or respiration rate

(panting frequency) provides valuable indicator for heat stressed cows, but

also milk production and reproductive performance are

considered as important indicators

for the biological functions in heat-

stressed dairy cows

Summer

21st June-2nd

August

Spring 1st March-12th April

Rectal temperature o C

Respiration rate Dry matter intake (kg/h/d)

Milk yield (L/h/d)

Milk protein %

39.8

18.6 26.7 3.01

39

23.2 29.5 3.31

0 0.2 0.4 0.6 0.8

1 1.2 1.4 1.6

con

ten

ts %

Milk protein fractions in cows during spring and

summer

spring

summer

Effect of season on the ovarian activity of buffaloes

0

20

40

60

80

Ovarian

activity

%

cycling subactive anoestrus

100

200

300

400

500

600

prolactin

ng/

ml

5

8

11

14

17

20

23

26

FSH LH

ng/

ml

cycling anoestrus

Hormonal pattern in cycling and anoestrus cows

LH=luteinizing hormone , FSH=follicle

stimulating hormone

Roy, D. J., (1972)

The Egyptian buffalo cow It expresses a high fluctuating

degree of seasonal fluctuation

in oestrus activity.

Oestrus activity is low (29%)

during the hot season (April to

September) and high(71%)

during the temperate season

(October to March).

Seasonality in buffalo

reproduction has been

attributed to environmental

factors more directly than the

genetic factors

Suckling is a very powerful

stimulus in inhibiting oestrus

activity after calving. (M.M.El Fouly,1983)

Hyper- prolactinaemia decreases oestradiol

hormones secretion in the ovary

reduces luteinizing hormone and follicle stimulating hormone

anoestrus cows

Heat - stressed cows

Effect of heat- stress on cow fertility

a- postpartum

Hot

climate Hypothalamus

Pituitary

gland

Ovary

gland

b- during gestation Calves born to cows exposed to heat stress during

late gestation (i.e., the dry period) have lower birth

weight , lower weaning weight and lower

immune transfer compared with those born to cows

that are cooled

Other Biological phenomena

in heat- stressed cows

Respiratory Alkalosis. Panting sharply increases the loss of Co2 via pulmonary ventilation, reducing the blood concentration of carbonic acid and upsetting the critical balance of carbonic acid to bicarbonate necessary to maintain blood pH, resulting in a respiratory alkalosis

Electrolyte imbalance •In bovine sweat, a sharp increase in the K secretion occurs during hot climate

•A dramatic increase of 29% occurred in water intake that is accompanied by increased water loss via skin surface, respiratory tract, and urine may change the electrolyte balance in heat –stressed cows

Produced more

rapidly than excreted

Accumulate in blood Deplete blood

alkali reserves

ketosis

acidosis

Excreted in urine

Acetoacetate

Acetone

3-hydroxybutyrate

ketones

Low feed intake Low energy intake

Accelerate body fat catabolism

Management strategy

to improve cow performance

during heat stress

Shading is one of the

more easily implemented and economical methods to minimize heat from solar radiation.

Additionally, cooling is

necessary for lactating dairy cows in a hot climate

Cows in shaded versus no shaded environment had lower

rectal temperature (38.9 vs. 39.4 C), lower respiratory

rate (54 vs. 82 breaths/ min), and higher milk yield

0.85

0.89

0.93

0.97

Evaporate Shade

kg /

h/d

Effect of shade system (shade or shade

+evaporate)on milk fat and protein

yields

fat yield protein yield

10

15

20

25

30

35

Evaporate Shade

Kg

/h

/d

Effect of shade system (shade or shade + evaporate) on DMI and FCM in cows

DMI

3.5% FCM

Nutritional strategy to improve performance of

heat- stressed cows

Protein intake

Heat-stressed cows undergo negative N balance as a

result of reduced feed intake, increased protein

mobilization for energy, and increased energy lost

in converting NH3 to urea. So, ruminal un

degradable protein should be increased ( not > 61

% of dietary CP ) in diets of heat stressed cows

Nutrients utilization

It could be improved using ruminal modifiers that

increase diet digestion. One of them is live yeast

Water intake Abundant water must be available at all times

Energy intake Increasing the energy density of diet (low fiber and high concentrate) has lower dietary heat increment compared with higher fiber diets, but this effect must be balanced with the potential for acidosis associated with high grain diets.

Dietary cation anion difference (DCAD) (DCAD=Na+ K- Cl = mEq./100g DM)

During heat stress DMI could be improved by increasing DCAD from 12 to 46.4mEq./100g DM. regardless of whether Na or K was used

34

34.5

35

35.5

36

36.5

37

37.5

0 0.5 1

En

erg

y c

orr

ecte

d m

ilk

kg

/h/d

Live yeast g/h/d

1.6

1.65

1.7

1.75

1.8

1.85

0 0.5 1

feed

co

nv

ersi

on

Live yeast g/h/d

Live yeast for dairy cows under heat stress

strategy for

anoestrus cows

Various hormonal treatment regimens are being used to overcome the problem of summer anoestrus aimed

at stimulating ovarian activity, inducing synchronizing behavioral oestrus

or controlling ovulation. In that regard, a number of hormones either alone or in different combinations have been tried with varying degree of success

Progesterone either alone or in

combination with gonadotrophins proved to be very effective in inducing ovarian activity in summer anoestrus cows (The higher progesterone level in blood sensitizes the hypothalamus and pituitary to the gonadal feedback )

In buffaloes , the oestorus onset is a nocturnal , so, the heat detection during night hours using an entire male may improve the conception rate

Various strategies

(environmental

modification, nutritional,

breeding, suckling

management and

hormonal therapy)

can be used to improve

reproductive efficiency in

anoestrus cows

via the resumption of

ovarian activity

Genetic strategy

• More heat tolerant cows can be selected genetically, and cross-breeding can also be an effective tool to produce heat tolerant offspring

• Selection for heat tolerance without selection for an accompanied greater productivity would likely result in lower overall performance of cows

• Molecular biology could allow to directly achieve genotypes with the necessary phenotypic characteristics

Rectal

temperature that

appears to be a

main measuring

for heat tolerance

than does

respiration rate,

varies genetically

among different

species of cattle

Various cooling and shading

systems,

certain strategy of nutrition,

specific hormonal treatment

must be carried out for

heat- stressed cows

to alleviate the heat stress

effect on their production

and reproduction

performance to reach a level

similar to that in winter

Conclusion Comment

Global warming is occurring at an alarming rate.

There are predictions that air temperature will continue to increase during this century via continuous emission of gases such as carbon dioxide,

methane, nitrous oxide, and

ozone in our atmosphere . This phenomenon poses a more

attention toward heat- stressed

cows from the nutritionists and

all dairy researchers in the

world at large

References

.

Kadzerea, C.T. et al.,(2002) Heat stress in lactating dairy cows: a review. Livestock Production Science 77, 59–91

Kelly, C. F., and T. E. Bond.( 1971). Bioclimatic Factors and Their Measurement: A Guide to Environmental Research on Animals.

National Academy Press, Washington, DC

Nardone, A. et al., (2010). Effects of climate changes on animal production and sustainability of livestock systems. Livestock Science 130 (2010) 57–69

Perdomo, M.C., et al., (2020). Effects of feeding live yeast at 2 dosages on performance and feeding behavior of dairy cows under heat stress. J. Dairy Sci. 103:325–339

Roy, D. J., et al., (1972). Oestrus and ovarian activities of buffaloes in different months. Indian Vet J 49, 54–60.

Vitali, A. et al., (2009). Seasonal pattern of mortality and relationships between mortality and temperature-humidity index in dairy cows. J. Dairy Sci. 92 :3781–3790

West J. W. , (20003), Effects of Heat-Stress on Production in Dairy Cattle. J. Dairy Sci. 86:2131–2144

Armstrong, D. V. (1994). Heat stress interaction with shade and cooling.. J. Dairy Sci. 77:2044–2050

Bernabucci, U., et al.,.( 2002b). Effects of the hot season on milk protein fractions in Holstein cows. Anim. Res. 51 (1), 25–33

Chen, K.H. et al., (1993) Effect of Protein Quality and Evaporative Cooling on Lactational Performance of Holstein Cows in Hot Weather. J Dairy Sci. 76:819-825

Das, G.K. and Khan, F.A. (2010). Summer Anoestrus in Buffalo – A Review. Reprod Dom Anim 45, e483–e494

De Rensis, F., I. et al., (2015). Seasonal heat stress: Clinical implications and hormone treatments for the fertility of dairy cows. Theriogenology 84:659–666

El- Fouly, M.M.(1983).some reproductive aspects of the Egyptian Buffalo cow. Buffalo Bulletin, vol.2, No. 3, p,4

Huhnke, R. L., et al., ( 2001). Determining the frequency and duration of elevated temperature-humidity index. ASAE Annu. Int. Mtg., Sacramento, CA. Am. Soc. Agric. Biol. Eng., St. Joseph, MI.

Would camel be the

hope for human ,

in the next

century

ᴉ

Under severe climate change