PHOTO: ANNE VAN DER WOUDE
NUTRITION ▶▶▶
Nutrition as a tool to adapt to heat stress
Production responses to heat stress may vary depending on factors such as cattle breed, body size, milk yield and degree of exposure to heat stress. Several feeding strategies will help dairy cows adapt to hot climates.
BY DR SALAH HAMED ESMAIL, FREELANCE CORRESPONDENT A
A cow fed at 8am will have her peak of heat production at 11am to noon when the day is hotter.
nimals go through heat stress when the body temperature is higher than the optimal range specified for normal activity because the total heat load is greater than the capacity for heat dis-
sipation. Temperate dairy cows are particularly susceptible to heat stress and often show marked decreases in feed intake and productivity in hot climates or when introduced into tropical or subtropical regions for genetic improvement of local breeds. We take a look at some nutrition strategies that will help in adapting dairy cows to heat stress conditions.
Theories of heat stress effects Under heat stress conditions, a great deal of blood circulation is directed to the peripheral parts of the body to feed the sweat glands instead of being directed to the rumen to stim- ulate motility. With the lower rate of rumen motility, there will be only small amounts of feed passing towards the lower part of the gastrointestinal tract, thereby making the animals feel full and have no desire to eat more for long periods.
Heat-stressed animals not only eat less but also return less weight per unit of intake. Animals expend more energy activating heat-dissipating processes such as sweating, heart- beat and respiration, with only a little energy left over for productive purposes. Heat stress also affects pancreatic activity and its capacity to produce the enzymes needed to digest carbohydrates and proteins when reaching the intestinal area, thereby further reducing again the utilisation of such nutrients for productive purposes. In addition to its effects on animals, heat stress also affects the yield and quality of animal feed as it leads to growth de- pression, enzyme inactivation and reduced metabolic synthe- sis, in addition to its effects on germination, vitamin stability and increasing mycotoxin levels in feeds.
Nutritional strategies For animals under heat stress conditions, the strict recom- mendation is to manage diet composition, properly supple- ment essential nutrients, consider timing and frequency of feeding and supply adequate water.
Concentrate-to-roughage ratio Reduction in feed intake under heat stress may be recovered partially by increasing metabolisable energy (ME) and nutri- ent densities of diets. This may be a nutritionally and possibly economically feasible means to increase milk yield, particu- larly if concentrates are available and the milk price-to-con- centrate ratio is favourable. The ME requirement for mainte- nance rises by 10–30% at 30–40°C compared with 18–20°C because extra energy is needed for heat dissipation. There- fore, by increasing ME intake (by increasing the concen- trate-to-roughage ratio), more ME remains available for productive functions.
Protein nutrition Feeding protein-deficient diets results in an increased heat load on animals due to increased heat production for the turnover of tissue proteins. Therefore, supplemental protein is needed to alleviate heat stress. A study was conducted to ex- amine the effect of protein supplementation for Holstein cows during natural heat stress. Dry matter intake was 11% greater with the high-protein diet, and the fat-corrected milk
10 ▶ DAIRY GLOBAL | Volume 9, No. 2, 2022
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