HEALTH ▶▶▶
The effect of cold exposure was more obvi- ous in the calves compared to the matured cows.
plasma magnesium concentrations but did act synergistically with starvation to induce hypomagnesemia. Increased rates of lipolysis during cold exposure was the likely precipitating factor since the hypomagnesemia response to acute cold ex- posure was inhibited by the anti-lipolytic agent sodium nico- tinate. Elevated thyroid hormone levels in a cold environment may potentiate the effect of rapid lipolysis.
Production responses Growth Growth rate and feed conversion efficiency of cattle are clear- ly reduced under cold stress as a result of the combined ef- fects of cold on digestive function and increased basal me- tabolism. Also, the maintenance energy requirement of cattle has been calculated to increase by 0.91% for each degree be- low a temperature of 20°C to which animals have been adapt- ed, thereby reducing the efficiency of energy utilisation for growth and other biological functions. Studies have also shown that cold stress influences protein turnover in ruminants. The protein degradation rate was in- creased more than synthesis, resulting in a loss of muscle mass and carcass quality.
Pregnancy Pregnancy may not be detrimentally affected by cold stress. If, however, too much reliance is placed on using body energy reserves where the feeding level is insufficient or protein is deficient, complications such as the weak calf syndrome may arise. Furthermore, if body condition is severely reduced, cows may have reduced lactation potential and may experience delays in rebreeding.
Lactation Cold stress causes a reduction in milk secretion in lactating cows. Local cooling of the mammary gland and reduced
16 ▶ ALL ABOUT FEED | Volume 27, No. 9, 2019
mammary blood flow may contribute to the decline in yield but cannot account alone for the response. It was demon- strated that cold exposure for 24h decreased glucose extrac- tion by the udder, while glucose utilisation by non-mammary tissues tended to increase, as occurs in non-lactating rumi- nants. The increased responsiveness of non-mammary tissues to insulin during prolonged cold exposure would, therefore, reduce glucose availability to the udder. When coupled with changes in blood flow, this may account for the reduced mammary gland glucose uptake and lactose secretion.
Management strategies Weather conditions cannot be controlled, but there are some management strategies to reduce the effects of cold on cows and hence reduce costs and improve production efficiency: • Monitoring temperature and increasing feeding in re- sponse to cold weather. Cows in the last trimester require additional grain feeding during periods when the effective temperature falls below the lower critical level.
• Protecting animals from the wind which increases cold stress on animals.
• Providing adequate dry bedding makes a significant differ- ence in the ability of cattle to withstand cold stress.
• Keeping cows clean and dry greatly improves insulating properties and make cows less susceptible to cold stress.
• Providing additional hay and grain. If wet feeds are fed, they should not be frozen.
• Making sure that cows have ample water available at all times. Limiting water will limit feed intake and make it more difficult for cows to meet their energy requirements. Frozen troughs and excessively cold water seriously limit water intake.
• Cold weather may interact with the maturity and composi- tion of feed materials. The formulation of the diet fed to cold- stressed animals should, therefore, be adjusted accordingly.
PHOTO: HENK RISWICK
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