PHOTO: CANVA


(FCM) was 4.3% higher. Excess protein should, however, be avoided as it would be metabolised and excreted by the cow, a process that creates heat and consumes energy that could be used to produce milk. Adjustment of protein levels may not be possible in some cases, such as with cows grazing very high-protein oat pastures.


Protected fat It makes sense that enhancing ration energy density by utilis- ing fats could be particularly beneficial during hot weather. However, research on the effects of feeding high-fat rations during hot weather has yielded inconsistent results. This is probably because it is very easy to overfeed unprotected fat sources, such as whole oilseeds, when the cow’s feed intake is significantly reduced due to heat stress. If fat is overfed, then the negative effects of the fat on fibre digestibility will negate any possible gains with increased ration density. Because by- pass fats do not affect rumen fermentation, they should probably make up a greater percentage of the total fat included in the ration during hot weather.


Mineral supplement Supplementation of minerals, particularly potassium (K) dur- ing heat stress is a recommended practice, considering that there are fivefold increases in K loss from the skin via sweat- ing from cows under heat stress compared to those under normal temperature. Increased use of concentrates for heat- stressed cows also contributes to higher K requirements, since most concentrated feeds are K-deficient. K supply should be considered along with the supply of sodi- um (Na), since both are closely related to the regulation of many body functions. Urinary losses of Na increase during heat stress, due to decreased levels of blood aldosterone. Such losses should then be balanced out through dietary supplementation. Studies have shown some improvement in milk yield with 1.5% K and 0.38% Na but when the 1.5% K was combined with 0.67% Na, milk yields were superior.


Vitamin supplement Among vitamins, niacin (vitamin B3) was studied for its action on vasodilatation in the mammalian and for its role in lipid metabolism. It helps to alleviate heat stress both by increas- ing evaporative heat loss from the body and also by reducing the effects of heat at the cell level. Including niacin (6 g/cow/ day) may be beneficial as it reduces skin temperature and in- creases milk yield. Supply of vitamin C may also be recom- mended in this case due to the effect of heat stress on the plasma and tissue levels of this vitamin.


Buffers Buffers such as sodium bicarbonate should be used during hot weather, especially in low-fibre, high-concentrate diets. Diets should contain at least 0.75% sodium bicarbonate on a


dry matter basis. This amounts to a minimum of 0.15 kg of buffer per day for a cow consuming 20 kg of dry matter.


Frequent feeding As a further strategy, increasing feeding frequency should reduce heat production because this would promote a uniform rate of absorption of nutrients and spread the total heat increment due to feeding over a longer period. This should not overload the animal’s heat-dissipating mecha- nism at any one period. Frequent feeding of heat-stressed cows also helps prevent the milk fat problem by maintaining uniform rumen fermentation and permitting a higher intake of concentrates without a decrease in the rumen pH or the acetate-to-propionate ratio.


Feeding time By feeding cows in the early morning (5am to 6am), the heat of digestion peaks at 8am to 9am and allows the cow to dissi- pate some of that heat before the day gets hot. A cow fed at 8am will have her peak of heat production at 11am to noon when the day is hotter, which is undesirable. Similarly, cows fed during the evening will be more comfortable and likely to consume feed, and their peak of heat production will occur during the night when environmental temperatures are lower.


Water Under heat stress conditions, the cow loses water via the skin and respiration as she works to minimise her rise in body tem- perature. In one study, the loss of water increased by 59% via the skin and 50% via respiration when ambient temperature increased from 18°C to 30°C. It is, therefore, important to pro- vide cool, clean water ad libitum and eliminate any manage- ment factor that may inhibit cows from drinking. References are available from the author upon request


▶ DAIRY GLOBAL | Volume 9, No. 2, 2022 11


Under heat stress condi- tions, the cow loses water via the skin and respiration as she works to minimise her rise in body temperature.


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