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Heat waves and dairy cattle

As temperature rises, so cows move less and eat less - yet their energy needs actually increase. The gap between their feed requirements and intake widens. Maintenance energy requirement increases if she is heat stressed. Environmental heat will increase body temperature, respiration rate, and loss of electrolytes. The critical temperature for a cow ranges from 80 to 85˚F (26.7 to 29.4˚C), well within heat wave temperatures in Britain this year. She needs energy to rid of her extra heat.
Heat stress lowers dry matter intake, especially forage intake, making it difficult to meet energy needs. It's a common assumption that cows don't need so much food in hot weather, as they don't seem hungry. In fact their diet needs become more complicated, and their need for water increases. Feeding management and forage quality become critical during heat stress.

Water: Since water is the most essential nutrient and milk contains 87% water, the importance of an adequate supply of clean, fresh water is vital. Cows drink more water right after milking or after eating. While in winter they like warm water, when it's hot they like their drinks ice cold! Adding water to a TMR can increase water intake by 5-10%. Cows that are hot need more water. The table below shows the differences in water intake that may be seen with changes in environmental temperature.

Drinking water intake and ambient temperature

	Drinking Water Intake at 4.4˚C (l/day)	Drinking Water Intake at 15.6˚C (l/day)	Drinking Water Intake at 26.7˚C (l/day)
Heifer, 90.9 kg	8	9	12
Heifer, 181.8 kg	12	17	23
Heifer, 272.7 kg	24	30	40
Heifer, 545.5 kg	33	41	55
Dry Cow, 636.4 kg	37	45	61
Milking Cow, 636.4 kg, 27.27 kg milk	86	90	94
Milking Cow, 636.4 kg, 36.36 kg milk	102	121	147
Milking Cow, 636.4 kg, 45.45 kg milk	120	140	172

(Adapted from Eastridge and Watson, 1990)

While the cows need more water, so supplies from springs, bore holes and the mains decreases. As those committed to dairying lift cow numbers, so the pressure on water supplies can in some instances become difficult.
Many farmers invest in larger water troughs so more can be stored. Maintaining high, or even adequate water quality in these tanks is difficult. Cleaning out means wasting the 500 galls, and waiting - hoping - the tank will refill. Some farmers might consider using a large bowser tank fitted with troughs around its sides and back. The tank could be an MOT failure milk tanker or other - re-registered for agricultural use. Filling with a cleaned out slurry tank would allow water to be collected from a natural source, and transfered quickly into the tank. Large herds will need a fast flow into the side troughs, which might be best done using a large bore direct feed from a central holding tank.
These are ideas FARM IDEAS has discussed with various farmers, and one may shortly be built. Email me if you want further information.

Feed requirements: Cows require more energy when it's hot, but raising energy levels in their diet may not be the way to go about it. Heat stress lowers dry matter intake, especially forage intake. Since fiber undergoes more fermentation in the rumen than grain, it increases body temperature more. Cows will often decrease forage intake during hot weather. Extra effort should therefore be made to feed forages with higher digestable fibre in order to reduce the heat of fermentation in the rumen. More evening feedings and good trough management are important, as feeds spoil more quickly in warm weather. It may be especially helpful to feed more often. Don't let silage sit for hours in a wagon prior to feeding.

Minerals: Although cows do not have many sweat glands, they will sweat a certain amount during hot weather and lose electrolytes. Heat-stressed cows lose a lot of potassium and they can become potassium deficient. The loss of potassium increases blood acidity. Generally, it will require 1.5% dietary potassium or 0.45 kg of added buffer, plus sodium to provide a balance, but chloride levels need to be controlled. Potassium carbonate will need to be used rather than potassium chloride (a more popular source of potassium in the feed industry).

Conclusion: By far the best solution to heat stress is not to have it in the first place. The dairy producer’s goal should be to keep body temperatures below 39.2˚C and respiration rates below 80 per minute. Keep a close eye on cows in collecting yards. Ventilation is critical. Fans are used in hot countries on a regular basis, and dairy men with access to grain drying fans might be able to set these up to turn on tick-over so they create a low-cost draught. Shade needs to be provided, and providing a water mist creates evaporative cooling.