30 January 2015
Right diet helps cows keep their cool
Choosing the right supplementary feed can help farmers turn down the heat in their cows’ digestive systems as hot, humid
summer conditions increase the risk of heat stress in herds.
Science Extension Officer for animal nutrition company SealesWinslow, Sarah Morgan, says all cows generate heat when
they digest feed, but feeds requiring less energy to digest will also result in less heat generated and more comfortable
cows as the average daytime temperatures stay high.
“Fibre produces more heat in the rumen than other carbohydrate feed sources. Feeds that have high oil content also
require more energy to digest and reduce the efficiency of nutrient metabolism. Low fibre feed sources usually result in
less heat from digestion than feeds that are higher in fibre.”
Sarah says cows tend to protect themselves against heat stress by eating less to avoid temperature increases during
digestion, but this often comes at the cost of milk production. “The combined effects of higher temperatures and
humidity can put a strain on the herd, and this is particularly so for high producing dairy cows. These higher producing
cows generate more heat during digestion than lower producing cows,” explains Sarah.
“The main reason for the drop in milk production in these conditions is that the cows eat less to avoid further
temperature rises during digestion; so minimising any environmental effects on dry matter intake is critical to
maintaining productivity in times of heat stress.”
Ready access to shade and plenty of cool, clean, fresh water is the number one thing farmers can do to support the herd
to keep temperatures down.
Sarah recommends increasing the energy density of the diet to help compensate for reduced dry matter intake, and
providing a good source of protein to help stimulate hunger and avoid temperature increases will help maintain
production in herds still being milked. “Fat, such as a coated or bypass fat, is a good way to increase energy density
in the diet and compensate for the difficulties of achieving target intakes through pasture alone.
“The quantity of quality protein over the warmer summer months also becomes important, particularly as pasture quality
drops. Protein in the diet not only supports milk production and milk protein content, but also plays a hand in
stimulating intakes or hunger.”
Sarah says that the best protein sources at this time of year are feeds that are higher in bypass protein or rumen
undegradable dietary protein, which passes through the rumen and digests in the lower intestine. These protein sources,
such as SealesWinslow MaxiPro 20%, require less energy for digestion and hence produce less heat.
For cows that are being dried off, feeding levels would be below the levels heat stress would impact on them, so water
and shade are the most important factors for keeping them cool.
Heat stress – what you need to know
• Heat stress occurs when the cow’s ability to cool down is compromised because the temperature is high.
• Humidity further impacts this by affecting the cow’s ability to cool down by sweating and panting.
• Signs of heat stress in lactating cows include reduced feed intakes, lethargic behaviour and lower milk
• Provision of shade and a good supply of cool, clean, fresh water can support the herd to keep temperatures down.
• Heat production increases following a meal - this is a result of the heat energy from fermentation and heat of
• Different feed types result in differing levels of heat from digestion – increasing energy density by
incorporating more fat in the diet and decreasing heat from digestion with the right protein can help to maintain feed
intake milk production.