Written by Armor Animal Health Professional Services Team

Summer is upon us, with the heat that corn plants crave. Every dairy farmer dreads the drop in milk production, components and fertility brought on by heat and humidity though. While it is easy to focus mainly on lactating cows, there are two other groups equally harmed by high temperatures: dry cows and calves.

Heat stress occurs when animals generate and/or absorb more heat from the environment than they can dispel. In adult cattle, heat stress begins when the temperature humidity index (THI) reaches 65° F. The higher the THI, the more energy animals expend to cool themselves. Feed intake drops to decrease the amount of heat generated in the rumen, directly causing a decrease in milk production. Heat damages eggs within the cows’ ovaries as well as early embryos, leading to decreased pregnancy rates. Cows spend more time standing as well.

Dry cows are not immune to heat stress despite not producing milk. Heat-stressed dry cows calve sooner, and their calves have lower birth weights. Those calves have lower average daily gains (ADG) and hip heights as well. Heat-stressed dry cows produce less milk even after outside temperatures fall. Heat has further-reaching consequences than just the dry cow though, affecting THREE generations. If the cow is pregnant with a heifer, that heifer’s milk production is decreased once she calves. Because a heifer is born with all her eggs and heat stress affects even those tiny eggs, her future heifers produce less milk. Don’t let heat stress hurt the milk production of your current cows, as well as their daughters and granddaughters!

Calves have better heat tolerance due to their higher surface area, so heat stress starts around 77° F. Like cows, calves use energy to cool themselves, which diverts energy from growth and immune system function. Grain intake is decreased, leading to a further reduction in ADG. Heat stress requires just as many extra calories from milk as cold stress. Without an increase in milk, disease incidence and death loss increase.

Here are some quick tips to minimize heat stress:

·        Provide shade for animals kept outside.

·        Position hutches to take advantage of prevailing winds.

·        Use a block under the back of the hutch to increase ventilation.

·        Feed calves more milk and keep grain fresh.

·        Feed cows more often and work with your nutritionist on energy density.

·        Within a barn, increase ventilation to 60-90 air changes per hour.

·        Utilize fans to reach air speeds of at least 6 miles per hour.

·        Place fans over the stalls to encourage stall usage.

·        Fans should bring in fresh air, not just recirculate the already-hot air in the barn.

·        Clean and maintain fans for maximum efficiency.

·        Use sprinklers over the feed bunk combined with fans to evaporatively cool cows. Cycle sprinklers so water doesn’t run down to the udder!

·        Evaluate drinking water space and water trough cleanliness as cattle need more water as temperatures increase.

·        Work animals in the morning.