Shield cattle from heat stress

Written by Dr. Jim White on .

One of the great challenges the dairy industry faces, especially during the summer, is heat stress. Increased temperatures, together with higher humidity, result in a decrease in milk production, feed intake, feed efficiency and growth rate in heifers. Reproduction and health are also negatively affected by heat stress.

There are different ways to reduce the effects of heat stress on cows, such as fans with water sprayers or cow housing and shading. However, not all operations are able to implement such management systems, and even with these measures, cows can still experience a certain amount of heat stress.

The thermal comfort range of lactating dairy cows is estimated to be from 32 to 75 degrees. Temperature, however, is not the only factor that plays a role in heat stress. An increase in relative humidity also increases heat stress in animals. Both temperature and humidity are used to calculate Thermal Heat Index (THI). The comfort threshold is considered to be a THI of 72, but high-producing milk cows start to experience heat stress from a THI of 68. The estimated response is that milk yield drops by half a pound for every unit increase in THI above 72.

Effects on production will not necessarily be directly after cows experience heat stress. There is often a lag time between increase in THI and the full effects on production. The first day of stress is not so bad, but dry matter intake is most sensitive to the mean air temperature two days earlier.

Lactating dairy cows produce a large quantity of metabolic heat and accumulate additional heat from the environment. A dairy cow produces more heat than a 1,500-watt hair dryer running full blast. Cattle decrease feed intake in an attempt to create less metabolic heat, as the heat increment of feeding is a large portion of whole body heat production. In addition to reduced nutrient intake, heat-stressed cows have an increase in maintenance cost. Maintaining body temperature has a large energy cost. Because of decreased energy availability and increased energy utilization, heat-stressed cows enter into negative energy balance. Methods to counteract the negative energy balance include increasing energy density of the diet or improving digestibility of feed components. Inclusion of feed additives, such as ionophores, yeast or MFA Shield Technology can improve nutrient digestibility.

Three management strategies to minimize the effect of heat stress are:

  1. Physical modification of environment
  2. Genetic development of heat-tolerant breeds
  3. Improved nutritional management practices

Since I’m a ruminant nutritionist, I am after the third strategy. If I only have a hammer in the toolbox, everything looks like a nail.

Feed intake plays a significant role in production—both the amount of feed being consumed per day and the feed intake pattern. Uneven feed intake during the day can have a negative effect on the rumen environment by increasing the fluctuation of rumen pH. During heat stress, cows will have decreased feed intake. As a result, cows tend to consume more feed during the night with cooler temperatures, causing increased variation in feed intake.

When adding Shield to the diet of heat-stressed cows, it is common to see dry matter intake increase by 8 to 10 percent, or rather come back two-thirds of where we would expect cows to be if they were not stressed. Also, we see a reduced size in the first morning meal. I am not certain if there is increased meal frequency or not; some farmers report “yes” and others “no.”

Water is arguably the most important nutrient for dairy cows. Shield Technology tends to increase water intake, similar to what we see with niacin. Both have a vasodilation or increased blood flow effect. Increases in water intake, especially during heat stress, can have a positive effect on the decrease in body temperature as well as an increase in performance. In dairy cows, Shield has also been shown to increase saliva production during feeding compared to TMRs without Shield components.

Heat-stressed cattle show a reduction of antioxidant activity of plasma, which means they are experiencing an increased oxidative stress. Oxidative stress can lead to damaged molecules and disruption of normal metabolism and physiology. Feeding

Shield components has been shown to reduce oxidative stress.

Visit with your local MFA feed specialists for more information on how Shield Technology can help mitigate the effects of heat stress this summer.

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