Dairy Feeding Programs to Combat Heat Stress

Adapted by Gerald E. Higginbotham, UCCE Fresno/Madera Counties

Now is the time to examine what changes can be made on the dairy to lessen the impacts of hot weather on dairy cows. Besides changing the cows' environment to lessen the effects of heat stress, dairy producers may also modify their feeding program in order to give their animals additional relief during hot weather. Here are some key points to consider in feeding dairy cows during heat stress:

1. Heat Stress Effects on Feed Intake

Voluntary intake of feed dry matter during hot weather has been shown to decrease to about 55% of that eaten by cows when temperatures are between 40°F to 75°F. Dry, dusty feeds are not as preferable during hot days. For this reason, wet feeds such as wet brewers or distiller grains, wet citrus pulp, corn silage, winter forage, alfalfa haylage or green chop should be utilized during hot weather. It is important to remember that wet feeds can mold easily, therefore, a load should be consumed within 5-7 days. If one is unable to utilize wet feeds in their ration, simply adding 10-20% water to a mixed dry feed can do wonders for feed intake during hot weather. One should also clean the feed bunk area frequently in order to prevent mold buildup.

The time that you feed your cows during heat stress can also influence feed intake. In periods of hot weather it is recommended to feed 60 to 75% of the mixed ration after 6:00p.m. The remaining 25 to 40% is to be fed before 6:00 a.m. Cows do very little eating during the day in heat stress conditions so more feed needs to be offered in the cooler hours of the day. Feed that is in the sun all day is not very palatable to the cows.

2. Possible Feed Additives

Buffers: Decreases in forage intake will lead to rations containing over 60 to 65% concentrate. This will lead to digestive upsets known as ruminal acidosis. This is due to the pH of the rumen becoming too acidic which leads to the growth of undesirable rumen bugs. Buffers are added to rations to help maintain a more desired rumen pH. Generally, symptoms such as cows off feed, low butterfat test or loose manure may indicate an acidosis problem. To help achieve optimum rumen fermentation during the summer, rumen buffers are generally recommended.

Added fat: Feeding of fats increases the energy density of the ration enabling one to decrease slightly the amount of concentrate which is fed. When feeding fat, be careful not to feed over approximately 6-7% total fat in the ration dry matter. Higher levels can affect palatability and fiber digestion by rumen microbes. Ration adjustments should be considered when fat is added, such as to feed adequate amounts of fiber to maintain rumen digestion. In addition, higher levels of calcium (0.8 to 1.0 percent) and magnesium (.25 to .30 percent) in the total ration dry matter are recommended.

Minerals: Sodium (Na) and Potassium (K). Raising dietary Na from 0.18 to the 0.4 to 0.5% range of DM resulted in up to a 10% increase in milk yields. Research has also shown increasing K to 1.53% of dietary DM resulted in greater feed intake and higher milk yields. The increased dietary requirement of K in heat-stressed cows was attributed to greater excretion of K in sweat in hot compared to cool weather. Also, less forage is eaten in hot weather, which usually decreases K content of the ration.

Fungal Cultures: Studies in Arizona have shown reduced rectal temperatures and respiratory rates as well as increased milk yields in cows fed an Aspergillus oryzae extract. We examined the addition of Aspergillus oryzae during hot weather on a commercial dairy in Fresno County. Cows fed Aspergillus oryzae had lower rectal temperatures compared to controls for 9 of 12 weekly determinations. In another trial conducted under hot summer conditions in Arizona, cows fed yeast culture produced 2.0 pounds more milk per day than controls.

Summary

Milk production decreases during heat stress primarily because of reduced feed intakes. Water is the primary medium for dissipation of excess body heat and milk contains about 88% water. Cows need an abundance of clean, cool water. Remember to consider if you would drink the water from the trough that the cows are drinking from. Feeding of buffers and/or supplemental fat often allow for feeding high concentrate rations without the undesirable effects. Several by-product feeds (beet pulp, soy hulls, citrus pulp, etc.) might also aid in keeping milk fat at acceptable levels during heat stress. Milk yields were higher in heat-stressed cows when Na and K in the diet were increased. Feeding of fungal cultures (both from Aspergillus oryzae and Saccharomyces cerevisiae) modified heat stress effects while increasing milk yields and feed intakes.