Adapt Your Feeding Strategies for Summer Conditions

Summer season negatively affects dairy cow performance in Pennsylvania as temperature and humidity rise. The main effects associated with summer conditions in dairy cows are a notable drop in milk and fat yield along with increased health and fertility problems. These can obviously have considerable impact in profitability, so we all must make adjustments to management and feeding practices to get through this challenging period.

Hot, humid summer conditions cause bunk problems such as mold and fermentation that affect feed quality. Molds grow more readily in hot, wet weather, while feeds exposed to these conditions will undergo fermentation and heat in the feed bunk. Spoiled and heated feed is a real problem as it not acceptable for dairy cows. Even heifers will back off from this type of feed if it is fed to them the following day after being refused by the cows.

The intensity of heat stress can be measured by the temperature humidity index (THI), which combines the effects of temperature and humidity. Until recently, heat stress for dairy cows was thought to begin at a THI of 72. However, research using modern cows with greater milk production has determined that heat stress can begin at a THI of 68. At this level body temperature reaches 101.3°F and respiration rate is 60 breaths per minute; milk losses and reproductive losses also occur at this threshold.

To diminish the effects of heat stress, cows decrease feed dry matter consumption, drink more water, and attempt to evaporate water from lungs and skin. Heat stressed cows eat less to avoid excess of heat from digestion, which is even more critical if the diet digestibility is low. When a cow's dry matter intake (DMI) decreases, the amount of nutrients available to support high milk yield is limited. In addition, energy expenses to maintenance are increased mainly due to efforts to stay cool, such as increased panting activity. If cows are refusing food, they have a greater chance of increased sorting for smaller particle size that can in turn increase the risk of sub-acute ruminal acidosis.

Increased respiration rates increases the amount of carbon dioxide lost from the blood and bicarbonate excreted in urine, so less bicarbonate goes to saliva. Heat stressed cows also have less chewing activity and fewer ruminal movements due to less feed/forage intake. Hence, the buffering capacity of the rumen is reduced and they become prone to develop ruminal acidosis. Increased sweating makes the cow lose electrolytes, mainly potassium and sodium that are important for the overall animal cation-anion balance.

In addition to cooling, shade, and ventilation considerations that are very important, strategic adjustments to diet formulation and feeding management can have a significant importance in allowing cows to better cope with extreme weather conditions. Strategies should be considered according to specific farm conditions, and some of these are:

Adjust nutrient concentration

Adjust nutrient concentration in the diet to help account for the drop in DMI, thereby keeping the same amount of nutrients in less feed. Special considerations to neutral detergent fiber (NDF), protein, potassium, and sodium are needed. Because forages produce greater heat of fermentation and have less energy than grain, decreasing forage to concentrate ratio can help to reduce NDF and the load of heat from digestion while increasing energy density of the diet. However, if NDF levels are already close to NRC recommendations, a decrease in fiber can risk leading to acidosis problems. The use of high quality forages and more digestible fiber in those forages could play a key role in this as it improves diet digestibility and lessens the heat impact. Additives that improve fiber digestibility, such as yeast culture, can also be helpful.

Increased protein concentration is important to maintain high milk yield with low DMI; however, keeping the amount of protein supplied in balance with the cow’s needs is essential to controlling diet costs and limiting nutrient losses in manure. Reducing rumen degradable protein and balancing for amino acids can be particularly helpful in diets for cows under heat stress. It is important to check that potassium and sodium concentrations are at least at 1.5 and 0.5% of ration dry matter respectively to facilitate electrolyte equilibrium and restore minerals lost due to increased respiration and perspiration. Adjust ration magnesium levels accordingly (0.35 to 0.40%).

Feeding buffers such as sodium bicarbonate or sodium bentonite might help to prevent rumenpH drop and problems related to acidosis, including milk fat depression.

Including or increasing inert fats can help to maintain energy intake when DMI is depressed by heat. In addition, fats produce less heat than fiber or starch when they are digested.

Adjust feeding frequency

Adjusting feeding frequency so cows are fed more than once a day could contribute to maintaining the freshness offered. Attention should be given to the feed quality in order to observe molds or feed heating and to cleaning the bunk more frequently.

Feed animals several hours before or after the daily THI peak. Early morning and late afternoon feeding can avoid the coincidence of peak THI with the peak of digestion heat, which often occurs some four hours after feeding.

Provide ample water

Allow for ample drinking water. Water is a very important nutrient to produce milk, it becomes the most critical during heat stress as cows use it to refresh. Cows should have free and easy access to drink fresh and clean water; watering units have to be working well, without leaks and they have to be cleaned often to avoid algae or other contaminants. Providing more water space per cow can be beneficial in the summer months.

Manage the environment

It has to be kept in mind that environmental management can have a great impact on alleviating heat stress. Fans and sprinklers are effective tools to keep cows cool; adequate cow density, ventilation, and shade should also be provided to avoid heat stress. Summer conditions can be tough on high producing dairy cows, but adequate feeding practices can help to mitigate the effects of heat and humidity on cows’ well-being and performance.

- By Elmer Edgardo Corea, profesor, University of El Salvador, and visiting Fulbright Scholar; Dr. Jud Heinrichs, professor, Penn State Department of Dairy and Animal Science, ajh@psu.edu; and Coleen Jones, Penn State Extension Dairy Team, cjones@psu.edu