When you think about it, dairy producers impose a lot of stress on their cattle. Cows are bred to calve once a year or so; they are pregnant for 9 months and lactating for 10 or more months; they are machine milked 2 to 4 times daily; and we continue to feed and genetically select them to produce even MORE milk. Consequently, as the demands for increasing milk yield and efficiency continue, more and more stress is placed on the cow’s productive capacity. Thus, it makes sense to keep them as comfortable as possible.
For example, to enhance cow comfort, we provide housing with freestalls of the proper dimensions filled with bedding that is soft, clean, and dry. Our pastures contain shade structures and are maintained in a clean and dry condition. Water is available ad libitum and provided fresh, clean, and cool. Lastly, we manage our herds to counter heat stress in the summer season, and, because we expect higher production from our cows, controlling heat stress becomes extremely important.
The stresses associated with hot and humid environments have huge adverse effects on a dairy cow’s metabolism by greatly increasing her body maintenance requirements. It must be kept in mind that dairy cattle are of northern European origin and are generally intolerant of high environmental temperature above 77°F, especially when the relative humidity is greater than 80%. Moreover, older, heavier, high-producing cows are more susceptible than smaller or younger animals.
The negative effects of heat stress include:
Several factors influence heat stress such as air temperature, air flow, wind velocity, ventilation, relative humidity, animal health, solar radiation, animal crowding, insect pests, location, and breed. The cow herself can control her body temperature to some degree by:
But, under conditions of excessive heat and humidity, we need to help her keep more comfortable. Strategies to control heat stress are aimed at maintaining feed consumption, preventing milk production losses, and minimizing mastitis and other disorders such as acidosis, ketosis, and dystocia.
Methods to minimize stress include:
Helping the cow to cool herself is probably most important, and shade is probably the easiest and least expensive way to do this. However, it is important to keep shade structures away from feed bunks because cows tend to defecate and urinate where they eat. If there is shade over the bunk, they will lie down in feces and urine, which is a prime environment for mastitis-causing bacteria, which grow even better when it’s hot and humid. Under these conditions, factors such as rain, mud, manure, and bedding become important as they influence the numbers and types of microorganisms present on udders and teats. Environmental mastitis pathogens such as E. coli and Strep. uberis grow where it is warm and moist, so it is imperative to keep bedding materials and calving areas as clean and dry as possible and to avoid wet, muddy areas where cows lie down.
Cooling with water and/or fans includes:
In addition to decreasing milk yield and quality and increasing mastitis and SCC, heat stress impairs animal reproduction. Factors include:
Bottom line: Properly cooled cows are more productive because they are comfortable. Cooled cows produce more milk (up to a 10-pound increase/day) and have less mastitis and lower SCC. Likewise, they experience fewer metabolic disorders such as acidosis and fewer feet and leg problems. Reproduction is also improved such as higher conception rates, fewer embryonic deaths, less dystocia, and having larger calves.
Stephen C. Nickerson, University of Georgia