Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, offers herd health advice as part of the weekly series known as the "Cow Calf Corner" published electronically by Dr. Peel and Dr. Glenn Selk. Today, Dr. Selk investigates how heat stress can reduce the pregnancy rate of the cattle in your herd.
"The effects of heat stress on reproductive performance of beef cows has been discussed by many animal scientists in a variety of ways. After reviewing the scientific literature available up to 1979, one scientist (Christenson, R.K. 1980, J. Anim. Sci. 51: Suppl II: 53.) wrote that the most serious seasonal variation in reproductive performance was associated with high ambient temperatures and humidity. He further pointed out that pregnancy rates and subsequent calving rates of 10 to 25% were common cows bred in July through September.
"Typical Oklahoma summer weather can fit the description of potential heat stress, where many days in a row can exceed 95 degrees and night time lows are often close to 80 degrees. Many hours of the day can be quite hot and cause the slightest rise in body temperature of cattle. Research conducted several years ago at OSU illustrated the possible impact of heat stress of beef cows on their reproductive capability. These cows were exposed to bulls as one group (while in a thermo-neutral environment) and one week later exposed to the environmental treatments listed below in Table 1.
"They found that heat stress of beef cows from day 8 through 16 affected the weights of the conceptus (embryo, fluids, and membranes) and the increased body temperature may have formed an unfavorable environment for embryo survival. As noted in table 1, the percentage of pregnancies maintained throughout the week of severe heat stress was considerably reduced.
Click here to see more...