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 thermoneutral environment) and one week later exposed to the environmental treatments listed below in Table 1. 

Table 1. Effects of Imposed Heat Stress on Reproduction in Beef Cows  
(Biggers, 1986;OSU) 
 
 

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. 

Florida scientists studying dairy cows reported that for high conception rates the  temperature at insemination and the day after insemination was critical to success.  They stated that the optimal temperature range was between 50 degrees F. and 73 degrees F.  Marked declines in conception occurred when temperatures did not fall in this range. 

Beef producers conducting Artificial Insemination or Embryo Transfer may want to take heed of this information.  Make certain that cows are allowed access to shade and adequate air movement, at breeding, and immediately following breeding.  Of course, adequate cool water is important anytime during the summer months.  Avoid forcing  recently inseminated cows to stand in treeless, drylot situations where relief from the Oklahoma heat is impossible.