Using AI in Very Warm Weather
The hottest part of the day should be avoided when breeding, despite traditional a.m./p.m. rule.
As the breeding season for spring-calving herds is getting underway, understanding heat stress in cattle takes an increased importance. Producers who choose to synchronize and then artificially inseminate (AI) replacement heifers or adult cows may have already started, or will begin the process in the next few weeks. If the hot weather arrives during the AI breeding season, some management and breeding alterations may be helpful.
For years, producers who bred artificially upon detected standing estrus (heat) would wait 12 hours before breeding the female in heat. If she was first observed in standing heat in the morning, she would be inseminated that evening. If she was first observed in standing heat in the evening, she would be inseminated the following morning. This was called the a.m./p.m. rule of artificial insemination.
Recent extensive research with dairy cattle has indicated that there is no significant advantage to the a.m./p.m. rule. Similar pregnancy rates have resulted from inseminating in the morning only compared to following the a.m./p.m. rule. Plus, new research at Oklahoma State University on the internal temperature of heat-stressed cattle adds even more concern about handling and inseminating cattle in the evening.
Research with rumen temperature boluses has shown that the core body temperature of beef cows peaks two to five hours after the highest daytime temperature (Pye, Boehmer, and Wettemann. 2011 ASAS Midwest Abstracts Page 104; Abstract 285). On a hot day, the highest daytime temperature is often during late afternoon. Therefore, the peak body temperature of cattle will occur during the window from 6 p.m. to 11 p.m. Elevated core body temperatures have been implicated from other research in reduced pregnancy rates in heat-stressed cattle.
Inseminating all cattle in the morning hours would avoid the heat stress of evening breeding. Some would be bred at first standing heat, others would be bred at the conventional 12 hours after standing heat. If timed AI is the method of choice, cattle work (especially the actual insemination) should be scheduled for the morning hours.
Editor’s note: This article is reprinted with permission from the April 22 Cow-Calf Corner, a newsletter published by the Oklahoma Cooperative Extension Service, for which Glenn Selk is an emeritus extension animal scientist.
