Research Update: Duration of postpartum anestrus in cows and heifers

The length of time it takes for a cow to resume fertile cycles after calving directly affects the reproductive performance and efficiency of a cow-calf herd. Dr. Robert Larson, professor of production medicine, collaborated with Dr. Doug Shane, Dr. Mike Sanderson, Dr. Matt Miesner and Dr. Brad White to develop a model investigating the effects on herds with differing lengths of time to resume fertility after calving over the course of 10 years.

Ideally, the average cow in a herd takes 50-60 days to resume cycling following calving when the cows are in good body condition. However, herds with a high percentage of thin cows, cows that experienced calving difficulty, or cows that are slower to resume fertile cycles after calving due to presumed genetic reasons may average slightly to much longer length of post-calving infertility.

“Relatively small increases in the length of post-calving infertility have detrimental effects on the herd’s productivity and those effects can persist for several years,” Dr. Larson explained. “Conversely, relatively small improvements also have important benefits.”

While the differences between a herd with optimal reproductive efficiency and less efficient herds can be difficult, if not impossible to see outwardly, the model provides quantitative evidence of change.

Calving heifers ahead of cows
In a separate study, the group developed a 10-year model determining the effects of breeding heifers before mature cows. One of the challenges when managing the length of post-calving infertility is to ensure that the youngest group of cows that just had their first calf are ready to breed by the start of the breeding season. These young cows tend to take longer to return to fertility than mature cows and good reproductive management of this important age-group starts long before they are bred for their first pregnancy.

“Focusing on development of replacement heifers is critical for good overall herd reproductive efficiency,” Dr. Larson said. “If replacement heifers can be managed so that all those that are selected to enter the herd will calve before the start of the mature cow calving season, all (or nearly all) of this age-group will have time after calving to resume fertile cycles by the start of their second breeding season.”

While breeding replacement heifers earlier than the mature cows provides benefits, it also requires additional management and may be inconvenient. The second model investigated how to select the optimum length of time to breed heifers ahead of mature cows. While the optimum heifer lead time is different for different herds, in general, the greatest bang for your buck occurs when heifers are bred to calve three to four weeks ahead of mature cows. While breeding even earlier provides additional benefits, the amount of improvement in reproductive efficiency decreases with each week earlier that heifer breeding is moved.

Read the published abstracts, papers and key points below.

Journal of Animal Science, Volume 95, Issue 4, April 2017: A deterministic, dynamic systems model of cow-calf production: The effects of the duration of postpartum anestrus on production parameters over a 10-year horizon
Key study findings

Journal of Animal Science, Volume 95, Issue 10, Oct. 2017: A deterministic, dynamic systems model of cow–calf production: The effects of breeding replacement heifers before mature cows over a 10-year horizon
Key study findings

Theriogenology, Volume 105, January 2018: Determining potential pregnancy status differences based on a new method of yearling heifer prebreeding examination
Key study findings