Growing Beef Newsletter
April 2025, Volume 15, Issue 10
Facilitating timely return to estrus
Chris Clark, ISU Extension and Outreach beef specialist
With spring calving season well underway across the Midwest, it will soon be time to breed those females that have given birth this spring. As producers prepare for breeding season, it can be valuable to think about how to minimize postpartum intervals and support timely return to estrus. For those who may not be familiar, postpartum interval is simply the time between birthing a calf and rebreeding, and “return to estrus” refers to coming back into heat after a period of not cycling after giving birth (postpartum anestrus).
To keep females on a 365-day calving schedule they must rebreed by day 80-85 postpartum. Cows naturally go through a period of postpartum anestrus, in which a process called uterine involution occurs. Uterine involution involves the uterus shrinking in size and returning to its normal, nonpregnant state, a process that takes at least 20-40 days for most cows. Upon return to estrus, the first heat may be shorter in duration and less fertile than normal, adding another approximately 21 days postpartum until they get to a solid second estrus. One simple take-home message is that the calendar is pretty tight and it’s asking a lot of our cows to stay on that 365-day calving schedule.
Why is this 365-day calving schedule important? This schedule affects efficiency and profitability of the herd as well as longevity of individual cows. Calves born in the first 21 days of the calving season tend to out-perform later-born counterparts throughout their lives and throughout all stages of production. It only makes sense that more calves born early in the calving season would result in more individual animals with that age and weight advantage and contribute to overall productivity and profitability. Beyond that, it gives cows some "cushion" so that if they do happen to fall back a little bit from their 365-day calving schedule, they can still calve in the heart of the calving season and not risk falling completely out of a defined calving season. For cows that calve at the end of a calving season, if they fail to maintain that 365-day schedule, they are at risk of coming up completely open and being culled. For herds without a defined calving season, these cows can calve later and later over time, further spreading out the calving distribution.
What can producers do to facilitate timely return to estrus? The first major factor is nutritional management and overall body condition score (BCS) of the cows. Cows should be in a BCS of 5-6 at calving time. Numerous studies show that in addition to other benefits such as greater calf vigor, shorter time to stand, better colostrum, etc., a BCS of 5-6 at calving time is associated with shorter postpartum intervals or quicker return to estrus.
Obviously, at this point, cows that have already calved or are soon to calve at a lesser BCS are at a disadvantage. The only option is to improve their nutrition as soon as possible and feed them adequately to meet their nutritional requirements of lactation plus nutritional requirements of BCS gain. This likely means working with a nutritionist, extension specialist, or other similar expert to balance the diet. In many cases, more nutrient-dense feeds such as concentrates, high quality hay, silage, etc. may be required until spring pasture is ready to be grazed. And even upon pasture turnout, these females may benefit from supplementation with nutrient-dense feeds.
What can be done to shorten postpartum intervals in late-calving cows to make them calve earlier in the subsequent calving season? One strategy is to use progestin-based estrus synchronization protocols which have been shown to increase the proportion of anestrous cows to cycle and become pregnant. Numerous protocols exist that utilize controlled intravaginal drug release (CIDR) devices as slow-release progesterone sources. This progesterone exposure has been shown to manipulate cycles and, in some cases, “jump start” cyclicity in anestrous cows. Research has shown that inserting the CIDR no sooner than 20 days post-calving can initiate cycling earlier than may occur naturally. Whether or not artificial insemination is being utilized, estrus synchronization can help to hasten return to estrus and shorten postpartum interval for late-calving females.
Are there other strategies that can help support return to estrus? There are several other strategies that can be helpful. Dystocia, or difficult birth, tends to increase postpartum intervals so minimizing dystocia can help to facilitate “normal” return to estrus. Use of calving ease bulls, knowledge of the stages of labor, prompt assistance when problems occur, etc. all can help improve the likelihood of prompt rebreeding in the subsequent breeding season. A few other things like short-term calf removal and bull stimulation can be used to influence hormone levels of females and promote cyclicity.
Producers should evaluate calving distribution this season and consider using some of these strategies to improve this distribution moving forward. Some extra attention to detail this breeding season may pay dividends at this time next year.
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