A high percentage of a cow herd calving during the first 21 days of the season provides multiple benefits to the cow-calf producer. During a recent media event hosted by Boehringer Ingelheim Vetmedica Inc., Kansas State University veterinarian Brad White, DVM, MS, outlined how good management and timely breeding of replacement heifers can create long-term momentum, with more early calving females resulting in heavier weaning weights and better cow longevity.
White notes that in most well-managed herds, fertilization at first breeding occurs about 90 percent of the time. However, early embryonic loss results in first-breeding pregnancy rates averaging around 60 to 65 percent. For this reason, it is unrealistic to expect all heifers and cows to calve during the first 21 days of the calving season, but producers can use strategies to optimize early breeding and early calving.
A good target, White says, is to have 65 percent of the herd calving within the first 21 days of the season, 20 percent calving in the next 21 days and 10 percent in the final 21 days. This assumes a 5 percent incidence of open cows at the end of the 63-day breeding season. White refers to this situation as being “front-end loaded” in terms of reproduction.
Numerous studies have shown multiple benefits resulting from two-thirds or more of the herd calving in the first 21 days. White cites a 13-year summary from Rick Funston, PhD, at the University of Nebraska. In that study, 70 percent of females that calved in the first 21 days were cycling at the start of the breeding season the following year, compared with 58 percent of the cows that calved in the second 21 days and 33 percent for the cows that calved in the final 21 days.
In that same study, 81 percent of the cows that calved during the first 21 days were pregnant after first breeding the following season, compared with 69 percent for the middle group and 65 percent for the late-calvers. That benefit carries over from year to year, as the cows that calved in the early group were more likely to do so the next year and subsequent years.
Calves born in the first 21 days of the season tend to have heavier weaning weights than later-born calves, and that benefit carries over, with the Funston study showing hot-carcass weights averaging 816 pounds for those calves compared with 803 for the middle group and 777 pounds for the late group.
Data on more than 18,000 cows at the U.S. Meat Animal Research Center at Clay Center, Neb. shows those that calve in the first 21 days also stay in the herd longer. Average age those cows were diagnosed as open following breeding was 8 years, compared with 7.5 years for the second group and 7 years for the late-calving group. Weaning weights were heavier for the early calving group out to 6 years, and added up to the equivalent weight of one extra calf from the early calving versus late-calving cows.
White stresses that once a cow falls into a later-calving schedule it is difficult to bring her back to early calving. The typical post-partum interval for cows, or the time it takes to return to estrus after calving, is about 55 to 60 days. Cows that calve during the first 21 days of the season will have about 62 to 82 days between calving and the start of the next breeding season, meaning virtually all have begun cycling at breeding. Cows that calve during the second 21 days of the season have only 41 to 61 days between calving and breeding, while those that calve in the final 21 days have only 20 to 40 days between calving and breeding. So, the later a cow calves, the less likely it becomes that she is cycling at the start of breeding, meaning she will again conceive later and calve later.
Heifers have a longer post-partum interval of around 80 to 100 days, which is why it is important to breed heifers at least 30 days prior to breeding cows, to set them up for a lifetime of early calving.
So, if a herd has shifted away from the ideal front-end-loaded calving schedule, such as with one-third of the herd calving in each of the three 21-day periods during the season, what can the producer do to shift more cows into the group calving during the first 21 days? White outlined several options:
· Cull late-calving cows and replace them with heifers bred to calve early. Depending on the situation, this could be a costly and drastic option.
· Shift the calving season later by intentionally moving early calving cows into the later groups. This involves numerous tradeoffs, including likely lighter calf weaning weights, but could be a viable option in some cases. It does not address whatever underlying problems moved cows into later-calving groups, and over time the trend probably will repeat itself.
· Fix the problem with replacement heifers and natural attrition of older cows. This option, while it takes time, probably is the most viable for most producers. By managing replacement heifers appropriately, with good nutrition, health and timely breeding, a producer can increase the percentage of early calving females while some late calvers fall out of the herd each year. Over time, the herd becomes more front-end loaded and probably more profitable.
Click here for a short video of Dr. White discussing heifer development and reproductive momentum.