Lifetime productivity of a beef cow begins at the conception of her first calf as a heifer. Replacement heifers conceiving earlier in their first breeding season will calve early in subsequent calving seasons and have greater longevity and lifetime productivity than heifers that conceive later in their first breeding season.
Beef researchers from South Dakota State University (SDSU) and the U.S. Meat Animal Research Center (MARC) studied the effects of heifer calving date on longevity and lifetime productivity of commercial beef cows. Heifers that conceived during their first breeding season were observed until being culled from the herd. Heifers from cow-calf herds (2,195 head) in the South Dakota Integrated Resource Management (SDIRM) program and 16,549 heifers from the MARC herd were included.
The heifers were divided into 21-day calving interval groups. Heifers and cows were determined to have left the herd when they were diagnosed as not pregnant at the end of the breeding season. Animals that departed the herd for reasons other than reproductive failure weren’t included in the study.
Heifers calving during the first 21-day period of the calving season had more longevity than heifers that calved in the second or later 21-day periods. The average longevity for the South Dakota commercial heifers calving in the first period was 5.1 years and later periods was 3.9 years. Comparatively, the average longevity for MARC heifers calving in the first, second or later periods was 8.2, 7.6, and 7.2 years, respectively.
It’s interesting to note that the heifers in the SDSU commercial beef herds averaged three years’ less longevity than heifers in the MARC research herd. And 67% of the MARC heifers calved during the first 21-day period compared with 58% of the SDIRM heifers, perhaps reflecting a difference in replacement heifer selection and development.
Within the MARC heifers, calving period influenced average and total weaning weight. Heifers calving in the first 21-day period weaned heavier calves during the first five years of production, but not years six through nine.
The average weaning weight of calves born to heifers during the first, second and third 21-day periods was 453, 427 and 383 lbs., respectively. Lifetime weaning weight was 286 and 396 lbs. less for heifers calving during the second and third periods vs. the first-period heifers. That weight is nearly equivalent to an additional calf or year of longevity.
Selection and developing replacement heifers to calve early in their first calving season pays nice dividends.
Find the links to the full research reports below:
Scott B. Laudert, Ph.D., is a beef cattle technical consultant and former Kansas State University Extension livestock specialist based in Woodland Park, CO. He can be reached at 719-660-4473.