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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Nutrition, Growth and Physiology » Research » Publications at this Location » Publication #332698
Title: Calving distributions of individual bulls in multiple-sire pastures

Author
item ABELL, KAITLYNN - Kansas State University
item THEURER, MILES - Kansas State University
item LARSON, ROBERT - Kansas State University
item WHITE, BRAD - Kansas State University
item HARDIN, DAVID - University Of Nebraska
item RANDLE, RICHARD - University Of Nebraska
item Cushman, Robert - Bob

Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2017
Publication Date: 1/8/2017
Citation: Abell, K., Theurer, M.E., Larson, R., White, B.J., Hardin, D., Randle, R., Cushman, R.A. 2017. Calving distributions of individual bulls in multiple-sire pastures. Theriogenology. 93:7-11. doi: 10.1016/j.theriogenology.2017.01.010.

Interpretive Summary: Our previous research has clearly demonstrated that calving distribution is a critical economic component for cow-calf producers because heifers that give birth early wean heavier calves for the first six years and have greater reproductive longevity. In addition, our research demonstrated that the timing of initiation of estrous cycles at puberty or post-partum had very little influence on the date when a cow conceived in Bos taurus cows. Since a very high percentage of the cows have initiated reproductive cycles at the start of breeding, this indicates that early embryonic loss is the major contributor to cows that give birth late or fail to conceive and the quality of both the egg and the sperm can contribute to early embryonic loss and the patterns of calving distributions. Previous research using parentage genotyping to identify sires in a multi-sire pasture has shown that among bulls that pass a breeding soundness exam, there are still bulls that dominate pastures in terms of calf production. Therefore, we examined calving distributions by bulls to see if the pattern of dominance differed within 21-day periods. Distributions of the top three bulls were very similar across calving periods. This indicates that this is more likely a libido effect than a sperm quality effect among bulls that pass a breeding soundness exam. Thus, egg quality may contribute more greatly to early embryonic loss in cows and among bulls that have passed a breeding soundness exam, libido may have a greater influence on number of calves sired.

Technical Abstract: The objective of this project was to quantify patterns in the calving rate of sires in multiple-sire pastures over seven years at a large-scale cow-calf operation. Data consisted of reproductive and genomic records from multiple-sire breeding pastures (n=33) at the United States Meat Animal Research Center from 2007 to 2013. Calving intervals were analyzed in 21-day periods. A ranking system for each bull was developed based on the calving rate per pasture over the breeding season, with Rank 1 = the bull with greatest calving rate, Rank 3 = the bull with the least calving rate, and Rank 2 = all other bulls. A total of 179 bulls and 3,703 calves were successfully genotyped over seven years. A uniform distribution was used to describe the expected percentage of calves sired per rank within pasture. Rank 1 bulls sired 113% greater calves than the expected pasture-average, Rank 2 bulls sired 6% less than expected, and Rank 3 bulls sired 81% less than expected. A rank by calving interval interaction was identified (P < 0.05). A Rank 1 bull in calving interval 1 produced a greater average percent of the total calf crop over the entire season, compared to a Rank 2 and Rank 3 bull. The calving rate for individual sires is not homogeneous and there is a large difference between bulls siring the greatest and least number of calves. More research is needed to determine how rank changes over multiple breeding years and its association with dominance, libido, and fertility.