|MCWHORTER, TAYLOR - UNIVERSITY OF GEORGIA|
|NORMAN, H - COUNCIL ON DAIRY CATTLE BREEDING|
|LOURENCO, DANIELA - UNIVERSITY OF GEORGIA|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2020
Publication Date: 11/1/2020
Publication URL: https://handle.nal.usda.gov/10113/7130119
Citation: McWhorter, T.M., Hutchison, J.L., Norman, H.D., Cole, J.B., Fok, G.C., Lourenco, D.A.L., Van Raden, P.M. 2020. Investigating conception rate for beef service sires bred to dairy cows and heifers. Journal of Dairy Science. 103(11):10374–10382. https://doi.org/10.3168/jds.2020-18399.
Interpretive Summary: Sire conception rate has been used as a phenotypic evaluation of bull fertility in US dairy cattle since 2008. With the increasing use of beef semen in dairy herds, evaluating the fertility of beef bulls becomes of utmost importance. It is expected that the use of beef semen will increase calf value substantially, transforming practices in the dairy industry. We investigated sire conception rate of beef bulls with the objective of providing a tool for dairy producers to evaluate fertility. Mating beef bulls to dairy cows not needed to produce replacement heifers can result in more valuable crossbred calves for beef output. Sire conception rate provides the knowledge of fertility and ranking of beef bulls mated to dairy cows.
Technical Abstract: The widespread use of sexed semen on US dairy cows has led to an excess of replacement heifers’ calves, and the sale prices for those calves are much lower than in the past. Cows not selected to produce the next generation of replacement heifers are increasingly being bred to beef bulls to produce crossbred calves for beef production. The purpose of this study was to investigate the use of beef service sires bred to dairy cows and heifers and to provide a tool for dairy producers to evaluate beef service sires’ conception. Sire conception rate (SCR) is a phenotypic evaluation of service sire fertility that is routinely calculated for US dairy bulls. A total of 268,174 breedings were available which included 36 recognized beef breeds and 7 dairy breeds. Most of the beef-on-dairy inseminations (95.4%) were to Angus (AN) bulls. Due to the limited number of records among other breeds, we restricted our final evaluations to AN service sires bred to Holstein (HO) cows. Service-sire inbreeding and expected inbreeding of resulting embryo were set to 0 as pedigree data for AN bulls was unavailable. There were 233,379 breedings from 1,344 AN service-sire to 163,919 HO cows. A mean conception rate of 33.8% (47.3% SD) was observed compared with 34.3% (47.5% SD) for breedings with HO sires mated to HO cows. Publishable AN bulls were required to have 100 total matings, 10 matings in the most recent 12 months and breedings in at least 5 herds. Mean SCR reliability was 64.5% for 116 publishable bulls, with a maximum reliability 99% based on 25,217 breedings. Average SCR was near 0 (on AN base) with a range of -5.1 to 4.4. Breedings to HO heifers were also examined which included 19,437 breedings (443 AN service sire and 15,971 HO heifers). A mean conception rate of 53.0% was observed (49.9% SD), compared with 55.3% (49.7% SD) for breedings with a HO sire mated to a HO heifer. Beef sires were used more frequently in cows known to be problem breeders, which explains some of the difference in CR. Mean service number was 1.92 and 2.87 for HO heifers, and 2.13 and 3.04 for HO cows mated to HO and AN sires, respectively. Mating dairy cows to beef bulls may be profitable if calf prices are higher, fertility is improved, or if practices such as sexed semen, genomic testing, and improved cow productive life allow herd owners to produce both higher quality dairy replacement and increased income from market calves.