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Investigating conception rate for beef service sires bred to dairy cows.

T. M. McWhorter




Investigating conception rate for beef service sires bred to dairy cows.
T. M. McWhorter*1, J. L. Hutchison2, H. D. Norman3, J. B. Cole2, G. C. Fok3, D. A. L. Lourenco1, P. M. VanRaden2. 1Department of Animal and Dairy Science, University of Georgia Athens, GA, 2USDA Animal Genomics and Improvement Laboratory Beltsville, MD, 3Council on Dairy Cattle Breeding Bowie, MD.

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; therefore, final evaluations were restricted to AN service sires bred to Holstein (HO) cows. 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 (SD) conception rate of 33.8% (47.3%) was observed compared with 34.3% (47.5%) for breedings with HO sires mated to HO cows. 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 (SD) conception rate of 53.0% (49.9%) was observed, compared with 55.3% (49.7%) 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.

Keywords: sire conception rate, beef-on-dairy, beef bull fertility.

Biography: I am a second-year graduate student pursuing my Ph.D. at the University of Georgia (UGA) working with Dr. Daniela Lourenco. This will be my first graduate degree after receiving a B.S.A. in Animal Science at UGA. During my graduate studies, I was given the opportunity to complete a joint internship at the Council on Dairy Cattle Breeding and the USDA Animal Genomics and Improvement Laboratory in the summer of 2019 where the beef-on-dairy research was conducted.