Proceedings, Western Section, American Society of Animal Science Vol. 59, 2008 EVALUATION OF CALF OUTPUT AND PROGENY CARCASS DATA OF COMMERCIAL BEEF BULLS A.L. Van Eenennaam†, D.J. Drake*†, and D.J.Garrick‡ †University of California, Davis, CA and ‡Iowa State University, Ames, IA ABSTRACT: Multi-sire breeding pastures preclude visual paternity identification; limiting opportunities for evaluation of sire prolificacy or progeny performance. Furthermore, few producers retrospectively receive individual carcass data resulting from the harvesting of their calves. As a result, commercial cow-calf producers have little opportunity to evaluate the performance of their herd bulls. In this study, DNA-based testing was used to assign paternity to a cohort of 205 steers from a cowherd bred to 19 registered Angus bulls that had passed a breeding soundness exam. Carcass data was collected following a feedlot phase where all steers were fed as a contemporary group. Gross income was assigned to carcasses based on carcass weight and a $2.87/kg carcass value, adjusted by the American Angus Association grid. One hundred and eighty calves were assigned to single sires (87.8 %), and all sires were excluded from the remaining 25 (12.2%) animals. The number of steer calves per bull varied from 0 to 22. The two highest output bulls accounted for nearly a quarter of all the calves assigned. Carcass data showed significant differences between sires for carcass weight, yield grade, marbling score, fat thickness, grid value, and value per carcass. Breed association EPDs for these young bulls were low accuracy, about 0.05 for carcass traits and 0.3 for ultrasound carcass traits and some were poorly correlated with observed carcass measurements: reflecting the shortcomings of the low accuracy EPDs that are associated with young sires. The average carcass value of steers from different sires varied by as much as $160. The total value of steer calves produced showed large variation between sires, ranging from $0 to $21,098. Calf output was more important than average carcass value in determining the gross income per sire. The five most prolific bulls contributed half of the total income from the steer calf crop. This work demonstrates the need for accurate tools for early decisions regarding bull selection. Key Words: parentage, bull, evaluation, EPD Introduction Many beef cattle are produced in multi-sire breeding pastures limiting opportunities for visual sire identification and genetic evaluation. Single bull breeding pastures can provide paternity but are not typically used due to extensive land use, inadequate fences, risk of bull failure, and the increased labor costs associated with pasture subdivisions. DNA-testing offers an approach to assign parentage without changing production practices (Dodds et al., 2005), and provided the tests are sufficiently powerful they can even be used to assign paternity in large multi-sire groups (Van Eenennaam et al., 2007). Multi-sire breeding pastures have shown large variation in calf output (number of calves) by individual sires (DeNise, 1999; Holroyd et al., 2002; Van Eenennaam et al., 2007). Age of bull, breed, fertility- associated antigen status, sperm motility, and morphology, and social dominance have been associated with variation in calf output in multi-sired herds (Whitworth et al., 2003). In the absence of progeny information, genetic evaluation of herd bulls has been limited to that derived from their pedigree. Although breed-based EPDs are the most effective selection tool currently available for yearling bulls, the low accuracy of young sire evaluations means that considerable genetic variation remains among bulls with similar EPD profiles. DNA-testing allows progeny testing to be undertaken on commercial bulls and offers an approach to develop on- ranch or “commercial ranch” genetic evaluations of herd bulls based on the performance of their offspring under field conditions. Such evaluations may help producers identify bulls whose progeny perform well in their ranch environment. Tracking the performance of individual offspring through processing and grading further presents an opportunity to improve the accuracy of carcass trait genetic evaluations for herd bulls. Genetic evaluations for beef carcass traits have not been reported from multi- sire breeding herds. The objective of this work was to use parentage assigned from DNA markers to determine calf output, progeny carcass trait performance, and gross carcass value derived from commercial sires in multi- sired breeding pastures. Additionally, commercial carcass trait genetic evaluations were developed and compared to the low accuracy pedigree-based genetic evaluations typically associated with yearling bulls. Material and Methods Animals and ranch operation. This study was conducted on a commercial farm using animals that were owned by the cooperator and standard animal husbandry practices were employed. Nineteen bulls registered with the American Angus Association (AAA) were randomly assigned to three multi-sire breeding pastures with mature cows. All bulls were in good body condition and had passed a breeding soundness examination (BSE) by a licensed veterinarian prior to the breeding season. Bulls were assigned to achieve approximately a 25:1 female:bull ratio. Injuries and fighting, as well as changes in body condition of bulls, contributed to management decisions to move bulls among breeding groups to maintain an approximate 25:1 ratio throughout the breeding season. A single Angus AI sire selected for calving ease was used to breed a group of first-calf heifers. Calves were born between 1/4/06-3/3/06 and steers were shipped and fed together on a commercial 122