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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #146483
Title: MARKED PHYSICAL CHANGES OCCUR IN YEARLING BEEF BULLS DURING NATURAL BREEDING

Author
item ELLIS, ROGER - UNIV. OF NEBR.-LINCOLN
item RUPP, GARY - UNIV. OF NEBR.-LINCOLN
item CHENOWETH, P. - KANSAS STATE UNIV.
item Cundiff, Larry
item Lunstra, Donald

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/9/2003
Publication Date: 6/22/2003
Citation: ELLIS, R.W., RUPP, G.P., CHENOWETH, P.J., CUNDIFF, L.V., LUNSTRA, D.D. MARKED PHYSICAL CHANGES OCCUR IN YEARLING BEEF BULLS DURING NATURAL BREEDING. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. Vol. 81(Suppl. 1) p. 144. 2003.

Interpretive Summary:

Technical Abstract: To assess changes in body condition score (BCS), body weight (BW), scrotal circumference (SC), mating activity and semen quality during natural breeding, 74 yearling (15 to 16 mo) beef bulls were evaluated periodically before, during and after a 63d pasture breeding period (mid-June to August). Bulls used for breeding (UFB; n=60) were compared to control bulls not used for breeding (NFB; n=14). For multiple sire breeding, subgroups of nine to ten UFB bulls were exposed to cows at a bull/cow ratio of 1:20 in 80 to 160 acre pastures. At the start of observations, all bulls averaged 6.1 ± 0.1 BCS, 554 ± 5 kg BW, 36.3 ± 0.2 cm SC. In UFB bulls during the 63d breeding period, BW decreased 73 ± 3 kg (P < 0.001; ranged = -.25 to -103 kg), BCS declined 1.5 ± 0.1 units (P < 0.01; ranged = -1.0 to -2.5 units), and SC decreased 1.4 ± 0.2 cm (P < 0.01; range = -0.5 to -4.0 cm), compared to values observed in NFB bulls. Percentage of normal spermatozoa decreased in both UFB and NFB bulls through the observation period. In general, mating proficiency increased and abortive mounting activity decreased as UFB bulls gained mating experience. In UFB bulls, 75% (n = 45) incurred musculoskeletal (n = 38) or reproductive (n = 7) injuries and 42% (n = 19) of the injuries were classified as major (>4d duration). Pregnancy palpation of cows from each breeding pasture at 65 to 87 days post-breeding indicated 91 to 95% pregnancy rates (parental parentage will be determined after calves are born). We conclude that yearling beef bulls used for multiple-sire natural mating exhibit surprisingly high injury rates and large losses in body weight and testis size with declining semen quality during the breeding season. Additional emphasis on increased management and supplemental nutrition is needed in beef bulls used for multiple-sire breeding, and the impacts of injury rate and losses in BW and SC upon individual bull fertility remain to be elucidated.