Breeding Soundness Evaluations of Beef Bulls at Approximately 14 and 20 Months of Age Developed on Forage

The objective of this study was to determine the percentages of forage-fed bulls passing a breeding soundness exam (BSE) at two different ages (14 and 20 mo). Thirty-six bulls representing 5 breeds completed the 168 d Clemson University, Edisto Forage Bull Test and were consigned for sale 332 d from the start of test. The bulls consigned fell into senior (Sr) and junior (Jr) divisions based on birth date and were developed on forage without any type of supplementation. Bulls were weighed, scrotal circumference measured and semen collected at 13.6 ± 0.5 and 14.8 + 0.6 mo of age (BSE 1) and at 19.4 ± 0.5 and 20.9 ± 0.6 mo of age (BSE 2) for Jr and Sr bulls, respectively. Percent motile sperm and sperm morphology were assessed, with the number of normal sperm and sperm with cytoplasmic droplets, mid-piece or tail, or head abnormalities recorded. Statistical analyses were conducted using LS mean procedures (SAS Institute, Cary NC), with division, age at BSE and their interaction as main effects. Means were compared using Student t-test. Chi square analysis was used to evaluate significance for the percentage of bulls passing at BSE 1 or 2. Scrotal circumference was lower at BSE 1 compared to the BSE 2 (33.8 ± 0.4 and 37.6 ± 0.4 cm, respectively; P = 0.0001); however, no difference in SC was observed for bull division or division by age at BSE interaction. There was a significant division by age at BSE interaction for the percentage motile sperm, with the highest motility observed for the Jr bulls at BSE 1 compared to all other observations (P = 0.04). Age at BSE significantly impacted sperm morphology, as the number of normal heads increased (77 ± 2.1 compared to 83.6 ± 2.1 % for BSE 1 and 2, respectively; P = 0.03) and the number of cytoplasmic droplets decreased (10.9 ± 1.7 and 2.7 ± 1.7%, for BSE 1 and 2, respectively; P = 0.001) at BSE 2. A numerically higher number of bulls failed a BSE during at BSE 1 than BSE 2 (83 versus 94%, respectively; P = 0.13). These data show that the numerically higher number of bulls at BSE 1 failed due to the poor semen quality and not SC. These data also show semen quality improves with age and developing bulls on forage did not appear to negatively impact breeding potential as evaluated by BSE.