204 Relationships between semen quality and scrotal circumference, adiposity, and rumen conditions of developing bulls

Abstract

Abstract Growing concern over breeding soundness examination failures has led to increased interest in identifying factors that may influence semen quality of developing bulls. An experiment was conducted to evaluate relationships between semen quality and scrotal circumference, adiposity, and rumen conditions of Angus bulls (n = 48; 332 ± 47 d of age) that were developed over an 84-d period. Bulls underwent breeding soundness examinations at each of four 21-d intervals. Backfat thickness was measured on d 0 and 84, and rumen pH and temperature were continuously monitored throughout the experiment via rumen boluses (eBolus; eCow, Devon, UK). Simple linear regression was conducted (JMP 13.0; SAS Institute Inc., Cary, NC) to determine independent relationships between semen characteristics and respective explanatory variables. Change in scrotal circumference between d 0 and 84 was directly related to change in percent morphologically-normal sperm (R2 = 0.12; P < 0.05), but no other semen quality characteristics (P ≥ 0.17). Change in backfat thickness throughout the experiment tended to be inversely related to change in percent morphologically-normal sperm (R2 = 0.06; P < 0.10), but was directly related to changes in semen volume (R2 = 0.10; P < 0.05) and total sperm per ejaculate (R2 = 0.12; P < 0.05), but not change in motility (P = 0.24). Mean rumen pH tended to be directly related to changes in semen volume (R2 = 0.07; P < 0.10) and total sperm per ejaculate (R2 = 0.07; P < 0.10), but not changes in motility (P = 0.28) or percent morphologically-normal sperm (P = 0.94). Mean rumen temperature was not related to any semen quality characteristics (P ≥ 0.15). Collectively, these results suggest that rumen pH, as well as changes in scrotal circumference and adiposity are related to and independently explain variation in semen quality of developing bulls.