Associations among age, scrotal circumference, and proportion of morphologically normal spermatozoa in young beef bulls during an initial breeding soundness examination
Coe, P.H.
Journal of the American Veterinary Medical Association 214(11): 1664-1667
1999
ISSN/ISBN: 0003-1488 PMID: 10363101 Document Number: 511644
Between 1993 and 1997 the scrotal circumference and semen quality of 1173 beef bulls (<15 months of age) from Michigan were examined. The scrotal circumferences of bulls producing >=70% morphologically normal spermatozoa were compared with those of bulls producing <70% morphologically normal spermatozoa. Mean and 95% confidence intervals for age and scrotal circumference were constructed to detect differences between groups of bulls over all observations and within the 5 most common breeds. For these 5 breeds (American Angus, Simmental, Hereford, Limousin and Maine-Anjou), chi superscript 2 analysis was used to examine differences in the proportion of bulls that had values less than the population mean for scrotal circumference, age and percentage of morphologically normal spermatozoa. Multivariate regression was used to quantify variation in the proportion of morphologically normal spermatozoa that could be explained by age and scrotal circumference. Mean (+or-SD) age and scrotal circumference differed significantly (P<0.05) between bulls that produced >=70% morphologically normal spermatozoa (12.7+or-1.1 months and 35.6+or-2.7 cm) and bulls that produced <70% morphologically normal spermatozoa (12.1+or-1.2 months and 34.8+or-3.3 cm). The proportion of bulls younger than the mean age at first examination and the proportion producing >=70% morphologically normal spermatozoa differed among breeds. Age and scrotal circumference explained 11% of the variation in semen quality. Bulls that were older and had larger testes were more likely to produce >=70% morphologically normal spermatozoa. It is concluded that age and scrotal circumference are not good predictors of semen quality.