Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/1998
Publication Date: N/A
Citation: Interpretive Summary: Breeding soundness and fertility in beef bulls is essential for reproductive efficiency in beef cattle. Semen evaluation and spermatozoal morphology have been widely used to eliminate subfertile and infertile bulls. The current study detailed for the first time the relative prevalence of various types of abnormal spermatozoal morphology in young beef bulls and the changes in prevalence that occur with increasing age. Results indicated that opportunity for re-evaluation of spermatozoal morphology must be provided for young bulls, particularly for those defects that decreased with age.
Technical Abstract: Objective - The objective of this study was to describe the overall prevalence of sperm morphologic defects and to determine if the prevalence of those defects varied with the age of the bull. Design - This was an cross sectional, retrospective, observational study of 2497 beef bulls evaluated for breeding soundness by 29 practicing veterinarians in a 5 state geographic region in 1994. Procedure - The spermatozoal morphology slides for each bull were made and submitted by the practicing veterinarians. The first author observed 100 spermatozoa on each slide and classified each into one of nine morphologic defects or as normal. Results - 63% of bulls evaluated were 10-12 months of age and 20% were 13-18 months of age. On average 70.6% of spermatozoa were normal. The most common defects were distal droplets (3.8%), proximal droplets (8.4%), separated heads (5.5%), and distal midpiece reflexes (6.7%). Other defects were seen less than 2% of the time. Young bulls (10-12 months of age) had a higher frequency of proximal and distal droplet defects than older bulls (13-18 months of age). Clinical Implications - Practitioners conducting breeding soundness evaluations in beef bulls must be aware of the most frequently found spermatozoal defects. Bulls that are evaluated at a young age will have more defects than older bulls. The opportunity for re-evaluation must be provided for young bulls particularly for those defects that decrease with age.