Abstract #453

# 453
Effects of label-dose permethrin administration on reproductive function and testicular histopathology in yearling bulls.
Tyler M. Dohlman*1,2, Darin M. Madson1, Patrick E. Phillips1, Chris A. Clark3, Patrick J. Gunn2, 1Veterinary and Diagnostic Production Animal Medicine, Iowa State University, Ames, IA, 2Department of Animal Science, Iowa State University, Ames, IA, 3Armstrong Research and Demonstration Farm, Iowa State University, Lewis, IA.

The objective of this experiment was to study the effects of a commercial, pyrethroid-based pour-on product, permethrin, on reproductive parameters and testicular histopathology of yearling beef bulls. Black Angus bulls (n = 60; 369 ± 17 d of age; 509 ± 33 kg; 6.2 ± 0.5 BCS) were assigned to either (1) saline control (CON) or (2) permethrin pour-on administered at label dose (PYR). All bulls had blood samples collected and were subjected to an industry standard breeding soundness exam (BSE) via electroejaculation at both 5 d before and 14 d post-treatment. Progressive motility and Eosin-Nigrosin stained morphology were analyzed using high power magnification with phase contrast microscopy. Plasma testosterone concentrations were analyzed via RIA. At 34 d post-treatment, bulls were slaughtered and one testicle per bull was collected for histopathological examination. Categorical and continuous data were analyzed with the GLIMMIX and MIXED procedures of SAS, respectively. Change in motility between BSEs was not different due to treatment (P = 0.69). Although morphology improved across treatments between BSEs, PYR bulls had less improvement in percent of head (P < 0.001) and tailless sperm (P = 0.05) abnormalities compared with CON, resulting in less improvement of primary abnormalities (P = 0.04). Nonetheless, morphological differences did not change the overall outcome for satisfactory breeder status (P = 0.82). Change in testosterone concentration did not differ due to treatment (P = 0.22). Histopathological examination determined that testicular degeneration and tubule diameter did not differ as a result of treatment (P ≥ 0.19). It should be noted, however, that degeneration score (higher score having more degeneration) was positively correlated with primary abnormalities (P < 0.01; r = 0.35) and negatively correlated with normal sperm cells (P < 0.001; r = −0.43). In summary, these data indicate that a single use of permethrin at label dose in yearling Angus bulls results in minimal detrimental effects on semen morphology, but not to a degree that affects the ability of bulls to pass a standard BSE.

Key Words: permethrin, breeding soundness exam (BSE), sperm