Effects of Label Dose Permethrin Use in Yearling Angus Beef Bulls on Reproductive Function and Testicular Histopathology

and Implications To eliminate the potential for insect borne diseases and improve productivity in cow-calf operations, many producers use pour-on pyrethroids. However, popular press literature has identified potential links between use of pyrethroids and reproductive function failures in bulls. While literature in mice and rats have reported potential endocrine disruption of sex steroids resulting from pyrethroid exposure, effects of pyrethroid use on bull fertility is still questionable. The objective of this study was to measure reproductive parameters in peripubertal Angus bulls using a commonly used pyrethroid pour-on. We hypothesized that use of a pyrethroid pour-on at labeled dose would have limited effects on semen and testicular characteristics. Results from this study revealed pyrethroidtreated bulls had greater spermatozoa head and midpiece abnormalities compared to controls, resulting in higher primary morphological abnormalities. Although some morphological semen parameters appear to be negatively affected by use of pyrethroid administration in bulls, biological relevance of this result needs to be further elucidated as the ability to pass a breeding soundness exam was not affected. Moreover, further research should be conducted to determine the effects of pyrethroid pour-ons on fertility when used with other pyrethroids such fly tags or perimeter sprays. Based on these results, pour-on pyrethroid use in yearling bulls is still recommended for label dose administration.