Effects of Label-Dose Permethrin Administration on Reproductive Function and Embryo Quality on Superovulated Beef Heifers

and Implications Commercial pyrethroid pour-ons are commonly applied in cow-calf operations to eliminate the potential for insect borne diseases and to improve productivity. However, recent literature has focused on potential negative reproductive effects in the bull after exposure to pyrethroids. While the female bovine has been primarily neglected from the debated pyrethroid concern on reproduction, literature in mice and rats have reported potential endocrine disruption of sex steroids resulting from pyrethroid exposure, with potential detrimental effects on female fertility. The objective was to study the effects of a commercial pyrethroid-based pour-on product, permethrin, on reproductive performance in superovulated beef heifers by assessing steroid biosynthesis and embryo quality. It was hypothesized that exposure to pyrethroid pour-on at label dose would cause minimal effects on embryo quantity/quality and steroidogenesis in the female bovine. Results from this study revealed pyrethroid-treated heifers had a tendency for reduced progesterone, but embryo quantity and quality were not affected compared to controls. Introduction Pyrethroid exposure has been implicated to disrupt important reproductive and endocrine functions. In addition, endocrine disruption is speculated to influence the hypothalamic-pituitary-gonadal axis and impair the necessary feedback mechanisms of hormones that provide the required stability to regulate normal reproductive physiology. Previous observational findings have claimed that bulls exposed to pyrethroids have decreased reproductive function. However, recent literature has refuted that claim. It is important to note that endocrine disruption is not believed to be sex specific, and thus likely to potentially affect female reproductive physiology by inhibiting normal reproductive functions. Previous research has indicated pyrethroids may inhibit progesterone concentrations by