Effects of Different Applications of Pyrethrin/Pyrethroid Insecticides on Bull Reproductive Parameters

Abstract Text: Objectives of this experiment were to evaluate the long-term effects of pyrethroid and pyrethrin sprays, in combination with ear tag and pour-on insecticides, on bull semen quality and serum testosterone concentrations. There are concerns in the beef industry over the impacts of pyrethrins on fertility. Short-term (9 wk) studies have shown no effects of pyrethrin and pyrethroids on sperm quality in beef bulls, but one study reported reduced serum testosterone concentrations at wk 9. Therefore, we hypothesized that exposing bulls to the fog and premise sprays, in combination with the fly tag and pour-on treatments, would reduce semen quality and decrease serum testosterone over an extended time (18 wk), compared to no treatment or fly tag and pour-on. Angus, Simmental, and Angus x Simmental bulls (n = 28) were randomly assigned to 1 of 3 treatment groups: (1) no exposure to pyrethrin applications (CONT; n = 10), (2) fly tags and pour-on (TAG+POUR; n = 9), or (3) fly tags, pour-on, premise spray and fog spray (TAG+POUR+SPRAY; n = 8). Bull BW, semen, and blood were collected every 3 wk during the 18 wk trial. Semen was collected via electroejaculation and assessed, using computer-assisted semen analysis, for overall and progressive motility, and morphology. Blood was collected from the tail vein and serum testosterone concentrations were analyzed. Data were analyzed using the MIXED procedures in SAS (SAS Inst. Inc, Cary, NC) with repeated measures for motility, morphology, serum testosterone, and BW. There was a treatment × wk interaction (P < 0.01) for sperm with primary defects. At wk 18, CONT bulls had a greater (P = 0.01) percentage of sperm with primary defects than bulls treated with insecticides. Insecticide treatment did not affect overall motility (P = 0.84), progressive motility (P = 0.68), percent normal sperm (P = 0.43), or percent of sperm with secondary defects (P = 0.38). However, over time, overall and progressive motility, and normal morphology of sperm samples decreased (P < 0.01). There was no treatment × wk effect (P = 0.81) or treatment effect (P = 0.25) on serum testosterone concentrations. However, serum testosterone decreased (P < 0.01) over time. Bull BW, BCS, and scrotal circumference were not affected (P ≥ 0.14) by treatment. The use of pyrethrin and pyrethroid based insecticides, regardless of application, did not negatively impact reproductive parameters in beef bulls.

Keywords:

insecticides, beef bulls, reproduction