Long-Term Effects of Clinical Applications of Pyrethrin and Cyfluthrin, a Synthetic Pyrethroid, on Bull Reproductive Parameters

Effective fly control is crucial for cattle health and well-being; however, pyrethrin and pyrethroid insecticides can impair semen quality and inhibit testosterone production in mammals. Previous experiments demonstrated pour-on, ear tag, and spray applications of pyrethrin and pyrethroid insecticides had no effects on bull semen quality in the short-term (zero to nine weeks). However, spray applications of these insecticides decreased serum testosterone concentrations at nine weeks, suggesting potential detrimental effects on reproductive parameters if used long-term. The objectives of the current study were to determine the effects on bull reproductive parameters of pyrethrin and beta-cyfluthrin spray applications, used at labeled dosages over 18 weeks, in combination with cyfluthrin pour-on and ear tags. [...]