177 Early Weaning Impairs Reproductive Development and Fertility of the Male

Abstract

Abstract Reproductive failure remains a major limitation to the efficiency of livestock production. Early weaning has been linked with reduced male fertility; however, the biological mechanisms mediating this effect are largely undefined. The objective of this study was to develop a murine model to examine the effects of early weaning on testis development and function. Neonatal CD-1 mice were reared with their dams and littermates; pups were randomly assigned to either conventional (21 d; n = 12) or early (18 d; n = 12) weaning. At maturity, males were paired with a primiparous, non-littermate female. Copulatory plugs were detected daily, and females were euthanized at d 14 of gestation to assess reproductive traits; males were also euthanized to evaluate reproductive development. Gravid uterine weight tended to be reduced (P = 0.09) in females bred to early-weaned males, which was likely due to differences in litter size because early-weaned males tended to sire fewer viable fetuses (P < 0.08). Implantation rate was not different between treatments (P > 0.10), but the number of fetal reabsorptions tended to be greater in litters produced from early-weaned males (P = 0.10). Early embryonic survival was unaffected by treatment (P > 0.10), but late embryonic survival tended to be reduced (P = 0.08) in litters sired by early-weaned compared with conventionally-weaned controls. Furthermore, average conceptus weight was greater in litters sired by early-weaned males, which may be a reflection of their smaller litter sizes. These data suggest that early-weaned males produce sperm that yield defects in embryonic development not conception. Notably, testis and seminal vesicle weights were reduced (P < 0.01) in males weaned early versus conventionally-weaned controls, even when adjusting for body weight. Smaller testes and seminal vesicles suggest impaired sperm production capacity and testosterone biosynthesis, respectively. Together, these results indicate that early weaning impairs the development and function of the murine testis leading to reduced male fertility.