Effects of feeding endophyte-infected fescue seed on reproductive traits of male mice divergently selected for resistance or susceptibility to fescue toxicosis

Our objective was to determine whether consumption of endophyte-infected fescue seed affected male reproduction differently in a mouse line previously selected for susceptibility (S) to fescue toxicosis than in a line previously selected for fescue toxicosis resistance (R). For 8 weeks following weaning, 48 males per line were provided diets containing 50% of either endophyte-infected (E+) or endophyte-free (E-) fescue seed. Each male was then paired with a female for 1 week, with litter size and weight recorded from subsequent births. Males were then killed, testes and seminal vesicles were weighed, cauda epididymal sperm were collected and testis cross-sections were fixed. The E+ diet reduced litter size by 0.5 in mates of S males but increased it by 1.0 in mates of R males (line by diet interaction P=0.05). Testis traits were not affected by diet or the line by diet interaction. Sperm integrity was adversely affected by the E+ diet (P<0.01) but did not differ significantly between lines, nor were line by diet interactions important. In earlier work, the E+ diet reduced long-term reproduction by a larger amount in S- than in R-line mated pairs. Because the E+ diet had similar effects on reproductive traits in R and S males in the current experiment, we infer that the differential impact previously reported acted primarily through traits expressed in females.