REPRODUCTIVE-PERFORMANCE OF CD-1 MICE FED DIETS CONTAINING ENDOPHYTE-INFECTED PERENNIAL RYEGRASS SEED THROUGH CONTINUOUS BREEDING

This study was undertaken to further determine the sensitivity of the mouse to a diet containing endophyte-infected (Acremonium lolii) perennial ryegrass (Lolium perenne L.) seed. The degree to which the mouse is affected by the endophyte will determine its value as a bioassay to study ryegrass toxicity in livestock. The focus of this study was to determine the effects of the endophyte on the reproductive performance of mice (Mus musculus) using a continuous breeding protocol for three parturitions. Thirty-six CD-1 mice were randomly assigned to one of three dietary treatments and housed separately by sex for 42 days before pairing. The diets contained 50% Purina rodent chow (w/w) and: (1) 50% endophyte-infected perennial ryegrass seed; (2) 25% infected seed and 25% uninfected seed; or (3) 50% un-infected seed. The intake for Diet 2 and Diet 3 was limited to the average daily intake of Diet 1. The mice were allowed to cohabit through three parturitions. Litter parameters assessed included dam weight at parturition, total liner weight, number of pups born per litter, and sex of each pup. Adult mice were sacrificed after the third parturition. Female parameters assessed were total ovarian and uterine weights. Male parameters assessed were total testicular and epididymal weights. Diet 1 and Diet 2 mice had significantly (P < 0.01) lower dam weights, lower live litter weights and fewer live pups per litter than Diet 3 mice. The mean weight per pup per litter for Diet 1 mice was significantly (P < 0.01) lower than for Diet 2 and Diet 3 mice. There were significant differences (P < 0.05) in ovarian and uterine weights between Diets 1 and 2 versus Diet 3 mice but no differences were noted in testicular weights among the dietary treatments. The epididymal weights of Diet 1 males were significantly lower (P < 0.01) than Diet 2 and Diet 3 males. These results suggest that large herbivores feeding on endophyte-infected perennial ryegrass may also have reduced reproductive potential.