Seventy five purebred heifers were used to determine whether
Monensin, (trade name Rumensin) fed during the initial growing period
after weaning, would affect the reproductive performance of yearling
heifers. Rumensin had virtually no effect on reproductive performance as
determined by the percentage of heifers cycling at the start of the
breeding season or the percentage of heifers that conceived at first
service and during the breeding season. A slightly higher percentage of
the Rumensin fed heifers were cycling at the start of the breeding season.
Although the study shows that replacement heifers on roughage rations
can successfully be fed Rumensin, causing both a savings in feed as well
as improved growth rate, current clearance of Rumensin does not recommend
its use with breeding animals.
