Milk production effect of a morantel tartrate treatment at calving in dairy cows with subclinical parasitism.

A field trial involving 217 dairy cows from 13 herds located in four different areas of Quebec was conducted to determine the level of subclinical parasitism. The effect on milk production was evaluated on 116 cows following a single anthelmintic treatment with morantel tartrate administered at freshening. The results showed that this treatment increased milk production in nine herds, which was statistically significant at P </= 0.05 in one of the herds and decreased yields in four herds. Overall, this treatment increased milk production by an average of 255 kg per cow for the official 305 day production period. This increase was found to be not statistically significant (P>0.05).