THE USE OF SHEEP AS A MODEL TO PREDICT THE RELATIVE INTAKES OF SILAGES BY DAIRY-CATTLE

A study was carried our to determine if sheep could be used as a model for predicting the intakes of silages by cattle. Fifty ewes and 45 co ws were offered five grass silages unsupplemented in two parallel rand omized-block experiments over a 4-week period. Each silage had been ma de using the same equipment over a range of cutting dates (May July, A ugust 1991). The silages differed in fermentation characteristics, wit h lactic acid concentrations varying from 15.3 to 90.7 8/kg dry matter , and ammonin-nitrogen concentrations from 77 to 198 g/kg nitrogen. Wh en expressed on a metabolic live-weight basis, the mean intakes of sil ages silages by cows were 2.25 times those of the sheep, with the mean intakes being 35.1 and 79.1 g/kg M(0.75) for the sheep and cows respe ctively. However, there was no significant correlation between recorde d intakes during the 4th week of the study by the two species (y (cows ) = 0.62x (sheep) + 58.40; r(2) = 0.03). It was concluded that sheep w ere not a useful model system to predict the intakes of a range of gra ss silages of similar chop length by dairy cows.