THE PRODUCTIVITY OF DAIRY-COWS FED IRRIGATED SUBTERRANEAN CLOVER HERBAGE

A number of experiments were undertaken to establish the productivity of lactating dairy cows when offered green, immature subterranean clover (Trifolium subterraneum) herbage and to study its utilization by these cows. The research included indoor feeding and grazing experiments and intensive metabolism studies. Levels of daily intake varied from 8 to 22 kg DM/cow and in early lactation, milk yields as high as 28 kg/day were sustained. Marginal returns to extra feeding, up to 15 kg DM/day in early lactation, averaged 1.4 kg milk for each additional kg of DM eaten above 8 kg DM/day. In late lactation, the return to additional feeding was 1.0 kg milk/kg of extra DM consumed over a similar range. Beyond 15 kg DM/day, the return increasingly diminished. Consideration of products of digestion suggested that fermentation of subterranean clover herbage in the rumen resulted in a balance of metabolites that is unlikely to be detrimental to animal production. Although the milk production data for the cows in the early lactation experiments fitted well together, one grazing experiment (in winter) did produce an unusual result. In this experiment, the cows offered most pasture did not perform as well as those offered an intermediate amount. It was considered that this was due to a characteristic of subterranean clover whereby the leaves are considerably less digestible than the rest of the plant; this resulted in selection of a lower quality diet by the supposedly best fed cows. The implications of this are discussed. It was concluded that, while few problems exist with the use of vegetative subterranean clover for lactating dairy cows, lenient grazing is not the most productive strategy when leaves constitute a large proportion of the sward.