The effect of the level of roughage during the rearing period on the utilization of food by adult cattle.

In preliminary accounts of this experiment we have discussed the view, widely held by farmers and advisory workers, that cattle reared for the first z years or so of their lives on diets containing a good deal of roughage are able subsequently to make better use of roughages than are similar animals reared on diets containing a higher proportion of concentrates (Balch, Campling, Johnson & Roy, 1958, 1959). This view embodies a theory that the efficiency of roughage utilization can be improved by training. The theory appeared not to have been tested experimentally, although some of the experiments carried out on methods of rearing had tended to suggest that it was invalid (Balch et al. 1959). In the experiment monozygous twin heifers were used to find the importance of the level of roughage given during the main rearing period, extending from weaning at about 34 months until first calving; the subsequent digestive ability, appetite for hay, and milk production of the heifers were observed.