The intake of roughages and consequently their contribution to the nutrient status of animals consuming them rises with improvements in overall diet quality. However, the mechanisms which govern this response are not clearly understood and it is therefore difficult to make quantitative predictions of the effects of intervention aimed at improving diet quality.

Documents

Summary

Ten experimental trials were carried out feeding sheep a basal diet of poor quality veld hay supplemented with different levels of either Napier hay or groundnut hay.

Veld hay intake was always greater than would have been predicted had the supplements simply replaced the hay. The increased intake did not appear to be a result of increased digestibility of the veld hay, as evidenced by the concomitant increases in faecal output reflecting greater digesta flows. Greater intakes of nitrogen (N) and total digestible energy resulted in better N retention, the linear relationships between N retention, N intake and total DE intake demonstrating that supplementation had no 'synergistic' effect on N balance.

Supplementation tended to result in higher ammonia concentrations. However, incubation of veld hay in the rumens of sheep given Napier hay or groundnut hay as supplements or sole feeds, showed no effect on the degradation rate of veld hay. Therefore increased intake was not due to any improvement of the rumen environment increasing breakdown of the poor quality basal forage. Measurement of rumen pool sizes of DM and turnover rates showed pool sizes to be largely unchanged by supplementation, although the fractional outflow of digesta tended to increase. Daily feeding pattern (i.e. feeding the supplement in one or two meals per day) had no effect on digestibility or intake. As expected from the higher N intakes, although sheep lost weight on a basal diet of veld hay alone or with supplements of 150 or 300g/day Napier hay or groundnut hay, losses decreased with increasing level of supplementation.