Patterns of intake and digestibility by cattle and sheep of feed mixtures with roughage source, particle size and level of inclu

It has been postulated that intake of feed mixtures will increase with increasing levels of concentrate until a peak is reached, whereafter it will decline again due to a lack of roughage to ensure a healthy rumen environment. Thus, it should be possible to determine the most desirable level of inclusion of a particular roughage in a feedlot diet for example, if peak intake results are also substantiated by observations that the rumen is in a satisfactory functional condition. The postulate referred to above was tested in a series of 6 experiments with cattle and sheep involving the following roughages: Eragrostis curvula hay milled through screens with different apertures, lucerne hay, wheat straw - also milled through different screen apertures, sunflower hulls and sugarcane bagasse in the pelleted and unpelleted form. The studies confirmed the postulate and clearly emphasized that peak intake is a function of type of roughage, its particle size, the mass/volume ratio of the feed mixture and also type of animal (sheep or cattle). It was also evident that the most desirable level of inclusion of a roughage in a feedlot diet can be established in this way. The digestibility of different feed mixtures is apparently not necessarily additive due to feeding level effect~ and probably also, associative effects.