The value of faecal nitrogen and faecal crude fibre in estimating intake of four subtropical grass species

Abstract

For each four subtropical grasses there is a significant correlation between daily dry matter intake and total nitrogen in faeces per day. The data have been tested for homogeneity under two hypotheses. In the first a test of the difference in slope between the four regression lines showed that they were not statistically different. It was shown that for a common mean value for total faecal nitrogen, the calculated mean daily dry matter intakes of Paspalum commersonii Lam., Urochloa pullulans Stapf, and Chloris gayana Kunth were similar and the relationship for these three could be expressed by one regression line. However, the calculated mean daily dry matter intake for Panicum maximum var. trichoglume (K. Schum.) Eyles was significantly different from those for the other three grasses and P. maximum var. trichoglume cannot be included in a general regression. In the second hypothesis it was shown that all regression lines could pass through the origin. However, as in the first hypothesis, P. commersonii, U. pullulans, and C. gayana could be represented by a common regression line whllst the regression line for P. maximum differed significantly in slope from those of the other three grasses. The results indicate that species can be grouped for this relationship, and that it could be used to measure intake of the free grazing animal on monospecific swards or on mixed swards of species with similar relationships. Lancaster's technique for determining digestibility is discussed in the light of these relationships. Neither percentage faecal nitrogen nor faecal crude fibre was found to be satisfactorily correlated with dry matter digestibility.