The metabolic excretion and true digestibilities of nitrogen and fat by cattle and sheep with particular reference to forage-faeces relationships

Abstract

The non-dietary nitrogen excretion in faeces and the true digestibility of nitrogen determined in 23 digestibility experiments with grasses were respectively 0.60 ± 0.063 g N per 100 g forage organic matter and 84.9 ± 2.29%, when estimated from the regression of digestible nitrogen on percentage dietary nitrogen, and 0.60 ± 0.026 g N and 82.9 ± 2.33%, when estimated from data obtained by separating dietary and nondietary faecal nitrogen with detergent solution. The true digestibility of nitrogen, estimated similarly in four digestibility experiments with legumes, was higher than that in grasses. Among grasses and legumes but not within grasses, digestible organic matter was more closely correlated with non-dietary faecal nitrogen than with total faecal nitrogen. Among and within grasses and legumes the apparently digestible protein was more closely correlated with faecal nitrogen when undigested dietary nitrogen as a proportion of total faecal nitrogen was included as a variate in a multiple regression equation.

The endogenous excretion of saponifiable fat was negligible and its average true digestibility estimated from regression analysis was 52. .6 ± 5.55 %.