The accuracy of using the ratio of nitrogen to acid detergent fibre in faeces to partition nitrogen between faeces and urine in total excreta collections from ewes

A comparison was made of the estimates of the outputs of nitrogen (N) in faeces and urine on Awassi ewes using two methods: (1) conventional collection in digestibility crates, with urine acidified to prevent volatilization (separation method); (2) collection of both faeces and urine together in bags placed over the tail of the ewe and using the ratio between N and acid detergent fibre (ADF) in samples taken from the rectum to partition the total N output between faeces and urine (N:ADF method). The comparison was made on eight ewes in a crossover design using three collection periods of 5 d. There were no significant differences between the methods in the estimates of nitrogen in urine and faeces, although differences between methods in the estimation of total N output were close to being significant. The precision of the estimates was lower with the N:ADF method.