Validation of the n -alkane technique to estimate intake, digestibility, and diet composition in sheep consuming mixed grain:roughage diets

The usefulness of the n -alkane technique to estimate intake, digestibility, and diet composition in sheep fed mixed diets was tested in an experiment with 16 ewes consuming 4 different proportions of barley grain and straw ranging from 15:85 to 60:40. Two cases were considered: ( 1 ) straw as one component or ( 2 ) straw separated into leaves and stems. The relationship between estimated ( Y ) and observed ( X ) proportion of grain in the diet was highly significant (1: Y = 0.2355 + 0.9945 X , r 2 =0.9999; 2: Y = –2.472 + 1.0063 X , r 2 =0.9999). Actual intake was overestimated in ( 1 ) by 3.43–12.40%, the largest discrepancies corresponding to the lowest proportions of grain. In ( 2 ) actual intake was either overestimated (2.69%) or underestimated (5.38–6.85%), without a clear effect of the diet. A similar pattern was observed for digestibility, which was overestimated in ( 1 ) by 1.65–9.59% and overestimated, (by 2.07%) or underestimated (by 3.80–4.62%) in ( 2 ). Due to the small discrepancies between observed and estimated values, it may be concluded that the n -alkane technique might be a valid method for estimating intake, digestibility, and diet composition in sheep consuming mixed diets, for the two latter provided that faecal recovery of individual n -alkanes is calculated with enough accuracy.