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 + 0.9945X, r(2) = 0.9999; 2: Y = -2.472 + 1.0063X, 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.