Effect of dosing regime on intake estimation using the n-alkane technique in sheep fed pelleted grass meal

An experiment was carried out to evaluate the n-alkane technique for estima ting the voluntary intake of pelleted grass meal by sheep. Two groups of 12 Scottish Blackface sheep were dosed once daily or twice daily with paper p ellets containing 130mg of C-32 alkane. Mean daily intakes over a 5 day per iod were estimated from n-alkane concentrations in faeces and compared with actual intakes measured by weighing of food. Two faecal sampling frequenci es were compared (once or twice daily) at each dosing frequency. Diurnal pa tterns of intake were determined by weighing food residues every 3h for 4 d ays. Diurnal patterns of faecal n-alkane concentration were determined from rectal grab samples collected every 3h for 2 days. There was no effect of dosing frequency on actual intake. Estimated intake was higher for twice-da ily than once-daily dosed animals when twice-daily faecal sampling was empl oyed (P < 0.05), although differences between mean actual and estimated int akes were not significant. The accuracy of estimation of individual intakes was better for sheep dosed once daily, at both faecal sampling frequencies , than for sheep dosed twice daily. This may have been due to diurnal varia tion in food intake and digesta outflow from the rumen, demonstrating the i mportance of matching n-alkane dosing and sampling regimes to the digesta k inetics of the diet fed. (C) 2000 Society of Chemical Industry.