Animal Science, Department of



R. M. Lewis

Document Type


Date of this Version



Lewis, Magadlela, Jessop & Emmans in Animal Science (2003) 77.


Copyright 2003, British Society of Animal Science. Used by permission.


This study assessed the efficacy of the n-alkane technique to estimate intake and diet composition in animals given single foods or a choice of two. In thefirst experiment intakes of pelleted ryegrassand lucerne, given eitheralone or as a choice, were measured in lambshoused indoors in individual pens. Each of the three feeding treatments was given to 12 lambs at two degrees of maturity (0.30 and 0·45 of estimated mature sizes). The 12 lambs were constituted as three replicates of the two sexes of each of two breeds. The measured intakes werecompared with those estimated using the n-alkanes C31 andC33, found naturally in thefoods, andC32 whichwasgiven as a dose. On the choice treatment diet composition was estimated using. a non-negative least squares procedure and data onC31 and C33 alone. The agreement between actualand predicted intakewas good: R2ofO·938for log-linear regression with a residual standard deviation of 0·0845. Intake of lucerne when offered alone was slightly yet significantly over~ predicted. The proportion of ryegrass in the diet was also accurately predicted (R2of 0·950 and residual s.d. of 0.0398). Using the data on C2l and C29, in addition to that on C31 and C33, gave a poorer agreement with the observed diet compositions. The low and similar levels of e2l in the two foods meant that ihisn-alkane provided little extra information that couldbe used to estimate diet composition. In a second experimentfaecal samples were collected every 4 hours over a 24-h period in six lambs on ad libitum, and in six lambs on a restricted quantity, of pel/eted ryegrass. There was no significant diurnal variation in the ratios of either C31 or C33 to C32 on either ad libitum or restricted feeding. The time offaecal collection within a day should not therefore affect the reliability of the predictions. The study confirmed the value of using n-alkanes in methods to determine the intake of forages by sheep, and that the time of faecal collection within the day does not affect the reliability of these predictions. The results also confirm theuWity of the n-alkane method for estimating diet choice, at least with two-component mixtures.