Using n-alkanes and known supplement intake to estimate roughage intake in sheep

Abstract

In animals consuming known amounts of supplement, total intake of roughage plus supplement could be estimated by dividing known supplement intake by the supplement proportion in the diet, if the latter were estimated using the alkane patterns in roughage, supplement and the faeces of the animals consuming them. The roughage intake could then be obtained by multiplying total intake by the estimated roughage proportion in the diet. This approach was tested using data from a previous study, and the results of a second experiment. In the first experiment, perennial ryegrass chaff and sunflower meal labelled with beeswax alkanes were fed in different proportions to young sheep. Known roughage intake was significantly under-estimated (P<0.05) by about 8% using this approach, due mainly to the 12% under-estimate in animals receiving the lowest level of supplement. This reflected the compounding of errors in estimating the dietary proportion of supplement in that treatment. In the other treatments, there was a smaller and non-significant difference between known and estimated roughage intakes. In the second experiment, similar animals were fed either subterranean clover chaff alone or known proportions of chaff and cottonseed meal labelled with beeswax. There was excellent agreement between the known proportions of supplement in the diet and those estimated using alkane patterns in the chaff, meal and the faeces obtained by total collection. As a result, total intakes and thus chaff intakes were estimated very accurately; mean estimated chaff intake was less than 1% different from known mean chaff intake. The results suggest that in animals such as the dairy cow, where daily supplement intake is known or can be controlled, the intake of pasture or its components could be estimated using the approach described, without the need to dose the animals with synthetic alkanes.