It is important to recognize that the replication adopted will depend on the purpose or objective of the work.If a feed is evaluated and the results are to be used in diet formulation or to estimate rumen environmental conditions, then the values have to be applicable to the animal population.Mehrez and Ørskov (1977) observed that the greatest source of variation was between-animal variation.The variations within animals and between days within animals were small in comparison with between-animal variation.They came to the conclusion that, for such purposes, three cannulated animals had to be used and that replication within animals and between days was not worthwhile and made little difference to the total variance.However, if the purpose or objective is to rank the feed potential of forages, which may be the case for plant breeders at early stages of selection for forage or straw quality, then only one animal needs to be used.In fact, perhaps only one sample is required.Here a word of caution.Many research workers use 48 h degradability as it is close to in vivo digestibility.However, if the objective is to rank them, some indication of A, B and C is required.This is best obtained if, for instance, 24 h is used, rather than 48 h.Degradability values at 48 h tend to blur differences in rate of degradation, the C value. ...
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