The usual method of fitting the model y = Anb exp(−cn) to lactation data, by a multiple regression of logey on n and logen, can result in an ill-fitting curve. An analysis of the untransformed data provides a better fit but requires more extensive computation and a simple approximation to this procedure is given. Since the parameters of this model have no direct biological interpretation two alternative models are introduced, each having a parameter measuring the persistency of lactation.

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Four experiments were conducted to assess the performance of ranked set sampling relative to random sampling for the estimation of herbage mass and clover content in grazed swards. The expected theoretical efficiencies were not observed due to the method of selection of quadrats and the nature of the distribution of herbage mass. Nevertheless there should be worthwhile improvement in precision over random sampling, provided that the quadrats within a set are as well spaced as possible, allowing, if necessary, for visual comparison.

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