FROM FEEDING STATION TO PATCH - SCALING-UP FOOD-INTAKE MEASUREMENTS IN GRAZING CATTLE

The technique of grazing cut sods was used in combination with sound a nd video recording to examine the feasibility of using small-scale dep letion curves derived from stall trials to estimate forage intake of c attle at the pasture. Setaria lutescens sods were grazed for a variabl e number of bites to generate patch depletion curves. Depletion curves characterize forage intake as a function of the number of bites taken at a single feeding station. Thus, the method agrees with a hierarchi cal approach to foraging and it could be used as a basis for scaling u p food intake measurements to larger spatial scales. Two sod experimen ts were carried out, with the second experiment as a validation for pr edictions of intake. A field experiment was carried out to validate th e predictions from the sod experiments with respect to both the amount and the rate of intake. Bite weight was largely determined by initial sward height and depletion level. Cumulative dry matter intake from t he sods was well described by a rectangular hyperbola including the va riables of number of bites and sward height. Bulk density added little to the explained variation, but was an important factor to account fo r the dry matter intake on short, dense sods from the second experimen t. Feeding time could be explained to a great extent by the number of bites and chews taken, both in the sod and in the field experiments. H owever, the animals were substantially faster when grazing in the fiel d than on the sods due to a relatively smaller chewing effort. The est imate of bite weight in the field based on the sod depletion curves wa s validated by an independent estimate derived from the chew to bite r atio. Bite weight estimates that ignored feeding station depletion wer e significantly greater than the independent estimates. We conclude th at the sod grazing technique is an adequate tool to investigate food i ntake and forage depletion by grazing. It shows promise as a tool to e xplicitly scale up of foraging behaviour from the level of the feeding station to that of larger patches. (C) 1998 Elsevier Science B.V. All rights reserved.