Patch choice by cattle grazing tropical grass swards: A preliminary study

Relatively little information is available on patch choice by ungulates grazing tropical grass swards despite extensive works on temperate grass swards. The present study tested various vegetation variables as a reward to cattle grazing patchy tropical grass swards. The study comprised three trials. Trials I and 3 used a pasture dominated by bahiagrass (Paspallum notatum Flugge) and Japanese lawngrass (Zoysia japonica Steud.), and Trial 2 used a pasture dominated by centipedegrass (Eremochloa ophiuroides (Munro) Hack.). In each trial, three Japanese Black cows were allowed to graze for short periods (30 min) areas (20 m x 20 m) consisting of two equal-size patches, with combinations of patches of H-L, H-M and M-L (H, high; M, intermediate; L, low in height and mass). Patches were created by varying regrowth durations after mowing the swards. Animals always showed significant preference for one patch to the alternative. Variations among individuals were almost always very small. Regression analysis using a preference-currency model showed that animals perceived CP concentration and sward bulk density as rewards and selected patches having higher levels of both currencies. When there was a tradeoff between the two currencies, animals prioritized the currency that showed a greater variation between the patches. With respect to CP concentration, patch preference exhibited a pattern of overmatching, i.e. a patch was disproportionately preferred or avoided, depending on whether it provided higher or lower CP concentration than the alternative. The estimated degree of overmatching, i.e. sensitivity to the reward, was high (exponent = 9.6 +/- 2.3). Comparison of the results with the literature suggests that animals grazing patchy tropical grass swards are more sensitive to quality than those grazing temperate grass swards. (c) 2005 Elsevier B.V. All rights reserved.