Co-Authors:
Ungar, E.D., Department of Agronomy and Natural Resources, Institute of Field and Garden Crops, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Griffiths, W.M., Department of Agronomy and Natural Resources, Institute of Field and Garden Crops, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Abstract:
Grazing by cattle on the scale of a single feeding station was studied to determine the patterns of defoliation and bite dimensions in short bite sequences. The sward was a continuous and homogeneous expanse of alfalfa without any imposed patchiness of structure. Treatments were bite sequences of 3, 6, 9 and 12 bites, with the forelegs of the observed animal stationary. Four 18-month-old heifers were used and the treatments were conducted over two grazing cycles. The bite scale defoliation imprints (non-contiguous grazed areas separated by undefoliated vegetation) were marked with white spray paint and photographed for shape and area measurements. The mean pre-grazing plant heights for all lengths of bite sequence were 24.8 ± 0.6 cm (cycle 1) and 20.9 ± 0.7 cm (cycle 2), and the mean grazed (residual) plant heights within the defoliation imprints were 14.4 ± 0.6 cm (cycle 1) and 12.9 ± 0.7 cm (cycle 2). One or more separate defoliation imprints was/were obtained for each length of bite sequence. Each imprint was created by one bite or a number of bites in touching or overlapping locations, and contained few undefoliated plant elements. The bite sequences created a variety of defoliation imprints with irregular, often lobed or fingered shapes, which were clearly related to the number of bites removed. The maximum dimension of the grazed imprint tended to be perpendicular to the orientation of the animal, and increased from 46 and 40 cm in cycles 1 and 2, respectively, after three bites to 76 and 85 cm in cycles 1 and 2, respectively, after 12 bites. The overall mean effective bite areas were 101 ± 6.2 and 115 ± 7.5 cm2 per bite in cycles 1 and 2, respectively. The mean effective bite area tended to decline with bite number in cycle 1 only, but the effect was not significant in the overall model. In the absence of a discrete, imposed feeding station structure, bite placement may result in depletion without depression. Care should be taken in applying patch depletion curves to continuous swards when these are derived from discrete-patch studies in which patch dimensions constrain bite placement. © 2002 Elsevier Science B.V. All rights reserved.
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