Effects of sward structure on the diet selected by guanacos (Lama guanicoe) and sheep (Ovis aries) grazing a perennial ryegrass-dominated sward |
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| Authors: | M L Bakker I J Gordon & J A Milne |
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| Institution: | Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, UK |
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| Abstract: | The effect of three different vertical structures of a perennial ryegrass-dominated sward, defined by pseudostem heights (cm) — 1·3 low (L), 2·5 medium (M) and 3·5 high (H) — on the bite depth and selection of plant parts within the grazed horizon of the sward by sheep and guanacos was studied. The bite depth (cm) was similar between sheep and guanacos across the different swards (L, 1·5; M, 3·6; H, 3·8) and was related to pre-grazing sward surface height rather than to pseudostem height. There were differences in diet composition between species that were related to differences in selection for plant parts. Sheep had a higher proportion of green leaf in the diet than did guanacos in L (0·84 vs. 0·71, P < 0·05) and M (0·75 vs. 0·59, P < 0·05) swards, and possibly selected this plant part in H swards in which the proportion of green leaf in the grazed horizon was low (0·45–0·50). Guanacos had a higher proportion of dead leaf and sheath in the diet than did sheep in L (0·23 vs. 0·09, P < 0·05) and M (0·30 vs. 0·18, P < 0·05) swards, and possibly selected this plant part on these swards, in which the proportion of green leaf in the grazed horizon was high (0·70–0·95). The proportion of pseudostem in the diet of sheep and guanacos was similar across all swards (0·03) and was generally much lower than that in the grazed horizon (0·01–0·18). Guanacos had a higher proportion of dead stem in the diet than did sheep (0·06 vs. 0·02, P < 0·05) across all swards, but the proportion was similar to that in the grazed horizon of each sward. |
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