Discrimination and Patch Choice by Sheep Grazing Grass-Clover Swards

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The proposition that large herbivores make foraging choices which maximize intake rate was examined in two experiments on discrimination by sheep grazing pairs of swards (patches) varying in composition of two botanical components, grass and clover, and varying in sward surface height. 2. Patch selection was influenced by sward height and by clover content, and their effects were additive. Tall patches were preferred, and intermediate contents of clover were selected in preference to low or high contents. This would reinforce the patchy distribution of the grass and clover components of mixed swards. Sheep did not exploit local variation in clover content within patches. 3. There was no evidence that patch choice was influenced by differences in the intake rate obtained from the two alternatives at hand, although on average the highest intake rates were obtained on tall patches with intermediate clover contents, coincident with the pattern of preference. 4. During frequent switching between patches, components of the functional response such as bite depth, bite weight and intake rate were modified by patch composition and also by the composition of the alternate patch. This short-term carry-over effect must increase the discrimination difficulties on heterogeneous vegetation. 5. It is argued that pre-consumption cues signalling patch quality are of less use to sheep than the information gained about a patch during grazing, but that this is initially distorted by recent experience; and that information constraints on the maximization of long-term intake rate will occur during frequent switching within heterogeneous vegetation.

Feeding behaviour and intake of heifers fed on hays of various quality, offered alone or in a choice situation

“…Partial choices could also result from difficulties in discriminating between the characteristics of each food [12,30]. This would not be the main reason here because the temporary higher preference for the hay which was not given before the choice subperiod indicates that the heifers were able to discriminate well between the hays and in particular between the two coarse ones.…”

Herbage intake, ingestive behaviour and diet selection, and effects of condensed tannins upon body and wool growth in lambs grazingLolium perenneandHolcus lanatusswards in summer

“…Diet and sward composition (above 4 cm) were similar (Table 4). In temperate swards, there is evidence suggesting that the diet of oesophageally fistulated animals may reflect the composition of the top strata of the sward, indicating substantially unselective grazing (Milne et al 1982;Illius et al 1992;Clark 1993;Montossi et al 1994). Though oesophageally fistulated animals were older than the experimental lambs, this is unlikely to have materially affected diet selection (Hodgson & Rodriguez 1971).…”

Preferência De Eqüinos Em Pastejo: Efeito Da Altura De Dosséis De Gramíneas Do Gênero Cynodon

“…As dietas selecionadas por animais em pastejo geralmente contêm uma maior quantidade de folhas e menores quantidades de caule e de tecido senescente, quando comparada às quantidades totais existentes nas pastagens (ILLIUS et al, 1992;DISTEL et al, 1995). A massa de folhas verdes tem mostrado ser o melhor determinante da massa do bocado e da taxa de ingestão instantânea em diferentes estágios fenológicos das pastagens e tem mostrado ser um forte indicativo da preferência entre espécies forrageiras (PRACHE, 1997).…”

“…A espécie vegetal não é a única variável que interfere na preferência de herbívoros em pastejo, pois tem sido comprovado que a estrutura da planta, como a altura, a quantidade de folhas e a altura e firmeza do pseudocolmo afetam a preferência de ovinos e bovinos (ILLIUS et al, 1992;PENNING et al, 1993;DISTEL et al, 1995).…”