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 preference of sheep for two temperate grassland species, ryegrass and white clover, was tested by releasing flocks (of three ewes) onto swards (0-25 ha) that contained adjacent monocultures of grass and clover, and observing their intake behaviour over 6 days. The test paddocks contained either 20, 50, or 80% clover by ground area to distinguish partial preference from indifference. 2. To test whether recent diet affected preference, separate groups of dry (nonpregnant, non-lactating) ewes grazed prior to testing on one of three diet 'backgrounds': an all-grass sward, an all-clover sward, or a 50:50 grass/clover sward by area. To consider the effects of physiological state on preference, a further group of lactating ewes, also from a 50:50 grass/clover 'background', were tested. 3. In all cases, the mean diet obtained was a mixture of grass and clover, even though greater intake rates would have been obtained eating pure clover. There was a consistent temporal pattern to preference, with ewes showing the greatest preference for clover in the morning. The results suggest that previous diet 'background' can have lasting effects on preference. Ewes that had been recently grazing monocultures initially showed an increased preference for the opposite species to the one they had been grazing. Over 6 days these animals gradually reverted to a preference for their 'background' diet. 4. Despite major differences in the energy requirement and intake behaviour of dry vs. lactating ewes, no significant effects of physiological state on preference were detected. Sheep grazing from swards of 20% clover spent a smaller proportion of time grazing clover and had a smaller proportion of clover in their diet than those grazing from 50% or 80% clover swards though, in all cases, behaviour was consistent with a preference for a high proportion of clover: sheep were not grazing at random. 5. Overall, the results demonstrate that sheep sustain a mixed diet even in situations where a monospecific diet is readily possible. Several alternative hypotheses to explain this (partial preference, novelty, rarity, 'sampling') are discussed. We suggest the results provide evidence of partial and changing preference by sheep. Our results urge caution in infering long-term grazing behaviour from short-term tests of preference and suggest why knowledge of diet preference even in common herbivores remains equivocal. Journal of Animal Ecology (1994) 63, 465-478 Diet preference of sheepanimal grazing unselectively could take its entire daily intake of dry matter from a few square m...

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Four groups of ®ve spring-calving Holstein±Friesian cows were given a daily grass allowance in a stripgrazing system after either morning (AM; two groups) or afternoon (PM; two groups) milking over a 10week period. The dry-matter (DM) concentration of the grass tended to be higher after afternoon milking [AM, 178 vs. PM, 197 g DM (s.e.d. 5á32) kg ±1 fresh matter], and water-soluble carbohydrate concentrations were signi®cantly higher [AM, 175 vs. PM, 204 g kg ±1 DM (s.e.d. 6á67)]. Although the total times spent grazing (AM, 461 vs. PM, 462 min day ±1 ) were similar for both groups, cows receiving their allocation in the afternoon had a longer evening meal (>4 h duration) compared with those receiving their allocation in the morning (2±3 h), which also spent more time ruminating [AM, 454 vs. PM, 433 min day ±1 (s.e.d. 1á80)]. This short-term study demonstrated how a relatively simple change in management practice in strip-grazing systems could bene®t milk yield and pasture utilization. This is because the DM and watersoluble carbohydrate contents of the herbage are higher in the evening than in the morning, and this is when grazing animals concentrate much of their daily grazing activity.

A study was made to characterize the effect of the duration of regrowth on the pattern of changes in the major physiological processes involved in the net accumulation of herbage, and so to provide a rational basis for optimizing production under rotational grazing.During regrowth following a severe defoliation, rates of canopy photosynthesis, and so the rate of production of new leaves, increased rapidly but there was a delay before there was a corresponding increase in the rate of leaf death. Although the amount available for harvest (crop live dry weight, IV) continued to increase as the duration of regrowth was extended from 'short' (12-13 days), through 'medium' (19-23 days) to "long' (30-34 days), there was not a continued increase in the average growth rate -the increase in the weight ofthe crop. (W-Wo), divided by the duration of regrowth, t. In this study, the average growth rate (based on changes in the weight of lamina alone) increased as the duration of regrowth was extended from 12-13 to 19-23 days but changed little as the duration of regrowth was extended from 19-23 days to 30-34 days. In spring and summer, elongating stems increased the average growth rate (of lamina plus stem) up to 30-34 days but the accumulated stem material could not reliably be harvested by sheep.A mathematical model was used to explain why the average growth rate is characteristically

Perennial ryegrass pastures were maintained at sward surface heights (SSH) of 30, 60, 90 and 120 mm by continuous variable stocking using lactating ewes and their twin lambs in spring and non-lactating (dry) ewes in autumn.The effects of SSH on ingestive behaviour, herbage intake, animal performance and sward structure and production were measured in spring, and again in autumn, when an additional SSH of 20 mm was also established.

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The poteniia] productivity of perennial ryegrass/ white clover swards (GC) under continuous stocking management was assessed by comparing their performance, when grazed by sheep at sward surface heights of 3, 6 and 9 cm, with that of an all-grass sward (G) maintained at 6 cm and fertilized with 420 kg N ha " '. The grass/ clover swards received no nitrogen fertilizer. The different grazing treatments had a marked effect on animal performance. In the first year for example, for treatments GC3, GC6, GC9 and G6-420 respectively, mean stocking rates to weaning were 19-7, 14-3, 8-9 and 18-4 ewes ha " ' {plus twin lambs); lamb growth rates were 223, 268, 295 and 260 g d "' and so total lamb liveweight gain was 1054, 920, 630 and 1148 kg ha"'. The relative performance of the treatments was similar in all three years. All three grazing treatments had a similar effect on the composition of the grass/clover swards. Clover content increased in 1985, and was sustained in 1986 and 1987 during the main grazing season, although a marked decline in clover content during the winter led to a progressive long-term decline in both the proportion and the amount of clover.It is suggested that a management based on maintaining a sward surface height close to 6 cm {as in all-grass swards) leads to optimum performance in grass/white clover swards grazed using continuous stocking with sheep. Despite

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