During the years 2000–2001, 7 non-lactating beef cows, 40 ewes and 40 does were managed in mixed grazing on a natural heathland vegetation plot (22 ha) with 20% improved pasture (perennial ryegrass) on a hill (1000 m a.s.l.) experimental farm located in the NW of Spain. Samples of faeces and vegetation components were collected monthly to estimate diet selection, using the alkane markers, and diet overlapping level. Animals were weighed monthly to quantify live weight changes and performance of the three livestock species during different periods (spring, summer, autumn, winter) of the grazing season.
The percentage of shrubs in the diet was significantly higher in the small ruminants (ranging between 36% and 85%) than in cows (less than 25%) in any period. Gorse (Ulex gallii) and heather (Erica spp., Calluna) percentages were always significantly higher in does than in ewes, except in autumn for heather. Herbaceous component (namely grasses) was higher in cattle (75–99%) than in small ruminants (15–64%). The lowest mean dietary overlap was found between cattle and goats (50.4%), with large differences during the grazing season, ranging between 20% and 70%.
The three animal species increased their live weight in the first grazing period (spring), when the mean sward height on the improved area was higher than 6.0 cm. However, when the sward height was lower than 3.5 cm (summer–winter), cows lost weight (− 437 g/day) while ewes and goats were still able to increase their weight (29 and 5 g/day, respectively).
Therefore, it seems that small ruminants, mainly sheep, are more suitable than cattle from the vegetation utilization and animal performance points of view, as cows were unable to maintain live weight when the preferred grass availability decreases. Goats were the species that included the highest proportion of heathland vegetation components in the diet, especially gorse, although their performance was significantly lower than in sheep. In consequence, small ruminant production systems could be more sustainable than cattle. The results indicate that mixed grazing of sheep and goats could be appropriate in these vegetation communities, allowing the development of sustainable systems, in which animal performance and the efficiency of resource use are maximized. 相似文献
The objectives of the two experiments presented were to determine the separate effects of diet and mobility associated with grazing on the metabolic potential of muscles of Charolais steers reared at similar growth rates and slaughtered at the same age (31 months on average).Glycolytic [lactate dehydrogenase (LDH), phosphofructokinase (PFK)] and oxidative [β-hydroxyacyl-CoA dehydrogenase (HAD), citrate synthase (CS), isocitrate dehydrogenase (ICDH), cytochrome c oxidase (COX)] enzyme activities were measured spectrophotometrically in semitendinosus (ST), a glycolytic muscle, and rectus abdominis (RA), an oxidative muscle.In Experiment 1, 24 weaned steers were assigned to two groups: grazing grass (GG) and maize silage (MS). In Experiment 2, 30 weaned steers were assigned to five groups: grazing grass (GG), cut grass without walking (CG), cut grass with walking (CGW), maize silage without walking (MS) and maize silage with walking (MSW). Both experiments lasted for 2 years. All grass fed animals were fed grass silage during the two winter seasons. During the two summer seasons, GG steers were grazing and did not receive any supplementation while CG and CGW steers were fed indoor freshly cut grass alone. MS and MSW steers were fed maize silage indoor during the entire experiment. For the second summer before slaughter, half of the indoor fed steers on each type of diet (CGW and MSW groups) was submitted 7 days a week to a 5.2 km walk daily.At slaughter, carcass weight and composition did not differ between groups. Oxidative HAD, CS and ICDH enzyme activities were higher for GG, as compared with MS group, in RA muscle in both experiments (P < 0.05 to 0.01) and in ST muscle (P < 0.05) in Experiment 2. Muscles from the GG group were thus more oxidative than those of the MS group. It was further tested whether these effects could be specifically attributed to the nature of the diet or to differences in mobility. A cut grass diet (vs. maize silage) increased HAD and ICDH activities (P < 0.05) and mobility induced by walking increased HAD and CS (P < 0.01) activities. In conclusion, the more oxidative metabolic orientation of muscles of grazing steers originates from a combination of two effects: an increase mobility at pasture and a grass (vs. maize silage)-based diet. 相似文献
