The effect of Calluna vulgaris cover on the performance and intake of ewes grazing hill pastures in northern Spain

The effect of the proportion of Calluna vulgaris cover on diet composition, intake and performance of sheep grazing hill vegetation communities in northern Spain is examined. A total of 591 non-lactating Gallega ewes grazed for five consecutive grazing seasons (June to September) on replicated plots of hill pastures (1700 m.a.s.l.) composed principally of Festuca, Agrostis, Nardus and Calluna spp. but with different proportions of Calluna vulgaris cover, either 0.3 (C-0.3) or 0.7 (C-0.7) of the total area. In 1 year, twenty-eight ewes suckling single lambs also grazed the plots. The mean stocking density over the 5 years was 8.7 ewes ha(-1). On treatment C-0.3, daily liveweight gains (33 g d(-1)) of non-lactating ewes were significantly (P < 0.001) greater than on treatment C-0.7 (12 g d(-1)). Likewise in lactating ewes the difference in mean daily liveweight change was 40 g d(-1) (-5 vs. -45 g d(-1) for C-0.3 and C-0.7 treatments respectively; P < 0.001). Liveweight gains of lambs were only 80-100 g d(-1) from June to August and lambs only maintained live weight during August and September. The effect of lactational status on liveweight changes was not significant. Liveweight gains of non-lactating ewes increased significantly (P < 0.001) from the first to the last year of the experiment on both treatments. The composition of the diet was significantly affected by treatment (P < 0.001), with a higher proportion of grass species on the C-0.3 treatment and a higher digestibility of the diet in the first half of the grazing season (P < 0.001). The proportion of C. vulgaris in the diet was significantly (P < 0.001) higher on the C-0.7 treatment and increased significantly (P < 0.001) from July to September on both treatments. There were no significant differences in the composition of the diet selected by lactating and non-lactating ewes. The results demonstrate that on hill vegetation communities, in which the grass components (Festuca rubra, Agrostis capillaris, and Nardus stricta) cover at least 0.3 of the area and on which the preferred grass component (Festuca and Agrostis spp.) is maintained at a sward height of at least 2.5 cm, non-lactating ewes can increase their live weight and body condition, but this increase is influenced by the proportion and quantity of species of grass in the diet, which is affected in turn by the species of grass available and their nutritive quality. However, ewes suckling lambs were not able to maintain their live weight and body condition except when Calluna cover was 0.3 and grass height was more than 3.5 cm. It is concluded that these indigenous vegetation communities can be used in sheep production systems to complement the use of improved pastures at other times of year. In particular, they can be utilized during the non-lactating period (summer) to increase body condition before the beginning of the mating period in autumn.