Diet selection and performance of sheep and goats grazing on different heathland vegetation types
Introduction
Semi-natural vegetation communities differ in terms of their botanical and structural composition, and they can change according to their management (grazing system, stocking rate, animal species, breed, flock type) and other environmental circumstances as soil conditions, climate, incidence of fires, etc. (Crawley, 1997). As a result, animal performance could be positive or negatively affected (e.g. Common et al., 1991, Osoro et al., 2007, Critchley et al., 2008).
Heathlands cover large surfaces across the humid temperate areas of Western Europe and particularly in the Cantabrian Mountains of northern Spain. Small ruminants could be the most appropriate domestic animal species to look for sustainable systems under these marginal conditions (Celaya et al., 2008, Osoro et al., 2011). Their ability for diet selection is known, as well as their lower total nutrient requirements and shorter gestation and lactation periods compared with larger herbivores such as cattle. Sheep are recognized as having selection capacity for diets with higher nutrient content and digestibility (Hodgson et al., 1991, Osoro et al., 1999, Fraser et al., 2009), whilst goats have the ability to use woody plants such as heather (Erica spp., Calluna vulgaris) and gorse species (Ulex spp.) (Bullock, 1985, Radcliffe, 1986, Celaya et al., 2007). Thus, under these heathland conditions sheep and goats could provide more opportunities for the development of sustainable extensive grazing systems than large herbivores. Gallega sheep, a local breed from Galicia (NW Spain), have good productive responses in grassland–heathland mosaics in the Cantabrian Mountains due to their small body size (Osoro et al., 1999, Osoro et al., 2000b). On the other hand, foreign Cashmere goats are well suited to Cantabrian heathlands, either associated or not with improved pastures (Osoro and Martínez, 1995, Osoro et al., 2007), adding extra output as quality fibre to traditional meat production systems. However, more information is needed to assess the influence of heathland botanical composition on the foraging behaviour and performance of these small ruminants. This will contribute to appropriate management decision-taking aiming to increase the efficiency of grazing systems in these marginal lands.
The objective of this work was to study the diet selection, live weight (LW) and body condition score (BCS) changes of non-lactating Gallega sheep and Cashmere goats grazing on three different heathland vegetation types (dominated by heather or gorse, or a mixture of native heath-grasses and gorse) during the grazing season.
Section snippets
Study site
The experiment was conducted at the Carbayal Research Station, Sierra de San Isidro, Illano, western Asturias, NW Spain (43°21′N, 6°53′W). The experimental field was located at 840–950 m.a.s.l. and presented pronounced slopes and shallow acid soils. Mean temperature during the study years (2003–2007) was 10.1 °C and annual rainfalls averaged 1498 mm, being more abundant from October to April (Fig. 1). A severe summer drought was noticeable in 2005.
The characteristic plant community in the area is
Available vegetation
The three heathland types differed (P < 0.05) in plant cover, height, phytomass amount and its composition across the experimental years. Control of shrub encroachment and canopy height was higher (P < 0.01) under goat grazing in all shrubland types. In fact, in grass- and gorse-dominated shrublands grazed by sheep, gorse cover increased through the experimental period whereas it was relatively constant under goat grazing. Similarly, a decrease in the heather cover was observed in heather-dominated
Discussion
The chemical composition of the vegetation components in these heathlands reveals their poor nutritive value, as previously observed in other studies (Milne, 1974, Celaya et al., 2007, Fraser et al., 2009, Mandaluniz et al., 2009). It hinders small ruminants from meeting their nutrient requirements (Luo et al., 2004, NRC, 2007).
It is generally accepted that goats eat more browse than sheep (Malecheck and Provenza, 1981, Lu, 1988, Narjisse, 1991). Goats’ higher preference for woody plants has
Conclusions
The low nutritive quality of available plant components in these heathlands restricts positive LW and BCS changes in non-lactating ewes and goats to short periods in spring–summer. Goats generally consume more heather and gorse and less herbaceous plants than sheep, but both species adapt their preferences to season and available botanical composition. The higher browsing ability of goats was not reflected in a great advantage in performance over sheep. Goats performed better in grass and
Acknowledgements
We thank the staff of the Carbayal Research Station for their field work in animal management and sampling assistance. This study was funded by the Spanish Ministry of Education and Science, project AGL2003-05342. R. Celaya is funded by the European Social Fund. B.M. Jáuregui was recipient of a pre-doctoral fellowship from INIA.
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