Diet selection and performance of sheep and goats grazing on different heathland vegetation types

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Abstract

Heathlands can be utilized with different efficiency as a feed resource for sheep and goats, depending on their botanical composition. The aim of this work was to compare diet selection and performance of Gallega sheep and Cashmere goats grazing on three different heathland types: grass-dominated, gorse (Ulex gallii)-dominated, or heather (Ericaceae)-dominated. A factorial design of 2 animal species × 3 heathland types with 2 replicates was established on 12 plots in a mountain area of northern Spain. The experiment lasted five years (2003–2007) and the grazing season extended from May to October–November. Animals were regularly weighed and their diet selection was estimated across the grazing season using the alkane markers. Results indicated that goats selected more woody species (both heather and gorse) and less herbaceous plants than sheep. Goats controlled shrub encroachment and canopy height more than sheep in the three shrubland types, resulting in a higher herbaceous cover under goat grazing. Degree of selection–rejection for a particular plant component varied depending on its availability in the plot. Averaging the five year period, goats presented better LW changes than sheep (6.1 g/day vs. −3.7 g/day). Both animal species gained similar live weight (LW) during spring (55 g/day), but sheep lost more LW during summer (−27 g/day vs. −16 g/day), whereas both species showed similar LW losses during autumn (−31 g/day). Goats improved their body condition score (BCS) more than sheep during spring, and presented lower BCS decreases in summer. However, differences between species depended on the vegetation type, with goats showing more favourable LW changes in grass- and heather-dominated shrublands, and with no differences in gorse-dominated ones. Sheep had more favourable LW changes during 2003 and 2004, but such trend reversed from 2005 onwards, probably reflecting the different trends in shrubland botanical composition over time under sheep or goat grazing. The poor nutritional value of the vegetation is a key factor limiting the development of animal production systems in Cantabrian heathlands. The acceptable performances of sheep and goats during spring were offset during summer, especially in the case of sheep, as the available green foliage was reduced. Grazing for 4 months provides maintenance as long as summer rainfall exceeds 40 mm/month. Development of profitable performances in these nutritionally poor areas is limited to grazing periods of 3–4 months between weaning and mating before LW and BCS decline.

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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    Present address: Servicio de Investigación, Desarrollo e Innovación, Obrascón Huarte Lain, S.A., Paseo de la Castellana 259D, Torre Espacio, 28046 Madrid, Spain.

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