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.
