Foraging behaviour of equines grazing on partially improved heathlands

Abstract

Heathlands are widespread in the north of the Iberian Peninsula and are usually used by feral horses. Knowledge on foraging behaviour of equines in these areas is important for their efficient utilization. In this study, grazing time (GT), diet selection (DS), feed intake (FI) and digestibility (DMD), of five mares grazing on heathlands with an area of improved pasture (IP, ryegrass-white clover) was measured in June and September. Animals’ GT on each vegetation type was determined by recording their activity every 15 minutes from dawn to dusk during two consecutive days. DS, FI and DMD were estimated using n-alkane markers. IP availability was assessed by recording sward surface height. Effect of grazing season on DS, FI and DMD was examined by ANOVA. Equines showed an average daily GT of 621 min/day, with no differences between seasons, despite the shorter observation period in September. In June, mares spent most of their GT on the IP (0.847) whereas in September they spent more time on heather-gorse communities (0.516). DS results showed an almost total selection of herbs (0.971) in June, decreasing (P<0.001) its proportion to 0.823 in September in response to the decrease in IP availability (9.6 to 4.0 cm). Higher participation of woody species in September diet resulted in lower (P<0.001) DMD (368 vs. 685 g/kg DM) due to its higher fibre content. Daily FI was higher (P<0.001) in June than in September (233 vs. 119 g DM/kg LW0.75). Data obtained in this study showed that equines primarily select herbaceous plants, but they are also able to modify their foraging behaviour in response to modifications in the availability of these more nutritional feed resources.