Foraging behaviour and diet selection of free-ranging sheep and goats in the Negev Desert, Israel

Abstract

SUMMARYThe foraging behaviour and dietary selection of free-ranging Awassi sheep and Negev goats when shepherded in the Negev Desert was determined. Measurements were made for 9 weeks (W1–W9) from the beginning of February, following winter rains and emergence of annual plants, to the end of March, after the herbaceous vegetation dried up. Since sheep are grazers and goats are intermediate feeders, it was predicted that goats would browse more and consume proportionately more browse than sheep. These predictions were only partially supported. In fact, the foraging pattern was similar between sheep and goats (Mantel test, P<0·05) until W8 and only towards the end, at W9, did patterns differ significantly (Mantel test, P=0·214) between these two ruminants. There was no difference (P=0·575) between sheep and goats in foraging; however, a period effect was found (P<0·001). In February (W2), sheep and goats grazed 0·69 and 0·71 of the time allotted for foraging and neither species browsed. Browsing commenced only at the beginning of March (W4), when goats browsed 0·08 of the time and sheep 0·07 of the allotted time for foraging. The proportion of time spent browsing increased at the end of March (W9) when annuals disappeared, but the total time spent foraging decreased: goats browsed 0·29 and grazed 0·25, while sheep browsed 0·19 and grazed 0·26 of the time allotted for foraging. Goats increased the proportion of browse consumed gradually throughout the season, whereas sheep maintained a relatively higher proportion of herbaceous plants and only in late March (W8), at which time very little herbaceous plants were available, shifted abruptly to consume mainly browse. In W8, browse composed 0·85 of the dry matter (DM) intake in goats and 0·62 of the DM intake in sheep. A simultaneous analysis of foraging time allocation and relative diet composition revealed that both small ruminants were more efficient in consuming browse than herbaceous plants, more so in goats than sheep. It was concluded that vegetation availability and foraging habits affected dietary selection. Both sheep and goats only grazed when herbaceous plants were abundantly available; differences between ruminant species were apparent when herbaceous plants became scarcer, at which time goats browsed more and consumed proportionately more browse than sheep. The results contribute to better understanding of feeding behaviour and dietary selection of sheep and goats under natural desert pastures and could be useful in the management of mixed flocks.