Productivity of an Atriplex halimus shrubbery and effects of grazing on lambs

Abstract

The objectives of this study were to 1) evaluate the productivity and forage quality of Atriplex halimus, 2) investigate modifications to shrub structure induced by grazing, and 3) assess live weight changes in lambs grazing on A. halimus with and without a feed supplement (wheat straw ± barley grain). The results showed that A. halimus had low productivity (approximately 1000 kg DM ha–1) but high tolerance to grazing by lambs, although minor modifications in plant structure due to grazing were observed. Lambs grazing A. halimus as a sole diet lost weight (about 60 g lamb−1 d–1; P < 0.01), probably as a consequence of the high salt content of the forage reducing both intake and digestibility. No significant benefits were obtained from the provision of wheat straw as an ad libitum supplement, possibly because the lambs were able to utilize understorey plants having a chemical composition similar to straw. Lambs supplemented with both wheat straw and barley grains (200 g lamb−1 d–1) had a significantly higher live weight (P < 0.01) than those grazing on A. halimus alone. The results suggest that a diet of A. halimus is not sufficient to maintain lamb live weight, and that supplementation with an energy source is necessary for lambs to gain weight.