Nutritive value, behaviour, and growth of Barbarine lambs fed on oldman saltbush (Atriplex nummularia L.) and supplemented or not with barley grains or spineless cactus (Opuntia ficus-indica f. inermis) pads

This study had three objectives: (i) estimation of biomass availability of atriplex (Atriplex nummularia Lindl.) foliage and wood (Trial 1), (ii) assessment of the effect of energy supplementation on feeding behaviour and growth performance of grazing lambs (Trial 2), and (iii) determination of in vivo digestibility of atilplex-based diets and nitrogen balance on lambs housed in metabolism cages (Trial 3). In Trial 1, twenty-five unbrowsed shrubs of atriplex were used for height, circumference, crown, and ellipsoid volume measurements. Thereafter, they were cut and their foliage and biomass weights were recorded and were regressed on dimension parameters. The best equations to estimate foliage biomass (FB = 0.69 x V, r(2) = 0.90) and wood biomass (WB = 1.56 x V, r(2) = 0.91) involved shrub volume (V). In Trial 2, 24 Barbarine lambs (17.9 +/- 1.63 kg) were allotted into three equal groups and were housed in individual boxes. They were allowed to graze daily from 10:00 h to 16:00 h in a 5 ha shrubland. They had free access to water while browsing and as well as in the barn where they received either no supplement (group 1, control), 0.4 kg barley grains (group 2) or ad libitum fresh cactus cut into small pieces (group 3). The experiment lasted 85 days (10 days for adaptation and 75 days for measurements). During the measurement period and in every 15 days, three lambs from each group were observed for three consecutive days to record their behavioural activities. Lambs representing the three groups were observed simultaneously by three different observers. Times spent by lambs browsing atriplex or other vegetation, resting, walking or drinking water were recorded for 30 min at 10:30 and 15:00 h. Feeding behaviour recorded in the morning and the afternoon was similar (P > 0.05). Lambs spent most of their time consuming atriplex and other vegetation. Both supplements reduced the time spent in atriplex browsing, increased the time spent in eating other vegetation and that spent in walking. without any change of resting time. Compared to the control group, barley and Cactus supply decreased (P < 0.05) the time spent time atriplex consumption (-31% and -37%, respectively). Lambs on atriplex without supplementation lost weight (35g/day). However, lamb given barley or cactus grew at rates of 67 and 20 g/day, respectively. In Trial 3, compared to the control group. barley-supplemented lambs and to a lesser extent cactus-supplemented animals exhibited higher organic matter and crude protein diet digestibilities and nitrogen balance, These results may explain why these lambs grew better than those of the control group. It was concluded that supplementation of free-browsing or stall-fed Barbarine lambs on atriplex with energy source is necessary, Both barley and cactus supply improved lamb performance, (c) 2005 Elsevier B.V. All rights reserved.