Spineless cactus ( Opuntia ficus indica f. inermis) and oldman saltbush ( Atriplex nummularia L.) as alternative supplements for growing Barbarine lambs given straw-based diets

Abstract

Atriplex nummularia L. foliage (atriplex) and Opuntia ficus indica f. inermis pads (cactus) have been used as alternative N and energy supplements, respectively. Twenty-four Barbarine lambs (7-month-old, 19.5±0.5 kg BW) were allotted into four homogeneous groups and housed in individual crates. Each group received barley straw ad libitum and was supplemented on fresh weight basis with either barley grains (0.2 kg) and soybean meal (0.18 kg) (BS); or barley grains (0.2 kg) and atriplex (1.7 kg) (BA); or cactus (3.5 kg) and soybean meal (0.18 kg) (CS); or cactus (3.5 kg) and atriplex (1.7 kg) (CA). Urea was added to make 2 diets iso-nitrogenous. Animals were adapted for experimental conditions for 15 days before starting the 60-day growth trial. At the end of the growth trial, animals were housed in metabolic cages for total faecal collection during 10 consecutive days. Replacing soybean meal by atriplex had no effect on straw DMI ( P>0.05). However, sheep fed cactus consumed less straw than those given barley. Crude protein digestibility was high (71–74%) and similar ( P>0.05) among diets. Diets BS, BA and CS had the same organic matter and fibre (NDF and ADF) digestibilities, which were significantly lower than those of diet CA. Nitrogen retention was high for all diets ranging between 9 and 12 g per day. Difference in N balance among diets was ascribed to the different amount of N consumed, since N loss was quite similar among dietary treatments. Urinary excretion of allantoin and microbial N supply were highest in sheep fed cactus-containing diets (8.3 and 11.4 g microbial N/kg DOMI, respectively, with CS and CA diets) as compared to barley-containing diets (3.5 and 3.2 g microbial N/kg DOMI, respectively, with BS and BA diets). Daily gain of lambs averaged 119, 108, 81 and 59 g, respectively, for diets CS, BS, CA and BA ( P<0.05). These results suggest that in presence of soybean meal as N source, cactus may replace barley grains without any effect on growth rate ( P>0.05). The lowest growth recorded in sheep receiving atriplex (CA; BA) may be ascribed to the high level of soluble N in this shrub species. In practice, growth rate (81 g per day) obtained without use of classic costly concentrate feeds (barley grains and soybean meal), which were replaced by cactus and atriplex (CA diet), would satisfy smallholders when considering feeding cost.