NITROGEN SUPPLEMENTATION IMPROVES THE NUTRITIVE VALUE OF OPUNTIA FICUS-INDICA F. INERMIS- BASED DIETS AND SHEEP GROWTH

Abstract

Two experiments have been carried out to study the effect of nitrogen supplementation on the nutritive value of spineless cactus (Opuntia ficus-indica f. inermis) based diets. In experiment 1, 18 Barbarine lambs were divided into three equal group and given freshly cut pads of cactus ad libitum. Each group was supplemented with either barley straw (600 g) (C+US), urea-treated barley straw (600 g) (C+UTS) or a mixture of barley straw (600 g) and fresh foliage of Atriplex nummularia L. (400 g) (C+A). A fourth group of six lambs received a common diet including barley straw ad libitum and a mixture of barley grain and wheat bran (400 g, 50:50) (US+BW). In the experiment 2, five groups of six Barbarine lambs receiving fresh pads of cactus and barley straw both ad libitum were supplemented or not (C) with either 10 g urea (CU), 200 g soybean as it is (CS), treated with formaldehyde (CSF), or supplemented with 100 g (CSA100) or 200 g (CSA200) of air-dried Acacia cyanophylla Lindl. foliage. In both experiments, a growth trial (60 days) followed by a total faecal collection trial (8 days) were performed. Atriplex, soluble nitrogen rich shrub, was more effective in improving diet digestibility and average daily gain than urea-treated straw (experiment 1). In both experiments, urea and atriplex had no effect on cactus intake. By contrast, soybean meal proteins increased significantly cactus intake, apparent diet digestibility and sheep growth. These positive effects were substantiated when sheep were offered a small amount (100 g) of acacia foliage, a source of condensed tannins, and 200 g of soybean meal. It was therefore concluded, that dietary proteins rather than non protein nitrogen improved the nutritive value of cactus-based diets and lamb growth, and acacia condensed tannins supplied in a fixed amount seem to increase the level of bypass proteins. It is also worth to note that cactus may overcome watering problem for sheep in arid zones.