Supplementation of Zebu cattle grazing Sahelian pasture. I. Diet selectionand intake

From 1990 to 1992, diet selection and nutrient intake of Zebu cattle grazin g Sahelian pasture were studied in Central Mall. Forty-five intact males an d 12 oesophageally fistulated animals were separated into three groups of 1 5 intact and 4 fistulated animals. The control group (C) grazed natural pas ture only, while the moderately supplemented group (M) additionally receive d 0.8-1.5 kg OM/day of crop by-products during the dry season (November-Jun e) and the first month of the rainy season. The third group (H) was highly supplemented with 1.7-2.7 kg OM/day in the dry season and 0.8-1.2 kg OM/day in the rainy season. Oesophageal extrusa was collected during 5 consecutiv e days at intervals of 4-5 weeks. Samples were analysed for contents of org anic matter (OM), crude protein (CP) and neutral detergent fibre (NDF). Dig estible organic matter (DOM) and metabolizable energy content (ME) were cal culated from in vitro gas release. Intake of organic matter (IOM) of the fi stulated animals was determined from faecal organic matter excretion (FOM) and extrusa DOM content. Intake of CP (ICP) and ME (IME) were calculated fr om IOM and the respective nutrient contents of extrusa samples. Extrusa CP, DOM and ME contents did not differ significantly between the th ree groups either in the dry or in the rainy season. The CP content was c. 230 and c. 197 g/kg OM during the rainy season, and declined to values less than or equal to 70 and less than or equal to 95 g CP/kg OM at the end of the dry season of 1990 and 1991, respectively. Average DOM and ME contents were c. 668 g DOM and c. 9.9 MJ ME/kg OM during rainy seasons. At the end o f the dry seasons, these values decreased to < 550 g DOM and < 8.0 MJ ME/kg OM. Per kg of metabolic body mass, IOM of group C was c. 89 g/day during t he early dry season. It was accompanied by a daily ICP of 8-10 g and by an IME of 691-765 kJ/day. Due to a higher nutrient content in the selected die t, energy intake was slightly increased and protein intake was significantl y higher during the rainy than during the dry season, although IOM was only 77-81 g/day. At the end of the dry season, unsupplemented animals ingested < 70 g IOM/day and the concomitant CP and ME intake were < 6 g CP/day and < 500 kJ ME/day, respectively. Feed intake from pasture was stimulated by a moderate supplementation, but reduced by a high supplementation. The resul ts indicate that on slightly degraded Sahelian rangeland, the nutrient inta ke of cattle is in the first place limited by biomass availability and only secondly by the quality of the vegetation.