Promising tropical grasses and legumes as feed resources in Central Tanzania V. Effect of supplementing Cenchrus ciliaris hay with leaves from four legumes on intake and digestibility by growing Mpwapwa bulls

In Trial 1, six growing Mpwapwa bulls (mean age 1.5 years, mean body weight 158 kg) were used in a 6 × 6 Latin square design to study the effect on intake and digestion of supplementing Cenchrus ciliaris cv. Kongwa hay with four different legume leaf proteins. Hay alone and fish meal (FM) treatments were included as negative and positive control treatments, respectively. The grass hay was fed allowing above 40% refusal to maximize selectivity and contained 5.1% crude protein (CP), 76.1% neutral detergent fibre (NDF), 9.9% lignin and 3.1% silica. The protein sources were dried leaves of Macroptilium atropurpureum cv. Siratro (MAS), Macrotyloma axillare (MAA), Neonotonia wightii cv. Mpwapwa (NWM), Stylosanthes scabra cv. Seca (SSS) and FM. The protein sources were fed aiming at supplying approximately 150 g CP/day. The legume CP contents varied from 18.6–20.6% and the FM contained 54.7%. In Trial 2 in a completely randomised block design, 8 bulls were used to measure the digestibility of the legumes alone. Selective feeding resulted in consumption of hay containing 6.2% CP. The apparent digestibility of organic matter (OM) and NDF were 58.3 and 62.5%, respectively. Supplementing the hay resulted in intake of a diet with CP ranging from 8.0–8.5%. Despite the increased CP intake, neither the digestibility of OM nor NDF increased significantly, implying that the protein was not a first limiting factor for fibre digestion. The grass hay OM intakes varied between 21.0 and 22.2 g/kg body weight (BW) per day (77.3–86.0 g/kg BW0.75/d) and were not improved by protein supplementation. Significant improvements (P < 0.001) in daily intakes of total OM and CP were observed by supplementation, although total NDF was not improved. All protein supplements except MAS improved (P < 0.05) digestible OM intakes compared to the unsupplemented hay. Calculated digestible and metabolizable energy values for the diets were not improved by supplementation. However, an improvement in total energy and protein intake may be obtained as a result of supplementation. It is concluded that it is beneficial to use MAA, NWM, SSS and also FM in C. ciliaris-based diets to improve total intake of CP by growing bulls. Total intake of OM and digestible OM may also be improved, but the levels are only on the order of 10%. The use of legume supplements and allowing ample feed refusals may result in an estimated daily BW gain of 200–400 g.