Prediction of responses of indigenous Boschveld chickens to probiotic-yeast additive levels using a quadratic optimisation model.

This experiment was performed to determine the nutrient content of yeast (Saccharomyces cerevisiae) and effect on carcass characteristics, relative internal organ weights, digesta pH, and lengths and weights of the different segments of the gastrointestinal tract (GIT) of indigenous Boschveld chickens. Six hundred-day-old unsexed Boschveld chicks were divided into six groups of 100 birds with each group replicated five times. Birds were fed broiler starter from 1 to 49 days and grower diet from 50 to 91 days. Each group was allotted to commercial broiler mash diet supplemented with yeast designated 0 g kg-1 feed (T0), 2.5 g kg-1 feed (T1), 5.0 g kg-1 feed (T2), 7.5 g kg-1 feed (T3), 10.0 g kg-1 feed (T4) and 12.5 g kg-1 feed (T5) in a completely randomised design. Proximate composition of yeast was assessed using the standard method. Live weight, carcass characteristics, organ weights, digesta pH and the lengths and weights of the different segments of the digestive tract were measured and analysed statistically. Probiotic-yeast levels for optimal productivity were determined using a quadratic optimisation model. Results revealed that probiotic-yeast is rich in crude protein (496.0 g kg-1), ash (61.60 g kg-1) and moderate in crude fibre (29.0 g kg-1). Birds in groups fed with diets supplemented with yeast at 7.5 and 10.0 g kg-1 feed gave the best (p < 0.05) carcass characteristics, organ weights, length and weight of the different sections of the digestive system in Boschveld chickens. The optimal inclusion rates of probiotic-yeast that gave the best live weight, carcass characteristics, organ weights and linear measurement of the GIT were found 6.9 and 8.5 g kg-1 feed, suggesting that no single inclusion level optimised all the parameters measured in Boschveld chickens in the present study. In conclusion, yeast is suitable for use as a feed additive and for optimal productivity; it should be included at the rates of 7.5 and 10.0 g kg-1 feed in Boschveld chicken diet. It is recommended that yeast supplementation level beyond 10.0 g kg-1 feed may not be well-tolerated by the Boschveld chickens for best live weight, carcass characteristics, organ weights and linear measurement of the GIT.

Effect of dietary lysine to crude protein ratio on performance of male Ross 308 broiler chickens.

Two experiments were conducted to determine the effect of dietary lysine to crude protein ratio on performance of male Ross 308 broiler chickens. In each experiment the diets were isocaloric and isonitrogenous but with different lysine to crude protein ratios. A complete randomized design was used in both experiments, the starter (1-21 days) and grower (22-42 days) experiments. The three starter diets, based on lysine to crude protein ratios, were L(0) (0.055), L(1) (0.066) and L(2) (0.077), while grower diets were L(3)(0.047), L(4)(0.061) and L(5)(0.074). A quadratic type equation was used to determine ratios for optimum growth rate, feed conversion ratio, breast meat yield and breast meat nitrogen content. Dietary lysine to crude protein ratios of 0.066 and 0.077 supported optimum growth rate and feed conversion ratio, respectively, during the starter period. Dietary lysine to crude protein ratios of 0.073, 0.073, 0.069 and 0.079 supported optimum growth rate, feed conversion and breast meat yield and nitrogen content during the grower phase. Dietary lysine to crude protein ratio had no effect on diet intake and digestibility. The results indicate that at each phase a single dietary lysine to crude protein optimized both growth rate and feed conversion ratio. However, the ratio for optimum breast meat yield was lower than that for optimum growth rate and feed conversion ratio. These findings have implications on ration formulation for broiler chickens.