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.