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BACKGROUND: Probiotics are being developed for use in animal feed to enhance production performance and prevention of gastrointestinal infections. The ban on using antibiotics as growth promoters, antibiotic resistance and the inherent problems of developing new vaccines make a compelling case for developing alternatives for in-feed antibiotics. The alternatives of choice have to be considered under the environmental conditions of the animal. Among the probiotics in use today, Lactobacillus has been shown to play a vital role in disease prevention, immune enhancement, improved growth and carcass yield in poultry. The present study investigates the effect of Lactobacillus bulgaricus (LB)-based probiotic on the growth performance, nutrient digestibility and immune response of broilers under tropical environmental conditions. RESULTS: Broilers fed LB diets consumed more feed (P < 0.05) and had greater body weight gain than the control group. Feed/gain ratio improved significantly (P < 0.05) with the 20, 40 and 60 mg kg −1 LB diets compared with the control or 80 mg kg −1 LB diet. The apparent digestibilities of nitrogen and fat increased with LB supplementation. However, there was no significant difference (P > 0.05) in fibre digestibility. White blood cell count increased significantly in broilers fed higher levels (>40 mg kg −1 ) of LB compared with the control group. Antibody production measured as antibody titre against Newcastle disease vaccine showed a curvilinear response over the range of LB concentrations examined. CONCLUSION:The results indicate that LB addition to broiler chick diets significantly improved growth performance, increased nutrient digestibility and stimulated humoral immune response.

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As the search for alternative sources of energy for non ruminants continues, this review was undertaken to examine the potential value of cassava (Manihot utilissima Pohl.), sweet potato (Ipomea batatas Poir.), cocoyam (Xanthosoma sagittifolium Schott.) and their by-products as dietary supplements for non ruminants. Studies on these roots and tubers showed that, on a dry-weight basis, contained 2.0 -7.9% crude protein, 0.3 -3.1% crude fib re and 72.4 -77.9% starch. The practical use of these roots and tubers in non ruminant feeds is generally low. Th is level of utilizat ion is attributed to the low protein and dry matter and the potentially to xic cyanogenic glycosides in fresh cassava and irritating substance in cocoyam. Processing techniques such as fermentation, soaking, boiling, ensiling and sun-drying are adopted to remove the deleterious substances, and effects on animals. The co mparable performance of pigs and poultry fed vary ing levels of roots and tubers and their by-products with those maintained on maize showed that they can be used as substitutes in non-ru minants diets at certain levels without detrimental effects. To achieve increase in the use of these root crops and their by-products for maize replacement in intensive non-ruminant production systems, adequate protein supplementation and proper processing are essential.