Evaluation of Marama bean as an alternative to soybeans in broiler nutrition

Abstract

The incorporation of non-conventional feed ingredients in poultry diets could potentially promote sustainable poultry production. Marama bean (MB) (Tylosema esculentum) is one such non-conventional feed resource with potential applications in poultry nutrition. However, its utility as a feed ingredient for poultry may be limited by the presence of high levels of trypsin inhibitors and other antinutritional factors. Therefore, this study was designed to evaluate the soyabean replacement efficacy of MB in broiler chicken diets. The first experiment investigated the maximum tolerance level of raw full-fat marama bean meal (MBM) as a partial alternative protein source in Ross 308 broiler chicken diets based on nutrient digestibility, haematological and biochemical indices, and growth performance. The second experiment assessed the effect of graded levels of raw full-fat MBM on carcass attributes, meat quality measurements, and meat stability. Three-hundred and eighty-five, two-week old Ross 308 broiler chickens (359.7 ± 25.48 g live-weight) were reared for four weeks (14 – 42 days). The broilers were fed five isonitrogenous and isoenergetic experimental diets containing graded levels of raw full-fat MBM in place of soyabean products as follows: 1) MBM0 = a standard grower diet with no MBM, 2) MBM4 = a standard grower diet in which soyabean products were replaced with MBM at 40 g/kg, 3) MBM9 = a standard grower diet in which soyabean products were replaced with MBM at 90 g/kg, 4) MBM14 = a standard grower diet in which soyabean products were replaced with MBM at 140 g/kg, and 5) MBM19 = a standard grower diet in which soyabean products were replaced with MBM at 190 g/kg. The five experimental diets (in mash form) were randomly allocated to 35 pens (experimental units) resulting in seven replicates per dietary treatment. The level of MBM inclusion induced neither quadratic nor linear responses (P >0.05) for methionine and lysine digestibility, and feed intake, however, negative quadratic responses (P <0.05) were recorded for all other nutrient digestibility values. Positive and negative quadratic effects were recorded for final body weight (R2 = 0.724, P = 0.011) and feed conversion ratio (R2 = 0.806, P = 0.0004), respectively, in response to increasing MBM levels. Hot and cold carcass weights were quadratically reduced with increased levels of MBM. Meat pH, redness, and shear force showed a negative linear response (P <0.05) to MBM levels. For these experiments, it was concluded that while replacing up to 190 g/kg of soyabean products with raw full-fat MBM in broiler diets did not affect mortality and feed intake, it resulted in poor calcium, and sodium utilization, growth performance, and carcass yield and heavier visceral organs (P <0.05). It was established that the protein value of MB in broiler diets is limited by antinutritional components such as trypsin inhibitors and possibly phytate and tannins. The trypsin inhibitor activity (TIA) in MB may negatively affect digestion and absorption of nutrients, which results in growth inhibition, hypertrophy, and hyperplasia of visceral organs such as the pancreas. The outcomes of these two experiments afore-mentioned, instigated the need to evaluate strategies that would improve the nutritive value of MB by ameliorating the TIA. This was investigated in the third experiment, by applying physical treatments including soaking, cooking, and autoclaving to MB and soyabean samples. Soyabean was used as the control sample due to it being the ‘golden standard’ protein source in animal nutrition. The effects of these treatments were assessed on crude protein (CP), amino acids composition and TIA of MB and soyabean. Triplicate samples of MB and soyabean were independently subjected to the physical treatments. Soaking, cooking, and autoclaving caused a significant (P <0.05) increase in CP concentration of the beans compared to raw samples. However, ash content was lower (P <0.05) in treated samples than the raw, especially the samples that were soaked or steamed before autoclaving. All the treatments (except soaking MB for 24 hr) decreased the concentrations of TIA (P < 0.0001) and ash content (P <0.05) when compared with the raw samples. Soaking for 24 hr alone was less effective than any of the thermal methods in reducing the TIA in soyabean. More importantly, soaking prior to autoclaving yielded (P <0.05) beans with lowest TI concentrations. While most of these methods may reduce the TI contents of the beans, they also resulted in lower ash content and amino acids concentration. In conclusion, this study showed that feeding raw MB to Ross 308 broiler chickens is detrimental to the growth performance, haematological and biochemical features, as well as meat quality properties of the chicken. Hence, thermal pre-treatment of MB would be necessary to reduce the anti-nutritional activities of TI in MB and improve its nutritional value for animal nutrition. Therefore, in vivo trial involving the incorporation of pre-treated MB in the diets of broiler chickens requires further research to enhance the utility of MB as an alternative protein source.