| dc.description.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. | en_US |
