Effect of Processed Cowpea-based Diets (Vigna unguiculata) on Intake and Digestibility, Growth Performance, Meat Quality and Sensory Characteristics of Broiler Chickens

Abstract

The objective of this study was to increase knowledge on the effectiveness of processed cowpeas as a soybean supplement in broiler diets. The main goal was to improve domestic self-sufficiency in supplementary protein in poultry diets and lowering imports of soybeans. Three experiments (I – III) were conducted to determine the effects of processed cowpea-based diets on feed intake and growth performance (I), protein digestibility and ammonia emissions (II) and meat quality and sensory characteristics of broiler chickens (III). A total of 210 unsexed day-old broiler chicks were randomly allocated to seven dietary treatments in a completely randomized design. The dietary treatments included maize and cowpeas in partial substitution of soybean namely: maize-soybean-based (control), raw cowpea-based, boiled cowpea-based, roasted cowpea-based, dehulled cowpea-based, dehulled boiled cowpea-based and dehulled roasted cowpea-based diets. Diets were formulated to be iso-energetic and iso-nitrogenous. Dietary treatment had no effect (P>0.05) on feed intake nor live weight gain (LWG). Diets containing boiled, roasted and dehulled-roasted cowpea had similar (P>0.05) true protein digestibilities as the basal diet (64.9%). True protein digestibility in raw, dehulled-boiled, and dehulled cowpea-based diets were lower (P<0.05) ranging from 51.0 to 55.2%. Dietary treatment had no effect (P>0.05) on the feed conversion ratio (FCR) and ammonia emission but influenced meat chemical composition (P<0.05). The average weekly FCR per bird ranged from 1.70 to 1.80. The average weekly ammonia emission ranged from 1.2 ppm in broilers fed diets containing dehulled cowpea meal to 1.5 ppm in broilers fed diets containing raw cowpea meal. Dietary treatments influenced the proximate composition of broiler meat (P<0.05). Treatment significantly affected (P<0.05) broiler meat pH and water holding capacity. Meat from broilers that were fed with diets containing roasted cowpeas had the highest water holding capacity of 74.1% and the meat from broilers that were fed with diets containing raw cowpea meal had the lowest water holding capacity (61.5%). The diets containing boiled cowpea meal produced broiler meat with the highest pH of 6.6 and the raw cowpea meal treatment group had the lowest (6.0). Meat from broilers that were fed with diets containing raw cowpea meal and boiled cowpea meal had the highest crude fiber of 1%. Meat from broilers fed diets containing roasted, dehulled-roasted and dehulled-boiled cowpea meals had the lowest crude fibre (0.8% each). Dietary treatments had an influence (P<0.05) on the color, texture, taste, and vi tenderness of broiler meat. Meat from broilers fed diets containing raw cowpeas had the lowest colour and texture scores, while the rest of treatments were similar in the two parameters. There were no differences in the aroma scores of all treatments. The meat from dehulled-boiled, dehulled and boiled cowpea-based groups had the highest taste scores (5.0). Meat from raw cowpea-based treatments had the lowest taste score (2.0), while the rest of the treatments were similar. The meat from the control, dehulled-boiled cowpea and boiled cowpea-based diets had the highest tenderness scores and raw cowpea-based diet had the lowest. The remaining dietary treatment groups were not different. Therefore, dehulled, dehulled-roasted, dehulled-boiled, boiled and roasted cowpeas can be included in broiler starter and broiler finisher diets at 10 and 15% inclusion levels respectively without negatively affecting broiler feed intake and protein digestibility, growth performance, carcass quality and sensory characteristics of broiler meat.