Effect of Imbrasia belina (Westwood) or Vigna subterranea (L) Verde or Tylosema esculentum (Burchell) Schreiber as protein sources in diets fed to Tswana hens on egg quality

Abstract

A 90 days study was conducted to compare the effects of feeding Tswana hens reared under intensive system and fed diets formulated from Imbrasia belina (Westwood), Vigna subterranea (L) Verde and Tylosema esculentum (Burchell) Schreiber as sources of protein on egg quality. Four isonitrogenous and isocaloric diets were formulated by totally replacing soybean meal (SBM) with I. belina, V. subterranea and T. esculentum as protein sources while commercial layer diet was used as control diet. Twelve eggs from each pen were collected at 28, 33 and 38 weeks of age for egg quality analysis in a completely randomized design. Egg weight (EW), shell weight (SW), shell thickness (ST), shell index (SI), shell percentage (SP), egg surface area (ESA), egg volume (EV), egg contents (EC) and Haugh units (HU) were measured. Repeated measure analysis showed significant (P<0.05) week × diets interaction effect on EW and SW.  At week 28, hens on T. esculentum diet had the highest (P < 0.05) EW while those on control diet attained the highest (P < 0.05) EW at week 33. Hens fed I. belina diets had the highest (P < 0.05) SW at week 28. However, at weeks 33 and 38, hens on I. belina diets had the smallest (P < 0.05) SW. Hens fed V. subterranea and T. esculentum diets had significantly lower overall SI compared to those on control and I. belina diets. Tylosema esculentum diets did not promote (P<0.05) ESA, EV and EC. However, no influence (P>0.05) of dietary treatments was observed on overall ST, SP and HU. The inclusion of I. belina and V. subterranea on layer diet had no adverse effects on egg quality while the totally replacement of SBM with T. esculentum as protein source impaired egg quality. These results, suggest that I. belina and V. subterranea could completely replace SBM as protein source in the layer diets without any detrimental effects on egg quality.