Effects of dietary marula seed cake on indigenous boschveld chickens productive performance, health, gut metagenomes and meat quality.

Abstract

The rapidly growing human population particularly in developing countries demands sustainable production of poultry as a source of food to meet human protein requirements. As the most popular poultry species in rural areas of Southern Africa, indigenous chickens provide cheap animal protein in the form of meat and eggs and contribute significantly to the socioeconomic wellbeing of rural communities. However, their contribution to food and nutrition security is suboptimal due poor nutrition ascribable to dependence mostly on scavengeable feed resources. Also, commercial feeds that could be used to feed these birds are unaffordable due to costly dietary protein sources especially due to environmentally and economically unsustainable soybean meal (SBM). Therefore, there is a need to seek cheaper locally available alternative protein ingredients for poultry feeds such as Marula seed cake (MSC) whose amino acid profile closely mirrors that of SBM. This study thus aimed to evaluate the effect of dietary replacement of SBM with MSC on Boschveld indigenous chickens' performance, carcass traits, viscera macro-morphometry, haematology and clinical biochemistry, gut metagenomes and meat and bone quality. Four hundred (400) 3-week-old Boschveld chicks were randomly allocated to and fed, for 9 weeks, 5 iso-energetic-nitrogenous maize and SBM-based grower diets with 0, 10, 15, 20, and 25% MSC replacing SBM, each with 5 replicate pens of 16 birds, in a completely randomised design (CRD. Feed intake (FI), weekly body weight gain (BWG) and feed conversion efficiency (FCE) were determined. A day before slaughter, blood was collected from 2 birds randomly selected per pen. At the end of the feeding trial, following a 12-hour fast but with access to drinking water, the chickens were slaughtered, dressed. Immediately thereafter viscera morphometry, carcass trait, meat and bone quality were determined. Caeca digesta samples were randomly collected from 2 birds per pen (n = 10 and pooled for shotgun metagenomics analysis. All data were then statistically analysed using the LM procedure (PROC GLM) of SAS (SAS, 2012). Dietary MSC decreased FI (quadratic: P< 0.001) and BWG (quadratic: P < 0.01), as it linearly decreased their weights of the hot carcass (HCW; P < 0.05), spleen (P < 0.05), jejunum (P < 0.05), ileum (P < 0.001), and caecum (P < 0.001). The MSC increased chickens' serum glucose (linear: P < 0.05), cholesterol (linear: P= 0.001) and phosphate (quadratic: P < 0.05) concentrations but it decreased their plasma/serum amylase activity (linear: P < 0.01). Dietary MSC decreased meat lightness at 45 min (linear: P < 0.05) and yellowness at both 45 min (quadratic: P < 0.001) and 24 h (quadratic: P < 0.001). However, it increased the meat's redness both at 45 min (linear: P < 0.01) and 24 h (linear: P < 0.05) post-slaughter. MSC decreased the chickens' bone medial diaphysis (P < 0.05). Dietary MSC had no effect (P > 0.05) on feed conversion efficiency (FCE), gastrointestinal tract viscera morphometry, haematology, other carcass traits and meat qualityand bone morphometry. Gut metagenomic analysis showed in chickens fed diets with 0%, 10%, 15%, 20% and 25% MSC inclusion the most predominant microbial communities in the chickens' ceaca bacteria with, 99.63, 99.66, 99.99, 98.31 and 99.99% frequency, respectively. In chickens fed the control (0% MSC) diet, Bacteroides (60.52%) and Firmicutes (34.15%) were predominant microbial phylla. The Firmicutes were abundant across treatment groups while the Bacteroidetes were abundant in birds fed diets with 10 and 20% MSc inclusion but their (Bacteroidetes) was lower in chickens fed diets with 15 and 25% MSC inclusion. In conclusion, indigenous chickens can be fed grower diets supplemented with MSC up to 15% inclusion level without detrimental effects on FCE, carcass characteristics, haematology parameters and bone size.