Impact of phased nucleotide supplementation on gut function, performance, and meat quality in densely stocked broilers.

Abstract

Poultry production plays a significant role in ensuring food and nutrition security in South Africa and beyond. However, this enterprise relies heavily on antibiotic growth promoters (AGP) to control disease outbreaks and boost growth performance. The use of AGP is increasingly frowned upon due to their role in antimicrobial resistance and unsafe antibiotic residue-rich poultry products. As such, there is a need for AGP alternatives that would ensure that sustainable poultry production is economically efficient, environmentally friendly, and promotes consumer health. Exogenous dietary nucleotides are increasingly investigated as potential alternatives to AGP; however, their continuous supplementation across the broiler production cycle may impose higher costs. Given that nucleotides are conditionally essential nutrients, required primarily during periods of rapid growth, stress, immunological challenge, or tissue repair; strategic, phase-specific inclusion rather than continuous provision may be both biologically justified and economically advantageous. Therefore, this study investigated the comparative effects of phased vs continuous yeast-based nucleotide supplementation on growth performance, physiological function, meat quality parameters, and gut microbiome in densely stocked Ross 308 broilers. This study is split into two experimental chapters (3 and 4). Chapter 3 presents the effects of phased yeast-based nucleotide supplementation on growth performance, haemato-biochemical parameters, and meat quality traits. Chapter 4 investigates how phased supplementation with yeast-based nucleotides affected visceral morphometry and gut microbiome of the broilers. The feeding trial was carried out at Rooigrond poultry farm, near Mahikeng (North West, South Africa). A total of 900, one-week-old, unsexed Ross 308 broilers were evenly allotted to 36 experimental units (25 birds/1.2 m2), to which six feeding strategies were randomly allocated in a completely randomized design. The feeding strategies were: a basal diet without AGP or nucleotides (NEGCON) fed continuously, a basal diet with AGP (POSCON) fed continuously, and a basal diet containing 0.05% nucleotides in place of AGP fed either continuously (NCC), during the starter phase only (NCS), during the grower phase only (NCG), or during the finisher phase only (NCF). Body weight and feed intake measurements were recorded weekly. Mortalities were recorded daily and replaced with birds of similar weights to maintain stocking density and correct the feed conversion ratio. The collection of blood was performed on day 40 of the feeding trial. Feeding strategies influenced (p < 0.05) feed intake, weight gain, and feed conversion ratio. The positive control outperformed (p < 0.05) all the feeding strategies in relation to growth performance, while phased and continuous supplementation with yeast-based nucleotides yielded similar results. In addition, phased yeast-based nucleotide supplementation significantly (p < 0.05) increased heterophils, platelet and monocyte count, and blood urea nitrogen, albumin, alanine aminotransferase, and total bilirubin. This indicates that phased supplementation with yeast based nucleotides can enhance immunomodulatory responses and increase metabolic activity as a stress response mechanism, thereby rendering phased supplementation efficient. Birds were slaughtered at 6 weeks of age for post-mortem measurements and analysis. Meat tenderness and drip loss were the only parameters influenced by feeding strategies. No effects were observed on carcass yield, meat pH, colour, water holding capacity, and cooking loss. In Chapter 4, the sizes of proventriculus, ventriculus, spleen, liver, duodena, jejuna, and caeca were not affected by feeding strategy (p > 0.05). However, the positive control notably increased the ileal size. The alpha and beta diversity analysis revealed similarity across all feeding strategies. Statistical analysis revealed that the relative abundance of Alistipes inops species was higher in the negative control and yeast-based nucleotide-supplemented broiler caeca. Although they did not differ (p > 0.05) across the feeding strategies, the five most abundant phyla and genera indicated that birds had healthy gut functions. It was concluded that phased and continuous yeast-based nucleotide supplementation resulted in comparable outcomes in broiler chickens. Therefore, phased supplementation of yeast-based nucleotides in broiler diets is recommended as a cost-cutting strategy.