Yeast cell walls support higher growth than whole yeast when fed in broiler chicken diets

I. INTRODUCTION

Non-therapeutic in-feed usage of antibiotics in animal diets has been implicated in development of antibiotic-resistant bacteria, some of which are zoonotic and pathogenic to humans (Stanton, 2013). Based on this fact, the European Union placed a ban on such usage of antibiotics 12 years ago (European commission, 2005; Castanon, 2007). However, the continuous incidence of antibiotic resistance in other regions is fueling the consideration and legislation of a global ban on in-feed antibiotics usage in animal production (Laximinarayan et al., 2013). A global ban on non-therapeutic antibiotic usage in poultry production without a suitable alternative will have adverse effects on the global poultry production. Based on this premise, researchers and poultry feed industries globally have intensified efforts towards identification of suitable alternatives to in-feed antibiotics. The growth-promoting and immunomodulatory potentials of polysaccharides such as β-1-3 glucan and manno oligosaccharides are well documented and gaining research interest (Roto et al., 2015).

Yeast (Saccharomyces cerevisiae) contains β-1-3 glucan and manno oligosaccharides in their cell wall, therefore making it a suitable potential alternative to in-feed antibiotics for broiler chickens. Results, however, have been inconsistent and many yeast-based products have been used without proper evaluation (Gao et al., 2009). Rather than consider the efficacy of yeast as an alternative to antibiotics alone, evaluation should also be based on quality, efficacy and optimum level of yeast inclusion. Therefore, this study was conducted to investigate the effect of whole yeast and yeast cell wall products at different levels on the performance of broiler chickens.

II. MATERIALS AND METHODS

Four hundred and eighty six day old Ross 308 broilers were obtained and used during the trial in a 2 x 4+1 factorial design conducted in completely randomized experimental design. Nine diets based on maize and soybean were offered to the 486 Ross 308 broiler chickens from 0 to 35d.

The diets consisted of control (without yeast supplementation), whole yeast (WY) at four levels: (0.5, 1.0, 1.5 and 2.0 g/kg), and yeast cell walls (YCW) at the same four levels. The WY product is a fine inactive baker’s yeast protein-rich powder while the YCW product is an insoluble, purified and dried cell wall component with high levels of glucans and mannans, derived from pure culture yeast of the species S. cerevisiae. Both were supplied by AB Vista (UK). Feed and water were offered ad libitum. Feed intake (FI) and body weight gain (BWG) were measured on d10, d24 and d35, while mortality-corrected FCR was calculated from FI and BWG. On d10 and d24, one bird per replicate was electrically stunned, killed by cervical dislocation and key visceral organs were weighed. At d35, two birds per replicate were similarly euthanised and dissected to obtain the relative weight of breast, thighs and drumsticks.

Data were analysed using the general linear model of Minitab 17. Differences between mean values were established using Fisher’s least significant test, while differences between treatments were compared using orthogonal probability contrasts. Significance was declared at p ≤ 0.05.

III. RESULTS AND DISCUSSION

The effects of treatments on growth performance of broiler chickens fed whole yeast and yeast cell wall components are summarized in Table 1. The results show that, throughout the experiment, no significant (P > 0.05) differences were observed in feed intake across the treatment groups. However, there was progressive improvement (p < 0.05) in BWG, FCR and weight of small intestine (SI) at d10 and d24 for birds on the higher levels of both whole yeast and yeast cell walls compared to birds on the control diet. Although all groups consumed similar quantities of feed, the growth-promoting effect inherent in the yeast groups appears to have led to better nutrient absorption, BWG and improved FCR of broiler chicken fed whole yeast and yeast cell wall especially as the levels increased. The results of the present study are in agreement with reports by Gao et al. (2008) of similar improvements in BWG, FCR and intestinal weight of Arbor Acres broiler chickens fed diets containing 2.5 g/kg yeast culture in a 42-day trial.

At day 35, there was also significant (p < 0.05) improvement in BWG, FCR, SI weight for broiler chickens fed higher levels of whole yeast and yeast cell walls compared to birds on the control diet. (Table 1). The better BWG, FCR and increase in weight of the SI could be due to enhanced enzymatic activities caused by polysaccharides and unidentified growth-promoting agents present in the yeast and these activities became more pronounced as the level of whole yeast and yeast cell wall increased, resulting in improved performance even though the birds consumed similar amount of feed. This result is in agreement with the reports by Rajput et al. (2013) and Mutassim, 2013 who observed similar increases in BWG, FCR and SI weight of broiler chickens fed diets containing the yeast, Saccharomyces bourladii and yeast culture at 3 kg/t.

Table 1 - Effect of yeast supplementation on response of broilers chickens during 10, 24 and 35 days of age.

Table 2 - Day 35 dressing percent and relative meat cut parts weights of broilers fed different dietary treatments.

Table 2 shows the relative % meat cut parts of broiler chickens fed diets containing whole yeast and yeast cell wall components. There were no significant (P > 0.05) differences in thigh and drumstick weights. As the level of whole yeast and yeast cell wall increased, there was a progressive increase (p < 0.05) in the dressing % and the relative breast weight. Birds on 2.0 g/kg YCW diet had better dressing % and the relative breast meat yield than birds in the control and the WY groups. These results tend to follow the overall trend observed in BWG and FCR throughout the experiment. According to Nawaz et al. (2015), dressing % and relative breast weight are influenced by dietary supplementation with probiotics. Khan (2001) also reported an improvement in dressing percentage of broilers fed distillery yeast sludge.

In conclusion, supplementation of diets with inactive whole yeast and yeast cell walls at 2.0 g/kg diet improved broiler chicken performance, with the cell wall components being superior to the whole yeast.

ACKNOWLEDGMENTS: This study was supported by the University of New England, Australia & AB Vista, UK.

Presented at the 29th Annual Australian Poultry Science Symposium 2018. For information on the latest and future editions, click here.