Effects of yeast and its derivatives on meat yield and hematological indices of broiler chickens challenged with Salmonella lipopolysaccharide

The present experiment was designed to determine the effects of yeast and its derivatives on meat yield and hematological indices of broiler chickens challenged with Salmonella lipopolysaccharide, a component of Salmonella bacterial cell wall.

Eight diets based on maize and soybean were offered to 432 Ross 308 broiler chickens in a 35 days experiment. Each dietary group had six replicates having nine birds each. The eight treatments groups consisted of a negative control (NC) (without supplementation and not challenged); positive control (PC) (without supplementation + LPS challenged); whole yeast + LPS challenged (WYC); yeast cell wall + LPS challenged (YCWC); yeast glucan + LPS challenged (YGC); yeast manno-protein + LPS challenged (YMPC); zinc bacitracin + LPS challenged (ZNBC); Salinomycin + LPS challenged (SalC). All yeast treatments were included at 2 g/kg diet while zinc bacitracin and Salinomycin were included at 0.03 and 0.05 g/kg diet, respectively. At d24, mean corpuscular volume, mean corpuscular hemoglobin concentration, and counts of eosinophils, neutrophils, basophils, red blood cell, hemoglobin and platelets were not significantly affected (P>0.05) by LPS challenge.

Birds in the PC group had approximately 25% (P<0.05) increase in the white blood cell (WBC) count compared to birds in the NC group. However, supplementation with WYC, YCWC YGC, YMPC, and ZNBC, resulted to a lower (P<0.05) WBC count compared to birds in the PC group. Birds in the SalC and PC groups had similar (P>0.05) WBC counts. Relative to birds in the NC group, birds in the PC group had increased (P<0.05) lymphocyte and monocyte counts of 20% and 26%, respectively. The WYC, YCWC, YGC, YMPC and ZNBC-supplemented groups had lower (P<0.05) lymphocyte count of 12% and monocyte count of 13%, compared to birds in the PC group. However, it was observed that birds in the SalC group had similar lymphocyte and monocyte counts to birds in the PC group. Dressing %, the weight of breast, thighs and drumsticks at d35 were depressed by LPS inoculation by approximately 14, 21, 14 and 3.5% (P<0.05) in the PC group compared to the NC group. However, supplementation with WY, YCW, YG, YMP, ZNB and Sal in the challenged groups improved (P<0.05) the dressing %, weight of the breast, thighs and drumsticks relative to the PC group. This present study shows that whole yeast and its derivatives can improve meat yield of broilers and, through its effect on white blood cell, lymphocyte and monocyte counts, may be associated with an amelioration of stress induced by Salmonella lipopolysaccharide in broiler chickens. This study also shows that autolyzed yeast, yeast cell wall, and its enzymatically hydrolyzed components when supplemented at 2g/kg diet may serve as a suitable alternative to in-feed antibiotics in broiler production. The non-therapeutic use of antibiotics in animal feed has been banned in some regions of the world and there are restrictions on the use of some products in other countries, including Australia (APVMA, 2017). This has led to a search for alternatives to antibiotics for use in poultry production. Yeasts and their by-products have been identified as potential alternatives to antibiotics. In a recent study, we demonstrated the positive effect of dietary supplementation with yeast and its derivatives supplemented at different levels of inclusion on healthy broiler chickens. In the current study, we tested the efficacy of whole yeast, yeast cell, yeast glucan and yeast mannoprotein in protecting broiler chickens that were challenged with a lipopolysacharide (LPS) extract from the cell wall of Salmonella Typhimurium, a gram-negative bacterium.

Exposure of healthy chickens to LPS has been shown to induce immunogenic response, non-specific inflammation and toxicity, leading to stress, poor body weight gain and reduced meat yield. Furthermore, Xie et al. (2000), reported that LPS challenge increased white blood cell (WBC), lymphocyte (LYM) and eosinophil (EOS) counts and several other hematological indices in broiler chickens.

The author suggested that the increase in these hematological parameters may be part of the reason for the stress and poor performance observed in birds treated with LPS. Yeast and several prebiotics have been reported to ameliorate the effect of stress on different

parameters of broiler chickens. However, to the best of our knowledge, research on the effect of yeast and its components on meat yield and hematological indices of broilers challenged with Salmonella lipopolysaccharide is scarce. Hence the need for this study.

Materials and methods

Eight diets based on maize and soybean were offered to 432 Ross 308 broiler chickens from d0 to d35. Each dietary group had six replicates having nine birds each. The eight treatment groups consisted of a negative control (NC) (without supplementation and not challenged); positive control (PC) (without supplementation + LPS challenged); whole yeast + LPS challenged (WYC); yeast cell wall + LPS challenged (YCWC); yeast glucan + LPS challenged (YGC); yeast manno-protein + LPS challenged (YMPC); zinc bacitracin + LPS challenged (ZNBC); Salinomycin + LPS challenged (SalC). All yeast treatments were included at 2 g/kg diet while zinc bacitracin and Salinomycin were included at 0.03 and 0.05 g/kg diet, respectively. Except for the NC group that was only inoculated with 3 ml (0.9% saline suspension), birds in the other groups were inoculated with 3 ml LPS (made up as 100 µg/ml in 0.9 % saline) intraperitoneally on days 13, 15 and 17.

Results and discussions

The results showed that, at d24, the mean corpuscular volume, mean corpuscular haemoglobin concentration, and counts of eosinophils, neutrophils, basophils, red blood cell, haemoglobin and platelets were not significantly affected (P>0.05) by LPS challenge. Relative to birds on the NC group, birds in the PC group had approximately 25 % (P<0.05) increase in the white blood cell (WBC) count. However, supplementation with WY, YCW YG, YMP, and ZNB to the challenged group led to a lower (P<0.05) WBC count relative to birds in the PC group. Birds in the SalC group had similar (P>0.05) WBC counts to birds in the PC group. Compared to birds in the NC group, birds in the PC group had increased (P<0.05) lymphocyte and monocyte counts of 20% and 26%, respectively. The WYC, YCWC, YGC, YMPC and ZNBC-supplemented groups had lower (P<0.05) lymphocyte count (12 %), and monocyte count (13%), compared to birds in the PC group. However, it was observed that birds on the SalC group had similar lymphocyte and monocyte counts to birds in the PC group. Wang et al. (2016) also observed that live yeast could alleviate LPS-induced inflammation, haematological indices and stress in broilers at d27.

Dressing %, the weight of breast, thighs and drumsticks at d35, were depressed (P<0.05) by LPS inoculation by approximately 14, 21, 14 and 3.5 % in the PC group compared to the NC group. However, the dressing %, weight of the breast, thighs and drumsticks was improved (P<0.05) in the WYC, YCWC, YGC, YMPC, ZNBC and SalC groups relative to the PC group. This observation is in agreement with the findings of Faithi et al. (2012), who concluded that yeast culture supplemented at 1.5 g/kg improved carcass yield and humoral immunity of broilers under the stress of challenge with Newcastle disease.

The results of the present study show that supplementation with whole yeast and its derivatives can improve meat yield of broilers and, through its effects on white blood cell, lymphocyte and monocyte counts may be associated with an amelioration of stress induced by Salmonella lipopolysaccharide in broiler chickens. It can also be concluded that autolyzed yeast, yeast cell wall, and its enzymatically hydrolyzed components at 2g/kg diet may serve as a suitable alternative to in-feed antibiotics in broiler production.

Acknowledgement: Research was funded by AB Vista UK

References are available on request From the Proceedings of the 2019 Autralian Poultry Symposium