Effect of betaine supplementation and stocking densities on growth performance, carcass characteristics and meat quality of broilers

Introduction: Stocking density is one of the important concern in the poultry industry and it is related to the poultry productivity and animal welfare. Stocking density for broiler chickens is defined as the number of birds or the total live weight of birds in a fixed space. Increasing broiler number in breeding environment increases led to a higher production of chicken meat, but, if stocking density exceeds over the proper range, the productivity is rather decreased because of increased health problems and decreased growth performance of broiler chickens. Natural betaine is found in several plants and organisms and it is commonly extracted and purified from beetroot. It is classified as a methyl-ammonia due to three chemically-active methyl groups bound to the nitrogen atom of a glycine molecule), and it is considered the only readily active methyl-group donor The biosynthesis of betaine is made by the oxidation of choline in the cell mitochondrion. However, this reaction is not interesting because choline deviated from its essential role in the transmission of nerve impulses, and in addition, choline content in typical corn- and soybean-based broiler diets is not sufficient supply their cell requirements for methylated compounds. Another positive aspect obtained with the dietary inclusion of betaine is the methionine-saving effect, that is, betaine donates methyl groups instead of methionine in a reaction with homocysteine.
Material and Methods: This experiment was performed to evaluate the effect of betaine supplement utilization on growth performance and carcass and meat quality of broilers at different stocking density. For this reason, 216 one-day-old male Ross 308 broilers were used in a 2×2 factorial arrangements with four treatments including two stocking density (7 and 15 chicks per m2) and two betaine levels (0 and 0.1 percent) and four replications. During the starter (0-10 days), grower (11-25 days), and finisher (26-42 days) phases, the birds were fed according to the Ross 308 recommendations. The diet and water were provided ad libitum during the trial. The body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR) were measured for each phases. At the end of the experiment, two birds per replicate with body weight close to the average of each cage were slaughtered to determine the Carcass characteristics after removal of head, feathers and feet. Carcass yields were calculated relative to the live body weight. After slaughter, the right thigh and breast of broiler chickens were separated and kept at 4°C for measuring meat quality traits including water Holding Capacity, cooking loss, pH and drip loss. To determine the WHC, 4 g of breast muscle were placed in a filter paper and centrifuged at 1500×g for 4 min, Then the samples were placed in an oven at 70°C for 24 h to be dried (Castellini et al., 2002). In the case of cook loss, a piece of 1 cm3 of breast muscle was weighed and kept at 4°C for 24 h, then placed in a water bath at 85°C for 10 min and finally cleaned and re-weighed with a linen cloth (Bertram et al., 2003). For the measurement of drip loss, a piece of breast muscle was weighed and placed in a plastic bag and kept at 4°C for 24 h. The meat was then gently rubbed into the cloth and weighed again (Christensen, 2003). All data were analyzed by ANOVA utilizing GLM procedure of SAS. Means were compared for significant differences utilizing the Tukey multiple range test (P˂0.05).
Results and Discussion: The results showed that feed intake and weight gain decreased significantly during the grower, finisher and whole production periods at high stocking density (P<0.05). These results agree with previous experiments that reported high stocking density decreased growth performance of broiler chickens compared with low stocking density. This could be related to various environmental and behavioral factors such as less birds’ movements in a given space, and more difficulty accessing to feeders and drinkers and also the competition for food intake (Cengiz et al., 2015). The addition of 0.1% betaine increased weight gain and decreased feed conversion ratio (P<0.05). This is in agreement with other researchers who reported that addition of betaine to broiler diet under heat stress increased growth performance due to antioxidant capacity and lowering stress indexes (Sakomura et al., 2013). Studies indicated that betaine supplementation may be beneficial to the intestinal epithelium due to its osmolyte function, maintaining villi integrity and consequently promoting better nutrient digestibility and absorption (Eklund et al., 2005). The broiler carcass and breast relative weights decreased as stocking density increased (P<0.05), however the effect of stocking density was not significant on the relative weights of thigh, liver, bursa of Fabricius, spleen and abdominal fat (P>0.05). The utilization of betaine supplement increased the relative weights of carcass and breast and decreased the relative weight of ventral fat (P<0.05). It was expected that the dietary supplementation of betaine would influence carcass and parts weights due to its methyl-group donor property, which would increase methionine, cystine, and glycine for protein synthesis and also its contribution to reduce fat deposition in the carcass (Sakomura et al., 2013). The cooking loss increased and meat water holding capacity decreased as stocking density increased, while the addition of betaine led to increase in meat water holding capacity and decrease in drip and cooking losses (P<0.05). osmotic property of betaine and its role in maintaining cell water, may be the reason of better meat quality of broiler with betaine supplementation.
Conclusion: Increasing the stocking density had negative effects on growth performance, carcass characteristics and meat quality. It seems that the dietary addition of betaine supplement could be a suitable approach for alleviating the negative effects of increasing the stocking density in broilers production via improvement in growth performance.