Enhancing the feed value of red grape pomace for broiler chickens using polyethylene glycol and fibrolytic enzymes
The use of non-conventional feedstuffs has the potential to sustainably intensify poultry production in resource-poor communities of South Africa. Red grape pomace (GP) is a feed resource that is rich in beneficial bioactive compounds with nutraceutical properties, which have useful application in poultry nutrition. However, its utility as a feed ingredient for poultry is constrained by the presence of high levels of fibre and tannins. This study was designed to evaluate and enhance red grape pomace as an ingredient in broiler chicken diets so as to contribute to food security and environmental stewardship. The objective of Experiment 1 was to identify an optimal inclusion level of GP in Cobb 500 broiler chicken diets based on growth performance measurements. Four hundred, two-week old Cobb 500 broiler chickens (279.2 ± 18.87 g) were reared using commercial grower and finisher diets to evaluate their physiological and meat quality traits in response to incremental levels of GP. For four weeks, broilers were fed five isonitrogenous and isoenergetic experimental diets containing graded levels of GP as follows: GPO = commercial chicken diet without GP; GP25 = commercial chicken diet containing 2.5% GP; GP45 = commercial chicken diet containing 4.5% GP; GPSS = commercial chicken diet containing 5.5% GP; and GP75 = commercial chicken diet containing 7.5% GP. The five experimental diets were randomly allocated to 40 pens resulting in eight replicates per dietary treatments, with each pen carrying 10 chickens. Level of GP inclusion quadratically influenced FCR but neither linear nor quadratic effects were observed for haematology, serum biochemistry and carcass characteristics. Linear trends were observed for breast meat pH, redness and hue angle. The grape pomace containing diets had the least average weekly feed intake (A WFI) (g/bird) when compared to the commercial broiler diet. The dietary treatments did not differ in terms of carcass characteristics and internal organs of broiler chickens. The diet, GP75 promoted the highest (0.75) redness of the meat meanwhile, GPO had the least (0.49). The hue angle was observed to decrease as the inclusion level of GP increased with GPO having the highest (1.54) and GP75 had the least value (1.52). However, there were no dietary effects on meat pH, meat temperature and chroma of the meat. It was established that GP can be incorporated in commercial broiler diets up to 7.5% without compromising the birds growth performance, health and meat quality. The amount of GP that can be incorporated in broiler diets is limited by antinutritional components such as fibre and condensed tannins. The fibre in GP may negatively affect digestion and absorption of nutrients while condensed tannins can bind and reduce availability of nutrients such as proteins and carbohydrates. Phenolic compounds of lower molecular weight may also get absorbed through the digestive tract and cause toxicity. Experiment 2 was designed to evaluate strategies that would improve the intake of GP by broiler chickens by ameliorating the negative effects of fibre and condensed tannins. This was tested by including GP in commercial broiler diets at a level (10%) greater than the optimum level identified in Experiment 1 and assessing whether prior treatments of GP with polyethylene glycol and fibrolytic enzyme treatments would improve physiological and meat quality parameters of broiler chickens. The treatment of GP with polyethylene glycol before incorporation into commercial broiler diets inactivated condensed tannins while treatment with the enzyme, Viscozyme® was designed to improve fibre digestion. For four weeks, broilers were fed five isonitrogenous and isoenergetic dietary treatments formulated as follows: Commercial chicken diet without red grape pomace (CON); Commercial chicken diet containing 10% red grape pomace (GP); Commercial chicken diet containing 10% red grape pomace pre-treated with polyethylene glycol (5% w/w) (PEG); Commercial chicken diet containing 10% red grape pomace pre-treated with Viscozyme® - L (0.1 % w/w) (ENZ); and Commercial chicken diet containing 10% GP pre-treated with both polyethylene glycol (5% w/w) and Viscozyme® - L (0.1 % w/w) (PENZ). There were no (P >0.05) week x diet interaction effects on average weekly feed intake, average weight gain and FCR. The slaughter weights of CON, PEG, ENZ and PENZ chickens did not differ (P >0.05). However, GP diet promoted the least slaughter weight (1468.4 g) in chickens. Broiler chickens on CON (1276.5 g) and PEG (1243 .6 g) diets had bigger HCW, which did not differ. However, GP promoted the least (1120.6 g) HCW, which was similar (P >0.05) to that of birds fed ENZ and PENZ diets. Meanwhile, the HCW of PEG, ENZ and PENZ chickens did not differ (P >0.05). Broilers on the CON (1227.4 g) and PEG (121 0.0 g) diets had higher CCW compared to GP, ENZ and PENZ fed chickens, whose CCW did not differ. Diets significantly affected the WHC of breast meat with PENZ promoting the highest WHC (8.316 % ) and PEG promoting the least (5.223 %). The dressing percentage, meat cooking loss, meat shear force (meat tenderness) and meat drip loss were not affected (P >0.05) by the experimental diets. There were no dietary effects on size of most internal organs except for duodenum, ileum, jejunum and ceca. It was concluded that the inclusion of 10% GP treated with PEG resulted in chickens with similar HCW as those on the conventional commercial diet. The treated GP had similar weight gain as commercial broiler diet suggesting that the antinutritional effects of tannins and fibre were successfully ameliorated. As such, prior treatments of GP to reduce the antinutritional effects of fibre and condensed tannins improves broiler performance by boosting feed utilization efficiency while providing health benefits to consumers of broiler meat.