Nutritional evaluation of wheat distillers dried grains with solubles for broiler chickens

Abstract

Wheat distillers dried grains with soluble (wDDGS) are a by-product from bioenergy production and available in increasing quantities. Three experiments were carried out to evaluate the effects of feeding wDDGS in the presence or absence of enzymes on the productive performance, carcass characteristics, digestibility, and behaviour of broiler chickens. Experiment 1 evaluated the effect of wDDGS inclusion on the acceptability of different inclusion levels (0, 10, 20, & 40%) of wDDGS when substituting for wheat and soybean meal in four isonitrogenous diets differing in slightly amino acid but mainly NDF and energy contents. Results showed significantly lower feed intake in broilers consuming the 40% wDDGS diet that might have been due to the high percentage of fibre and perhaps poor palatability of the diet. The best FCR was recorded from birds fed the 0 or 10% wDDGS diet compared to 20 and 40% wDDGS. Birds fed 40% wDDGS diet had poorer (P<0.05) crude protein digestibility, possibly due to the poor lysine digestibility of wDDGS as affected by the drying of insoluble residues after the fermentation of wheat. This effect was reflected in the linear decrease in the digestibility of diets with increasing wDDGS level. Total LWG of birds was lower with the 40% wDDGS diet which resulted in lower carcass weight. However, birds fed 10% wDDGS had a higher LWG and cold carcass weight, with similar edible carcass components comprising breast with bone, thighs, drumsticks neck and back to the 0% wDDGS diet. Experiment 2 tested the addition of an enzyme into the diets containing intermediate levels of the previously tested wDDGS to improve nutrient utilization. The study involved 168 broiler chicks in a completely randomized design with 3 X 2 factorial arrangement (3 wDDGS levels of 0, 15, 30% and 2 enzyme levels; No enzyme (NE) and with enzyme (E)). Six isonitrogenous diets were formulated and manufactured with and without enzyme inclusion (endo-1, 4-beta-xylanase 9200 U/g, alpha-amylase 1600 U/g and subtilisin as protease 16000 U/g). There were significant (P<0.05) decreases in digestibility of nutrients with increasing levels of wDDGS inclusion in broiler diets. A reduction in performance was also observed with increasing inclusion level of wDDGS up to 30%. This experiment provided an indication that 15% wDDGS could be used in practical broiler diets. At 30% wDDGS both feed intake and weight gain were lower in v the presence and absence of enzyme which resulted in similar FCR than other treatments. The same trend for wDDGS and enzyme inclusion was seen at starter, finisher and overall periods of this experiment. Enzyme addition had no effect on dry matter and protein digestibility, or on growth and feed intake. Enzyme addition increased only the digestibility of calcium but reduced the digestibility of protein. Inclusion of 15% wDDGS with enzyme did not affect (P>0.05) the carcass composition of broiler chickens, but 30% inclusion gave a poorer carcass and impaired performance. 30% wDDGS caused gizzard weight to increase, possibly due to accumulation of fibres which resulted in a slower passage rate of fibre fractions. The breast meat is considered to be the best meat, being the largest area of muscle concentration in broiler chickens, and was higher at 0 and 15% wDDGS level. Higher protein percentage of breast muscle at 0 and 15% wDDGS apparently revealed higher quality meat than in birds given the 30% wDDGS level. Enzyme supplementation showed a positive effect on some chemical components of broiler muscles where it increased the protein concentration in breast meat. Enzyme supplementation gave no performance benefits when added at manufacturer’s recommended level of 0.25kg/tonne in wDDGS-based diets, so increased inclusion rates for this enzyme and another enzyme mixture added to diets with moderate levels of wDDGS were investigated in experiment 3. Finally, experiment 3 compared the effects of the increased levels of two enzymes (A & B) on broiler performance, carcass characteristics, digestibility, fatty acids, and the gut microbial population. A total of 180 broiler chicks were used in a completely randomized design with 2 X 3 factorial arrangement by using 2 wDDGS levels (0, 15% in isonitrogenous diets) and 3 enzyme levels (no enzyme, NE and enzyme A= EA or B= EB). Here enzyme A contained 9200 U/g endo-1, 4-beta-xylanase, 1600 U/g alpha-amylase and 16000 U/g subtilisin as protease) & enzyme B contained 12200 U/g endo-1, 4-beta-xylanase, 1520 U/g endo-1,3(4)-beta-glucanase. The results demonstrated that neither the starter nor the finisher phase of the broilers showed any noteworthy differences in growth performance (daily feed intake, live weight gain and FCR) when fed 0 or 15% levels of wDDGS with or without the inclusion of enzymes. An increased digestibility of calcium was observed in the previous study as well as calcium and phosphorus in the present study. Improved digestibility of fibre fractions with addition of enzyme was not observed in this experiment. Some digestive organs such as the empty crop, total gut, empty gizzard and liver have had a higher weight due to the 15% vi wDDGS’s higher fibre content but this has no economic benefits. This study has concluded that the heightened quantities of enzyme A and the use of the improved enzyme B did not produce the desired effect on digestibility. The inconsistent results caused by these enzymes remain a great concern in this area of broiler production. In summary, these results indicated that feeding wDDGS-based diets with up to 10% inclusion in broiler production resulted in no negative impacts to broiler performance or carcass characteristics. 15% wDDGS inclusion resulted in increased protein content and reduced the ether extract content in broiler meat. Future studies should continue to investigate this technology of enhancing the nutritive availability to broiler chicken through the development and use of specific enzymes for wDDGS especially at high levels of their dietary inclusion. This should also investigate the optimum levels of enzyme to be applied as well as to develop a specific enzyme that would break the various structures of cell walls of NSP in wDDGS. There are currently no commercially prepared exogenous enzymes which target wDDGS NSP and these are needed to enhance the feeding values of wDDGS in terms of improved nutrient digestibility and performance of broiler chickens. Moreover, special emphasis should also be given to the economic aspect, broiler welfare and environmental impact concerning the use of enzymes together with wDDGS to replace wheat and soybean meal in broiler diets.