Potential of New-Generation Microbial Enzymes to Improve Energy Value and Ileal Nutrient Digestibility of Cereal Grains for Broiler Chickens

Abstract

<p>The major objective of this study was to investigate the efficacy of some new-generation microbial carbohydrases and phytase in diets based on three key cereal grains, wheat, maize and sorghum. The diets were supplemented with different levels of phytase, xylanase and β-glucanase in four individual experiments.</p> <p>The studies were carried out at the Centre for Animal Research and Teaching (CART), University of New England, NSW, Australia. The experiments were conducted in environmentally controlled rooms. Feeds, in form of crumbles or pellets, were provided <i>ad libitum</i> between hatch and 35 days. The enzyme products – (phytase (Quantum Blue), xylanase (Econase XT 25) and β-glucanase (Econase GT) – were supplied by AB Vista, Marlborough, UK. The grains were obtained from local suppliers in New South Wales, Australia, while the day-old Ross 308 chicks were purchased from a local hatchery.</p> <p>Gross response, in terms of feed intake (FI), body weight gain (BWG) and feed conversion ratio (FCR), was assessed at 10, 24, and 35 d of age. Visceral organ development and digestive enzyme activities were measured at 10 and 24 d of age. Nutrient digestibility (apparent and standardized) and energy utilization were investigated between 20 and 24 d of age. Meat part yield (breast, thighs and drumsticks) and bone development were measured at 35 d.</p> <p>Phytase supplementation in wheat-based diets increased the FI and BWG of the broiler chickens (Chapter 3). Nutrient digestibility and tibia bone breaking strength were improved with addition of phytase and β-glucanase. Endogenous enzyme activities were higher in birds with inclusion of phytase than in the birds fed the other test enzymes. Breast weight was increased in response to addition of all microbial enzymes.</p> <p>Chapter 4 illustrates the response of broiler chickens to the test enzymes added to maize-based diets in which the BWG and FCR were improved with addition of phytase throughout the production cycle. In general, endogenous enzyme activities, ileal nutrient digestibility and energy utilization were enhanced with phytase supplementation. The weight of all measured meat parts was highest when experimental diets were supplemented with phytase rather than xylanase and βglucanase.</p> <p>The growth of starting and growing birds was improved when sorghum-based diets were augmented with the test enzymes (Chapter 5). The pancreas, small intestine and bursa were heavier with phytase supplementation than with the other enzymes. General proteolytic and sucrase activities were increased with phytase addition. Fat and amino acid digestibility as well as energy utilization was increased with phytase addition in comparison to xylanase and β-glucanase. Adding phytase to sorghum-based diets also increased the thigh weight, breaking strength and mineral contents of tibia bone at 35 days of age.</p> <p>Apparent and standardized ileal amino acid digestibility was increased with addition of βglucanase in the experiment on wheat-based diets reported in Chapter 6. Protein digestibility was improved with β-glucanase supplementation, while the weight of drumsticks was better with xylanase than β-glucanase.</p> <p>Apparent metabolizable energy (AME) was improved in wheat- and maize-based diets with the addition of the three enzymes, with the best results shown in maize-based diets. On the other hand, the AME of sorghum-based diets was increased only in response to phytase.</p> <p>The results of these nutritional studies highlight the positive effects of the test enzymes (phytase, xylanase and β-glucanase) on the three cereal grains when fed to broiler chickens. However, there is a need for on-farm testing of the products as well as comprehensive economic analysis of feeding the supplements.</p>