Influence of feed processing and enzyme supplementation on performance, nutrient utilisation and gut morphology of poultry fed barley-based diets : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Poultry Nutrition at Massey University, Palmerston North, Manawatu, New Zealand
The first experiment (Chapter 3) determined the metabolisable energy and standardised ileal digestible amino acids of two barley cultivars (NSH [normal starch hulled barley] and WSHL [waxy starch hull-less barley]) and wheat for broilers. These values were used to formulate the experimental diets in subsequent experiments that evaluated the optimum barley inclusion rate in wheat-based diets (Chapters 4 and 5), optimum barley particle size (Chapter 6) and conditioning temperature (CT; Chapter 7), and potential interaction of carbohydrases with each processing parameter.
In Chapter 3, wheat and WSHL had the highest and lowest metabolisable energy and digestible amino acid contents, respectively, with NSH being intermediate. Supplemental carbohydrases increased the energy utilisation with a pronounced effect in WSHL.
Data reported in Chapter 4 showed that optimum inclusion level of NSH was 283 g/kg of diet. Nutrient utilisation linearly improved with increasing inclusions of NSH. Carbohydrases improved feed per gain (F/G) and nutrient utilisation.
Chapter 5 suggested that WSHL could be safely included up to 260 g/kg in a wheat-based diet with no adverse effect on growth performance. Carbohydrases improved the F/G and, starch and energy utilisation.
In Chapter 6, particle size effect was preserved after pelleting and, coarse barley and carbohydrases improved the F/G and nutrient utilisation. The combination of carbohydrase and phytase produced no further improvements in nutrient utilisation.
The final experiment (Chapter 7) demonstrated that better pellet quality achieved by increasing CT to 88 °C failed to ameliorate the negative impacts of high CT on nutrient utilisation and broiler performance. Carbohydrases improved weight gain, F/G and, starch and energy utilisation. The lack of interaction between the carbohydrases and CT indicated that carbohydrase had similar efficacy at each CT.
The primary finding of this thesis research was that if cultivar-specific values for metabolisable energy and digestible amino acids are used in feed formulations, barley has the potential to substitute up to 50% of wheat in broiler diets. Coarse particle size (8.0 mm) and conditioning the diets up to 74 °C is recommended for the tested barley type. Supplemental carbohydrases improved the feeding value of barley for broilers.