[Truncated abstract] Australia produces 87% of the world’s lupins (Lupinus angustifolius) which have the potential to be an excellent source of protein and energy in animal diets. However, feed manufacturers and poultry producers cannot use more than about 5% lupins in broiler and 7% in layer diets. The main reason is because 34% of the lupin grain comprises complex cell-wall polysaccharides that are indigestible. The main component of cell walls in lupins is pectin (33%). Poultry cannot digest pectin because they don't secrete the appropriate enzymes so their ability to use lupins is limited. Undigested pectins increase the viscosity of digesta in the bird's digestive tract, which in turn reduces the digestibility of dry matter and efficiency of feed utilisation. Pectins also increase water-holding capacity, a characteristic directly related to water intake and wet droppings. In this thesis, I tested the general hypothesis that breakdown of cell walls and pectins will improve the nutritive value of lupins for broilers and layers and reduce wet droppings. This hypothesis was tested in six experiments by treating lupins with specific exogenous enzymes (pectinases) or mechanical-heat treatment (expansion) plus pectinase. In the first experiment, attempts to break down the cell walls and pectins using four doses of pectinase, specifically polygalacturonase (PG), succeeded in improving the nutritive value of whole and dehulled lupins for egg layers. The lowest dose, 0.6g/kg diet, was the most effective dose for reducing water intake, wet droppings, the viscosity of the digesta and the number of soiled eggs. ... Equivalent figures for layers were 14, 15, 5 and 8%, indicating that the pectinases were slightly more effective in layers than broilers. For diets containing 20% dehulled lupins, pectinases were also very effective at breaking down both pectin and cell walls to release nutrients and, concomitantly, reducing water intake and wet droppings, but the magnitude of the responses was slightly less than with the 10% dehulled lupin diets. For diets containing 30% dehulled lupins, although the pectinases again were effective at breaking down pectin and cell walls and reducing viscosity, they did not reduce water intake or wet droppings. This might be due to the large amounts of nonmethylated pectic polysaccharides, which make up two thirds of the cell walls, by increasing water-holding capacity particularly when dehulled lupins are included in the diet at high levels (up to 30%). These polysaccharides might be broken down by appropriate enzymes. This hypothesis is worth testing in the future. Overall, the results of my study supported the general hypothesis. These in vivo results are conclusive and consistent. They show that an optimum combination of PME and PG is capable of including dehulled lupins up to 20% in broiler and layer diets without any nutritional or hygienic problems. The strategies I developed have proven very useful for breaking down the cell walls and pectins, improving the nutritive value of lupins for broilers and layers, and reducing wet droppings. By using the optimum combination of two pectinases, it should be possible to make substantial improvements in the nutritive value of lupins for broilers and layers, most importantly by reducing excessive water intake and wet droppings associated with feeding dehulled lupins. Without pectinases, the amount of dehulled lupins used in poultry diets is fairly small (7%), but if pectinases are used, this upper limit can be lifted to 20%.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2009|