Role of structural components on gut function and feed utilisation in poultry / Strukturelle komponenters betydning for tarmfunksjon og fôrutnyttelse hos fjørfe
In a series of experiments (Paper I-VI), the role of insoluble fibre and coarse cereal structure in poultry nutrition was studied.
Inclusion of up to 40% whole wheat in diets for broilers and layers did not decrease performance, and in some experiments, feed utilisation tended to increase by inclusion of whole wheat. Neither did addition of water-insoluble fibre in form of oat hulls to wheat-based broiler diets affect weight gain. Feed utilisation, corrected for insoluble fibre, tended to improve when insoluble fibre was added to wheat diets. The improved feed utilisation due to structural components can at least partly be explained by improved (P<0.05) starch digestibility for broilers as well as layers.
Structural components increased weight of the gizzard considerably, and this indicates an increased gizzard activity, which may play a role for the nutrient digestion. Total amount of bile acids in the gizzard increased (P<0.05) by access to insoluble fibre, thus indicating an increased gastroduodenal reflux, which may enhance digestion. Fibre concentration was considerably higher (P<0.05) in the gizzard contents than in the feed, indicating that coarse particles remain in the gizzard for grinding until degraded to a certain critical size. Duodenal particle size distribution was measured by laser diffraction, which allows measurement of particles to below 1 μm in size. As much as 50% of the particles in duodenum was calculated to be smaller than 40 μm in size. A remarkably consistent duodenal particle size distribution regardless of original particle size of the feed was observed. Also, the passage of coarse oat hulls through the gizzard was considerably (P<0.05> slower than for finely ground oat hulls. In addition, the passage of an indigestible marker tended (P=0.1) to hasten by inclusion of coarse oat hulls. These data demonstrate a selective retention of coarse particles in the gizzard, and a remarkable capability of modern poultry to grind coarse particles in the gizzard.
Layers on free range fed wheat diets with access to coarse wood shavings had up to 60% higher weight of gizzard and its content than caged layers fed the same diet. However, no such effect was found by feeding oat diets. This indicates that birds, when fed low-fibre diets start to eat litter from the floor to meet a need for structural components. Furthermore, in another experiment, a significant interaction was found between access to wood shavings and cereal specie, indicating that the appetite for wood shavings may be dependant on fibre content of the diet. Appetite for wood shavings and paper was numerically much higher in birds fed wheat diet than oats diet. However, the individual variation was high.
The amount of feather in the gizzard was less (P<0.05) in birds fed a commercial diet than those fed a rice-based diet with a small amount of structural components. Addition of 10% coarse oat hulls to a rice diet decreased (P<0.05) the amount of feather in the gizzard, but the effect of oat hulls diminished when they were finely ground. Thus, the amount of feather in the gizzard was closely related to structural components in the feed, indicating an interaction between consumption of structural components and feather pecking behaviour. This interaction may explain an improved (P=0.07) feed utilisation and better plumage condition in layers by replacing ground wheat with whole wheat.
It was concluded that the gizzard has an excellent ability to grind structural components and that such components may play a role for nutrient digestion as well as feather pecking behaviour.
