It is the structure and function of the digestive system of the goose which allows it to consume and digest large amounts of high-fibre feedstuffs and that sets it apart from other classes of poultry. This ability to utilise high-fibre feedstuffs, when combined with its foraging and scavenging ability and its aquatic nature, readily lends the goose to a number of sustainable agricultural systems.
At first glance, the digestive tract of the goose does not appear dissimilar to that of other poultry species. Its oesophagus is relatively long, with mucous glands to lubricate the passage of food and extends into the spindle shaped crop that serves as a reservoir for food storage. The food passes quickly into the proventriculus (stomach), the primary function of which is gastric secretion (acid and pepsin). The food then moves to the gizzard the function of which is firstly mechanical (grinding and crushing the food) and secondly to initiate protein digestion. The small intestine is the principal site of digestion involving bile, and intestinal and pancreatic enzymes. Microbiological fermentation of dietary fibre occurs in the caeca after which the digesta passes into the large intestine (there is also microbial digestion here) and then to the cloaca which is the site for both urinary and faeces excretion for all birds.
Rates of digestion of acid digestive fibre for the goose are from 15-30 percent depending on the material. The digestive system of the goose is able to digest this high level of fibre primarily for two reasons. The first is its large and muscular proventriculus and its extremely well-muscled gizzard that can develop pressures of up to 275 mm Hg as opposed to values of 180 and 125 mm Hg for the duck and the hen respectively. The action of these organs results in the release of cell sap and the crushing of the cells so that they can be subject to further digestion. The second is the microbial breakdown of fibre in the extremely well developed caeca and large intestine of the goose. This efficiency in fibre utilisation exists despite the fact that feedstuffs pass through the digestive tract of the goose relatively rapidly.
FIGURE 10. Digestive tract of the geese
1. Oesophagus
2. Crop
3. Proventriculus
4. Gizzard
5. Pancreas
6. Duodenum
7. Liver
8. Gallbladder
9. Ileum
10. Caecum
11. Cloaca(Source: Guy, 1996)
