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The Stomach of the Eclectus Parrot: Its Structure & Function Relative to Dietary Stomach Dysfunction

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Rob Marshall B.V.Sc., M.A.C.V.Sc. (Avian health) 

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Presented at ICARE (International Conference on Avian, Herpetological and Exotic Mammal Medicine) London April 28-MAY 2 2019

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Slide 1

Dietary stomach dysfunction occurs when the functional capacity of the gizzard is overwhelmed by hard or excessively fibrous foods.

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Eclectus parrots are more susceptible to this complex problem because their stomach is designed to digest large volumes of soft textured fruit pulp, which is their main food type.

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Slide 2

In order to investigate the pathophysiology of stomach dysfunction we compared the stomach morphology of several bird species belonging to different diet type categories. Comparative studies of this type are very useful as they train the eyes to detect subtle anatomic variations and to think deeply about their origins.

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For example, the eclectus parrot and lorikeet have equally long intermediate zones but different gizzard sizes. The question is why?  The simple answer is that stomach anatomy is strongly influenced by the chemical and physical attributes of the wild diet.

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Slide 3

In nature, fruit pulp is the main food of eclectus parrots. This food is wet bulky and protein poor. Large amounts of this bulky moist food must be eaten to overcome its nutritional dilution, especially in regard to its low protein content. The stomach design of this frugivorous parrot must be designed to fulfil this need. As a diet specialist the eclectus parrot is more susceptible to stomach dysfunction than other parrots because of its limited flexibility to adapt to extreme diet modifications.

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Slide 4 

This is an incised view of the stomach of an eclectus parrot. The three parts of the stomach; the glandular proventriculus, the intermediate zone and gizzard became readily distinguished after the surface was irrigated of the superficial and deeply adherent mucus layers. 

The long intermediate zone and large gizzard were the most intriguing design features.  This paper investigated their possible functions regarding healthy digestion.

 

Slide 5  

The glandular proventriculus is displaced cranially due the elongated intermediate zone. This feature is of clinical significance. Diagnostic imaging needs to carefully consider the position of the glandular proventriculus relative to the intermediate zone. Surgeons also need to be aware that they may be entering the intermediate zone when performing gastrotomies. 

 

Slide 6

The fact that the two diet specialists, the frugivorous eclectus parrot and the pollinovorous nectarivore lorikeet in this study had long intermediate zones confirmed to me that the intermediate zone provides a storage space for proteolysis. In the lorikeet it is a space where pollen, which is rich in protein but resistant to digestion can be retained for extended proteolysis. In the eclectus parrot, it is also a large space to store bulky protein poor food mass to remain for a protracted period of proteolysis.  

 

Slide 7 

The intermediate zone was lined by a compact layer of koilin. The surface was serrated. These findings suggest the intermediate zone fulfils a reduction function similar, but different to the gizzard. The serrated membrane is likely to perform a shredding action which is a more effective to reduce fibrous fruit pulp than a grinding action. Therefore the intermediate zone appears to fulfil a reduction function as well as a storage site for proteolysis. These coordinated digestive functions would aid the proteolysis of a protein poor main food.   

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Slide 8

The large gizzard resembled that of granivorous parrots. This was a confusing finding because the wild diet of eclectus parrots contains small moist fruit seeds and very few hard seeds. It would be expected that the gizzard would be be better designed as a storage organ as it is with non-parrot frugivores such as the fig parrot. I think the best explanation for the large gizzard is that it would be necessary to reduce large volumes of fruit pulp as quickly as possible.

 

The internal gizzard showed three surface patterns. Each surface performs a separate but coordinated function directed towards  the different physical qualities  of the wild diet. The small smooth area performs a grinding surface for pulverising small seeds; the transverse twisted folds across the caudal and cranial poles provide a cutting surface to slash and reduce fibrous fruit pulp: whist the longitudinal folds would direct the flow of sugary fruit juices towards the intestines where they are rapidly digested.

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Slide 9 

At this point I can explain the process of heathy stomach function. Above all, the gizzard is the pace maker of digestion and controls the rate of flow of food through the stomach. 

The gizzard is also distantly involved with proteolysis. When the thick crassus gizzard muscles contract partially digested gizzard contents are refluxed into the intermediate zone for further reduction and to mix with gastric juices. When the thin tenius gizzard muscles contract food from the intermediate zone is allowed to enter the gizzard. This co-ordinated oscillating digestion process is key to health digestion in the eclectus parrot as it lessens the gizzard’s workload regarding reduction and returns food to the intermediate zone in a reduced form providing smaller particles of food with a greater surface area for highly efficient proteolysis.

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The presence of mucus over most of the intermediate zone in the absence of compound glands confirms movement of proventricular secretions into intermediate zone. This finding supports the proposal that the intermediate zone is an additional site of proteolysis.

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Slide 10 

Eclectus parrots become susceptible to the harmful effects of stomach dysfunction when they eat hard or excessively fibrous foods that overload the functional capacity of the gizzard causing a backlog of food matter in the intermediate zone. It is the retention of this partially digested food in the intermediate zone and associated gas-forming fermentation that is responsible for the symptoms of pain, malaise and cognitive dysfunction that characterises stomach dysfunction.

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Slide 11

We see two forms of stomach dysfunction. 

The first occurs in juveniles due to a developmental failure of the gizzard and intermediate zone. This form of stomach dysfunction is a result of incorrect diet from an early age. Eclectus parrots require the introduction of soft solid foods.

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The second form occurs in adult birds with earthy stomach function. We see this form most commonly in females in breeding condition. These birds are prone to ingesting WOOD  and other substances as part of nest-making behaviour. It is this type of indigestible matter that initiates repeat episodes of stomach dysfunction.

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Slide 12 

This slide outlines our treatment and prevention approach for birds diagnosed with symptoms of stomach dysfunction, which include cognitive deficit, fermentative crop and stomach infection, visceral pain and associated localised feather destruction behaviour.

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Gastric lavage purges undigested food remnants from the stomach ands helps to remove mucus accumulation from the intermediate zone.  Culture and sensitivity determines the choice of antibacterial therapy. Dimetronidasole (flagyl) is administered when gas forming anaerobes are noted.  

Prevention focuses on dietary development or restoration of healthy stomach function by feeding foods with the nutritional and physical attributes of the main wild food of fruit pulp.

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Slide 13 

At this point I would like to mention Macrorhabdus and Bornavirus as infectious causes of stomach dysfunction. The question that must be asked “Is stomach dysfunction a cause rather than consequence of these diseases?”