Submandibular Lingual Entrapment in Herbivorous Waterfowl – A discussion of its Aetiology

Danny Brown BVSC(Hons) BSc(Hons) MACVSc(Avian Health)

Glasshouse Mountains, Queensland, Australia, 4518.

geckodan@bigpond.com

Exotic DVM (Vol 6.6, pg 4) featured previously an article by Dr Bruce Levine on a

unique method of surgical management of Submandibular Lingual entrapment in a goose.

In that article, the inciting cause of the initial entrapment was hypothesised to be

associated with a neurological deficit. This article will describe the aetiology of this

relatively common condition when seen as an early stage lesion, rather than as an end

stage lesion as Dr Levine had seen it.

As the Federal patron of our national Pheasant and Waterfowl Association, I am exposed

to an above average number of waterfowl cases (from an Australian perspective). The

aetiological precursor to tongue entrapment is seen regularly throughout Australia. This

has been reported in Brown (1997) and Brown (2002)

I have been involved in 14 cases from clientele plus numerous (>20) cases in my own

waterfowl collection and those of friends.

The primary initiating cause of this problem is that of food entrapment lateral to the

frenulum and within the intermandibular space. Under normal grazing conditions,

waterfowl have the opportunity to select grazing material that best suits their dietary

needs. In captive situations, they must make the best of what is available. Whilst

waterfowl keepers do their best to provide optimum access to suitable forage,

environmental conditions and local vegetation types may limit this. When these larger

herbivorous waterfowl (geese, swans and shelducks) consume grass forage it is usually

grasped by the anterior beak and pulled sideway across the lateral filtering lamellae

which act much like a serrated knife. With soft, supple greenery such as short, well

watered grass is grasped, it breaks away into short manageable pieces. When longer,

dryer or fibrous grass species are grasped it often requires repeated sideways movements

to break the grass or invariably it is pulled out from the base, leaving the waterfowl to

swallow a large length of grass. It is this material that may become rolled up into a small

ball which becomes lodged sublingually. Once a sublingual grass ball is in position it

then subsequently allows other food materials such as mash or grains to become trapped

and incorporated into a firmer, more resilient mass. In most cases, these masses are

eventually dislodged with normal mastication or whilst dabbling in water. In occasional

cases they may remain for extended periods resulting in the stretching of the

intermandibular skin and the subsequent accommodation of progressively larger food

masses. In extreme cases or cases of chronic food entrapment, the intermandibular skin

stretches to a size that allows the tongue to move ventrally and become trapped in such a

way that it cannot become spontaneously repositioned by the bird.

If observed early in the progression of the syndrome, the food material is easily expressed

with your finger and removed. If these birds are kept away from grazing for a period of 7-

10 days then the pouch usually tightens back to its original shape. I have two Black

Swans (Cygnus atratus) in my own collection that need to be caught up as often as

fortnightly in periods of dry weather (resulting in poorer grass quality) to dislodged

entrapped food material.

In more advanced cases, such as that reported by Dr Levine, the resultant pocket in the

intermandibular skin becomes permanent. Surprisingly, most of these affected birds are

still able to obtain enough nutrition to survive. One extreme case, (in a Black Swan,

Cygnus atratus) that I have treated had an entrapped tongue for a period of 18 years

before being presented to me (diagnosed as a young swan as having an inoperable throat

neoplasia). This swan’s sublingual pocket was not unlike that in the goose reported by Dr

Levine. It was treated surgically by resecting the redundant sublingual intermandibular

skin and placing an oesophagostomy feeding tube for 1 week to reduce downward

pressure on the suture line. Ironically, this bird was lost to follow up as it was eaten by a

fox 3 weeks after the feeding tube was removed. The utilisitaion of Dr Levine’s surgical

technique may have made the feeding tube unnecessary as downward pressure on the

suture line would have been limited. Another case, in an Australian shelduck (Tadorna

tadornoides), had resulted in the tongue being trapped under such tension that the tongue

tip was forced dorsally and at the time of surgery the tongue had bent upwards into a

hook. In addition to corrective surgery to the intermandibular space, the tongue tip was

amputated as its deformed position prevented the mouth from being closed. This

individual did well postoperatively.

I do not believe that there is any significant neurological damage causing or associated

with this condition. It is my opinion that failure to reposition the tongue is determined by

the depth of the sublingual pocket or by the degree of disuse atrophy in chronic cases. In

the majority of cases, the ability of the bird to withdraw the tongue from the pocket and

reposition it dorsally is inhibited by the physical ability to retract the tongue caudally

enough to clear the posterior margin of the base of the mandible. The majority of the

muscular development of the tongue revolves around dorsal and cranial tongue

movement and caudal movement is a lesser priority.

In cases where the entrapment has been chronic, I believe that simple disuse atrophy may

be involved. This is indicated by a degree of tongue weakness upon initial correction but

improved function over time.

The presentation of this syndrome in its early stages is significantly more common in

young birds particularly in cygnets between two and 4 months of age. Chronic cases are

more common in older birds, either due to neglect of younger bird conditions or due to

their ability to feed on coarser, more fibrous material (which is less likely to

spontaneously clear itself from entrapment).

Further Reading