Megacolon in spotted/checkered rabbits
Esther van Praag Ph.D.
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Hello, I am Zippy a small tricolor Charlie rabbit, over 2 years old. I was born with a congenital disorder that affects roughly 25% of all spotted and checkered rabbits with a butterfly surrounding the nasal region: megacolon.
We, Charlie’s, are bicolored or tricolored spotted straight eared or lop rabbits, characterized by fur is more white over our body than our litter brothers and sisters. Our nasal butterfly is reduced and stops in the middle of our upper lip already, which led to the surname “Charlie”, a reminder of the moustache of Charlie Chaplin.
Our eyes are surrounded by a ring of colored fur, our nasal region has typically a partial butterfly or spots, our ears are usually colored, a colored spot is found on our cheek and we have a finer and/or partial dorsal line. Spots on the hip region are reduced or absent.
The spotted fur is under control of the 'En' gene, which is dominant on the 'en' gene, responsible for colored fur throughout the body. An 'enen' individual will have colored fur all over its body, while an 'Enen' individual will be spotted/checkered, and an 'EnEn' rabbit will be a Charlie with a very white fur. Offspring of two spotted rabbits (e.g., the Swiss Petit Papillon Tricolor rabbit) that each necessarily have the 'En' gene, will thus be composed of newborns possessing:
· Heterozygous 'Enen' offspring with a spotted coat,
· Homozygotes 'enen' offspring with a harlequin coat,
· Homozygotes 'EnEn' offspring with the characteristic white fur characteristics and few colored regions only.
Charlie spotted rabbits suffer from the megacolon syndrome
The deleterious effects of the 'En' gene manifest themselves at several levels in homozygous 'EnEn' individuals. Many newborns die at weaning or shortly thereafter. Those that survive often develop chronic megacolon, a syndrome that worsens with age. This condition is caused by an abnormal dilation of the colon and by the absence of neuroganglionic cells (aganglionosis) regulating the muscular contractions of the digestive system, which allow its content to progress towards the anus. The activity of the intestine as well as the cecum is affected.
The small intestine is shorter in megacolon rabbits, compared to normal rabbits. The pH of the intestinal content at the initial portion of the small intestine (duodenum) is also lower than that observed in normal rabbits.
Absorption of sodium (Na+) through the wall of the cecum is much reduced. As a result, this organ has a reduced content of dry matter derived from the ingested food. Abnormal liquefaction of the intestinal content has also been observed in the first half of the colon (proximal colon).
The heart and adrenal glands of megacolon rabbits are larger than those of healthy rabbits. It is possible that the increase in the size of these organs is associated with the metabolic megacolon disorder.
Effects of megacolon on health and fecal production
Abnormalities of the intestine and the cecum result in a distension of the abdomen. Megacolon rabbits often have the appearance of having a pot belly stomach. These changes lead to intestinal food malabsorption and, consequently, nutritional deficiencies. These rabbits must receive a variety of food rich in fiber: good quality pellets containing minerals and vitamins, fresh hay and, if tolerated, a variety of fresh vegetables and aromatic herbs. In some megacolon rabbits, the administration of vitamin C or multi-vitamin supplements has allowed them to gain vitality and produce more normal looking and drier hard droppings.
Fecal production is also affected. The hard droppings are large, oval, and rich in water, like a sponge. It is impossible to detect the presence of fibers when fresh. The latter only appear once the droppings have dried out, which may take a few days.
Mucus is often present, which is indicative of a disorder or irritation in the intestine.
The loss of fluid mucus via the anus colors the hair of the perineal region. This characteristic helps confirm the diagnosis of megacolon in spotted rabbits.
Some anecdotic studies mention that megacolon rabbit may never produce cecal droppings. Zippy did, however, bend down towards his anus several times a day, then took the characteristic position of any rabbit ingesting his “trophy”.
A megacolon crisis is caused by the passage of a particularly large hard dropping and is accompanied by abrupt and violent abdominal spasms. Droppings collected at the end of such a crisis often present an outgrowth. Thir progression through the intestine was accompanied by severe pain. Zippy did often moan, in spite of analgesic medication, and he would knock strongly onto his abdomen with his nose during these episodes.
Help a Charlie rabbit during an acute crisis ?
More and more spotted straight-eared or lopped rabbits become pet rabbits nowadays. It is, therefore, important to understand the causes of intestinal crises and be able to treat them. To date, there is no consensus between veterinarians and experts.
Crises are episodic, characterized by sudden outbreaks and calm periods. Dehydration, lack of fiber, nutrient deficiencies, or stress (unusual noise, abrupt weather changes) may trigger them. During a crisis, Zippy had been administered a painkiller (Metacam) and received 2 ml of virgin olive oil orally. This oil has stimulating properties on the intestinal peristaltic movement. It acts softly, without intestinal cramps (there is a risk of rupture of the caecum during these crises) in contrast to chemical stimulants of the peristaltic movement (e.g. metoclopramide, cisapride). Zippy was kept hydrated orally with a syringe. Hay and fresh or dried greens possessing carminative or antispasmodic properties such as celery branches, coriander, fennel, thyme, lemon balm, or raspberry leaves were given on a daily basis, at will. If he tolerates it, his abdomen is gently massaged and he was encouraged to exercice. The longest crisis up to the age of 2 years lasted 9 hours. Luckily, Zippy came out well every time. The frequency of intestinal crises decreased after Zippy was given sunflower seeds daily.
Zippy died at the young age of 4 years and some weeks after struggling with renal failure during the last weeks of his life.
Many thanks to Michel Gruaz (Switzerland) for sharing his knowledge about megacolon in rabbits and for precious Zippy.