The liver, a delicate organ in rabbits

 

 

Michel Gruaz and Esther van Praag, Ph.D.

 

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The liver is a large organ that occupies a large part of the rabbit's abdomen. Its surface is homogeneous and red-brown in color. The liver has an endocrine and exocrine function, with the secretion of bile.

The liver is composed of 2 major lobes: right and left, which are separated by a medial fissure in between which the accessory lobes are found: the caudate lobe and the quadrate lobe. The liver is maintained in its placed in the abdominal cavity thanks to ligaments connected to the diaphragm and to the dorsal wall of the abdomen. The role of the liver is central in the synthesis of proteins, in the metabolism of sugars and the storage of nutrients, in the degradation of toxins and organic waste produced by the cells of the body. It has, in addition, an exocrine function, with the secretion of bile. This balance can be broken during a disease, the presence of bacteria, parasites or toxins in the diet.

Liver disorders are poorly recognized in rabbits because the clinical manifestations are ambiguous and not very characteristic.

Congenital double gallbladder

The gall bladder is a hollow, pear-shaped organ that is located against the liver, in the caudal surface depression. It produces bile, a viscous, yellow-greenish liquid that is released into the small intestine via the bile duct. The secreted liquid promotes the digestion of fatty foods. In rabbits, bile is produced continuously and is stored in the gallbladder before being released into the small intestine. The bile of the rabbit is composed mainly of biliverdin, which has strong antioxidant properties, and not bilirubin. The quantity of bile produced by a rabbit per day is enormous: about 250 ml. Based on weight, this represents 7 times the amount produced by a dog. A congenital double gallbladder is a rare observation. The doubling of the organs happens during the embryonic phase. During the formation of the gallbladder, there is a subdivision of the diverticulum, which results in two complete vesicles of normal size and volume. Their ducts transport the bile to the intestine: these may merge halfway or remain separate. The duplication of the gallbladder seems to affect herbivores more than carnivores or man: 1 case out of 28 in cattle and 1 case out of 85 in sheep. Some cases have been reported in rabbits. Various clinical manifestations are associated with this congenital anomaly: pain and loss of appetite in rabbits. In other animals biliary colic, acute inflammation of the gallbladder (cholecystitis) or the presence of gallstones (cholelithiasis) have been observed.

Normal rabbit liver and gallbladder (arrow)

Liver and double gallbladder (pocket filled with green liquid - arrows) in a Harlequin rabbit aged 3 months. Since weaning, this rabbit had regular digestive problems and weighted only 2.3 kilos, while his littermates weighed 2.8 kg.

Liver and double gallbladder is well visible in another Harlequin breed rabbit.

Liver lobe torsion

Torsion of a liver lobe is a sporadic (non-hereditary) finding whose cause is not well established. An abnormal dilatation of the stomach and intestine following intestinal obstruction is associated to liver lobe torsion in rabbits. Ligaments holding the liver in place in the abdomen become distended, allowing a twisting of a liver lobe. Other causes include external trauma, bacterial or parasitic infection, or a congenital absence of ligaments. A genetic predisposition has been suggested for Madagascan lop rabbits. But this remains to be verified as the breeding line of the affected lops could not be established. Gestation is not a cause of hepatic twisting in does or other female animals. In 63% of the cases, a torsion of the caudate lobe is observed in rabbits. This lobe is attached on a very small surface only to the liver, facilitating its movement in the abdominal cavity or its torsion. Blood circulation is altered, causing the atrophy of the lobe. Its consistency becomes hard and it takes a dark color. The condition is painful and leads to decreased appetite, followed by shock and death within the next days. If the lobe ruptures, the resulting hemorrhages lead to a rapid death. A minority of rabbits survive when they receive supportive care consisting of oral food assistance with a syringe (syringe feeding), sterile subcutaneous fluids, analgesic, antimicrobial/anticoccidial, and intestinal motility drugs (1 to 2 cc of olive oil has soft stimulatory properties on the intestine too).

Liver with torsion of the caudate lobe and section of this lobe

Spine deformation and congestion of the liver

A less common cause of liver disease is bone deformity of the spine such as lordosis. These are observed sporadically in rabbits. The inward curvature of the spine causes a pressure on the abdominal mass and compression of the blood vessels draining the blood from the heart to the organs and vice versa. The liver and kidneys are mainly affected. In the liver, the blood flow from the inferior vena cava may be restricted, resulting in a reduced hepatic activity. The secretion of bile in the intestine is low, leading to poor digestion of the ingested food. As a result, toxins accumulate in the liver, which becomes congested, with a dark red color, a slightly larger size than normal, and rounded and rough edges. Passive congestion of the liver may also be secondary to congestive heart failure.

Incidetal finding upon necropsy: lordosis of the spine (arrow) and congested liver

Bacteria, coccidian and parasites

Bacteria can invade the liver and cause abscesses. The most common ones are Pasteurella sp., Escherichia coli, or Clostridia sp.. If a rabbit is in contact with birds or cattle, its liver may become infected by salmonella, listeria or Yersinia sp. bacteria. The latter causes pseudotuberculosis.

Protozoan parasites that infect the rabbit's liver include those responsible for coccidiosis (Eimeria stiedae) and toxoplasmosis. Coccidiosis affects rather young animals. Their digestive system is particularly sensitive to this parasite during the food transition from breast milk to vegetable food, which is more difficult to digest than milk. Signs of infection include a decreased appetite, diarrhea, mucus stuck to hard droppings, weight loss, and death. Young rabbits often have a swollen belly. Older and healthy rabbits develop some immunity against this parasite. Liver examination reveals the presence of yellow-colored nodules on the surface that are difficult to differentiate from bacterial abscesses.

Liver and double gallbladder is well visible in another Harlequin breed rabbit.

Parasitic worms of the liver are occasionally observed in rabbits, after ingestion of food contaminated by snails, dogs or foxes. These are mainly the great liver fluke (Fasciola hepatica) present in grasslands, dogworm (Taenia sp.) and the fox worm (Echinococcus multilocularis). The rabbit does not host the adult parasite of the dog and fox worms, but an intermediate form: hydatid cysts containing the larvae of the parasite. These cysts can take a certain volume in the abdomen and compress the rabbit's liver. Few clinical signs indicate the presence of these worms in live rabbits.

Toxemia and liver lipidosis in gestating does

Pregnancy toxemia is a serious disorder caused by a disruption of energy metabolism in late gestational rabbits. The intrauterine growth of the fetuses till parturition requires a lot of energy. If this demand is not balanced by a calorie-rich diet, the blood glucose level of the doe will drop rapidly. Adipose (fatty) tissues will then start to release fats into the blood, leading to a poisoning of the body. The liver does not work properly anymore and is unable to eliminate ketones. Other vital organs are also affected, like the kidneys. The pH of the urine is lower (5-6) than normal, with a clear color and low in sediments. It contains, however, ketones and proteins. The transit of food through the digestive tract is decreased or even stopped. The occurrence of diarrhea and/or a decrease in the amount of produced droppings are common. During an autopsy, organs such as the liver, thyroid, heart, kidneys and adrenal glands are very pale. These organs may show fatty infiltrations and necrotic foci. The stomach contains only a little bit of food. Hemorrhages are visible in the placenta and uterus.

Very pale liver of a doe that suffered from pregnancy toxemia at the end of the gestation period.

Another consequence of a difficult gestation or giving milk of a large litter is hepatic lipidosis. The alternation of periods of feeding followed by refusal to eat by the does leads to an accumulation of fats in the liver and kidneys of the rabbit. Their functioning is altered. The rabbit eats less and less, becomes lethargic and loses weight.

For details, see: Pregnancy toxemia, dystocia and uterine prolapse observed in does at the end of the gestation period

Other causes of liver lipidosis include dental problems or a diet low in fiber. Rabbit obesity is also characterized by an abnormal accumulation of fat in liver cells linked to a diet that is too rich in sugars (not in lipids). Instead of metabolizing them properly and eliminating excess, the liver stores lipids in its tissues.

Toxins, fumes and pesticides

Different toxins can affect the liver of rabbits and alter its functioning. Aflatoxin is a fungal toxin contained in cereals contaminated by molds. It is very toxic to the liver and can cause death rapidly. Plant toxins are suspected to cause neurological problems such as headache. The rabbit keeps its head down, unable to lift it, with an arched back and refuses to move and feed itself. The severity of the syndrome varies from one individual to another. Some rabbits recover after a few days, others do not survive. This health problem is referred to as “Head-down syndrome” in rabbits.

Lead and heavy metals also cause serious disturbances in the function of the liver.

The use of pine or cedar sawdust, or vermiculite should be avoided in the cage or hutch, even if their smell is pleasant. Indeed, the emanations of these products have a toxic effect on the liver.

Pesticides do act on the nervous system of animals and rabbits, with signs of hyperactivity, hypersensitivity and / or paralysis accompanied by breathing difficulties, diarrhea, hypothermia and / or nasal bleeding. Young rabbits are more sensitive and more affected than adult ones. The general state of health and nutrition of the animal also plays an important role. The treatment of such intoxications in rabbits includes assisted feeding and administration of fluids to prevent dehydration. The autopsy of poisoned rabbits shows that the liver has a pale color with cellular hypertrophy and fatty degeneration. These disorders often precede coma and death of the animal.

For details, see: Accidental poisoning with the Lindane pesticide in a few rabbit

Typical hunched position of a female rabbit, with paralysis of the hind-limbs, after a pesticide intoxication.

Lungs of the above rabbit, showing multifocal hemorrhagic regions (arrows) in the lungs.

Finally, the liver of the rabbit can develop cancerous tumors or tumors of the bile ducts. Liver diseases are, thus, numerous and often difficult to detect in rabbits. Indeed, the clinical manifestations are not characteristic, in addition to the fact that rabbits tend to hide the presence of disease. Observation remains important: droppings, their smell and shape, the presence of mucus, amount of water drunk, in addition to veterinary tests to establish more precisely the presence of a liver disease.

Further information

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Cox JC, Edmonds JW, Shepherd RC. Toxoplasmosis and the wild rabbit Oryctolagus cuniculus in Victoria, Australia with suggested mechanisms for dissemination of oocysts. J Hyg (Lond). 1981;87(2):331-7.

Coudert P., Licois D., Drouet-Viard F., Provôt F. 2000. "Coccidiosis". In: Rosell J.M. (ed),  (Enfermedades del conejo), vol.II, chapter XVI, pp 219-234, Mundi-Prensa Libros, Madrid, Spain.

Dubey JP, Passos LM, Rajendran C, Ferreira LR, Gennari SM, Su C. Isolation of viable Toxoplasma gondii from feral guinea fowl (Numida meleagris) and domestic rabbits (Oryctolagus cuniculus) from Brazil. J Parasitol. 2011;97(5):842-5.

Grabarczyk M, Kopeć-Szlezak J, Szczepańska I, Woźniak J, Podstawka U. The effect of gamma-hexachlorocyclohexane (lindane) on blood cells, kidney and liver tissues in rabbits. Haematologia (Budap). 1990;23(3):171-9.

Gustafsson K, Uggla A, Järplid B. Toxoplasma gondii infection in the mountain hare (Lepus timidus) and domestic rabbit (Oryctolagus cuniculus). I. Pathology. J Comp Pathol. 1997a;117(4):351-60.

Kopeć-Szlezak J, Góralczyk K, Woźniak J. Changes in serum and internal organs during increased accumulation of gamma-hexachlorocyclohexane in adipose tissue of rabbits. Mater Med Pol. 1989 Oct-Dec;21(4):286-91.

Licois D, Coudert P, Bahagia S, Rossi GL. Endogenous development of Eimeria intestinalis in rabbits. J Parasitol. 1992; 78(6):1041-8.

Manning et al. The biology of the laboratory rabbit. 2nd ed. London, UK, 1994.

Milot L, Partensky C, Scoazec JY, Valette PJ, Pilleul F. Double gallbladder diagnosed on contrast-enhanced MR cholangiography with mangafodipir trisodium. AJR Am J Roentgenol. 2005;184(3 Suppl):S88-90.

Moores AL, Gregory SP. Duplex gall bladder associated with choledocholithiasis, cholecystitis, gall bladder rupture and septic peritonitis in a cat. J Small Anim Pract. 2007;48(7):404-9.

Palmer AK, Bottomley AM, Worden AN, Frohberg H, Bauer A. Effect of lindane on pregnancy in the rabbit and rat. Toxicology. 1978 Mar;9(3):239-47.

Pakandl M, Drouet-Viard F, Coudert P. How do sporozoites of rabbit Eimeria species reach their target cells? C R Acad Sci III. 1995; 318(12):1213-7.

Stingl H. Vesica fellea duplex and vesica fellea divisa in rabbits (Oryctolagus cuniculus). Berl Munch Tierarztl Wochenschr. 1971;84(21):420-2.

Stolkind E. Double gall-bladder report of a case and review of 38 cases. British Journal of Surgery Vol 27 (108),  1940: 760–766.

 

  

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