Morphology of the Southern Ground-Hornbill (Bucorvus leadbeateri) gastro-intestinal tract

Abstract

The Southern Ground-Hornbill (SGH) is the largest bird species that breeds cooperatively and the only entirely carnivorous hornbill. Currently, there are only an estimated 417 breeding groups in South Africa. As the bird is an obligatory carnivore the gastro-intestinal tract (GIT) may display specific adaptations which could be of significance in the husbandry of this endangered species. Factors that contribute to unnatural mortality in SGH’s in South Africa are poisoning, both primary and secondary; electrocution on transformer boxes; shooting; and illegal capture for trade. An undescribed threat is lead contamination of hunting offal from the use of lead-based ammunition as well as object ingestion as the SGH is a non-discriminate eater in the wild as well as in captivity. Carnivorous bird species have important gastrointestinal differences in anatomy, physiology, nutrition, and disease etiologies that greatly affect the success of medical and surgical intervention during gastrointestinal diseases. Nine adult SGH’s, of either sex, which succumbed due to natural causes, unknown causes, attack from other birds, euthanasia for humane reasons or untreatable conditions and management reasons (usually reproductive failure) were used in this study. Deceased birds were from Mabula Ground Hornbill project (Bela-Bela, Limpopo, South-Africa) and were transported to the Faculty of Veterinary Science for post-mortem examination. After the latter, the GIT with the liver, pancreas and spleen, were removed and immersion-fixed in 10% neutral-buffered formalin. In some instances, not all parts of the digestive tract were included in the study due to obvious pathology. The hollow organs were cut longitudinally to reveal and describe the inner surfaces. The topography of the organs was described and captured during postmortem examinations with a Go-pro HERO 7 action camera (American technology) and a Samsung A51 smartphone (Samsung electronics, South Africa). The terminology used in this study is that of Nomina Anatomica Avium (Baumel, 1993). After the gross description, samples for histology from the various sections of the GIT were taken, dehydrated and there after processed through 50:50 ethanol: xylol, 2X xylol and 2X paraffin wax using a Shandon model 2LE Automatic Tissue Processor. Tissue samples were then manually imbedded in paraffin wax in plastic moulds. Sections were cut at 3-5 μm and stained with Haematoxylin and Eosin (H&E), Peroidic Periodic acid–Schiff (PAS) and Masson’s Trichrome. The most notable organ from ventral view was the ventriculus situated between the two liver lobes. The coelom cavity is divided into cavities, cranial to caudal consist of a pericardial cavity (Cavum pericardii), four hepatic peritoneal cavities (Cavitas peritonealis hepatica), and an intestinal peritoneal cavity (Cavitas peritonealis intestinalis). The proventriculus is situated in the left Cavitas peritonealis hepatica dorsalis, the ventriculus is situated in the left Cavitas peritonealis hepatica ventralis, the intestine in the Cavitas peritonealis intestinalis and the liver in the left and right Cavitas peritonealis hepatica ventralis and Cavitas peritonealis hepatica dorsalis. The four Cavitas peritonealis hepatica are bounded caudally by the transversely oriented Septum posthepaticum and separates the Cavitas peritonealis hepatica from the Cavum intestinale peritonei. The proventriculus was small and the ventriculus large. Low longitudinal folds were present on the luminal surface allowing for distention, for large prey to move through. Gll. proventriculares profundae were visible macroscopically in the wall of the proventriculus and formed the main feature on the cut surface. Some of the glands emptied into the cranial aspect of the ventriculus and were more concentrated on the dorsal aspect, the Zona intermedia gastris. The proventriculus was seperated from the ventriculus by the Isthmus gastris. The large ventriculus displayed prominent longitudinal folds on the dorsal surface that ran perpendicular to the ventriculo-duodenal opening on the luminal surface and circumferentially around the Centrum tendineum. The pylorus was on the right lateral aspect of the ventriculus and was represented by the slit-like ventriculo-duodenal opening. The intestine consist of the duodnenum, jejunum, ileum and the large intestine, or the rectum. There is a total of 5 loops comprising the small intestine. The Flexura duodenojejunalis marked the transition from the duodenum to the jejunum. The point where the last branch of the cranial mesenteric artery supplied the small intestine marked the transition from the jejunum to the ileum, no Meckel’s diverticulum was present in order to identify this transition. The rectum was short and straight and slightly larger in diameter than the ileum. Ceacae were not observed. The pancreas was situated in the Ligamentum pancreaticoduodenale, between the descending and ascending duodenum, or the Ansa duodenalis. It was composed of three lobes, the dorsal lobe (Lobus pancreaticus dorsalis), the ventral lobe (Lobus pancreaticus ventralis) and the splenic lobe (Lobus pancreaticus splenalis). The Ductus pancreaticus ventralis, Ductus pancreaticus dorsalis and Ductus pancreaticus accessorius, were identified and drained into the ascending duodenum at the duodenal papilla, at the point where the bile ducts entered the ascending duodenum. The liver was large, with a smaller left lobe (Lobus hepaticus sinister) and a larger right lobe (Lobus hepaticus dexter). The two lobes were separated caudally by a complete deep, median, caudal interlobular incisure (Incisura interlobaris caudalis) and connected by the Pars interlobaris. Various organs made impressions on the liver. Two bile ducts were present, the Ductus hepatoentericus communis and the Ductus cysticoentericus.