The pancreas is a vital part of gastrointestinal system and endocrine system for digestive function and glucose metabolism respectively. Poultry and other birds have a well-developed pancreas, which is located between the loops of duodenum. It is relatively small in carnivore and granivore birds but larger in piscivore and insectivore birds.

Diseases of the pancreas can affect the exocrine pancreas, endocrine pancreas, or both¹. Pathomorphological studies of pancreas in avian diseases has been reported by Kumar et. al (2021). Pancreatic pathology can also develop due to non-infectious causes such as zinc toxicosis³, ⁴, ⁵or copper⁶ and selenium⁷ deficiency.

The pancreatic morphology also shows age related variations. Age related involution have been described in pancreas⁸. In senile conditions, pancreas undergoes atrophic changes and atrophy of acinar cells decreases the functional status of pancreas. Nature of diet has also been reported to alter the proportion of different enzymes in pancreatic secretion whereby the secretion of enzymes specific for particular diet shows enhancement. The highest percentage of enzyme in pancreatic secretion is made of procaroxypeptidase A and B (29.8%), followed by amylase (28.9%), chymotrypsin A, B and C (20%), trypsin inhibitor (11.3%) and trypsinogen (10%) (Pubols, 1993). The age related and diet related variation under the influence of different seasons and in different varieties of birds make poultry susceptible to physiological alterations, consequently having effect on their performance.

The incidence of various infectious diseases shows distinct age susceptibility and seasonal variations. Apart from characteristic pathology observed due to infectious, nutritional, toxic, or metabolic diseases; significant population of birds show poor body weight gain or run-down condition of idiopathic nature. In such birds, pancreatic dysfunction may constitute an important underlying factor for poor digestibility of carbohydrate, fat and protein or hormonal imbalance between glucagon, insulin and somatostatin with subsequent loss of body weight. Present study was taken up to evaluate the pancreatic pathology of poultry in different diseases in relation to season, age, sex, and varieties of birds.

Pancreatic pathology was assessed during postmortem (PM) examination of all the birds submitted to the Department of Veterinary Pathology, (CVSc & AH), Ranchi. Necropsy was carried out as per approved procedure described by Chauhan and Roy⁹. To avoid putrefaction, PM examination was conducted twice daily in the morning and evening. Pancreas and other organs were examined critically for the presence of gross lesions. For histopathological examination, pancreatic tissue was collected from the areas where gross changes were most distinct. The collected tissues were routinely processed for preparation of 4-5 p thick pancreatic section and stained with Ehrlich's haematoxylin and eosin stain¹⁰. Histochemical examination for detection of fibrous connective tissue was also carried out by Mallory's Trichrome method (Crooke-Russell Modification)¹¹. Preliminary diagnosis of the disease affecting the birds was made on the basis of gross pathological changes which were systematically recorded. Wherever required during the study, bacteriological, serological, or pathological examination was carried out for confirmation of the disease conditions.

Diagnosis of bacterial diseases such as colibacillosis, pasteurellosis was done on the basis of characteristic gross lesions followed by identification of the organisms on the basis of colony characteristics, staining property and biochemical characteristics after their isolation on bacteriological media such as nutrient agar, MacConkey agar or blood agar. Viral diseases such as infectious bursal disease (IBD), infectious bronchitis (IB) and ranikhet disease (RD) were diagnosed on the basis of classical gross lesion and serologically by ELISA tests, whereas diagnosis of fowl pox, lymphoid leucosis, cystadenocarcinoma and chicken infectious anaemia was based on characteristic gross pathology.

Diagnosis of brooders pneumonia was done on the basis of characteristic gross lesions and demonstration of fungal hyphae in a wet preparation stained with lactophenol cotton blue stain. Mycotoxicosis was confirmed by detection of mycotoxin in the poultry feed during disease incidence. Ascarids were detected during post mortem examination of diseased birds, while coccidiosis was diagnosed on the basis of gross lesions in intestine and confirmed by detection of oocyst in the fecal examination by direct method. Non-infectious conditions like gout, chick oedema disease and nephrosis was confirmed on the basis of gross lesions.

The statistical analysis and test for significance were carried out by calculating Chi-square statistics for 2x2 contingency table. Whenever and wherever required, Yates correction was employed as per standard protocol described by Snedecor and Cochran¹². All the data was entered in excel spread sheet and data was analyzed using SPSS software.

The pancreas play vital role in metabolic activities of poultry. Its dysfunction under different disease conditions might be an important contributory factor in the manifestation and outcome of diseases of poultry, particularly with respect to body weight and general health. Only little work has been done to study the pancreatic pathology under different disease conditions in domestic and wild birds.

Present yearlong study on 3796, birds irrespective of age, sex and breed revealed distinct pancreatic pathology in 22.23% of total birds examined. Our finding is similar to the report of Qamar et al.¹³ who have described pancreatic histopathological alterations in 16.65% birds. It the present study, group wise consideration showed highest incidence of pancreatic pathology in fungal (83.33%) and metabolic (82.86%) diseases which mainly included disease conditions like brooder pneumonia, gout and chick oedema disease. However, consideration of individual disease revealed thatin viral diseases like IBD, IB and bacterial disease like pasteurellosis, the incidence of pancreatic involvement was even higher i.e. 94.74%, 93.33% and 90.48% respectively. Such high incidence of pancreatic pathology in many of the disease conditions highlights the importance of pancreatic abnormality as one of the major contributory factor in disease development and poor production performance of such birds.

A number of reports are there which has observed significant pancreatic involvement and pathological alteration in different viral diseases of birds such as avian adenovirus, paramyxovirus type I, herpesvirus, Newcastle disease virus, avian influenza virus, avian parvo virus, avian encephalomyelitis virus, paramyxo-3 virus, polyoma virus, turkey viral hepatitis, West Nile virus, and psittacid herpes virus^14-21. No previous reports are available on some of the viral diseases examined in the present study such as IBD, IB, fowl pox, lymphoid leucosis and chicken infectious anemia.

In the present study, the major gross pathological changes of pancreas consisted of bleached appearance, congestion, mottling with multifocal pale yellowish often somewhat minutely nodular necrotic foci, pancreatic deformity, pancreatic atrophy and hypertrophy. Somewhat similar description of gross pancreatic pathology in birds has also been reported by Ranteer²² and Majumdar⁸. Out of all the gross pathological changes mentioned, highest incidence was recorded for bleached and congested appearance (36.97%). Similar to our finding bleached appearance of diseased pancreas as a major gross pathological alteration has also been reported by Qamar¹³.

Lower incidence of pancreatic deformity in young chicks is understandable because of poorly developed pancreatic and duodenal structures. In adult due to well-developed organ, increased resistance to disease process and stronger connective tissue framework, the probability of pancreatic deformity becomes less. In grower birds which have shown higher incidence of pancreatic pathology, the developmental changes in the organ are expected to be in active state. There is more proliferation of parenchymal cells and less support of connective tissue stroma. It is a well-established fact that avian exocrine pancreas has poor interacinar and intralobular connective tissue framework²³. Thus, any persistent injury to pancreas may bring about tissue necrosis and fibrous connective tissue proliferation which is often quite extensive as evidenced in histopathological study and histochemical demonstration of massive interstitial fibrosis. The resisting nature of interstitial and interlobular pathological fibrosis and proliferating nature of developing and regenerating exocrine pancreatic tissue may lead to distortion in the shape of pancreas which brings about concomitant spontaneous twisting of duodenal loop, matching each and every curve being developed in diseased pancreas.

Pancreatic deformity has the potential to bring about obstructive changes in pancreatic duct and blood supply. Any obstruction in the ductular passage may interfere with secretary function of exocrine pancreas. Degenerative changes and proliferative changes have been observed in ductular epithelium of birds examined along with periductular fibrosis on histopathological examination. Congestion has also been a consistent change in pancreatic parenchyma in the present study. All these points are clearly indicative of abnormal pancreatic function, thereby directly or indirectly responsible for poor body weight gain due to improper digestive and absorptive processes. The magnitude of pancreatic deformity exhibited by birds suffering from different disease conditions had been the high point of present study. Except for report of parvo virus initiated terminal bending of pancreas and duodenum published by Nunez¹⁴, no report is available on the incidence of pancreatic deformity both in domestic and wild birds. In the present study, highest incidence of pancreatic deformity was observed in chick edema disease and colisepticaemia. Both these conditions mainly affect grower birds and are associated with increased intra-abdominal pressure due to accumulation of transudate or exudates which may have interfering effect on thesecretary functions of pancreas.

Bleached appearance of pancreas was most prominently seen in coccidiosis, ascaridiasis, fowl pox, IBD and nephrosis. Anemia may constitute important underlying factor in giving bleached appearance to pancreas. Other changes such as thickening of capsule, increased interstitial fibrosis, atrophy, significant degenerative and infiltrative changes may play important role in development of bleached appearance. Congestion of pancreas is related to passive hyperemia associated with disorders such as pneumonia, viraemia and septicaemic conditions in cases of infectious bronchitis, pasteurellosis, colisepticaemia, yolk sac infection and oophoritis. Congestion was also prominently seen in chick edema disease which is characterized by increased intra-abdominal pressure and interference with venous return. Congestive changes have the potential to bring about significant histopathological alteration due to hypoxic injury such as cellular swelling and necrosis of parenchymal cells. These changes were very much evident in the histopathological study of pancreas which exhibited congestion. Similar to our findings, congestive changes in cases of pancreatitis has also been reported²⁴.

Atrophic changes in pancreatic parenchyma were not a consistent finding and constituted a minor pathological change characterized by shrunken white pancreas giving lesser gross visibility of the organ during postmortem examination. It was most evident in cases of ovarian cystadenocarcinoma of adult hen. Hyperplasia of pancreas was seen in a very small percentage (2.61%) of birds. Exact cause of hyperplastic changes could not be ascertained. It may be considered as developmental anomaly or increased local availability of growth factors.

The most frequent histopathological alteration found in the study was interstitial fibrosis. It was most evident in the cases of pancreatic deformity. In advanced lesions, pronounced interlobular and periductular fibrosis was observed. Pancreatic stellate cells have also been recognized as an important participant in mammalian pancreatic fibrogenesis²⁵, ²⁶. In case of pancreatic injury, the stellate cells undergo myofibroblastic transformation with capability to synthesize fibrillar collagen. However, this mechanism in avian pancreatic fibrosis needs further exploration and confirmation. Interstitial fibrosis may play important role in development of pancreatic deformity since fibrous tissue being firm and strong may resist expansive growth of pancreatic parenchyma particularly in grower birds with resultant curving, bending or twisting of duodeno-pancreatic complex.

Congestion was a consistent change in most of the disease; if persistent it can bring about hypoxic damage to the parenchymal cells. Hypoxia often leads to cellular swelling, vacuolar degeneration and necrosis. These changes were found in the acinar cells of pancreas showing hyperemia. Increased intra abdominal pressure in conditions like chick edema disease, oophoritis, egg peritonitis, colisepticaemia or mushy chick disease brings about passive hyperemia due to compression of inferior vena cava.

Significant number of diseased pancreas exhibited individualization of acinar cells. Any deficiency or toxicity which can specifically damage the basement membrane of acini and adjacent interstitium will lead to acinar cell dissociation. Residual bodies develop within the acinar cells⁶. The cells finally loose their polarity and get dissociated. Deficiency of essential nutrients like copper and selenium or zinc toxicosis has been reported to be the underlying factor in the development of individualization of acinar cells. It is quite possible that birds suffering from various infectious and metabolic diseases might have developed nutritional deficiencies, thus initiating loss of polarity or individualization of acinar cells. The reason for individualization of acinar cells in poultry needs further exploration.

Histopathological study of diseased pancreas in the present investigation brought forward two more important microscopic alteration of relatively high frequency viz. multifocal necrotic lesion with infiltration of inflammatory cells and vacuolar degeneration of the pancreatic acinar cells with formation of residual bodies considered to be a manifestation of apoptotic changes characterized by shrinkage in size of the cells with or without pyknotic nuclei²⁷. Residual bodies thus represent degenerated acinar cells often surrounded by clear halo. Similar description of pancreatic necrosis and associated lesions was also described²⁸. Multifocal exocrine pancreatic necrosis was registered in all groups of diseases; however its incidence was significantly higher in viral diseases such as IB, fowl pox, lymphoid leucosis, Chicken infectious anaemia, RD and IBD. Affinity of viral diseases for pancreatic parenchyma with multifocal necrosis of exocrine pancreas has also been reported in mammalian diseases such as canine distemper, canine parvo virus infection, felid herpes virus infection, FMD, classical swine fever, paramyxo virus infection, and type I avian influenza²⁸, ²⁹.

Thickened capsule in the present study has been observed as associated change with inflammatory conditions in pancreas. Thickened capsule may give pancreas a bleached blood. Thickening of capsule and associated fibrous changes may make the organ susceptible to adhesive changes with organ of digestive system as seen in lymphoid leucosis or cystadenocarcinoma where the pancreas becomes completely embedded in thickened capsule from where connective tissue infiltrated the parenchyma to bring about degenerative and necrotic changes in pancreatic acini.

Thus it is evident from the study that both gross and histopathological changes of diseased pancreaswere mostly non-specific in nature and doesn't carry any significant diagnostic value for a particular disease condition. However, their presence is clear indication of pancreatic dysfunction and its effect on the health of the birds.

Kadaknath and broiler birds showed greatest susceptibility to pancreatic abnormalities. The stressful conditions of overcrowding, poor ventilation and poor litter management in which broiler birds are mostly kept, might lead to stress related immunosupression and higher incidence of different disease conditions and pancreatic abnormalities. Other supposedly disease resistant indigenous breeds like jharsim also showed significant susceptibility to pancreatic abnormalities, though to a lesser extent as compared to broiler birds. High incidence of pancreatic pathology (46.65%) in broiler birds has also been reported by Qamer¹³ and Nunez¹⁴. Amongst bacterial diseases, E.coli infection showed consistent pancreatic lesion in different poultry varieties. Metabolic diseases like chick oedema disease and gout showed discrete pancreatic lesions in all varieties except in broiler birds. Most of the reports pertaining to avian pancreatic pathology are in wild birds or game birds such as pigeon, ostrich, macaw, cockatiel, free flying trumpeter, swan, wild water fowl etc^5,18,30.

Incidence of pancreatic pathology was higher in monsoon than summer and least in winter. In monsoon high humidity, poor ventilation, high moisture, and poor control of flies and insects could make the birds stressful and prone to suffer from disease conditions. Managemental lapses due to heat stress during summer season must be the underlying condition for compromised immune status and higher incidence of disease. In winter, the weather showing low humidity and lack of heat stress, keep birds healthy and immunologically strong to resist invasion by disease-causing agents.

Age of the birds has definite effect on pancreas, younger birds have poorly developed pancreas whereas old birds show significant replacement of exocrine and endocrine pancreas by fibrous connective tissue as a senile change. Under both the age groups, pancreatic function is sub optimal⁸, ²¹. In the present investigation, highest incidence of pancreatic pathology was observed in grower birds (33.69%) while the incidence of pancreatic pathology was in the range of 19-20% in both chicks and adult birds. Higher incidence of pancreatic pathology in chicks were observed in cases of chick oedema disease, IBD, and brooder pneumonia; whereas in grower, it was observed in cases of IB, fowl pox and colibacillosis while in adult birds, incidence was higher in cases of pasteurellosis, mycotoxicosis, cystadenocarcinoma, lymphoid leucosis and oophoritis. It is important to consider the fact that nature of disease varies amongst the three age groups due to age susceptibility and other important contributory factors such as management, biosecurity, vaccination practices etc. No clear-cut observation on age susceptibility to various diseases and related pancreatic pathology has been mentioned in any of the previous reports, though disease incidences and pancreatic pathology in chicks and grower has been reported²¹, ¹⁹.

The variation in the incidence of pancreatic pathology in different sex was found to be significantly higher in female. Study revealed that diseases in which pancreatic pathology was found to be higher in female birds were IBD, colibacillosis, yolk sac infection, pneumonia, and brooder pneumonia. For rest of the diseases with pancreatic pathology, the incidence was higher in male or equal in both the sexes such as coryza and ascaridiasis. No clear-cut predisposing factors could be ascertained for variation in disease incidence and pancreatic pathology under the influence of sex.

Thus, we can conclude that frequent pathology of pancreas in different disease conditions of poultry bird suggests suboptimal functioning of pancreas. Therefore, it would be beneficial to add pancreatic enzyme as a feed supplement in poultry as well as vitamin A and vitamin E to support the regenerative process in damaged pancreas of diseased birds as a routine practice for early recovery of the flock from disease condition and production loss.

^**Highly Significant, p<0.01; "Significant, p<0.05; NS - Non-significant, p>0.05

References