Calf diarrhoea is among the most common diseases of cattle and buffalo worldwide. It causes acute dehydration, acidosis and death in both thebeef and dairy animals¹. The National Animal Health Monitoring System (NAHMS) for U.S. dairy in 2011 reported that 52.2% of weaning calves die due to diarrhoea; and most cases occurred in calves less than 1-month-old. A similar mortality rate for dairy calves due to diarrhoea was recently reported in South Korea². During the last previous years, surveys of calf diseases and mortality carried out in more than 100 herds in different states of India revealed an average mortality rate amongst cattle calves as 10.59% (range 1.54 to 24.24%) for the age group of 1 day to 2 months and 21.91% (range 12.70 to 26.50%) in 1-day to one-year-old calves. In buffalo calves the average mortality rate of 33.50% (10 to 62.26%) has been recorded for calves less than 2 months of age in 23 herds (AICRP Report, 1974).

Many infectious agents like bacteria, virus and protozoa had been incriminated either alone or in association as a cause of diarrhoea in neonates. Major enteric pathogens known to cause calf diarrhoea include bovine rotavirus, coronavirus, bovine viral diarrhoea virus, Salmonella enterica, Escherichia coli, Clostridium perfringens, Cryptosporidium parvum, and newly emerging enteric pathogens such as bovine torovirus and caliciviruses³,⁴,⁵-⁶. Among these, bovine rotavirus diarrhoea ranks highest to cause the neonatal calf mortality³,⁴,⁷. Diarrhoea in calves due to E. coli infection usually common in 3–5 days old calves and due to corona and rotavirus infection in 5–15 days old calves, although it can affects calves up to several months of age. Cryptosporidiosis most commonly affects calves aged 535 days. Salmonella can cause diarrhoea in both adult cattle and calves; infection is much more common and oftencauses severe symptoms in 10-days to 3-month-old calves⁸. The Pasteurellosis, FMD and coccidiosis are also known to affect intestine in calves directly or indirectly⁶. In the present study, the bovine calf carcasses were examined for intestinal pathology irrespective of affections occurring in other organs.

A total of 40 carcasses of calves (Vrindavani-32; buffaloe-8) aged less than 6 months were necropsied at the Post-mortem Facility of Division of Pathology, IVRI, Izatnagar. Samples of intestinal contents and different tissues viz. intestine, mesenteric lymphnodes, spleen, liver, lungs, kidneys and heart were collected in 10% neutral buffered formalin (NBF) and in RNALater. The samples collected in RNA Later were stored at −20°C for molecular study.

Various intestinal affection in 40 dead calves are detailed in Table 1. The infection of rotavirus was observed in combination with other disease conditions.

There are several reasons of diarrhoea in calves, and among them the infectious agents are strong contenders to cause mortality either singly or in combination. The rotavirus especially Group A, is the well-recognized entero-pathogen in acute diarrhoea in young calves. However, it is not uncommon that both rotavirus and other microorganism can concomitantly infect calves. In the present study, the rotavirus enteritis was found in association with coccidia, pasteurella and foot-and- mouth (FMD) virus. In these cases, the enteric lesions of rotavirus infection as well other pathogens were evident. Histological changes of coccidiosis along with rotavirus enteritis were exhibited as villous atrophy with different developmental stages of Eimeria in the lamina propria, akin to changes described by others¹¹, ¹², except, the lamina propria was infiltrated with mast cells and with few eosinophils. Similarly, in another case of rotavirus and concomitant infection with pasteurellosis, grossly, the congestion in mucosa and serosal surface, and microscopically the aggregation of lymphocytes in the lamina propria have been found. However, primarily pasteurellosis causes fibrinous pneumonia, but some workers described as a new finding of Pasteurella multocida type B the aggregation of lymphocytes in the lamina propria due to invasion of this bacteria in the lamina propria¹³. In an outbreak of FMD, 23 calves which died due to massive necrosis of the heart muscles, 2 of them also concomitantly infected with rotavirus gastroenteritis and the same has been described in the literature¹⁴, but without mentioning microscopic details. In the present study, besides changes of enteritis, focal necrosis of muscularis layer of the intestine and mild to moderate mast cells infiltration in the lamina propria were also present. In all these affected cases, the vesicular lesions in different organs were indistinguishable from FMD as described in the literature¹⁴, ¹⁵. Being crossbred calves, the lesions of acute necrotizing myocarditis were remarkable. The virus from pharyngeal and other sites makes its way to the lymphatics and then undergoes viremia to replicate in epithelial target organs¹⁶. The mortality usually reaches to about 70% in young animals due to cardiac failure¹⁴. It is well known that in acute FMD infection “tiger heart” lesions are observed leading to heart failure and sudden death¹⁵, ¹⁷. The gross lesions ranged from mild to distinct areas of pallor on the heart surface that extend into subjacent myocardium¹⁸ and the same was noticed in the present episode together with the lymphoid tissues necrosis/apoptosis.

Enteritis due to aflatoxicosis in 5% of cases was observed associated with pericellular cirrhosis with veno- occlusive lesions in the liver. The large size of hepatic cells and bile duct hyperplasia in the liver; mild fibrosis in the lamina-propria with crypt atrophy; moth eaten appearance of the mesenteric lymphnode were the prominent changes as described earlier⁷, ¹⁹. The toxic metabolites (B1, B2, M1, M2) produced by certain fungi like Aspergillus spp. in stored feeds and fodders cause aflatoxicosis in livestock species and humans throughout the world. These toxic metabolites, particularly B1 (Aspergillus flavus) damage the liver and sometimes cause hepatic cancer. The toxic intermediates bind to cellular DNA, RNA, or proteins to cause carcinogenic and teratogenic effects. In the present study, the affected liver showed, degeneration, bile duct hyperplasia, bridging fibrosis and cellular atypia, as described inthe literature²⁰. The enteritis might have been caused due to secondary bacterial infection due to immunosuppression by the toxic metabolite. In cases of acute and septicaemic enteritis (2.5%), the lesions of neutrophilic infiltration in the propria, acutely engorged vessels and fibrino- hemorrhagic lesions together with fibrin thrombi in vessels due to involvement of E. coli and P. multocida type B were in consonance with the findings of author²¹. These bacteria cause cytolysis (leucocytes) and produce leukotoxin and lipopolysaccharide that result into circulatory disturbance and disseminated intravascular coagulopathy²⁰. The P. multocida has been isolated from the intestine in calf that died due to the intra-tracheal exposure; therefore it suggested that transmission of bacteria via the GIT of diseased animal is possible²².

Chronic necrotising enteritis in two cases, affecting the ileum and the jejunum, had necrotic Peyer′s patches and sloughing of the lining epithelium and nearby villi. The laminapropria showed infiltration with mononuclear cells. Similar type of enteric pathology has been described for bovine viral diarrhoea and parvovirus infections⁷, ¹⁴. However, in another case of buffalo calf (6 month), there was severe necrosis of crypts along with massive mononuclear cells infiltration, which could be due to either bacteria or virus. However, the same could not be proven in any of the cases. The jejunal haemorrhagic syndrome was recorded as a sporadic finding in the present study, characterized by enteritis of the small intestine that led to development of intraluminal hard blood clots. The aetiology of this syndrome is believed to be multifactorial mainly caused by Clostridium perfringens type A and Aspergillus fumigatus⁷,²³, because both the pathogens are common in gut and feed/forage, respectively. The primary lesion is caused by C. perfringens in young and rapidly growing animals. The physical obstruction by blood clots, with proximal accumulation of intestinal fluid and gas, develops clinical sings of hypochloremia, hypokalemia, dehydration, and varying degrees of anaemia. The hemorrhagic enteritis chronically causes necrosis that extends through the intestinal wall to cause a fibrinous peritonitis, profound toxaemia, and death. In the present case also fibrinous peritonitis was present.

A solitary case of toxocariosis in buffalo calf (6 months) was recorded, wherein bile duct squamous metaplasia was highly distinct together with portal fibro- cellular reaction due to obstruction of worms in the intestine and the common bile duct. Lymphoid depletion and extensive vascular changes in the kidneys noticed in the study might be due to the toxins released by the Toxocara parasite. These lesions were in concurrence with the findings of previous workers²⁴.

In present investigation, it was observed that rotavirus infection present in combination with the various other disease conditions, and due to that lesions were observed in different visceral organs, so it can be concluded that the rotaviral enteritis can produce the systemic effects when occurs concomitantly with other pathogenic agents.

The authors are thankful to the Director, IVRI for providing necessary facilities to carry out this work. The help rendered by personnel at Gwalior and Bareilly during sample collection is duly acknowledged. The timely financial support provided by ICAR Network Project on Neonatal Mortality in Farm Animals is duly acknowledged.

REFERENCES