Black quarter (BQ) is one of the important bacterial disease of domestic animals which affect mainly cattle, buffaloes and sheep. It is the second most important bacterial disease next only to hemorrhagic septicemia in causing death among bovids¹. The speed with which BQ kills usually makes individual treatment useless. In some cases, however animals treated early with antibiotics may survive, although they often suffer permanent deformity due to partial or complete destruction of muscles. The disease is a cause of severe financial loss to cattle raiser in many parts of the world. When the disease occurs within a space, several numbers of cattle are affected within a few days and mortality rate in BQ approaches 100%. Quick post-mortem examination and submission of samples to the lab by veterinarian is essential to confirm the diagnosis of BQ. A preliminary diagnosis of black quarter or malignant oedema may be made in the living animal on the basis of clinical signs and the presence of typical muscle swellings².

There is no consensus on the pathogenesis of black quarter but toxins and neuraminidase produced by the causative bacteria are believed to play a significant role. So, the mechanisms by which black quarter occur need to be thoroughly investigated for effective treatment, prevention and control. The new animal diseases are predicted to emerge because of global warming and changing environmental factors. Hence, the knowledge of the changing dynamics of disease is important in instituting control measures³,⁴. The present study was conducted to study the hemato-biochemical, gross postmortem and histopathological changes in naturally occurring cases of black quarter in cattle.

The present study was conducted on 42 clinical cases of black quarter in cattle admitted to Teaching Veterinary Clinical Complex, COVAS, Udgir and from the surrounding areas from onset of disease, treatment to complete recovery or death at Department of Veterinary Pathology, College of Veterinary and Animal Sciences, Udgir during period January 2016 to July 2016.

The blood samples were collected before offering treatment in EDTA vials (for hematology) and serum separation vials (for biochemistry) from jugular vein of black quarter affected cattle. For control purpose, the respective samples were collected from healthy animals from college farm of same sex, breed and age. The various haematological and biochemical parameters were estimated on automated analysers. The samples such as emphysematous exudate, muscles pieces and swabs were collected aseptically in sterile vials from crepitating swelling of black quarter suspected cases. These samples were subjected for isolation and identification of causative agent by traditional and molecular methods as well as for histopathological evaluation (muscle pieces collected in 10% formalin).

The cases died with presumptive clinical diagnosis of black quarter were subjected for detailed postmortem examination as per routine standard protocol and gross changes in various organs/body systems were recorded. The respective samples were collected for histo-pathological and microbiological evaluation. The tissue samples were collected either from live suspected clinical cases (muscle biopsy from crepitating swelling) or from postmortem examination of animals died with presumptive diagnosis of black quarter for histo- pathology in 10% formalin. The collected tissue samples were processed for routine Hematoxylin and Eosin staining procedure as per standard protocol⁵,⁶.

The voided urine samples were collected from black quarter suspected cases in sterile vials. The collected urine samples were subjected for Robert‘s Test (to detect proteinuria) & Benzidine Test (to detect haematuria). The data generated from different parameters in present the study were subjected to statistical analysis by using IBM SPSS Statistics (version 20.0) software.

The significant increase in absolute granulocytes count in present study attributes to an inflammatory reaction due to bacterial infection while the decrease in hematocrit level might be due to blood loss during hemorrhage or hemolysis due to toxins which also documented in gross and histopathological examination in present study. Similar hematological changes in black quarter affected cattle were reported by earlier research workers³,⁷,⁸,⁹-¹⁰.

The significant increase in the levels of CPK, AST while non-significant increase in case of LDH in present study might be primarily due to skeletal and cardiac muscle damage which can be also correlated with the gross and histopathological findings in present study. The similar biochemical changes were documented in earlier studies on black quarter³,⁸,⁹-¹⁰. The presence of haematuria and proteinuria can be attributed to renal damage due to bacterial septicaemia/toxaemia. These findings regarding urine analysis are not traceable in earlier reports.

The pathogenesis of blackleg is still not completely understood but certain aspects of disease progression have been confirmed. Cattle are exposed and become infected with C. chauvoei through ingestion of spores from pasture³,¹¹,¹⁵. Spores, either directly ingested or those formed after germinating in the gut, are then carried across the intestinal mucosa. There they are taken up by macrophages that distribute the spores throughout the body. C. chauvoei spores can be found in many tissues throughout the body of normal animals, including muscle, where they are stored for long periods of time in phagocytic cells¹²,¹³.

Activation of latent spores resulting in infection and disease is an area of conjecture, but evidence suggests that conditions resulting in reduced local oxygen content or muscle damage may enable the spores to germinate. These conditions could include muscle bruising, such as with transport, handling, intramuscular injections or strenuous exercise¹³. Stress, with resultant increases in cortisol levels and subsequent release of catecholamines was considered to induce sufficient physiological change in heart muscle to cause myonecrosis in lambs¹². After germination and proliferation, C. chauvoei releases several toxins and enzymes that result in severe local muscle damage and systemic organ dysfunction¹⁴, ultimately resulting in very rapid progression of clinical signs and death³. The various gross and histopathological lesions observed in present study correlates with the various pathogenic mechanisms in literature cited above by various earlier workers. The similar histopathological and gross lesions were also reported by various authors in black quarter ²,³,¹¹¹²,¹³,¹⁴,¹⁵,¹⁶,¹⁷,¹⁸-¹⁹.

In conclusion, the findings like granulocytosis, lymphocytopenia, anemia, elevated levels of SGOT and CK can be used as marker hemato-biochmical parameters for preliminary clinical diagnosis of black quarter in conjunction with other important parameters like clinical signs, conventional and molecular techniques for detection of causative agent, gross and histopathological changes.

NS-Non Significant; *Significant (P<0.05); **Highly significant (P<0.01)

NS-Non Significant; *Significant (P<0.05); **Highly significant (P<0.01)

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