Aim: The present investigation was conducted to study the association between udder morphology and in vitro activity of milk leukocytes in high yielding crossbred cows.

Materials and Methods: A total of 48 healthy high yielding crossbred cows were selected for the study. The udder configuration and teat/udder morphology were recorded before milking. Milk samples (100 ml/cow) were collected aseptically. Milk somatic cell counts (SCC) and milk differential leukocyte counts were performed microscopically. Milk leukocytes (viz., neutrophils, lymphocytes, and macrophages) were isolated from milk samples by density gradient centrifugation. Phagocytic index (PI) of milk neutrophils and macrophages were evaluated by colorimetric nitro blue tetrazolium assay. Lymphocytes proliferation response was estimated by MTT assay and expressed as stimulation index.

Results: There was a significant (p<0.01) positive correlation between milk SCC with mid teat diameter, teat base diameter and significant (p<0.05) negative correlation between milk SCC and the height of the teat from the ground. Milk SCC was found to be significantly (p<0.01) lower in bowl-shaped udder and higher (p<0.01) in pendulous type. Milk macrophage percentage was positively (p<0.01) correlated with udder circumference. PI of milk neutrophil was negatively (p<0.01) correlation between teat base diameter, and PI of milk macrophages was found to be positively (p<0.01) correlated with teat apex diameter. Both PI of milk neutrophils and macrophages was found to be significantly (p<0.01) lower in the animals having flat and round teat and pendulous type of udder. In vitro PI of milk neutrophils was found to be significantly (p<0.01) lower in flat teat. In vitro PI of milk macrophages was found to be significantly (p<0.01) lower in the round and flat teats compared to pointed and cylindrical teats.

Conclusion: Udder risk factors such as teat shape and size, teat to floor distance, udder shape, and size may decrease the in vitro activity of milk leukocytes hence facilitates the incidence intramammary infections.

Keywords: cows, leukocytes, milk, morphology, teat, udder.

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