Currently, somatic cell count (SCC) and bacterial culture are considered as the gold standard of detecting subclinical Mastitis. Mastitis leads to proliferation of lymphocytes in the supramammary lymph nodes and subsequent enlargement of ipsilateral lymph node. Ultrasonography can be used to survey these changes. A portable ultrasound machine with a 2-5 MHz convex transducer was used to identify the supramammary lymph node size in 35 cows in a herd with chronic Staphylococcus aureus mastitis. After premilking udder preparation, a California mastitis test (CMT) was performed and individual milk samples were taken from each quarter for bacterial culture and somatic cell count (SCC) in accordance with NMC recommendations. The mean length (range 5.77-12.90cm) and width (range 2.07-7.41 cm) of the lymph node were 9.2 and 4.03 cm, respectively. There was a positive correlation between lymph node size (length and depth) and culture of milk samples on ipsilateral quarters. Also, there was a significant difference correlation between CMT or mean log SCC of each side and size of supramammary lymph node in the same side. This study showed significant changes in supramammary lymph node dimensions in mastitis cases, so ultrasonography of this lymph node is probably a useful method for mastitis detection, especially in situations that test on milk is impossible.

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