Concentrations of triiodothyronine (T3), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in milk from healthy and naturally infected quarters of cows

Abstract The effect of naturally acquired bacterial infection of the bovine udder on the activity of 5′-thyroxine monodeiodinase (5′- MD ), and on the concentrations of the pro-inflammatory cytokines interleukin (IL) -6 and tumour necrosis factor (TNF) -α in milk, from healthy (control) and inflamed quarters, was determined. The diagnostic procedure included history and clinical examination of the udder, macroscopic evaluation of secretions, the Californian Mastitis Test, determination of somatic cell counts and bacteriological examination of milk. It has been found that the milk triiodothyronine (T 3 ) content and the 5′- MD activity from inflamed quarters were decreased when compared with controls. The decrease in the milk T 3 from subclinical mastitic quarters was manifested when somatic cell counts were >10 6  ml −1 . TNF -α was on average 2-fold higher in infected milk, and the concentration of IL -6 was unchanged. These results suggest that the decreased T 3 content in mammary secretions during naturally occurring mastitis is associated with the severity of inflammation, increased TNF -α concentration and impaired enzymatic activity of 5′- MD .