Interleukin-6 as a biomarker of clinical and subclinical streptococcal mastitis in cattle

Abstract

Interleukin-6 is one of the most important pro-inflammatory cytokines, activating the innate and acquired mechanisms of the immune response of animals. The aim of the study was to evaluate interleukin-6 as a biomarker of clinical and subclinical mastitis in dairy cows. For laboratory studies, milk and blood samples were collected from Holstein-Friesian cows with mastitis (n=20) and healthy ones (n=10) in the Novgorod region. The study to study the level of interleukin-6 (IL-6) included animals with infectious cow mastitis caused by Streptococcus spp. The levels of IL-6 in milk from cows with both clinical mastitis and subclinical mastitis compared with the control group at maximum values corresponded to: 1069.47±0.33 pg/ml versus 4004.96±0.25 pg/ml in group with clinical mastitis (CM), p < 0.05; and against 1903.22 pg/ml in the group with subclinical mastitis (SCM), p < 0.05. The levels of IL-6 in the milk of healthy cows were 1066.99±0.33 pg/ml and were significantly lower by 1.7-3.7 times than in the milk of all cows suffering from mastitis caused by Streptococcus spp. A difference was detected in the levels of IL-6 in the blood serum between the results obtained in the group of animals with CM and SCM (1069.47±0.13 pg/ml versus 700.99±0.22 pg/ml). The concentration of IL-6 in the blood serum of healthy cows was in the range of 633.49±0.53 pg/ml and differed from the level of IL-6 in the blood serum of all groups of cows suffering from clinical or subclinical mastitis (700.99±0 .52 pg/ml and 1069.47±0.33 pg/ml, respectively). Our results suggest that cows suffering from mastitis caused by Streptococcus spp. develop a local immune response in the udder in response to the pathogen. Thus, monitoring the level of interleukin-6 in milk may allow early detection of mastitis, which is especially important in cases of subclinical inflammation of the mammary gland.