Metabolic stress and interleukin-6 response in high-yielding, periparturient dairy cows

Increased disease rates are commonly reported among high-yielding dairy cows in the so-called transition period, extending from 3 weeks before to 3 weeks after calving. This period is characterized by the occurrence of a systemic inflammatory response in terms of both positive and negative acute phase proteins, with no signs of microbial infections. To determine the extent and the seriousness of the above inflammatory response, the authors have devised the Liver Functionality Index (LFI), which defines the above condition on the basis of the time-course of albumin, cholesterol and total bilirubin (direct or indirect indices of negative acute phase response) during the first month of lactation. In this respect, low LFI values are associated to a high inflammatory response and vice versa. The relationship between LFI and plasma interleukin IL-6 levels from day -28 to day +28 with respect to calving was investigated in 12 periparturient dairy cows showing the highest and lowest LFI values, respectively (6 cows each), within a cohort of 54 high-yielding dairy cows inside two experimental farms. As expected, low LFI cows experienced many more disease cases (100 vs 33 percent of cows had at least one affection) and drug treatments till day +28; their dry matter intake and milk yield were also lower (P<0.07). IL-6 concentrations were always higher in low LFI cows (P<0.06 from day +10 onwards; P<0.05 on day +21). IL-6 levels were lowest at calving in both groups, but the subsequent peak on day +3 was much higher in low LFI subjects (P<0.05). TNF-alpha values showed no significant differences between the two groups; these could be clearly recognized instead because of high versus low serum lysozyme concentrations in high and low LFI cows, respectively (p< 0.05). Our study confirms that disease cases of periparturient, high-yielding dairy cows are correlated with signs of systemic inflammation, characterized by a disregulated IL-6 response. This starts in the dry period and proceeds at much higher levels after calving.