Assessment of immune response in periparturient dairy cows using ex vivo whole blood stimulation assay with lipopolysaccharides and carrageenan skin test.

The transition period is known to be the most critical phase in the life of high yielding dairy cow. Changes in the immune functions have been observed during the transition period which may account for the onset of clinical and subclinical (e.g. inflammatory response) problems at calving or at the beginning of lactation however this relationship has not yet been adequately investigated. Thus, to establish the potential of the periparturient dairy cow's immune system to respond to stimuli, two challenges [an ex vivo whole blood stimulation assay (WBA) with lipopolysaccharides and a carrageenan skin test (CST)] were performed in addition to characterizing the metabolic and inflammatory profile. The WBA was performed using 0, 0.01 and 5 µg LPS/mL on whole blood and CST was administered by subcutaneous injection of 0.7 mL solution containing 4.2mg of carrageenan to the shoulder region of the cows. These tests were performed on 10 Holstein-Friesian cows at -45 ± 2, -20 ± 2, -3, 3, 7, 28 ± 2 days from parturition (DFP). Cows were also monitored for health status, body condition score, milk yield. The results demonstrate a higher production of IL-1ß and IL-6 from leukocytes after LPS stimulation around calving (from -3 to 3 DFP) compared to -45 DFP (P < 0.05). Moreover, IL-6 (but not IL-1ß) was able to reach close to the maximum response at the lower stimulus intensity (0.01 µg LPS/mL), maintaining a higher response over a longer time in early lactation. The release of higher levels of IL-6 in the transition period, with low LPS dose, suggests its crucial role in the regulation of inflammatory response around calving. The response of cows to CST decreased a few days before calving (-3 DFP) compared with response at -45 and 28 DFP (P<0.05), and remained low in the first week of lactation. This result suggests the reduction of the functionality of some vascular factors, which decreases diapedesis. Overall, the WBA and CST tests confirm changes in immunocompetence around calving. These tests are able to better describe the changes of the innate immune response at a local and systemic level, mainly when combined with conventional metabolic and inflammatory indices.