The effects of grain-induced subacute ruminal acidosis on interleukin-6 and acute phase response in dairy cows
Subacute ruminal acidosis (SARA) resulting from excessive grain feeding to dairy cows is accompanied by an acute phase response. Interleukin 6 (IL-6) has been proposed as a mediator of this response. We tested if the acute phase response associated with grain-induced SARA is mediated by IL-6. Six lactating Danish Holstein cows were used in an incomplete block design study that included two periods with two cows in a SARA-challenge treatment and two cows in a control treatment, and a third period with two cows in a SARA-challenge treatment. In the first two weeks of each experimental period, all cows received a control diet (17.4% CP; 19.2% starch; 6.28 MJ NEL/kg DM). In the third week, the diet for control cows remained unchanged, while for the SARA-challenge cows, 40% of the control diet was gradually substituted with grain pellets (50:50 wheat:barley) within 3 days to induce SARA. This SARA-challenge diet was fed for another four days. Jugular vein blood was sampled at 7 h post-feeding on Tuesday and Thursday of the second week and during the first two and the last day of the SARA-challenge diet feeding. ELISA kits were used for measurement of IL-6, and the acute phase proteins haptoglobin (Hp), LPS binding protein (LBP), and serum amyloid A (SAA). For data analysis, a mixed model was used, in which cow was treated as a random factor while treatment (SARA challenge vs. control), period, day within period, as well as the interaction between day within period and treatment were treated as fixed factors. Compared to control cows, the SARA challenge tended to increase LBP (7.54 vs. 10.23 mg/L, P = 0.10), and increased SAA (4.24 vs. 11.60 mg/L, P = 0.04) and Hp (3.57 vs. 22.09 mg/L, P = 0.04) in blood, confirming that the SARA challenge caused an acute phase response. Concentrations of IL-6 were not affected by the SARA challenge, and averaged 5.06 ng/mL across treatments. Our data does not confirm that IL-6 mediates the acute phase response during grain-induced SARA. This confirmation may require more frequent blood sampling around the time of the SARA challenge.
acute phase proteins, dairy cow, IL-6