Short communication: Grain-induced subacute ruminal acidosis is associated with the differential expression of insulin-like growth factor-binding proteins in rumen papillae of lactating dairy cattle

The objective of this study was to characterize the mRNA expression of genes involved in the insulin-like growth factor (IGF) axis in the rumen epithelium during grain-induced ruminal acidosis. Eight lactating dairy cattle were randomly assigned to a control (38% concentrate) or a high-grain (HG; 57% concentrate) diet in a randomized study. Dry matter intake, milk production, ruminal pH, and rumen papillae gene expression were measured before treatment allocation (d 0) and on the fourth day of treatment. On d 4, no differences were observed in total feed intake and milk production; however, the cattle fed the HG diet displayed lower ruminal pH (587 +/- 130 min/d below 5.6, mean +/- SE) compared with cattle receiving the control diet (169 +/- 145 min/d below 5.6). No change in the relative mRNA expression of IGF-1, IGF-1 receptor (IGF-1R), and IGF-binding protein 6 (IGFBP6) was detected between treatments. However, the relative expression value of IGF-binding protein 3 (IGFBP3) decreased (0.73 +/- 0.07 fold, mean +/- SE), whereas IGF-binding protein 5 (IGFBP5) expression increased (1.53 +/- 0.20 fold). These results indicate that the IGF axis may play a role in rumen epithelial adaptation to HG diets.