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The effect of subacute ruminal acidosis on milk fat synthesis and relative expression of key lipogenic enzyme genes in liver tissue in dairy cows
The effect of subacute ruminal acidosis on milk fat synthesis and relative expression of key lipogenic enzyme genes in liver tissue in dairy cows
Keywords: subacute ruminal acidosis, milk fat, key lipogenic enzyme
Abstract：The aims of this study were to 1) determine the variation of performance and relative expression of lipid anabolism related genes in liver tissue triggered by induced subacute ruminal acidosis (SARA); and 2) evaluate the ability of pelleted beet pulp (BP) as a substitute for ground corn to alleviate SARA. Eight mid-lactation Holstein cows were fed four diets during four successive17-day periods: 1) total mixed ration (TMR) containing 0% finely ground wheat (FGW) (W0); 2) TMR containing 10% FGW (W10); 3) TMR containing 20% FGW (W20); and 4) TMR containing 10% BP as a replacement for 10% ground corn (BP10). The SARA induction protocol reduced the mean ruminal pH from 6.37 to 5.94 (P<0.01), and the minimum ruminal pH decreased from 5.99 to 5.41 from baseline to challenge period. Mean ruminal pH increased from 5.94 to 6.05, and minimum pH increased from 5.41 to 5.63, when BP was substituted for corn. Dry matter intake and milk yield were not affected by the dietary treatments, however, milk fat percentage and yield were reduced (P < 0.01) in the W20 and BP10 treatments than the W0 treatment. Cows fed the W20 diet had a lower (P<0.01) plasma concentration of triglyceride and total cholesterol, and a higher (P<0.01) plasma concentration of glucose and insulin than cows fed the W0 diet. Liver tissue relative expression of acetyl-CoA carboxylase alpha (ACACA) (P=0.03), FA synthase (FASN) (P=0.05), sterol-response element binding protein 1 (SREBF1) (P<0.01) was increased in cows fed the W20 diet, but there were no significant differences among the W10, W20, and BP10 diets. Our results indicate that the SARA could decrease of milk fat synthesis and increase of relative expression of lipid synthesis key genes in liver tissue. The substitution of pelleted BP for ground corn in a high-concentrate diet could reduce the risk of SARA in dairy cows.