Metabolic effects of feeding high doses of propanol and propylacetate to lactating Holstein cows

Three lactating Holstein cows implanted with ruminal cannulas and permanent indwelling catheters in major splanchnic blood vessels were used to investigate alcohol metabolism and metabolic effects of feeding high doses of propanol and propylacetate. Cows were fed three diets control (basal ration; C), propanol (C plus 50 g propanol/kg DM; P), and propylacetate (C plus 50 g propanol/kg DM and 15 g propylacetate/kg DM; PPA) in a 3 × 3 Latin square design with 14 d period. Daily rations were fed in three equally sized portions at 8 hour intervals and 8 hourly sets of ruminal fluid, arterial, hepatic portal vein, and hepatic vein samples were collected at day 14 of each period. Milk fat yield decreased for P and PPA compared with C, however, dry matter intake and milk yield were not affected by treatment. Portal uptake of propanol accounted for 48 to 61% of ingested propanol and differed among all 3 treatments C ≪ PPA < P. A number of metabolic variables responded to P and PPA treatments including decreased proportion of ruminal acetate to total VFA; increased proportions of ruminal propionate, isovalerate, valerate, and caproate; increased arterial glucose concentration; decreased arterial BHBA and acetate concentrations; increased net portal flux of propanol; increased net hepatic flux of glucose; and increased propanol, isopropanol, and caproate uptake by the liver. Contrary to our hypothesis that propylacetate supplementation would exacerbate the metabolic effects of propanol, we observed for a number of variables that treatment differences between C and P were partly reversed in PPA. This applied to ruminal propanol and propylacetate; arterial concentrations of ethanol, propanol, isopropanol, and isobutyrate; net portal flux of ethanol, propanol, and isopropanol; net hepatic flux of BHBA, propanol, isopropanol, and isobutyrate; net splanchnic flux of propionate; hepatic extraction of ethanol and portal recovery of dietary ethanol. The overall metabolic effect of feeding large doses of propanol was a glucogenic response presumably driven by hepatic metabolism of propanol to propionate and the increased glucogenic status was followed by a decreased milk fat yield. Inclusion of propylacetate in the diet apparently activated increased metabolism of propanol in either the rumen or ruminal epithelium and reduced the metabolic impact of the combined presence of propanol and propylacetate.