Metabolism of propionate and 1,2-propanediol absorbed from the washed reticulorumen of lactating cows

To investigate the metabolism of 1,2-propanediol (PPD) in lactating cows independently of normal rumen microbial metabolism, three ruminally cannulated lactating Holstein cows were subjected to three experimental infusion protocols under washed reticulo-ruminal conditions in a Latin square design. Reticulo-ruminal absorption rates were maintained for 420 min by continuous intraruminal infusion of VFA and PPD. With the control treatment, 1,246 [+ or -] 39 mmol/ h of acetate and 213 [+ or -] 5 mmol/h of butyrate were absorbed from the reticulorumen. With the propionate treatment, 1,148 [+ or -] 39 mmol/h of acetate, 730 [+ or -] 23 mmol/ h of propionate and 196 [+ or -] 5 mmol/h of butyrate were absorbed from the reticulorumen. With PPD treatment, 1,264 [+ or -] 39 mmol/h of acetate, 220 [+ or -] 5 mmol/h of butyrate and 721 [+ or -] 17 mmol/h of PPD were absorbed from the reticulorumen. Glucose irreversible loss rate (ILR), as well as the relative enrichment of plasma lactate and alanine, were determined by primed continuous infusion of [U-[sup.13]C]glucose in a jugular vein. Treatments did not affect (P > 0.10) the plasma concentrations of glucose (4.2 [+ or -] 0.1 mmol/L), alanine (0.14 [+ or -] 0.01 mmol/L), or insulin (80 [+ or -] 25 pmol/L). The plasma concentration of lactate was higher (P < 0.05) with both propionate (0.84 [+ or -] 5 mmol/L) and PPD treatment (0.81 [+ or -] 5 mmol/ L) compared with the control treatment (0.29 [+ or -] 0.5 mmol/L). The plasma concentration of pyruvate was higher (P < 0.05) with the propionate treatment (0.09 [+ or -] 0.01 mmol/L) compared with the control treatment (0.03 [+ or -] 0.01 mmol/L). The plasma concentration of 3-hydroxybutyrate was lower (P < 0.05) with the propionate treatment (0.15 [+ or -] 0.03 mmol/L) compared with the control treatment (0.40 [+ or -] 0.03). With the PPD treatment, the plasma concentrations of pyruvate and 3-hydroxybutyrate were in between the other treatments and tended (P < 0.10) to be different from both. The plasma concentration of PPD increased throughout the infusion period with the PPD treatment and reached a concentration of 4.9 [+ or -] 0.6 mmol/L at 420 min. The ILR of glucose was not affected (P > 0.10) by treatments (441 [+ or -] 35 mmol/h). The relative [sup.13]C enrichment of plasma lactate compared with that of glucose decreased (P < 0.05) with the PPD treatment compared with the control treatment (44 to 21 [+ or -] 3%). It was concluded that PPD has a low rate of metabolism in cows without a normal functioning rumen, although about 10% of the absorbed PPD was metabolized into lactate. Key Words: Dairy Cattle, Gluconeogenesis, Metabolism, Propionic Acid, Propylene Glycol, Ruminants