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Danish Institute of Agricultural Sciences, Department of Animal Nutritionand Physiology, Box 50, DK-8830 Tjele, Denmark
2 Correspondence:
E-mail:
nielsb.kristensen{at}agrsci.dk.
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 ± 39 mmol/h of acetate and 213 ± 5 mmol/h of butyrate were absorbed from the reticulorumen. With the propionate treatment, 1,148 ± 39 mmol/h of acetate, 730 ± 23 mmol/h of propionate and 196 ± 5 mmol/h of butyrate were absorbed from the reticulorumen. With PPD treatment, 1,264 ± 39 mmol/h of acetate, 220 ± 5 mmol/h of butyrate and 721 ± 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-13C]glucose in a jugular vein. Treatments did not affect (P > 0.10) the plasma concentrations of glucose (4.2 ± 0.1 mmol/L), alanine (0.14 ± 0.01 mmol/L), or insulin (80 ± 25 pmol/L). The plasma concentration of lactate was higher (P < 0.05) with both propionate (0.84 ± 5 mmol/L) and PPD treatment (0.81 ± 5 mmol/L) compared with the control treatment (0.29 ± 0.5 mmol/L). The plasma concentration of pyruvate was higher (P < 0.05) with the propionate treatment (0.09 ± 0.01 mmol/L) compared with the control treatment (0.03 ± 0.01 mmol/L). The plasma concentration of 3-hydroxybutyrate was lower (P < 0.05) with the propionate treatment (0.15 ± 0.03 mmol/L) compared with the control treatment (0.40 ± 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 ± 0.6 mmol/L at 420 min. The ILR of glucose was not affected (P > 0.10) by treatments (441 ± 35 mmol/h). The relative 13C 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 ± 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
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