Rumen propionate and blood glucose kinetics in growing cattle fed isoenergetic diets.

The relationship between rumen propionate production and blood glucose kinetics was examined in four rumen-fistulated Holstein steers fed isoenergetic amounts of 80/20 (G) and 30/70 (R) grain/chopped alfalfa hay diets at 2-hour intervals. Single-injection rumen propionate and blood glucose kinetics were determined in consecutive 4-hour periods by using [6-3H]glucose intravenously then [1-14C]propionate intraruminally. Rumen propionate specific activity was determined after isolation and quantitation by high-pressure liquid chromatography. Average rumen propionate production rates and pool sizes were 441 g/day and 32.0 g when diet R was fed but increased to 510 g/day (P less than 0.05) and 36.5 g (P less than 0.10), respectively, when diet G was fed. Propionate production as related to digestible energy (DE) intake, averaged 0.56 mole/Mcal DE for R and 0.64 mole/Mcal DE for G. Rumen propionate turnover times were similar for both diets. Despite differences in propionate availability, there were no significant dietary differences in glucose kinetic parameters. Average glucose pool sizes and irreversible losses were 27.0 g and 585 g/day for R and 27.0 g and 582 g/day for G.