Effects of the synchronization of the rate of carbohydrates and nitrogen release of the concentrate on rumen fermentation, plasma metabolites and insulin, in the dry pregnant goat

Ruminal fermentation, plasma metabolites and insulin concentrations have been studied in eight dry pregnant goats, with sequential ruminal and blood samples taken during the 200 min after feeding, through ruminal cannulas with 400 g of four experimental concentrates + 100 ml of artificial saliva. The four concentrates used were iso-energetic and iso-nitrogenous, but they differed in the rate of degradation of the carbohydrate and protein fractions: RS-RN (rapid degradation of starch (S)— rapid degradation of nitrogen (N)); RS-SN (rapid degradation of S — slow degradation of N); SS-SN (slow degradation of S — slow degradation of N); and HDF-SN (highly digestible fibers — slow degradation of N). 3 days of adaptation to the concentrate, the increase in total volatile fatty acids (VFA) concentration and the decrease in pH in the rumen after feeding of the concentrate were greater in HDF-SN and lower for SS-SN than for the concentrates with rapidly degradable starch; the same tendencies were observed for acetate and propionate. Goats receiving HDF-SN concentrate had higher ruminal acetate molar proportions and lower proportions for butyrate and other minor VFA than any other concentrates. Differences in the molar proportions of any VFA were not significant between starchy concentrates. Differences in plasma concentrations of glucose, lactate, and insulin were not significant. Ruminal ammonia concentrations were higher for RS-RN concentrate (for 180 min) and for SS-SN (for the first 45 min) than for the other concentrates. Plasma urea concentrations reflected the ranking of ruminal ammonia concentrations.