Determining in vivo ruminal stability of three ruminally protected nutrients in lactating Jersey cows

Current methods to determine rumen escape (as stability) of rumen protected nutrients (RPNU), such as ruminal in situ evaluation, only estimate the rate at which nutrients leave the in situ bag (rather than the rumen) and thus can provide only a rough estimate of actual rumen stability, which is also impacted by actual ruminal RPNU release rate, rate of ruminal passage of the RPNU, as well as impacts of ruminative chewing on the RPNU product; all of which can only be estimated. The aim of our study was to use a novel in vivo dual liquid phase marker technique to measure actual ruminal stability of three fat coated RPNU products, and to determine if a common in situ incubation time could match the in vivo values determined among products. The three RPNU products were RP ascorbic acid, RP lysine and RP niacin, which were manufactured to contain Co-EDTA, and pulse dosed into the rumen at a single time for each experimental period, concomitant with an equal weight of Cr which was pulse dosed as free Cr-EDTA. The study was a 4 × 4 Latin square with 14 d periods using 4 multiparous ruminally cannulated lactating Jersey cows. Rumen instability of the RPNU products was measured as the proportion of the area under the curve from ruminal in vivo clearance of Co (manufactured into each RPNU product as Co-EDTA) relative to the clearance of Cr (simultaneously rumen dosed as free crystalline Cr-EDTA). The measured rumen payload of the three RPNU products differed despite having the same fat matrix coating and general characteristics, likely due to differences in the chemical interactions of the nutrients with the fat covering, with the in vivo measured payload of RP niacin highest at 656 g/kg, relative to RP lysine at 527 (P<0.05) and to RP ascorbic acid at 558 g/kg (P<0.10). In situ incubations of the RPNU products in the same cows, at the same time, suggested that in situ 30 h dry matter stability was the best predictor of their in vivo measured rumen stability. This novel in vivo dual liquid phase marker technique can be used to determine the actual rumen stability of any ruminally protected product under any target feeding scenario.