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Dr. Glen Broderick's contributions to in vivo quantification of ruminal nitrogen metabolism using the omasal sampling technique
Dr. Glen Broderick has made a significant contribution to improve understanding of protein and amino acid nutrition of dairy cows with the aim of improving overall nitrogen utilization and reducing the environmental impact of milk production. Development of in vitro method to determine ruminal protein degradability was one of his main contributions at earlier stages of career. More recently, he has focused on studying ruminal N metabolism in lactating dairy cows, with the main emphasis in optimizing the efficiency of microbial N synthesis. In these studies Dr. Broderick and his PhD students have applied and developed omasal sampling technique. The method is now widely replaced more invasive duodenal sampling technique, but it also allows studying ruminal N metabolism in more detail as sampling takes places before hydrolysis in the abomasum and endogenous contribution is less. Applying omasal sampling technique Dr. Brodrick demonstrated that the flow of soluble NAN fractions has an important contribution to feed N flow from the rumen. Soluble feed amino acid (AA) flow accounted approximately 10% of omasal total AA flow indicating substantial escape of dietary soluble AA from ruminal degradation. This calls into question the use of in situ estimations of protein degradation to predict RUP flow. Oligopeptides had the greatest contribution of soluble feed AA flow. The study investigating gradual replacement of solvent extracted soybean meal (SBM) with lignosulfonate-treated SBM concluded that NRC (2001) overestimated the supply of RUP from treated SBM. The other important conclusion from this study was decreased microbial protein synthesis with increased proportion of RUP in dietary protein. Consistently with this, replacement of solvent extracted SBM with urea and lignosulfonate-treated SBM decreased NAN and microbial N flow at the omasum demonstrating that microbial protein synthesis is stimulated by true protein RDP compared with NPN. Comparison of red clover and alfalfa silages supported the conclusions from previous studies; increased RUP supply from red clover was counteracted by reduced microbial protein synthesis. Meta-analysis of the data from omasal sampling studies indicated usually smaller residual variance of digesta flow estimates compared with studies applying duodenal sampling, probably reflecting more the marker system applied to estimate digesta flow than sampling site per se. The results suggested that the NRC (2001) system underestimates microbial N flow and overestimates the supply of RUP. The contributions Dr. Broderick emphasize the need for re-evaluation of the feed protein systems.
Keywords: Dr. Broderick, omasal sampling, dairy cow