Glen Broderick's contributions to improving in vitro methodologies for assessing ruminal microbial growth and ruminal protein degradation

Abstract Text: Dr. Broderick has supervised numerous graduate students during his career, been a very active contributor to scientific meetings throughout the World and also published 126 full papers in refereed journals (Web of Knowledge, Jan. 16, 2014) of which 28 with “in vitro” in the title. The most cited (707) paper of them is so far Broderick and Kang (J. Dairy Sci. 63:64-75, 1980), describing an automated method to analyze ruminal ammonia and amino acids. This method was essential for enabling use of the inhibited in vitro (IIV) system, previously developed by Broderick (J. Nutr. 108:181-190, 1978), to measure release of ammonia and amino acids. He subsequently compared the IIV method with solubility estimates (Broderick and Craig, J. Nutr. 110:2381-2389, 1980) and against in sacco estimates (Broderick et al., J. Anim. Sci. 66:1739-1745, 1988). In sacco rates were only 36% of those of IIV due to an immediate loss of more rapidly degradable protein in soluble and fine particle forms. This, however, did not prevent adoption of the in sacco method as a standard method for protein evaluation, at least in Europe. The theory of the IIV method is elegant: to inhibit microbial protein synthesis without affecting protein hydrolysis and to estimate degradation as the sum of microbial extra- and intracellular metabolism. The latter feature is attractive as casein data from Broderick and Craig (J. Dairy Sci. 72:2540-2548,1989) suggested that uptake of amino acids and peptides is too slow to be ignored. So far, this methodological feature is only shared with the gas-in vitro method of Raab et al., Br. J. Nutr. 50:569–582, 1983). However, the use of inhibitors has limited the use of long incubation times (>~ 4 h) due to a concomitant loss of microbial activity. Nevertheless, the IIV method seems to give biologically sensible degradation rates for sufficiently rapidly degrading proteins. Dr. Broderick has also been involved in developing a 15N based in vitro method to estimate microbial growth (Hristov and Broderick, J. Dairy Sci. 79:1627-1637, 1994). An important finding of this study was that microbial protein synthesis is positively related to protein degradation which implies a compensatory effect of low-escape proteins by an increased supply of microbial amino acids to the duodenum.

Keywords: in vitro, protein, dairy cow