Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/1996
Publication Date: N/A
Citation: Interpretive Summary: Dairy cows obtain their protein needs mainly from synthesis by the microbes living in the rumen, the first compartment of the cow's stomach. However, the rest of this protein, which comes from dietary protein that escapes degradation by the rumen microbes, is very important. This is because rumen microbes can reduce the value of feed proteins by degrading more protein then they resynthesize. Therefore it is important to know how muc protein from the feed would be degraded by the ruminal microorganisms and how much would escape the rumen. We developed a method for preservation of mixed ruminal microorganisms which could later be used for determination of ruminal protein degradation in the laboratory. A pre-incubation period for the mixed ruminal microorganisms that were frozen and reconstituted was used to increase their proteolytic activity, and the degradation rates obtained after 2 h incubations with frozen mixed ruminal microorganisms agreed closely with those obtained after 4 h incubations with fresh rumina fluid. Ruminal protein degradability determined using the preserved microorganisms was similar to that determined using the in situ method, a procedure commonly used to test ruminant feed proteins. Protein escapes estimated in the laboratory using pre-incubated, frozen mixed ruminal microorganisms were well correlated with values determined in animals for nine samples of heat treated soybeans and solvent soybean meal. These results indicated that mixed ruminal microorganisms, preserved frozen, may be used for the laboratory determination of ruminal protein degradation.
Technical Abstract: Mixed ruminal microorganisms were harvested from a lactating dairy cow and preserved frozen or lyophilized. Fermentation characteristics of fresh strained ruminal fluid, frozen microorganisms, or lyophilized microorganisms were evaluated during a 24 h pre-incubation period and during a 4 h incubation period. Differences in NH3 and total amino acid concentration, changes in optical density, pH and VFA concentrations, acetate: propionate ratio and lactate concentration, observed during the first 4 to 6 h, largely disappeared later in the pre-incubation period. Ruminal protein degradation rates determined for expeller soybean meal and solvent soybean meal were .015 and .092/h, .015 and .101/h, and .005 and .019, with fresh ruminal fluid, frozen microorganisms, and lyophilized microorganisms, respectively. Regression of degradation rates obtained with fresh ruminal fluid on those obtained with pre-incubated, frozen microorganisms indicated the two methods were well correlated (r**2 = .98 and .94 in two experiments). Although the mean in vitro degradability obtained with pre-incubated, frozen microbes for 17 feeds was 89% of that with the in situ method, in situ degradation rates for the same feeds averaged only 67% of those with the frozen microorganisms. Ruminal undegraded protein values for nine samples of heated soybeans and soybean meal, determined using frozen microbes, were overestimated relative to in vivo values (in vivo = 1.1 + .8 in vitro; r**2 = .77). Overall, these results indicated that ruminal microorganisms can be preserved by freezing and used as the inoculum for in vitro determination of ruminal protein degradation after an overnight pre-incubation.