Submitted to: Grass and Forage Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/27/1995
Publication Date: N/A
Citation: Interpretive Summary: Alfalfa is the major forage as well as an important protein source for dairy cows in the U.S. However, alfalfa protein, particularly that in alfalfa silage, is extensively broken down in the rumen, the first compartment of the cow's stomach; extensive protein breakdown results in inefficient utilization and depressed production of milk and milk protein. Excessive protein breakdown in the rumen comes about because the protein i alfalfa silage gets "pre-digested" in the silo. Most alfalfa fed to dairy cows in the U.S. is harvested as silage and stored in silos because this requires much less manual labor than harvesting alfalfa as hay. If protein predigestion in the silo can be reduced, then efficiency of utilization of alfalfa protein would be increased and nitrogen losses to the environment reduced. A laboratory-scale experiment was done with alfalfa silage and hay to compare the effects of formic acid (a costly and corrosive treatment used in Europe) to that of two other acids on the extent of protein breakdown in the silo and in the rumen. Protein predigestion in silage was dramatically reduced by all of the acids tested; ruminal protein digestion of alfalfa hay also was reduced by acid treatment. Formic acid was not any more effective than the other acids tested at reducing protein breakdown in the silo or in the rumen. These results suggest that cheaper, and perhaps less corrosive, treatments than formic acid would be beneficial to the utilization of alfalfa silage fed to dairy cows. These results were based solely on the chemical composition of alfalfa silage from small experimental silos and test tube studies of ruminal digestion. However, these findings suggest that protein utilization would be improved if these acid treatments could be applied in farm-scale alfalfa silos.
Technical Abstract: A laboratory scale experiment was conducted to determine the effects of acid treatment on proteolysis during ensiling and on ruminal protein degradation of alfalfa (Medicago sativa). Alfalfa (300 g DM kg**-1 forage) was either untreated (control) or treated with sulfuric, formic, or trichloroacetic acid at levels sufficient to immediately adjust forage pH to 4.0, and conserved as silage or hay. Time-course data of silage indicated that nonprotein N formation was 70-90% complete after 1 d of fermentation in the silo. After 60 d of fermentation, nonprotein N concentrations (g kg**-1 total N) were 567, 426, 398, and 263 in control, sulfuric, formic, and trichloroacetic acid silages, respectively. Ruminal protein degradation of all conserved forages was slower than that of fresh cut forage, preserved with dry ice prior to lyophilisation. Acid treatment of silage or hay resulted in increased or decreased, respectively, rates of fruminal protein degradation relative to no treatment. However, the estimated protein degradation rate for untreated silage (0.020 h**-1) appeared slow. There was a clear effect of acid treatment on reducing the rate of ruminal protein degradation and increasing the estimated ruminal escape of protein in alfalfa hay. Quantification of treatment effects on forage conserved as silage was impaired by methodological problems in estimating degradation rates of untreated silage.