Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/14/1995
Publication Date: N/A
Citation: Interpretive Summary: Alfalfa is the major forage as well as an important protein source fed 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 of protein and depressed production of milk and milk protein. Excessive protein breakdown in the rumen comes about becaus the protein in 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 could be reduced, then efficiency of utilization of alfalfa protein would be increased and nitrogen losses to the environment would be reduced. Modified gaseous atmospheres, composed of various combinations of oxygen, carbon dioxide, plus inert gas, have been found to reduce decomposition of vegetables during shipment to market. In two studies, flushing alfalfa silos for one week with gas mixtures consisting of 3% oxygen, 15 to 20% carbon dioxide, with the balance as nitrogen gas, reduced protein predigestion in alfalfa silage. The modified atmospheres were as effective as formic acid, a costly and corrosive treatment used in Europe, for reducing protein breakdown in the silo. These results were based solely on the chemical composition of alfalfa silage from small experimental silos and must be extended to feeding trials with large silos and actual milking cows. However, these findings suggest that protein utilization would be improved if the process could be applied in large alfalfa silos.
Technical Abstract: Two studies evaluated proteolysis in alfalfa ensiled in laboratory silos under different modified atmospheres. In the first study, fourth cut alfalfa was ensiled at 25% DM for 28 d. The forage treatments were a modified atmosphere composed of 3% O2: 20% CO2: 77% N2, formic acid (6 ml/kg fresh weight), and untreated control. Proteolysis was assessed from the concentrations of NH3 N, free AA N, and NPN. Peptide N was estimated as the difference between NPN and the sum total of NH3 N plus free AA N. Higher silage pH and lower concentrations of total organic acids suggested that the modified atmosphere reduced forage fermentation. The modified atmosphere was effective in reducing proteolysis to a level similar to that achieved with formic acid treatment. Modified atmosphere treated silage had more peptide N which may be an advantage over the formic acid treated silage. In the second study, alfalfa was ensiled at 20 and 28% DM and was untreated control, or treated with N2 gas or a modified atmosphere compose of 3% O2: 15% CO2: 82% N2. Higher NH3 N concentrations were observed in 28% DM silage ensiled under N2 gas and modified atmosphere. Concentrations of free AA N were lower at higher DM in all treatments. Concentrations of NPN were reduced 7.0, 7.0, 23.4 and 25.7% for low DM N2, high DM N2, low DM modified atmosphere, and high DM modified atmosphere, respectively. It was concluded that the modified atmospheres reduced the rate and extent of NPN formation in alfalfa silage.