Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: July 17, 1996
Publication Date: N/A
Interpretive Summary: When crops are stored in silos, much of the protein in the crop may be broken down into soluble nitrogen forms. This process is called proteolysis. Unfortunately when the ensiled crops or silages are fed to high-producing dairy cows, the nitrogen in protein is used more efficiently by cows than soluble nitrogen. Consequently, proteolysis lowers the feed value of the silage. In this study, we investigated how proteolysis varie among silages made from a variety of crops (alfalfa, red clover, orchard grass, sorghum-sudan grass, wheat, barley and corn) ensiled at different moisture contents and maturities. We found that the amount of soluble nitrogen in the silage was higher when the crop had a higher initial protein content (i.e., more immature) and at elevated moisture contents. In fact, we could explain much of the variation in the amount of soluble nitrogen across the silages within a crop using just the moisture and total lnitrogen contents of the silages. These results suggest that reasonable estimates of soluble nitrogen may be possible even if the silages are tested only for moisture and total nitrogen contents. This should help improve the balancing of dairy cattle rations.
Technical Abstract: Limited information is available on proteolysis during ensiling in forage silages other than in legume silages. Proteolysis was measured in alfalfa, red clover, orchardgrass, sorghum-sudan grass, wheat, barley and corn silages made in two harvest seasons at different cuttings, maturities and dry matter contents. The two years were substantially different in terms of rainfall, with approximately twice as much rainfall in the growing season in the first year as in the second. These conditions affected fermentation and final silage pH. In the wet year, silage pHs above 5.0 were common; however, relatively few silages had evidence of a clostridial fermentation. In contrast to the effects on fermentation, soluble nonprotein nitrogen (NPN) levels as a percent of total nitrogen were similar across years. On this basis, soluble NPN decreased with increasing dry matter content consistently across crops and years. Crude protein (CP) )content and silage pH affected soluble NPN (% total N) only occasionally and in an inconsistent manner. However, variation in soluble NPN on a dry matter basis within a crop was well predicted by CP and dry matter contents of the silages (60% for corn, 77 to 90% for others). Silage pH made slight improvements in prediction with some forages.