Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/1996
Publication Date: N/A
Citation: Interpretive Summary: The dry matter (DM) content at which alfalfa is harvested for ensiling in the United States varies from unwilted to greater than 70% DM, depending on management, type of storage structure and environmental conditions. Despite minor effects of silage DM on total crude protein and fiber content, DM at ensiling can cause profound changes in the nitrogen profile and the fermentation products in the silage. Soluble non-protein nitrogen, total amino acids and ammonia decrease with increasing DM in alfalfa silage. Increasing DM content also reduces the rate and extent of fermentation in alfalfa silage and results in higher pH. It is recommended that alfalfa be ensiled in bunker, tower or oxygen-limiting silos at, respectively, 30 to 35, 35 to 40 or 45 to 60% DM. Despite a wide range of DM contents of the silages ensiled in each of the storage systems, bunker silages were wetter and oxygen-limiting silages were drier than silage from tower silos. Silage estored in bunker silos had greater amounts of non-protein nitrogen and aci detergent insoluble nitrogen than silages with higher DM and stored in tower and oxygen-limiting silos. Important differences were found in the silage composition determined by conventional wet chemistry analysis and that obtained by near infrared reflectance spectroscopy (NIRS). The lower cost and rapid turnaround time of NIRS analysis makes it an attractive alternative; however, caution should be used when interpreting results obtained from NIRS analysis of alfalfa silages. Periodic analysis of the same samples by both NIRS and wet chemical methods should be done to validate NIRS results.
Technical Abstract: The objectives of this study were to evaluate the effects of DM content and three different storage systems on commercial farms on the quality of ensiled alfalfa and to compare near infrared reflectance spectroscopy methods of forage evaluation with conventional, wet chemical analyses. Alfalfa silage samples were collected from 21 bunker, 20 O2-limiting and 19 9tower silos on 43 commercial dairy farms. Bunker silages were wetter than those silages from O2-limiting and tower silos. Storage system had no effect on the crude protein content of the silages. However, silage from bunker silos had higher concentrations of ADFN and NH3 N than silages from the other two storage systems. Fiber components also were affected by DM content of the silages. Wetter silages had higher ADF and NDF concentrations. Lactate concentrations were higher in tower silages and butyric acid concentrations were higher in bunker silages. Except for DM content, slopes of the regressions of results obtained with near infrared reflectance spectroscopy on those obtained by wet chemistry were between .57 to .84 and correlation coefficients ranged from .64 and .84. These results indicated large differences in analytical results obtained by the two methods. The general effects of DM on quality of silages obtained on commercial farms are in close agreement with results obtained in laboratory silos.