Vet Column 8-24-09
August 24, 2009
Silage is an important feedstuff for cattle and sheep. Making proper silage is an art and various techniques for making silage can become tradition. The U.S. Dairy Forage Research Center and the University of Wisconsin-Madison recently hosted the 15th International Silage Conference, the first time it had been held in the U.S. since this conference was first held in 1970. Around 250 silage researchers from more than 20 countries attended. Silage could soon be engaged with more attention than many might realize.
Research was presented at this conference from the University of California-Davis regarding silage volatile organic compounds (VOCs). VOCs consist of more than 700 reactive gases, some of which contribute to the production of ground-level ozone (smog) by the gas-phase reaction of VOCs and oxides of nitrogen in the presence of sunlight. The Environmental Protection Agency (EPA) has instituted ozone standards, and some California dairy producers are currently incurring fines for exceeding air quality standards. Silages may have an air quality impact similar to vehicle emissions.
The practical implication of this research is that any management practice that helps conserve silage nutrients such as density, face management, minimal surface area exposure, additive use, etc., will reward producers with both improved feed quality and a reduction in silage-induced air quality issues. A major source of VOCs includes emissions from the mixer wagon (aeration of VOCs combining with oxides of nitrogen from the truck/tractor) and from feed in the feed bunk (a large surface area increases the volatilization of problematic VOCs).
Safety around silage structures cannot be ignored. The recommended safe distance to remain from the silage face is five times the height of the structure. Some companies now prohibit employees from taking samples directly from the bunker/pile face. Instead, they are recommending that samples be taken from the mixer wagon. This also will likely reduce sampling errors since these samples represent what is being delivered to the feed bunk.
Should it be necessary to submit silage samples for analysis for molds and yeasts, they should be shipped in plastic bags surrounded by a coolant pack. After approximately 36 hours, sample temperatures were close to ambient air temperatures. Proper handling and quick delivery are important. There were dramatic differences in yeast and mold counts between fresh and transported samples.
Silage variability relative to forage dry matter can be large. This is particularly important to dairy operations. Balancing the conflict between high nutrient demand and the need to maintain minimum fiber requirements is key. Data indicate that single-day variations in forage composition have an immediate effect on dry matter intake, and for every 2.2 pound decrease in dry matter intake, 1.8 pounds of milk were lost in each of the following two days. In non-arid environments, monitoring forage dry matter daily and implementing silage face management practices to reduce exposure to rain and snow events can pay dividends.
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Additional information can be found at http://www.dfrc.ars.usda.gov/ISC/Home.html or from your State forage extension specialist.