Test hay for quality of forage as part of marketing. Because of the general lack of standardization of the market, it is important to be able to show potential buyers test results that show that the hay is of high quality.
Also inspect the hay visually for quality. Things to check for include the presence of weeds, leaves damaged by disease or insects, mold, proportions of stems and leaves, forage maturity, color of the hay, and legume to grass ratio.
(Source: http://www.extension.uiuc.edu/~vista/html_pubs/haypay/sells.html )
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