I want to know if flax hay is worth buying and feeding to cattle
Hennepin County Minnesota
The answer is - maybe. Flax hay makes a perfectly acceptable cattle feed. The question is, what quality is the hay? I will assume that you are intending to feed beef cows (as opposed to inclusion as part of a feedlot diet or dairy cattle) to make a few points. First, the maturity could vary widely, so that the protein and energy may be better than many grass hays, or could be poorer (especially) in energy than wheat straw. Ideally, a forage analysis could be run to give at least an estimate of energy (NEm or TDN) and crude protein (CP). Regardless of the quality, it's value to you may be dependent on the class of cattle (late gestation cows, lactating cows, etc.), their needs, and what else you have to feed. As far as I know, there are no common anti-nutritional factors associated with flax hay.
Most forage labs can conduct a simple analysis for less than $30.
You can find a list of labs here: http://www.foragetesting.org/