Fresh flax forage
The in vitro OM digestibility of fresh flax forage was found to be quite high (76%) at stem extension and then to decrease linearly as the plant aged, down to 54% when the seeds matured. The optimal harvesting stage was considered to be at the brown capsule stage (in vitro OM digestibility 65%) as the n-6/n-3 fatty acids ratio was still low (Peiretti et al., 2008). However, flax forage is prone to HCN production and care must be taken to limit access for grazing (see Potential constraints above).
Flax straw is a poor quality roughage but it can be a useful livestock feed in times of scarcity (drought, feed shortages, etc.).
Flax straw is readily eaten by cows (Government of Saskatchewan, 2008b) but an early report found that it was unpalatable to sheep (Whiting, 1958).
Digestibility and energy value
The in vivo OM digestibility of flax straw is generally low (34-49%) (Mann et al., 1988; Howard et al., 1991; Neumark, 1970; Kolari et al., 1961; Whiting, 1958). In Canada, flax straw was found to have a much lower digestibility than wheat straw, wheat chaff (Mann et al., 1988), and oat straw (Whiting, 1958). In Egypt, a comparison of flax straw with other roughages (rice straw, sugarcane bagasse, date stones, berseem hay) found that flax straw contained the most fibre and had the lowest rumen gas production and estimated ME (3.93 MJ/Kg DM), as well as a very low in vitro OM digestibility (27%) (Sallam et al., 2007).
Treatment with anhydrous ammonia (3.5% DM basis) can improve the nutritive value of flax straw, as shown by two experiments carried out in Canada. Ammoniation increased the nitrogen content of the straw by 2 or 3 times, with increases also in feed intake and digestibility (Howard et al., 1991; Mann et al., 1988). In sheep, ammoniation significantly increased OM intake, so that ammoniated flax only required 25% supplementation with sweet clover (Melilotus officinalis) compared to 75% supplementation with untreated flax straw (Howard et al., 1991). In a comparison of flax straw, wheat straw and wheat chaff offered to steers, ammoniation increased in vitro OM digestibility (from 35 to 46%), in vivo OM digestibility (from 34 to 58%), ADF (from 10 to 40%) and NDF (from -0.6 to 38%) of the flax straw, while ammoniation failed to increase the in vivo digestibility of the other crop residues. Ammoniation did not change the lignin content of any of the crop residues. Winter feeding of young beef cows with ammoniated flax straw resulted in average daily gains almost as high as those obtained with hay, and significantly higher than with the other crop residues. Backfat thickness was higher with hay or ammoniated flax straw. It was concluded that for young wintering beef cows, ammoniated flax straw (3.2 kg/day) given with barley (5.6 kg/day) had a feeding value similar to that of medium quality bromegrass/alfalfa hay (Mann et al., 1988).