Because of their high level of lignified cell-walls and low protein, oat by-products that contain hulls have a low nutritive value and are typically used in ruminant diets to replace forages. Many studies have compared the nutritive value of oat hulls with that of other sources of fibre.
When included as a concentrate at 50% in dairy cows diets (forage:concentrate 1:1), oat hulls resulted in lower digestibility, milk yield and energy retention than other ingredients (soybean hulls, apple pulp, Jerusalem artichoke tubers, molasses and wheat). They did not provide enough fermentable energy for microbial synthesis and their use resulted in a higher urine-N:ingested-N ratio (Hindrichsen et al., 2006) and lower methane production (Hindrichsen et al., 2004).
In sacco DM degradability of oat hulls (particle turnover of 0.06 h-1) is about 40%, lower than that of soybean hulls (50%) and much higher than that of sunflower hulls (22%) (Pereira et al., 1999). Oat hulls showed a lower rate and a smaller 36h-extent of in sacco DM disappearance (0.8 h-1 and 66% respectively) than maize fibre or soybean hulls (about 7%/h and 90%). In vivo digestibility of OM, NDF and ADF in diets containing 80% seed hulls or maize fibre were lower for oat hulls and cottonseed hulls (less than 50%) than for maize fibre and soybean hulls (more than 75%) (Hsu et al., 1987).
The nutritive value of oat hulls estimated by in vitro measurements was found to be lower than that of maize fibre and soybean hulls, but slightly higher than that of cottonseed hulls. In vitro DM disappearance of oat hulls was much lower than the values obtained for maize fibre and coarse maize fibre (32%, 86% and 82% respectively) (Garleb et al., 1988).
Chemical and enzymatic treatments can improve the values of oat hulls. In growing steers, ammonia treatment (3% DM basis) increased the in situ potential degradability and degradation rate of NDF and ADF fractions, in vivo NDF digestibility as well as voluntary intake (Thompson et al., 2002). Alkali treatment increased in vitro and in sacco DM disappearance (Garleb et al., 1988; Pauly et al., 1992). In dairy cows, alkaline hydrogen peroxide treatment increased the in vivo OM and cell wall digestibility in diets containing from 20 to 60% treated oat hulls (Cameron et al., 1991b; Titgemeyer et al., 1991). This treatment increased digestible DM and fibre intake, and maintained growth in heifers (Cameron et al., 1991b) and milk production in dairy cows (Cameron et al., 1991a). Enzymatic treatments can enhance the in vitro (rumen fluid) DM degradation compared to wheat straw and alfalfa hay (Yu et al., 2005).
Other feed uses
Oat hulls have been proposed as a structure-enhancing ingredient for the storage of root peelings (beets, carrots, potatoes) when mixed with urea and molasses. Such feeds could be used as a supplement for dairy cows and as a sole feed for fattening bulls (Dornow et al., 1991).