Rapeseed hulls can used as an energy source for ruminants, due to their composition somewhat similar to that of alfalfa in terms of crude protein content and fibre content, but with a relatively high fat content. This fat content could help reducing enteric methane emissions, which could make rapeseed hulls a promising feed for ruminants in the climate change context (Carré et al., 2015; Beauchemin et al., 2009). Few trials are available: trials with cattle were relatively positive while a sheep trial resulted in poor performance.
Degradability and digestibility
When compared to soybean hulls and beet pulp in a digestibility trial with sheep, rapeseed hulls were found to have a much lower digestibility for organic matter (60% vs 84% and 85% respectively) and crude fibre (74% vs 91 and 85%). Protein digestibility was comparable (55% vs 48 and 56%). The low OM and fibre digestibiltiy could be explained by the high lignin content of the cell layer. Rapeseed hulls degrade relatively poorly in the rumen: after 72h in nylon bag in cannulated sheep only 61% of DM had disappeared (Grenet et al., 1990). Another experiment reported low degradability values for DM and protein (< 50%) and very low degradability values for NDF and ADF (< 20%) (McKinnon et al., 1995).
Dairy cows
While no dairy cow trials with rapeseed hulls seem available in the scientific literature, it can be noted that the introduction of oil-rich expeller rapeseed meal in dairy diets results in higher milk production with more protein and less saturated fatty acids (Brunschwig et al., 2006). The oil content of rapeseed hulls could thus be beneficial.
Beef cattle
Rapeseed hulls from glucosinolate-rich cultivars could be fed at 1% LW and 1.67% LW to growing cattle weighing 100 kg and 300 kg respectively (Ahlström, 1973). In growing heifers, rapeseed hulls could represent 50% of the diet concentrate for 13 weeks without impairing feed intake. In spite of the presence of glucosinolates and erucic acid, the hulls were well accepted by the animals. Growth rate was similar to that obtained with the control diet during 11 weeks, but performance decreased in the last 2 weeks, possibly due to a change in hull composition (the latter batch contained 20% oil vs 11% in the first batch) (Ahlström et al., 1978). Feeding 9 month-old steers during 6 months with 25% rapeseed hulls (DM dietary level) replacing maize silage resulted in a lower feed efficiency but did not affect growth rate, carcass weight and carcass composition (Baudet et al., 1978).
Sheep
In lambs fed on 25 to 75% rapeseed hulls, processed (ammonia treated, solvent extracted or a combination of both processes) or not, as a partial replacement for alfalfa hay, increasing the amount of rapeseed hulls decreased feed intake and the digestibility of energy and nutrients, whatever the process. Processing did not improve DM and nutrient degradability, which was low (McKinnon et al., 1995).