Sulla is a high quality forage for ruminants. In Australia, it is considered as ideal for finishing prime lambs or beef cattle due to enhanced growth rates. Sulla has the capacity to increase milk production in dairy cows (de Koning et al., 2010). However, most feeding experiments reported concerned sheep production.
Digestibility and nutritive values
Sulla is quite digestible, with OM digestibility values as high as 75%. The nutritive value decreases with maturity: in a trial in Tunisia, OM digestibility decreased from 74% at budding to 56% at flowering (Ben Jeddi, 2005). High levels of rumen protein degradability have been reported (> 70%) (Dentinho et al., 2011).
Sulla is very palatable to livestock, who will selectively graze it when sown in a mixed sward. Quality peaks just before flowering, but the foliage becomes less palatable once flowering starts as stems become more fibrous (de Koning et al., 2010). The stems are succulent and well accepted by livestock: in a trial, 85% of sulla stems were eaten by young lambs (Douglas et al., 1999).
Sulla has been shown to increase resistance to parasites (such as nematodes) in sheep and deer, an effect attributed to the presence of condensed tannins. It is considered as one of the best forages for sustainable long-term parasite control (Ramirez-Restrepo et al., 2005). Sulla tannins were effective in the inhibition of larval migration of deer lungworms and gastrointestinal nematodes (Molan et al., 2001).
Several experiments in New Zealand have shown sulla to be valuable for dairy cows. Sulla silage was found to be a suitable supplement for grazing dairy cows during summer. Dairy performance was similar with sulla and maize silages, with the sulla silage (6 kg DM/day) resulting in a higher DM degradation rate than the maize silage (Chaves et al., 2006). However, in another comparison, sulla silage resulted in less milk solids than Lotus corniculatus silage, perhaps due to its lower protein and lower condensed tannins (Woodward et al., 2006). Cows grazing sulla had a higher DM intake (13.1 vs. 10.7 kg DM/day) and milk solids production (1.07 vs. 0.81 kg/day) than cows grazing perennial ryegrass pasture (Woodward et al., 2002).
While sulla has been reported as ideal for finishing beef cattle (de Koning et al., 2010), there is no trial in the literature (as of 2013) reporting use of sulla for beef production.
There have been numerous trials in Italy, North Africa, Australia and New Zealand looking at the value of sulla in sheep for meat, milk and wool production. Grazing on sulla forage has been shown to have a positive impact on the productivity of meat and dairy sheep (Burke et al., 2002; Bonanno et al., 2007a; Molle et al., 2009). In grazing trials, better lamb performance was achieved from sulla than from grass/white clover, a result attributed to a very high readily fermentable to structural carbohydrate ratio (Terrill et al., 1992a). In Australia, ewes grazing a sulla-based pasture for 8 weeks had better growth rate, final weight and wool growth (longer wool) than ewes grazing a control pasture of grass and subclover (de Koning et al., 2010). In New Zealand, better performance of lambs grazing sulla compared with alfalfa was attributed to the protective effects of condensed tannins on nematode infection and protein protection in the rumen (Niezen et al., 1995). In a comparison of Lotus corniculatus and sulla grazed as sole diets for 4 months by young lambs, the condensed tannins in sulla were detrimental to carcass yield, but sulla produced more DM and was better utilized than Lotus, being able to sustain high levels of animal production per hectare (Douglas et al., 1999). In Italy, a comparison of sulla-oat hay and sulla-oat silage fed to lactating ewes did not show differences in DM intake, milk yield, milk protein, milk fat, cheese yield and cheese microbiological characteristics, and it was concluded that sulla silage was a good alternative to sulla hay (Leto et al., 2002). A diet of sulla minimized scouring and the formation of dags (locks of wool matted with dung that tend to attract flies) (de Koning et al., 2010).
The condensed tannins of sulla may have beneficial effects on product quality. Meat from lambs fed fresh sulla had a lower proportion of saturated fatty acids, higher n-3 fatty acids and conjugated linoleic acid, and lower n-6 fatty acids than animals fed concentrates (Priolo et al., 2005). Milk from dairy ewes grazing sulla at flowering had a lower content of conjugated linoleic acid, but was richer in n-3 fatty acid and had a lower n-6:n-3 ratio, than milk from ewes supplemented with PEG (which neutralizes the effect of condensed tannins) (Cabiddu et al., 2009).
In Italy, with goats grazing a sulla monoculture, a high stocking rate (70 head/ha) reduced sulla height and availability during the first 35 days. Intake and milk yield was higher at lower stocking rates (30 and 50 heads/ha). However, while overstocking led to a lower total milk yield per goat, it also produced the highest daily and total milk yield per ha (Bonanno et al., 2007b).
In New Zealand, young red and hybrid deer (75:25 deer:elk) grazing sulla had higher final live weights and carcass weights than deer grazing chicory (Cichorium intybus) or perennial ryegrass/white clover pastures (Hoskins et al., 1999).