Greenleaf desmodium can be a valuable protein supplement in ruminant diets based on fibrous by-products or low nutritive value forages (Tolera et al., 2000b; Mwangi et al., 2003; Boukila et al., 2009). The tannins can exert beneficial effects on protein metabolism by increasing the proportion of bypass protein without limiting the ammonia N level and microbial synthesis in the rumen (Perez-Maldonado et al., 1996; Tolera et al., 2000b). Tannins in greenleaf desmodium have also been able to reduce significantly the effects of intestinal parasites (Debela et al., 2012).
Degradability, digestibility and intake
The DM degradability of greenleaf desmodium hay measured in the rumen was 68% within 48 h of incubation (Tolera et al., 1997). Reported digestibility values have been rather low. A 1971 study reported an OM digestibility of only 39% in sheep, but for a fresh forage of poor quality (protein 10% DM) (Holm, 1971). In vivo (sheep) apparent DM and OM digestibility of greenleaf desmodium hay (10% bloom stage) were 49% and 53% respectively (Nurfeta et al., 2009). Due to its rumen degradable protein and condensed tannins content, greenleaf desmodium provides sufficient nitrogen for both rumen microbial protein and by-pass protein (Tolera et al., 2000b). However, some condensed tannins may be complexed with either cellulose or protein, protecting linkages from cleavage and thus limiting in vitro digestibility (Ford, 1978). Whole tannins limited ruminal DM degradability to 22% compared to 56% when polyethylene glycol (PEG) was added. Total tract DM digestibility increased from 39% to 66% when PEG was added (Kanga'ra, 1993). Condensed tannins in leaves reduced both in vitro DM and protein degradability (Getachew et al., 2000). Adding PEG increased NDF digestibility (Mbugua et al., 2008). When greenleaf desmodium hay (10% bloom stage) was offered as the sole feed to male sheep with an average weight of 26.3 kg, DM intake was 70.4 g/kg W0.75 (Nurfeta et al., 2009).
In Ethiopia, Desmodium intortum forage used as protein supplement (2 kg/d) with native grass given to pre-weaning calves (3-4 months) resulted in daily weight gain of 320 g/d (Larbi et al., 1992).
In Kenya, Desmodium intortum leaves used as protein supplement (20% of DM intake) with Pennisetum purpureum grass of low nutritive value (16 week regrowth, protein 6.4% DM) for growing heifers (271 kg) resulted in a daily weight gain of 638 g/d (Kaitho et al., 1998). In growing heifers (163-181 kg), greenleaf desmodium used either as an intercrop legume or as a hay supplement, both at 30% DM, with good Pennisetum purpureum (protein 12% DM) grass, gave better growth as an intercrop than as a hay supplement (450 vs. 420 g/d) (Kariuki et al., 1999). In Australia (Queensland) greenleaf desmodium implanted in a Setaria pasture and grazed by heifers gave a daily weight gain of 182 g/d at a low stocking rate of 1.1 head/ha, but much lower growth (66 g/d) when the stocking rate was up to 3 head/ha (Jones et al., 2003).
In Kenya, greenleaf desmodium, included at up to 30% of the diet for steers (411 kg) based on Pennisetum purpureum (protein 9% DM), increased the protein content of the diet from 9.1 to 11.7% DM, and significantly increased OM intake from 74 to 90 g/kg W0.75(Kariuki et al., 2001).
Several sheep trials have been undertaken in Ethiopia. Greenleaf desmodium hay (protein 15.5% DM) was used as protein supplement in sheep diets based on straw fed ad libitum and enset (Ensete ventricosum) pseudostems or corms offered at 107 and 165 g/d respectively. Desmodium hay offered between 100 and 300 g/d tended to increase DM intake by up to 200 g/d with pseudostem, and this was significant at the 300 g/d level. The DM and OM digestibility of the diet increased when more than 100 g/d of desmodium hay with enset pseudostems was offered, but no difference was observed with enset corms. Nitrogen retention was higher with pseudostems supplemented with 300 g/d of desmodium hay and with corm supplemented with 200 g/d of desmodium (Nurfeta et al., 2010). Greenleaf desmodium hay offered to growing lambs (18 kg) as a supplement with maize stover significantly decreased the intake of maize stover from 28-38.5 g/kg W0.75 to 17-22.9 g/kg W0.75 when desmodium hay increased from 150 to 450 g/d (Said et al., 1993; Tolera et al., 1997; Tolera et al., 2000a). In one trial, the DM and OM digestibility of the whole diet either increased from 52 to 67% and from 58 to 71%, respectively, with increasing levels of desmodium hay (Tolera et al., 2000a). However, digestibility did not change in another trial (Tolera et al., 1997). Daily weight gain increased from 7 g/d with 250 g/d desmodium, to 25-44 g/d with 350 or 450 g/d desmodium, depending on maize stover quality. Lambs fed with maize stover alone lost 32 g/d (Said et al., 1993; Tolera et al., 2000a).