Effect of sainfoin on in vitro digestion of fresh alfalfa and bloat in steers

Abstract

The effects of sainfoin (Onobrychis viciifolia) on digestion of alfalfa (Medicago sativa) were investigated in vitro and in vivo. Fresh alfalfa and sainfoin were incubated in an artificial rumen (Rusitec) in ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 (as-fed). Disappearances of dry matter and N from sainfoin were 77 and 65% of those from alfalfa, respectively. Protease and endoglucanase activities, NH3-N and methane production declined (P < 0.05) as sainfoin increased. Bacterial numbers and microbial outputs were unchanged (P > 0.05), but cells incorporated more 15NH3N as sainfoin in the diet increased. Chopped leaves (100:0, 95:5 and 90:10 alfalfa:sainfoin) were incubated for 48 h with diluted ruminal fluid containing 0 or 50 mg polyethylene glycol, which binds tannins. Gas and volatile fatty acid productions were similar (P > 0.05) across treatments, but including 10% sainfoin (without polyethylene glycol) reduced (P < 0.05) NH3 concentrations between 8 and 24 h. Sainfoin tannins reduced degradation of forage protein without affecting the digestibility of the nonprotein fraction. Alfalfa herbage was fed alone or with early- to full-bloom sainfoin herbage (at 10 or 20% of ad libitum alfalfa dry matter intake) or with sainfoin hay or pellets, to eight Jersey steers in crossover trials conducted over 4 yr. Including sainfoin in the diet reduced (P < 0.001) the incidence of bloat by 45 to 93% in 3 of 4 yr, irrespective of the form in which it was supplied. Co-feeding sainfoin can markedly reduce the incidence of bloat in ruminants consuming fresh alfalfa. Key words: Alfalfa, sainfoin, bloat, condensed tannins