Effects of mixing sainfoin with alfalfa on ensiling, ruminal fermentation and total tract digestion of silage

Alfalfa and sainfoin were ensiled individually and in combination to examine effects of sainfoin on silage fermentation and on in vitro and in vivo digestibility. In Exp. 1, chopped alfalfa and sainfoin forages were combined in ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 (fresh weight basis; denoted S0, S25, S50, S75, and S100, respectively) and ensiled in laboratory silos for 1, 7, 20 and 72 days. Sainfoin reduced silage pH (P≤0.03) during 72 days of ensiling, as well as total (P<0.001) and lactic acid-producing (P<0.001) bacterial populations at day 20. At day 72, concentrations of total volatile fatty acids (VFA) and lactic acid were highest at intermediate levels of sainfoin (quadratic (Q), P=0.006). Over the 72 days, soluble N, non-protein N and ammonia-N (mg/g total N) decreased linearly (P<0.01) as sainfoin increased, and insoluble digestible N linearly increased (P≤0.03). In Exp. 2, silages (from day 72) prepared from S0, S25, S50, S75 and S100 were freeze-dried and incubated for 48 h in ruminal fluid, with or without polyethylene glycol (PEG). In vitro dry matter (DM) disappearance (IVDMD) at 0 h of incubation (i.e., silage DM solubility) decreased linearly (P<0.001) as sainfoin content increased. Including PEG in the incubation did not affect gas production, IVDMD or accumulations of VFA or microbial N, but increased (P=0.008) ammonia-N accumulation with S100, at 12 h of incubation only. In the in vitro incubation, the intermediate proportions of sainfoin yielded the highest 12-, 24-, and 48-h IVDMD (P≤0.003) and gas production (P≤0.051), and the greatest accumulations of VFA (at 12 and 24 h only; P≤0.022), and microbial N (at 48 h; P=0.004). In Exp. 3, forages from alfalfa (Alf) and alfalfa:sainfoin mixed plots (AS; 355 g sainfoin/kg total DM) were preserved as hay or as silage and were fed to 10 ruminally cannulated wethers (n = 5). In silage, apparent digestibilities of DM, organic matter (OM), neutral detergent fibre (aNDF), acid detergent fibre (ADF) and N were all higher (P<0.05) with AS than with Alf; but with hay, only DM (P<0.001) and OM (P=0.028) apparent digestibilities differed (AS > Alf). Co-ensiling sainfoin and alfalfa improved fermentation in laboratory silos and in batch culture incubations, and increased total tract digestibility in wethers, suggesting positive associative effects of the two forages.