The effect of sainfoin (Onobrychis viciifolia Scop.) drying temperature and pelleting on in vitro fermentation characteristics using equine faecal inocula

This study was conducted to determine the effects of drying temperature and pelleting of the tanniniferous forage legume sainfoin (Onobrychis viciifolia Scop.) on the in vitro fermentation characteristics by equine faecal inocula. The sainfoin used for the experiment was air dried on the land and oven dried at 30, 70 and 130 °C for 2.5 h. Part of the dried sainfoin samples was left as dried hay, another part was pelleted, resulting in 6 different samples. The hay and pellets were tested for particle size distribution and pellets were tested for their pellet quality in terms of hardness, durability and bulk density. The gas production technique was used to simulate fermentation and faecal samples of eight randomly selected horses were used to create four independent inocula mixtures that were examined in two subsequent gas production runs. Per inocula mixture, the hay and pellet samples were incubated in triplicate as is, or in combination with polyethylene glycol to inactivate the tannins. Cumulative gas production, a proxy for the organic matter (OM) fermentation, was measured for 72 h, whereafter fermentation fluids were sampled and analysed for volatile fatty acids (VFA) and pH. The results of the pellet quality measurements showed that the particle sizes of the sainfoin particles in the pellets were decreased by a higher drying temperature or by the pelleting process, indicating a loss of fibre physical effectiveness, a factor that may be indicative for chewing activity and hence saliva production. The gas production results showed a significant (P < 0.05) effect of drying temperature and the addition of polyethylene glycol on the cumulative gas production, the VFA production and the percentage of branched chain VFA produced. Hay dried at 130 °C had a lower (P < 0.05) gas production compared to hay dried at 30 and 70 °C, which indicates a lower OM fermentability. The addition of polyethylene glycol increased the gas and total VFA production, which indicates that tannins in sainfoin decrease the production of gas and VFA in hay pellets compared to the hay product. The pelleting process had no effect on the fermentation characteristics, but pelleting conditions strongly decreased the level of the amino acid lysine and its reactivity. The results indicate the increase in drying temperature to cause a decrease in the OM hindgut fermentation and the total and reactive lysine contents of sainfoin. The positive effects of the tannins (a higher proportion of propionic acid relative to acetic acid and a lower protein fermentation) remain, despite of technological treatments.