Effect of a tannin extract and lactic acid inoculant on silage quality and nutritive value of grass

Grass silage is a cheap, home-grown basal feed in many cattle rations. To assure good fermentation and high voluntary intake, wilting grass to at least 35% dry matter (DM) is common practice. This is difficult in unfavourable weather conditions and increases the risk for bad silage quality, particularly when grass is high in protein and low in sugars. Nowadays, inoculants containing Lactobacillus strains are frequently used as natural silage additives. Less common are tannins, known to reduce protein degradation in the rumen, but may be able to do so in silages. We compared 4 treatments: 1) control grass without additive, 2) Tanno-SAN L (liquid hydrolysable tannin extract from sweet chestnut wood, Sanluc, Belgium) at 2.5 g/kg grass, 3) Bonsilage Fit G (mixture of L. buchneri, L. Plantarum and L. Rhamnosus, Barenburg, Belgium) at 2 mg/kg grass and 4) both additives combined at the same doses. The grass was harvested on 28/10/19 and wilted to 27% DM; it contained 230 g crude protein (CP), 480 g NDF, 66 g sugar and 148 g ash per kg DM. After treatment, the grass was put in PVC micro-silos (H: 35 cm, Ø: 10 cm, 5 per treatment), which were opened 90 d after ensiling. For each silo we determined weight loss, silage quality (pH, NH3, lactic and acetic acid (AA) and alcohols), chemical composition and in vitro digestibility and estimated net energy lactation (NEL), protein digestible in the intestines (PDI) and the degraded protein balance (DPB). The variance in the data was analysed with treatment as fixed factor and means were compared with Tuckey (p<0.05). In comparison to the control grass, tannin resulted in more CP, less ash and a higher NEL, PDI and DPB; the inoculant resulted in more weight loss, a higher pH, more AA and CP, less sugar and more DPB; the combination of additives gave a higher pH, lower NH3, more AA and CP, less ash and a higher NEL, PDI and DPB. Compared to the inoculant, the tannin resulted in lower loss, less NH3, AA and alcohols, more sugars and a higher NEL. The studied tannin improved silage quality, energy and protein value and will be further tested for an additional effect in the rumen.