The effect of in-silo effluent absorbents on effluent production and silage quality

Experimental data on the effects of absorbent inclusion in the silo on effluent production and silage quality is reviewed. The absorbent materials used in various studies include straw, hay, paper, bentonite, polymers, cereals, dried sugarbeet pulp, various byproducts and compound feeds formulated to reduce effluent and enhance silage quality. Most studies have shown absorbent inclusion (20-80 kg/t) to reduce total effluent production by 20-85%. The amount of effluent retained per unit of absorbent varied widely for different absorbents and for the same absorbent in different experiments. This variation cannot be attributed simply to differences in experimental procedures and implies that crop characteristics such as proportion of stem, amount of surface water, etc. influence the effectiveness of absorbents. Highly lignified materials (hay, straw, newspaper) and absorptive minerals (bentonite), though highly absorptive, adversely affect nutritive quality and are unlikely to find application in current conservation systems. The inclusion of cereals in the silo has generally improved fermentation and nutritive quality but their effectiveness as absorbents is questioned in several experiments. Inclusion of dried sugarbeet pulp has almost invariably reduced effluent production although the amount retained has varied widely between experiments. Sugarbeet inclusion improved fermentation and reduced losses when the untreated grass was poorly fermented. Silage quality was improved by sugarbeet inclusion; the overall efficiency of inclusion, compared to supplementary feeding, appears to depend on the extent to which sugarbeet inclusion influences in-silo losses and silage intake. The results repeated for proprietary absorbents have been generally similar to those for sugarbeet. The evidence available suggests that incorporation of sugarbeet or proprietary absorbents in the silo would be beneficial, particularly if the untreated crop is likely to be poorly fermented. The main factors mitigating against these or other absorbents is the unpredictability of effluent retention and the additional labour, resources and silo space required at harvest time.