Silage has substituted hay as the major conserved herbage in Galicia due to the well-known nutritional benefits of the former. However, the heavy spring rainfall has caused widespread problems in silage conservation quality. Consequently, silage additives are used increasingly and the benefits of formic acid under difficult ensiling conditions have been recognised. Recently, biological fermentation enhancers have become available but there is little knowledge of their usefulness under local conditions. Moreover, since silage is not generally used in sheep production systems in Galicia, an experiment was designed with the twin objective of determining the effectiveness of two silage additives whilst testing the suitability of silage for the finishing of spring-born lambs during the dry summer.

Using a double-chop silage harvester with additive applicator, three 15-tonne clamp silages were made from a predominantly ryegrass permanent pasture on 25 April 1991 during persistent rainfall (c.6.5 litres/m2/day) . Silage C (control) had no additive; silage F received 3.2 litres of 85% formic acid/tonne fresh herbage (FH); and silage B had l0g Sil-Add/t FH (Alltech Inc.). Sil-Add consists of lactic acid producing bacteria, an enzyme complex and an anticlostridial factor.