The effect of additives in silages of pure timothy and timothy mixed with red clover on chemical composition and in vitro rumen fermentation characteristics M. Hetta*, J. W. Cone†, A.-M. Gustavsson* and K. Martinsson* *Swedish University of Agricultural Sciences, Department of Agricultural Research for Northern Sweden, Umea ˚, Sweden, and †Animal Sciences Group, Nutrition and Food, Lelystad, The Netherlands Abstract The aim was to compare the effects of additives on direct cut silages of pure timothy and timothy mixed with tetraploid red clover. First and second growth cuts were ensiled during three consecutive years, 1994, 1995 and 1996, either without any additive or with the addition of formic acid, or lactic acid bacteria in combination with molasses. Effects of the additives on the degradation characteristics of the herbage and the silages were analysed using an automatic in vitro gas production (GP) technique. At the end of the in vitro procedures, organic matter and neutral-detergent fibre (NDF) degradabilities were determined. The tetraploid red clover persisted in the leys during the 3 years and was the dominant species at the second growth in the mixed leys. The herbage from the mixed crops had lower dry-matter contents, higher crude protein concentrations and higher buffering capacity compared with the pure timothy at both cuts. In general, the additives reduced pH, and the concentra- tions of ammonium-N and acetic acid in the silages. The treated silages had a more rapid faster GP in both crops. The silages from the mixed crop benefited more from the additives compared with the grass silages. The additives affected the soluble fractions as well as the NDF degradability of the silages of the mixed crop more than those fractions of the grass silages. The addition of molasses in combination with a commercial inocula resulted in increased production of lactic acid and ethanol in silages from both crops. The silages without additives could not meet the requirements for good silages according to the standards of the Swedish dairy industry. Keywords: red clover, timothy, chemical composition, organic matter degradability, neutral-detergent fibre degradability, in vitro gas production, formic acid, lactic acid bacteria, molasses Introduction Most of the harvested forages for dairy and beef production in Scandinavia are conserved as silage. Different ensiling additives may have profound effects on the nutritive value and quality of the forage (Kung and Muck, 1997; Muck and Kung, 1997). The effects of the additives depend upon the properties of the crops (in e.g. different plant species) (Nadeau et al., 1998). Because of an increased interest in organic farming in Europe and more forage-based animal production, the roles of red clover (Trifolium pratense L.) and other forage legumes have become more important in recent years. Red clover in Scandinavia is mainly grown in mixtures with grasses (Rinne and Nyka ¨nen, 2000) in order to reduce the risk of winterkill and to increase yield. It has been shown that red clover in rations for cattle increases intake and animal performance compared with grasses and other legumes (Castle and Watson, 1974; Thomas et al., 1981; Heikkila ¨ et al., 1992; Broderick et al., 2001). It is well known that timothy (Phleum pratense L.), which is one of the most winter-hardy grasses (Nissi- nen, 1998), produces highly digestible forage with good conservation characteristics under cold and temperate conditions (Deinum et al., 1981). The main objective for adding additives to the crop at ensiling is to reduce pH rapidly in order to preserve the rapidly degrading carbohydrates and proteins and to inhibit the growth of deteriorating microorganisms (Van Soest, 1994). Silage additives can be divided into two major groups, namely fermentation inhibitors (e.g. organic acids) and fermentation stimulators (e.g. strains Correspondence to: Ma ˚ rten Hetta, Swedish University of Agricultural Sciences, Department of Agricultural Research for Northern Sweden, Box 4097, S-904 03 Umea ˚ , Sweden. E-mail: marten.hetta@njv.slu.se Received 17 January 2003; revised 4 June 2003 Ó 2003 Blackwell Publishing Ltd. Grass and Forage Science, 58, 249–257 249