The effect of silage fermentation characteristics on dry-matter intake of steers

Abstract

Juke was expressed from two silages of contrasting fermentation type with either high (H) or low (L) levels of lactic acid and reconstituted either with the silage from which it had been expressed or the other silage. This procedure produced four dietary treatments (HH, HL, LL, LH) each differing in fermentation characteristics. The dietary treatments HH, HL, LL, and LH contained 81, 71, 59, and 49 g lactic acid per kg dry matter (DM) and 101, 133, 193 and 159 g ammonia-N per kg total nitrogen (TN) respectively. The four diets were offered to four steers (mean live weight 679 (s.e. 49) kg) in a four-period change-over design experiment. Each period was of 17 days duration. DM intakes were recorded daily, with intakes on days 8 to 17 used in the statistical analysis of data. On day 12 of each experimental period, rumen fluid samples were taken throughout a 24-h period. The rates of disappearance of DM, nitrogen (N), modified acid-detergent fibre (MADF) and neutral-detergent fibre (NDF) in the rumen were determined on days 14 to 17 using the polyester bag technique. DM intakes were 7·2, 6·9, 6·0 and 6·0 (s.e. 0·50) kg/day (P = 0·08) for HH, HL, LL and LH dietary treatments respectively. Diet had no significant effect on eating behaviour, rumen fermentation parameters or degradability of DM, N, MADF and NDF fractions (P > 0·05). Silage L increased rumen fluid pH (P < 0·05), reduced buffering capacity (P < 0·05) and increased the molar proportion of propionic acid and n-butyric acid (P < 0·05 and P < 0·01) compared with silage H. Silage L also had a lower DM apparent digestibility, D-value and DM, (P < 0·001), N and MADF (P < 0·05) degradabilities than silage H. The higher DM intake of dietary treatment HH compared with dietary treatments LL and LH could not be explained by any single constituent of the silages although it was apparent that physical characteristics of the silage were more important in determining intake than the chemical characteristics.