THE EFFECT OF SILAGE FERMENTATION CHARACTERISTICS ON DRY-MATTER INTAKE OF STEERS

Juice was expressed from two silages of contrasting fermentation type with either high (H) or low (L) levels of lactic acid and reconstitute d 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 treatm ents 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-Ai per kg tota l nitrogen (TN) respectively. The four diets were offered to four stee rs (mean live weight 679 (s.e. 49) kg) in a four-period change-over de sign experiment. Each period was of 17 days duration. DM intakes were recorded daily, with intakes on days 8 to 17 used in the statistical a nalysis of data. On day 12 of each experimental period, rumen fluid sa mples 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 us ing 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 treatment s respectively. Diet had no significant effect on eating behaviour, ru men fermentation parameters or degradability of DM, N, MADF and NDF fr actions (P > 0.05). Silage L increased rumen fluid pH (P < 0 05), redu ced buffering capacity (P < 0 05) and increased the molar proportion o f propionic acid and n-butyric acid (P < 0.05 and P < 0.01) compared w ith silage H. Silage L also had a lower DM apparent digestibility, D-v alue and DM, (P < 0.001), N and MADF (P < 0.05) degradabilities than s ilage H. The higher DM intake of dietary treatment HH compared with di etary treatments LL and LH could not be explained by any single consti tuent of the silages although it was apparent that physical characteri stics of the silage were move important in determining intake than the chemical characteristics.