Effects of intake of a mixed diet and time postfeeding on amount and fibre composition of ruminal and faecal particles and on digesta passage from the reticulo-rumen of steers

This study was conducted to examine the effects of intake of a mixed diet by cattle and time postfeeding on amount and detergent fibre contents of ruminal and faecal particle fractions and on digesta passage from the reticulo-rumen. Six ruminally cannulated steers received a mixed diet consisting on an average of (g/kg of dry matter) 430 Italian ryegrass silage, 250 maize silage, 300 concentrate and 20 mineral–vitamin mix. The experimental design was a repeated 3×3 Latin square with 21 day periods. The diet was offered twice daily (07:00 and 19:00 h) at approximately 1.0, 1.5 and 2.0 times of estimated maintenance energy requirements (denoted low, medium and high intake, respectively). The rumens were emptied manually at 3 h and 7.5 h postfeeding and total ruminal contents separated into mat and bailable liquids. Dry matter weight distribution of total recovered particles was determined by a wet-sieving procedure and used to partition ruminal mat and bailable liquids among percentages of large (≥4.0 mm), medium (<4.0 mm and ≥1.0 mm), and small (<1.0 mm and ≥0.125 mm) particles. The detergent fibre concentrations of particle fractions in ruminal mat and bailable liquids were constant across intakes, whereas fibre in faecal particles was higher at the high than at the medium intake. The fibre content of medium faecal particles was similar to that of the medium particle fraction of ruminal bailable liquids, whereas the fibre content of small faecal particles was similar to that of small ruminal mat particles. Amount of fibre in ruminal bailable liquids, the fraction assumed to be available for passage out of the reticulo-rumen, decreased with increasing intake. Rates of passage of ruminal fluid and particles increased linearly with increasing intake. It appears that rates of passage of ruminal fluid and particles and changes in the ratio of ruminal mat to ruminal bailable liquids, the latter indicating alterations in the physical consistency of ruminal digesta and in the pool of particles that are selected for passage, were of minor importance for ruminal escape of fibre when steers were fed a mixed diet at 1 to 2 times of maintenance energy requirements.