Rumen contents and ruminal and faecal particle size distribution in steers fed a mixed diet at three amounts of intake

This study was conducted to investigate the effects of intake of a mixed diet by cattle and time post-feeding on rumen contents and on particle size distribution of ruminal digesta. Six ruminally cannulated steers received a mixed diet consisting on an average of (% of dry matter) 43 perennial ryegrass silage, 25 maize silage, 30 concentrate and 2 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, 1.5 and 2 times of estimated maintenance energy requirements (denoted low, medium and high intake, respectively). The rumens were evacuated manually at 3 and 7.5 h post-feeding 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 ≥ 0.063 mm) particles. Intake did not influence markedly the distribution of different particle fractions, whereas time post-feeding had a pronounced effect. With increasing time after feeding, percentage of particles ≥ 1 mm decreased, whereas the percentage of particles < 1 mm increased, illustrating intensive particle breakdown in the reticulo-rumen. Dry matter contents and the proportion of particulate dry matter in the rumen increased as intake increased, i.e. ruminal mat increased at the expense of bailable liquids. From this study it can be concluded that feeding a mixed ration to steers at intakes of 1 to 2 times maintenance energy requirements influences the structure of rumen contents without changing the processes of particle breakdown.