EFFECTS OF INTAKE OF A MIXED DIET AND TIME POSTFEEDING ON AMOUNT AND FIBER COMPOSITION OF RUMINAL AND FECAL PARTICLES AND ON DIGESTA PASSAGE FROM THE RETICULORUMEN OF STEERS

This study was conducted to examine the effects of intake of a mixed d iet by cattle and time postfeeding on amount and detergent fibre conte nts of ruminal and faecal particle fractions and on digesta passage fr om the reticulo-rumen. Six ruminally cannulated steers received a mixe d diet consisting on an average of (g/kg of dry matter) 430 Italian ry egrass silage, 250 maize silage, 300 concentrate and 20 mineral-vitami n mix. The experimental design was a repeated 3 x 3 Latin square with 21 day periods. The diet was offered twice daily (07:00 and 19:00 h) a t 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 r uminal contents separated into mat and bailable liquids. Dry matter we ight distribution of total recovered particles was determined by a wet -sieving procedure and used to partition ruminal mat and bailable liqu ids among percentages of large (greater than or equal to 4.0 mm), medi um (< 4.0 mm and greater than or equal to 1.0 mm), and small (< 1.0 mm and greater than or equal to 0.125 mm) particles. The detergent fibre concentrations of particle fractions in ruminal mat and bailable liqu ids were constant across intakes, whereas fibre in faecal particles wa s higher at the high than at the medium intake. The fibre content of m edium faecal particles was similar to that of the medium particle frac tion of ruminal bailable liquids, whereas the fibre content of small f aecal particles was similar to that of small ruminal mat particles. Am ount of fibre in ruminal bailable liquids: the fraction assumed to be available for passage out of the reticulo-rumen, decreased with increa sing 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 ph ysical consistency of ruminal digesta and in the pool of particles tha t are selected fur passage, were of minor importance for ruminal escap e of fibre when steers were fed a mixed diet at 1 to 2 times of mainte nance energy requirements. (C) 1998 Elsevier Science B.V.