EFFECTS OF INTAKE LEVEL OF A MIXED DIET ON CHEWING ACTIVITY AND ON PARTICLE-SIZE OF RUMINATED BOLI, RUMINAL DIGESTA FRACTIONS AND FECES OF STEERS

This study evaluated the effects of intake of a mixed diet on chewing activity during eating and rumination and the relationship between the chewing activity and the particle size of the ruminated boli, ruminal digesta fractions and faeces in steers. Six ruminally cannulated stee rs received a mixed forage/concentrate diet (68:32, dry matter basis). The diet was offered twice daily at approximately 1, 1.5 and 2 times the estimated maintenance energy requirements (low, medium and high in take, respectively) in a repeated 3 x 3 Latin square design. The rumen s were emptied manually and samples of the ruminated boli and of the r uminal upper strata were collected at four different times throughout the day. The dry matter weight distribution of the total amount of rec overed particles was determined by a wet-sieving procedure. Numericall y, the effect of intake on the mean particle sizes of the different ma terials was small. However, the mean particle size was reduced by almo st nine tenths from their size at intake of the mixed diet (4.78 mm) t o defecation (0.51 mm). The total number of minutes chewing and eating and ruminating increased as the intake level increased. When related to 1 kg of dry matter intake, only the eating and chewing times were s ignificantly longer for the high as compared to the medium intake. Rum ination patterns were examined using a cosinor model. Data indicated t hat the average amount of time spent ruminating also increased as the intake level increased. The overall pattern of rumination was not impa ired by higher intake levels. The amount of Targe (greater than or equ al to 4 mm) particles that escaped per minute of rumination time betwe en 3 and 7.5 h postfeeding was similar for all the intake levels. It w as concluded that an active breakdown process occurred in the rumen wh ich could cope with the higher intake levels of the mixed diet over th e range of 1 to 2 times the maintenance energy requirement level.