Paper-Lecture11 - Aust J Agric Res 1985 36 819-28 Effect of...

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Aust. J. Agric. Res., 1985, 36, 819-28 Effect of Rumination on Reduction of Particle Size of Rumen Digesta by Cattle P. M. Kennedy Department of Animal Science, The University of Alberta, Edmonton, Canada T6G2P5; present address: Division of Tropical Animal Science, CSIRO, PMB, Aitkenvale, Qld 4814. Abstract Two Hereford steers, fitted with cannulas in the oesophagus and rumen, were given four forage diets in either the chopped or ground and pelleted form. Collections from the oesophageal fistula were made of boluses regurgitated during rumination of the chopped diets. Diets were given at 95% of voluntary feed consumption at intervals of 2 h. Rumination of the chopped diets required 28-36000 chews/day compared to values of 3-10 000 chews/day for the pelleted forms. The weight of material regurgitated during rumination averaged 786 g, of which 493 g was swallowed before chewing commenced. Fractionation of particulate DM by wet sieving showed that the material retained in the mouth for chewing contained 41% more large particulate matter than did regurgitated material. Approximately 70% of large particles in the mouth were comminuted to small particles during one cycle of rumination. Comminution per chew was positively related to the amount of large particulate matter retained in the mouth for chewing and negatively to the number of chews/cycle. Rumination accounted for approximately 85% of comminution of large particles which entered the rumen. Measurements of digestion of dietary materials from nylon bags and rates of outflow of small particles and water from the rumen were used in conjunction with intake and chewing measurements to predict the rumen content of large particles. Introduction The need for ruminants to comminute coarse rumen digesta to a size that can pass from the rumen is probably a factor limiting intake of forages (Van Soest 1982). Comminution is considered to result mainly from the chewing of plant fragments during eating and rumination, and the resistance of forages to comminution has been characterized by duration of chewing per unit of intake (Balch 1971). The latter 'roughage index' is considered to reflect the rate of breakdown of large particles per chew, analogous to the energy required to grind forages through small screens (e.g. Chenost 1966)' and to be related to intake through the rate of generation of small particles that can pass from the rumen (Troelsen and Campbell 1968) and the time expended in chewing. Rumination time in sheep and cattle has rarely been observed to exceed 10 h/day (Van Soest 1982; Welch 1982). Evidence of the importance of rumination in limiting forage intake may be adduced from depressions of intake resulting from physical inhibition of rumination (Pearce and Moire 1964; Welch 1982), and the increased intakes associated with the grinding and pelleting of forages, with concomitant reduction of rumination (Campling and Freer 1966; Osbourn et al.
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