THE INFLUENCE OF DENSITY AND SIZE OF PARTICLES ON RUMINATION AND PASSAGE FROM THE RETICULORUMEN OF SHEEP

Plastic particles with different densities (0.92, 1.03, 1.22 and 1.44 g/ml) and sizes (1, 10 and 20 mm) were introduced into the rumen of fistulated sheep kept on a roughage diet. The forestomach was emptied 12 and 24 h after the introduction of the particles, and the contents were replaced by the same amount of rumen contents without plastic particles. The proportions of particles which left the reticulo-rumen (RR) during the experimental period were determined by collecting the faeces during the following 5 d. Nonruminated particles were separated from the dried RR contents and from the faeces. Large particles were ruminated independently of particle size and density within the investigated range. After 12 and 24 h, 59 and 81% respectively of the particles initially introduced were comminuted due to rumination. During the 12 h period about four times as many particles with a density of 1-44 g/ml passed from the RR into the omasum compared with particles with a density of 0.92 or 1.03 g/ml. Three to ten times more 1 mm particles were excreted than originally-large particles (10 and 20 mm). Particles introduced with an original size of 10 or 20 mm were recovered mostly comminuted in the faeces. In a further experiment the rumens of eight sheep were emptied and filled with a buffer solution. Plastic particles (10 g) of each length (1, 5, 10 and 20 mm; all with a density of 1.03 g/ml) were introduced into the ventral rumen. Sedimentation of particles was prevented by gassing the solution in the RR. Of the initially introduced particles, 31.9, 25.4, 12.7 and 1.5% of the 1, 5, 10 and 20 mm long particles respectively left the RR within 4 h. It is concluded that rumination of particles is independent of particle density and size within the tested range. The probability of particles leaving the RR increases with the higher particle density and with the smaller size. If particle sedimentation is prevented in the RR even 10 mm long particles can leave the RR in considerable amounts.