Passage and rumination of inert particles varying in size and specific gravity as determined from analysis of faecal appearance using multicompartment models

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Abstract
Plastic particles of defined length (2, 5 mm) and specific gravity (sp.gr. 1.10, 1.34, 1.77) were administered just before feeding into the reticulo-rumen of four cattle and four swamp buffaloes given a diet predominantly of rice straw ad lib. Simultaneously, doses of ground rice straw marked with Cr and Yb were likewise given. Plastic particles were recovered from faeces for 12 d after dosing, and divided into non-ruminated (NR) and ruminated (R) particles. Excretion data of plastic particles were interpreted using a four-pool model incorporating passage of NR (k p) and R from the reticulo-rumen, post-ruminal passage, rate of chewing (k r) and two lag times. An inverse relationship was found between k r and sp.gr. The k r was higher for 5 mm than that for 2 mm particles. In contrast, k p was greatest for particles of sp.gr. 1.34, with higher k p for 2 mm than for 5 mm particles. Rates of passage and rumination (k p, k r) were higher for buffaloes than for cattle. Rumination time was related to k r, most highly (r 2 0.96) with k r of 2 mm, 1.10 sp.gr. particles. Fragmentation of 5 mm particles by rumination tended to increase the rate of passage from the rumen. Ruminal passage rates of Yb and Cr markers were poorly correlated with each other and with k p of any of the plastic markers. Reanalysis of published data from plastic particle studies supported the relationships between sp.gr., size, k p and k r. In view of the additional information (k r) obtained using plastic particles, we suggest their use may be appropriate in studies which investigate specific differences in digestive function, while being less suitable for investigating differences between diets.