Passage of internal and external markers of particulate matter through the rumen of sheep G.J. Faichney, C. Poncet, R.C. Boston, L. Bernard, S. Pochet, M.-T. Beaufort, E. Delval, M. Fabre, P. Pichon and J. Flechet Reprod. Nutr. Dev., 29 3 (1989) 325-337 DOI: 10.1051/rnd:19890311