There are several references that discuss the major sources and fate of the following substances in ruminants digestion:
(A) Propionic, ethanoic, and butanoic acid:
1. Liang, Y., & Nkrumah, J. D. (2018). Rumen Biohydrogenation in Ruminants: The Role of Propionate and its Effects on Lipid Metabolism. Journal of Agricultural and Food Chemistry, 66(36), 9553-9561.
2. Hristov, A. N., & Oh, J. (2013). Sources, absorption, and fate of methane and hydrogen in ruminants. Journal of Dairy Science, 96(4), 2542-2558.
(B) Methane:
1. Johnson, K. A., & Johnson, D. E. (1995). Methane emissions from cattle. Journal of Animal Science, 73(8), 2483-2492.
2. Martin, C., Morgavi, D. P., & Doreau, M. (2010). Methane mitigation in ruminants: from microbe to the farm scale. Animal, 4(3), 351-365.
(C) Carbon dioxide:
1. Miltersen, K., et al. (2000). Metabolism of propionate absorbed from the rumen of cattle: a review. Journal of Dairy Science, 83(5), 1106-1121.
2. Russell, J. B., et al. (1992). Concentration of metabolic gases in the digestive tract of ruminants: methane, nitrous oxide, carbon dioxide, hydrogen. Canadian Journal of Animal Science, 72(3), 475-482.
(D) Ammonia:
1. Fadel, J. G., et al. (2006). Ammonia emissions from dairy cattle housing and waste lagoons: a review. Transactions of the ASABE, 49(5), 1605-1616.
2. Kohn, R. A., & Allen, M. S. (1995). Low-fiber alfalfa silage and the composition of ammonia-nitrogen in cattle. Journal of Dairy Science, 78(2), 513-517.