Ration digestion and retention times of digesta in domestic cattle (Bos taurus), American bison (Bison bison), and Tibetan yak (Bos grunniens)

Digestive functions, digesta retention times, and plasma thyroid hormone concentrations were measured in three species of Bovidae: domestic cattle (Bos taurus; three breeds), American bison (Bison bison), and Tibetan yak (Bos grunniens), fed a pelleted ration (nitrogen, 2.62%) at a near maintenance level. Apparent digestibilities of dry matter, energy, and nitrogen components of the ration were not significantly different among animal groups except for one breed of cattle (Holstein–Friesian) which had higher dry matter and energy digestibilities than all the other animal groups and a higher nitrogen digestibility than the other breeds of cattle. Nitrogen disappearance from the gastrointestinal tract (apparent absorption) per 100 g of dry matter digested was greater in the bison and yak than in the cattle, and mean retention time of digesta in the gastrointestinal tract was 65–69 h in the cattle, compared with 79 and 78 h in the bison and yak, respectively. The longer total retention time of digesta in the bison and yak may account in part for their apparent improved nitrogen economy and greater ability to digest fibrous feed material.