Twelve lactating cattle × yak hybrids (B. taurus × B. grunniens) were investigated on five experimental pastures (Sites 1–5), following an up- and downward transhumance route (3,200, 4,000, 4,500, 4,000 and 2,600 m a.s.l.). Hybrids were kept in replicated groups of two (low SD) and four animals per paddock (high SD). As a control, yaks (with calves) were included at low SD at Sites 2–4. Performance was described by body weight, milk yield and composition. Herbage samples as selected by the animals were analyzed. Activity patterns of the hybrids were assessed at Sites 2–4. At similar body weight change and milk composition, the individual hybrids on average produced 26% less milk at high than at low SD. However, at high SD on average still 49% more milk/m2 of pasture area was produced. Milk fat increased with time from 5.4 to 7.1%, milk protein decreased from 4.2 to 3.3%. At high SD, the hybrids spent less time standing and more time lying. The yaks gained weight at 4,500 m a.s.l. while the hybrids lost weight (+836 and −653 g/animal/day, respectively). In conclusion, high SD reduced individual milk yield and forced hybrids to spend more time for feeding. The yaks apparently had an advantage over the hybrids at very high altitude.
