Productivity, requirements and efficiency of feed and nitrogen utilization of grass-fed early lactating cows exposed to high Alpine conditions

In this study, three groups of six cows each (two of them pastured during successive seasons, one housed indoors) were transported to a high Alpine area (2000 m above sea level) for 8 weeks after 2 weeks of trial under lowland conditions (400 m above sea level). The Alpine sojourn was divided into three periods of measurement (week 1, weeks 2 and 3, and week 8). Feed composition, voluntary feed and nutrient intake, as well as organic-matter digestibility were repeatedly measured using the double-indicator technique. Meteorologic data and milk yield were continuously recorded; milk-composition and live-weight changes (after some hours of feed withdrawal) were assessed at certain intervals. Climatic conditions at Alpine sojourn were characterized by a higher overall chilling rate without reaching extreme values. Between the two seasons, certain climatic differences occurred. In the lowland the cowshed. By contrast, consumption on Alpine pasture significantly exceeded intake in the Alpine cowshed. Based on common requirement values for lowland resting maintenance and for actual milk yield, the calculated net energy intake in the lowland period and in the Alpine cowshed was below requirements, whereas the cows on Alpine pastured ingested amounts exceeding these requirements by 31% on average. Alpine live weights were similarly lower in all groups than in the lowland period by 42 kg on average. Milk yield on pasture sharply declined during the 10 weeks of experiment from 28.0 kg on average to a final value of 13.0 kg. This was even more than in the cowshed (from 29.4 to 15.7 kg). In terms of the alterations of the milk constituents, no significant group differences were observed. Based on the increase in voluntary net energy intake and the level of calculated energy mobilization by the cows housed indoors, the maintenance requirements of cows exposed to high Alpine pasture were estimated to account for more than twice the values of the lowland resting requirements. The data suggest a certain decline in these requirements by long-term adaptation. Feed-conversion efficiency not only declined along with the experiment but was also lower for the pastured cows during the whole Alpine sojourn. Contrary to the lowland period, utilization of dietary nitrogen for milk nitrogen output was significantly lower in pastured cows, accounting for 19.3% on average, as compared to 27.3% measured indoors. This was a consequence of the inevitably higher nitrogen intake in order to ensure a sufficient energy intake from pasture at nevertheless slightly lower milk nitrogen output.