Rubrik: Science Life
Sinking milk yield during the Alp-grazing season
Healthier cheese makes up for losses
Published: 16.03.2006 06:00
Modified: 15.03.2006 22:16
Alpine air is too thin for milk cows. They eat less, give less milk and lose weight. Nevertheless, cheese made from the milk of cows that are grazed on Alpine meadows has a great advantage that compensates for the losses: it contains healthy fatty acids.
Cows belong to the picture of the Alps in Switzerland. The metallic tinkle of cow bells, cow dung in the middle of the hiking trails, the bearded cowherd sitting in the smoky hut making cheese in his copper cauldron over an open fire ... that's the cliché.
Scientists at the ETH Institute Institute of Animal Sciences have discovered that today's milk cows on the Alpine pastures are not just happy. The thin air in these altitudes is a far greater problem for cows than has been assumed until now. Both the cows that graze freely as well as those kept in the byre and fed with cut grass have a lower intake of nutryments and energy than their counterparts in the valleys. Nor does this seem to hold merely during a first acclimation phase. Seven weeks after being transported to an ETH trial Alp, the Alp Weissenstein in the Grisons, the cows had still not fully adapted to their changed environmental conditions (1) .Falling milk yield at higher altitudes
The quantity of milk the cows give declines perceptibly. By comparison with cows in the plains that are fed on typical silage rations, the milk yield of cows on the Alpine meadows sinks by roughly 25 per cent. This decrease also happened with a group of cows that were kept in the byre during the Alp-grazing season. For the scientists, this is a clear indication that the thin air is responsible for the sinking milk yields.
In addition to the quantity, the protein content of the milk also falls, something that is unfavourable, for instance, in cheese production. The coagulation of the cheese, i.e. the point at which the milk curdles after the rennet has been added, is less firm. With the increasing age of the Alpine sward–when the plants contain a lot of indigestible fibre–the characteristic protein, important for the production of cheese, declines even further.Lacklustre appetites
"The building up of protein in the udder uses up a lot of energy," says ETH Professor Michael Kreuzer, "and the thin air also increases the amount of energy needed." But cows take up rather less nutriment (or energy) on Alpine pastures. This lessens the protein content of the milk. Moreover, oxygen deficiency spoils the herbivores' appetite and so they eat less, regardless of climate and of the fodder's availability and quality. Other researchers have found the same thing happens also to humans. Above 3,000 metres mountain climbers become more sensitive to the tastes of dextrose and table salt. This results in them eating less and, consequently, to a 40 per cent lower energy intake.
"Cows might feel similar effects," explains Kreuzer. In order to furnish their organism with sufficient energy the animals mobilise their bodies' own reserves of fat and muscular protein. This causes them to lose body weight.
Calculations show that high altitude grazing of the cows is still worthwile. Among other things, the milk from cows grazed in high altitude contains more unsaturated fatty acids, above all the omega-3 fatty acids, than the milk of cows grazed in the plains. Why this should be so is a subject of research for animal scientists. Such fatty acids occur, for instance, in fish or linseed and are considered healthy as they efficiently prevent cardiovascular diseases.Agrarian policy promotes valley herding
With the argument of this additional value–natural functional food, so to speak–Alpine cowherds can compensate for the lower milk yields, says Kreuzer. It would therefore be a pity if cows could only be grazed in the lowlands, even though this is precisely what current agrarian policy calls for. In order to balance the negative effects of Alpine grazing, advises the ETH professor, the cows should be driven up to the Alpine meadows as early in the year as possible. The best time would be when the vegetation is still young and grass and herbs contain less indigestible fibre. Owners could also draw more profit from the Alp-grazing season if they set up a rotational grazing system, whereby the animals were herded higher up in stages, as grazing pastures gradually emerged from their winter cover.
For their investigation the scientists at ETH compared three groups of six typical Swiss Brown cows. One group served as a control group and were fed with control fodder of well-known composition during the entire experiment. After the preparation phase with the control fodder, the two other groups were given only grass. One group was fed in the byre with cut grass while the other was allowed to graze freely. During the summer the two grass-fed groups were taken up to the Weissenstein Alp at 2,000 metres. The control group remained in the plains, under observation, at 400 metres above sea level.Footnotes: