Protein composition, plasmin activity and cheesemaking properties of cows' milk produced at two altitudes from hay of lowland and high-alpine origins

Abstract

The influence of high altitude, alpine origin of the forage and roughage-only diets on milk protein content and composition, plasmin activity and cheesemaking properties was investigated. There were four treatment groups, each consisting of six dairy cows in early to mid-lactation. Two groups were fed only with hay ad libitum either at 2000 m or at 400 m a.s.l. One group, kept in the lowlands, was pair-fed to the alpine-site group and another group received a mixed diet of silages, hay and concentrates. Two hay types, harvested either at the alpine site or in the lowlands, were offered to all cows fed with hay alone, following a change-over design in three periods each of 3 weeks. In the respective third week, milk was sampled at every milking. Hay of alpine origin significantly reduced milk protein, in particular whey proteins, which is why the casein number increased. κ-Casein proportion in total casein was reduced and its glycosylation was increased by the alpine hay. The apparent plasminogen-derived activity was reduced when alpine hay was given, but apparent plasmin activity and rennet coagulation properties of the milk were not affected by hay type. Independent of hay type, the high altitude group showed a significantly reduced milk protein content, lower glycosylation of κ-casein and impaired rennet coagulation properties. For several of the traits, the trend was the same in the pair-fed group. There was no effect of altitude on apparent plasmin activity. Hay-alone v. the mixed diet resulted initially in marked declines in milk protein content but did not impair cheesemaking properties. Thus the extensive diet without concentrates, typical of high-alpine conditions, contributed less to the overall effect of extensive alpine v. intensive lowland feeding systems than hay quality and altitude did. In conclusion, certain positive influences of the alpine sojourn of cows on cheese processing quality are overruled by the major adverse impact of lower milk protein content.

Contribution of diet type and pasture conditions to the influence of high altitude grazing on intake, performance and composition and renneting properties of the milk of cows

“…This allowed the separation of direct altitude effects and diet effects, but was only possible with hay and under indoor conditions. The results indicated that diet affects performance, milk composition and cheesemaking properties similarly or even more than altitude as such [31,33]. However, altitude effects could be more pronounced on pasture, and interactions with maturity of the sward may mask either altitude or diet type effects.…”

“…Hard cheese is an important product manufactured in these systems; thus milk protein and fat contents and, particularly, rennet coagulation properties are the economic basis of these farmers' success. The milk protein content is often considerably depressed at high altitude [14,33,45], although this is not a general rule [43]. While other milk quality changes are clearly advantageous [29,32], protein quality and cheese-making properties have been reported to be adversely influenced by high alpine sojourn of cows [5,33].…”

“…The milk protein content is often considerably depressed at high altitude [14,33,45], although this is not a general rule [43]. While other milk quality changes are clearly advantageous [29,32], protein quality and cheese-making properties have been reported to be adversely influenced by high alpine sojourn of cows [5,33]. It is still unclear if and how milk activity of plasmin, as one important endogenous protease potentially influencing curd firmness and cheese-ripening, and its precursor, plasminogen, are influenced by high altitude grazing [12,33].…”

“…A first experiment compared standardised forages grown at two different altitudes and fed alternatively at both altitudes, and included the comparison with a typical silage-concentrate lowland diet [31,33]. This allowed the separation of direct altitude effects and diet effects, but was only possible with hay and under indoor conditions.…”

Milk quality – a future approach from a researcher’s point of view

“…Milk from pasture has in several studies led to dairy products which have often been regarded as better or as having different properties compared to products made from milk based on indoor feeding (Bartsch et al, 1976;Buchin et al, 1998;Bugaud et al, 2001;Jaros et al, 2001;Coulon et al, 2004;Hauswirth et al, 2004;Lieber et al, 2005 There is a particular interest among researchers for further studies on the effect of pasture on the milk quality and on the quality of the dairy products. We therefore believe that part of the future approach to milk quality will take this into account and lead to better understanding of how feeding may differentiate and influence the milk quality and the quality of the dairy products.…”