Changes in pasture and cow milk compositions during a summer transhumance in the western Italian Alps

Abstract

The changes occurring in pasture and milk compositions during summer grazing were studied following a transhumance of a dairy cattle herd in the western Italian Alps. During three consecutive grazing periods (P1, P2, and P3) the cows exploited, in sequence, mountain pastures located at 1200-1260 m a.s.l. (A1), alpine pastures at 2000-2200 m a.s.l. (A2), and then returned to A1 pastures. The botanical and nutritional compositions of pastures, as well as cow milk yield, gross composition and fatty acid (FA) profi le were assessed during the transhumance. Within the pastures, a cluster analysis allowed the recognition of five vegetation types and seven vegetation sub-types; their allocation and plant species composition differed among the exploited grazing areas. The average Pastoral Values were signifi cantly higher in the mountain (A1P1, A1P3) than in the alpine pastures (A2P2) due to the abundance of high- and medium-quality forage species such as Dactylis glomerata L., Polygonum bistorta L., and Festuca rubra s.l.. Nevertheless, the nutritional quality of the herbage offered to the animals did not differ between A1P1 and A2P2, while it was significantly higher in A1P3 due to a younger vegetation phenological stage. The nutritional parameters were found to be correlated to the pasture botanical composition and phenology: organic matter digestibility and net energy for lactation were correlated negatively to the phenological stage and the Specific Contribution (SC) of Poaceae and positively to the SC of Fabaceae and Asteraceae. Milk yield significantly declined while milk protein increased during the grazing season, following the advance of cows’ stage of lactation. Milk fat and lactose percentages did not vary significantly among the grazing periods. The same was also observed for milk FA, with the exception of palmitic acid, whose level was lower in A2P2 if compared to the other two periods. Significant correlations were found between the percentages of some FA in milk and the SC of the main botanical families of the grazed pastures. In particular, linoleic acid was negatively correlated with the SC of Poaceae and positively correlated with the SC of Fabaceae. Results showed that the changes in the nutritional composition of pastures depended on variations in pasture botanical composition and phenology at the time of grazing, and that such factors concurred with animal-related factors in affecting milk quality during the grazing season.