Supplementation of dairy cows grazing an alpine pasture. Effect of concentrate level on milk production, body condition and rennet coagulation properties

The aim of this research was to measure, in terms of milk quantity and quality and variations of live weight (LW) and body condition score (BCS), the effect of offering different levels of concentrate to dairy cows grazing at high altitude. The experiment, which lasted 8 weeks, was conducted on a pasture located at an altitude of 1800-2200 m. Three groups of 10 Italian brown cows were fed different levels of concentrate offered above a production of 7 kg energy corrected milk (ECM), which was assumed to be provided by the pasture: group L, 1 kg of concentrate as fed every 2.3 kg ECM; group M, 1 kg every 2.0 kg ECM; and group H, 1 kg every 1.7 kg ECM. Botanical and chemical measurements were performed on the grazed grass and temperature and rainfall recorded. The nutritive value of the herbage fell from 0.90 UFL/kg DM at the beginning of the trial to 0.65 UFL/kg DM at the end. The mean daily production of ECM was more than 1 kg higher for group H with respect to the other two groups (mean 17.2 kg). The protein level increased slightly with the increasing proportion of concentrate (difference 0.11 percentage points between groups L and H). The times for aggregation (k20) and gel firmness (a30) were better, but not significantly, in the milk from group H. The mean changes in LW and BCS were nil for group L and positive and increasing with the increasing level of concentrate in groups M and H. According to estimates based on productive performance and BCS variations, the overall mean herbage consumption was 12.2 kg DM, which would have supported a production of 7.4 kg ECM.