Effect of type and level of supplement on performance of dairy cows grazing on alpine pasture

An experiment was carried out on 32 dairy cows (average yield 21.9 ± 2.7 kg/d) grazing on summer alpine pasture, in order to examine the effect of two types of supplement - Starchy (42% of cereal) and Fibrous (41% of beet pulp) - both provided at two different levels - Low (1 kg of supplement per 5.0 kg of energy corrected milk (ECM)) and High (1 kg of supplement per 3.3 kg of ECM) - on herbage intake, milk yield and quality. The supplement was distributed twice a day, during milking, at a constant level throughout the experiment (July and August), as calculated according to the daily milk yield in a one-week preliminary period. Meteorological measurements, herbage quality and availability, herbage intake, animal body condition score (BCS), milk yield, chemical and rheological traits were determined. The herbage intake was higher (11.9 kg organic matter (OM)/d) with the Fibrous supplement at Low level. Even if the supplementation covered up to one third of the total intake of OM, none of the experimental groups increased BCS, and the Starchy-Low group showed a decrease in BCS significantly different from zero. The increase in the level of supplementation (from 3.5 to 5.0 kg OM/d in Low and High groups, respectively) improved the ECM yield by an average of 1.2 kg/d (P<0.05), without significant changes in the chemical composition of the milk, while the supplement type had no significant effects on either milk yield or composition. The mean coagulation properties were better with the Fibrous supplement as compared to the Starchy one - rennet clotting time (r): 16′24″ vs 19′15″ (P<0.05), time for aggregation (K20): 5′03″ vs 6′45″ (n.s.), gel firmness (a30): 26.1 mm vs 20.8 mm (P<0.05) - without significant differences derived from the level of supplementation.