Milk production from grazed pasture in mountainous regions of Austria - impact of calving season

Summary

The influence of calving season on milk yield, lactation length, composition of the diet, reproduction and nutrient supply for pasture-based systems in a mountainous region of Austria was examined with thirty-three dairy cows on an organic farm. Three groups of cows with a mean calving date of 17 November (group 1), 25 December (group 2) and 20 February (group 3) were compared. During winter periods the cows were housed and fed with grass silage, hay and a restrictive amount of concentrate. Cows were on pasture for 202 days in 2008 and 203 days in 2009 (177 day and night grazing days). The pasture area was continuously grazed
at an average sward height of 4.7 cm. Calving in February (group 3) significantly depressed lactation length and milk-fat yield and tended to decrease energy-corrected-milk yield. From group 1 to 3 the amount of concentrate fed per cow decreased from 669 to 373 kg DM y-1 and the grazed pasture proportion increased from 43 to 50% of total feeding ration per year. Calving date had no effects on reproductive performance and frequency of veterinary treatments. However, at the beginning of the grazing season live weight loss and contents of βHBA, FFA and AST were highest in blood samples of group 3.