The performance of Holstein-Friesian cows calved in winter and summer was compared on two farms. The milk yield in early lactation (in first 100 days) differed; the cows calved in winter produced more milk (0-10%) than the cows calved in summer. The difference is mainly expected for multiparous cows. The maximum daily milk yield and the standard lactation performance (kg/305 days) differed only in the multiparous cows, the production of cows calved in winter was higher. No significant difference in FCM performance (kg/305 days, corrected for 4% fat) was detected. In the first 100 days, the protein content of the milk may also be more favourable after winter calving, but this does not apply to total lactation. No clear difference was found in the somatic cell count of milk. The time of calving (winter or summer) affected also the reproductive performance of the cows, particularly the length of the service period. There were significant differences in the frequency of the service period shorter than 60 days (very good), and longer than 120 days (unfavourable), both in case of primiparous and multiparous cows. After winter calving, the favourable service period and after summer calving, the unfavourable service period occurred in more cows. The results confirm the importance of protecting of dairy cows from summer heat stress, even under the temperate climate.

Holstein-Friesian, heat stress, milk production, reproduction

biology

Presentation: poster