Reproductive Performance in Cows with Extended Calving Interval*

Contents The effects of increased calving intervals on reproduction were studied in two herds. In Herd 1 cows were managed for 12‐ or 15‐month calving intervals and in Herd 2 for 12‐ or 18‐month intervals. Data from the study revealed that managing cows for a longer calving interval improved the fertility. Animals with a short interval needed more hormonal treatments to be inseminated on time due to anoestrus, compared to animals with longer intervals. Once the animals were inseminated there was a tendency for a higher conception rate at first AI in the 15‐month group compared with the 12‐month group. The cows in the 15‐month group needed a lower number of AIs per serviced cow and a shorter period from the first AI to conception. Culling due to fertility problems was more frequent in the 12‐month group. A longer period of days open did not imply an increased risk for development of cystic ovaries and did not result in weaker heat symptoms over time.