An optimal transition period is a determining factor for the health of dairy cows, and physiological changes during this period can alter subsequent fertility. Body condition score is a useful tool in monitoring the nutritional status of dairy cows, and Body condition change is related to postpartum health. The main objective of this survey is to study the relationship between calving interval and body condition change during the dry period and the first month of lactation and their relationship to the chance of pregnancy following the first service, fertility, occurrence of periparturient diseases, and culling in dairy cows. The study was conducted on the recorded data of 3820 Holstein dairy cows that calved between 2020 to 2023 on two large-scale dairy farms situated in Varamin. The difference between body condition score at dry-off and calving and the time of calving to the first month was calculated and based on that, the cows were divided into 5 groups and the relationships were computed by statistical tests. According to the results, longer calving intervals were related to a greater loss of body condition score during the dry period and early lactation (p<0.001). Cows with a calving-to-pregnancy interval shorter than 130 d had more chance of maintaining or gaining body condition during the dry period (P<0.001) and 30 days after calving (P=0.05). Body condition score loss had a negative effect on reproductive performance and fertility and it also increased the risk of peripartum disorders occurrence and the chance of being culled (P<0.05).

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