Calving date, body condition score, and response to a timed artificial insemination protocol in first-calving beef cows

In experiment I, it was evaluated the body condition score (BCS) change during pre and post-partum in 155 heifers, inseminated to calve from September to December. The BCS was monthly evaluated from June to February, during the pre and post-partum periods. In experiment II, 538 primiparous cows were synchronized with a timed artificial insemination (TAI) protocol which used estradiol associated with an intravaginal progesterone device (CIDR (R)). The cyclicity, synchronization, and conception rates were evaluated by ultrasound. In experiment I, the animals that calved earlier had higher (P < 0.001) reduction on BCS. In experiment II, it was observed higher BCS (P < 0.0001) in cows with lower days in postpartum, higher (P < 0.05) synchronization rate in cows with a better BCS, and also an increase (P < 0.0001) in conception rate as BCS got better (increase in six percentual points in conception for each increase of 0.25 in BCS). Beef heifers should not calve earlier when is planned to submitt these animals to TAI at the beginning of the next breeding season.