Effect of a reused CIDR in the pregnancy rate of postpartum primiparous beef cows according to the body condition score

The body condition score (BCS) and serum progesterone concentration are important points to the success of fixed time artificial insemination (FTAI) programs in beef cows. In this way, the aim of the present work was to evaluate the pregnancy rate of postpartum primiparous Bos taurus beef cows with BCS <= 3.0 or >3.0 submitted to fixed time artificial insemination using a new or second use CIDR. Primiparous cows (n=237), received a new (New CIDR, n=122) or second use (Used CIDR, n=115) CIDR and 2mg of estradiol benzoate on day 0. All cows received an injection of 12.5mg of dinoprost on day 7 and 0.5mg of estradiol cypionate on day 9, when CIDR was removed. Also, on day 9 calves were separated from their dams until FTAI, 48h after CIDR removal. Ultrasonographic pregnancy evaluation was performed 35 days after FTAI. The overall pregnancy rate was 48.1% (114/237). Regardless of BCS, the difference in pregnancy rate almost reached significance (P=0.057) between groups; 54% (62/122), for New CIDR and 41% for Used CIDR group. When including the BCS effect, no differences were observed between groups. However, a tendecy (P=0.087) was observed for lower pregnancy rate in Used CIDR group in cows with BCS <= 3.0. Concluding, despite only a tendency, cows with low BCS submitted to FTAI with second use CIDR had lower pregnancy rate.