184 PREGNANCY RATES AFTER ESTRUS SYNCHRONIZATION TREATMENT WITH NEW AND REUSED CIDR-B DEVICES

Abstract

It is not well known whether used CIDR devices containing progesterone (P4) combined with estradiol benzoate (EB) and prostaglandin F2α (PGF) can provide acceptable estrus synchronization rates (ESR) and pregnancy rates (PR) in ET or AI programs. Three experiments were designed to study the effect of new and used CIDR-B, with different P4, EB and PGF treatments on ESR and PR in a reproductive program in beef cattle in a tropical climate. Experiment 1 was a control to evaluate ESR and PR in lactating recipient females. All cows (n = 284) were treated with a new 1.9-g CIDR (CIDR-B, InterAg, New Zealand), combined with 2 mg EB and 50 mg P4 on Day 0. CIDR devices were removed on Day 8 and all cows received 0.25 mg cloprostenol at that time. Estrus was expected to occur 24 h later. Seven days after estrus, all cows showing heat were examined by rectal palpation and those with a CL 15 mm in diameter or larger were selected to receive a frozen/thawed embryo (1.5 M ethylene glycol = EG) by nonsurgical direct transfer (DT). PR were determined by rectal palpation 60 d after estrus. Ninety percent of the cows displayed signs of estrus (256/284) and 40% of those that received a frozen embryo were pregnant (96/239). Experiment 2 was designed to evaluate ESR and PR in dry recipient cows treated with a used CIDR-B (first reuse). All cows (n = 274) were treated with a reused 1.9-g CIDR combined with 2 mg EB and 50 mg P4 on Day 0. CIDR devices were removed on Day 8 and all cows received 0.25 mg cloprostenol at that time. Estrus was expected to occur 24 h later. Seven days after estrus, all cows that showed estrus were rectally evaluated and those with a CL 15 mm in diameter or larger received a frozen/thawed embryo (1.5 M EG) by DT. A total of 93% of the treated cows showed signs of estrus (254/274) and 51% of those that received an embryo were pregnant (110/217). Experiment 3 was designed to evaluate ESR and PR in virgin heifers, treated with a used CIDR (second reuse). All heifers (n = 414) were treated with a reused 1.9-g CIDR combined with 1 mg EB on Day 0. CIDR devices were removed on Day 8 and all heifers were expected to show estrus 24 h later. Approximately 12 h after estrus, all heifers that showed signs of estrus were inseminated, using frozen/thawed semen from a single bull. Of the treated females, 78% showed signs of estrus (323/414) and 69% of the inseminated were pregnant (223/323). These results suggest that in a CIDR that was used in two previous occasions, there is still a remaining amount of P4 that allows estrus synchronization in heifers. Furthermore, the reutilization of CIDR-B devices can contribute to reduce the costs related to ET or AI programs in cattle. However, the diverse existing conditions among the 3 experimental groups in this study make a statistical comparison impossible. Therefore, further studies are needed, under controlled experimental conditions, to confirm the results obtained.