Induction of cyclicity in prepubertal nelore heifers using new or previously used Cronipres® mono dose devices originally containing 1 g P4

The aim of this study was to investigate the efficacy of using and reusing the intravaginal device Cronipres Mono Dose originally containing 1 g P4 (Biogenesis Bago, Brazil) to induce cyclicity in prepubertal Nelore heifers. A total of 227 Nelore heifers aging 16-24 months old, with minimum body weight of 250 kg and minimum BCS of 2.5 (1 to 4 point scale) from two commercial farms located in Nova Bandeirantes, Mato Grosso State, Brazil were evaluated by ultrasonography (uterus and ovaries; Mindray DP2200VET). Heifers without CL on their ovaries and with immature uterus (1 and 2, in a 1-4 scale of uterine thickness) were considered prepubertal and were subjected to treatments for cyclicity induction. Heifers were homogenously (BCS, body weight and age) distributed to receive (D0) a new or a previously used (for 8d) Cronipres Mono Dose device originally containing 1 g P4. The devices removal was performed after 10 days (D10) concomitant with the administration of 0.5 mg estradiol cypionate (Croni-Cip, Biogenesis Bago, Brazil) IM. All heifers were reevaluated (uterus and ovaries) 30 days after devices withdrawal (D40). Data was analyzed by logistic regression (PROC GLIMMIX from SAS). Similar average BCS (2.91 ± 0.02 and 2.91 ± 0.02; P = 0.77), body weight (269.0 ± 3.9 and 267.7 ± 3.9; P = 0.64) and score of uterine maturity on D0 (1.55 ± 0.05 and 1.53 ± 0.05; P = 0.64) were observed in heifers treated with new and previously used devices, respectively, demonstrating that an homogenous distribution between groups was guaranteed before treatment. At cyclicity evaluation 30 days after the end of treatment, it was observed increased score of uterine maturity in heifers of both groups compared to D0. No differences (P = 0.88) were observed regarding the uterine maturity of heifers treated with new (3.00 ± 0.06) and previously used (3.00 ± 0.06) devices. Moreover, similar percentage of heifers with CL on D40 was detected between groups (new device: 65.5%, previously used device: 68.7%; P = 0.55). Finally, the rate of induction of cyclicity was also similar (P = 0.99) between heifers treated with new (81.3%, 91/112) or previously used (81.7%, 94/115) devices. In conclusion, protocols with Cronipres Mono Dose devices containing 1 g P4 both new and previously used for 8d were equally efficient to induce cyclicity in prepubertal Nelore heifers.