Comparative conception rate of cyclic Nelore heifers treated with Cronipres® mono dose devices containing 0.558 g or 1 g progesterone

The aim of this study was to comparative evaluate the rates of estrus and pregnancy of cyclic Nelore heifers subjected to TAI using Cronipres® Mono Dose intravaginal device containing 0.558 g or 1 g progesterone (P4; Biogenesis Bago, Brazil). A total of 288 cyclic Nelore heifers aging 18-24 months old, with average body weight 316.1 ± 2.0 kg and average BCS 3.15 ± 0.02 (1-4 point scale) from two commercial farms located in Nova Bandeirantes, Mato Grosso State, Brazil were used herein. All heifers had a CL and were treated with the same protocol to synchronize follicular wave emergence and ovulation for TAI, except for the concentration of P4 of the intravaginal device. Briefly, at random days of the estrous cycle (D0) heifers were homogenously (BCS, body weight and age) distributed to receive one Cronipres® Mono Dose intravaginal device containing 0.558 g or 1 g P4. At that same time, they also received 1 mg estradiol benzoato (Bioestrogen®, Biogenesis Bago, Brazil) and 75 µg D-Cloprostenol (Croniben®, Biogenesis Bago, Brazil) IM. On D8, the device was removed and 75 µg DCloprostenol, 200 IU eCG (Ecegon®, Biogenesis Bago, Brazil) and 0.5 mg estradiol cypionate (Croni-Cip®, Biogenesis Bago, Brazil) IM were administered. On D8 heifers were also painted with chalk on their tailheads, and removal of chalk was used as an indication of estrus. TAI was performed by a single veterinary 48h after device withdrawal (D10) and concomitant with estrus determination by visual analysis of tail-paint score. Semen of a single Aberdeen Angus bull was used. Pregnancy diagnosis was done 40 days after TAI (Mindray DP2200VET). Data was analyzed by logistic regression (PROC GLIMMIX from SAS). Similar rates of estrus (P = 0.61) and conception (P = 0.16) were observed when heifers were treated with Cronipres® Mono Dose device containing 0.558 g P4 [estrus: 76.2% (109/143) and conception: 45.8% (65/142)] or 1 g P4 [estrus: 73.1% (106/145) and conception: 54.2% (78/144)]. Thus, increasing P4 concentration from 0.558 g to 1 g in the intravaginal device did not affect negatively conception rate in zebu heifers. Therefore, it is possible to infer that both Cronipres® Mono Dose devices (0.558 g and 1 g P4) can be used in TAI protocols for cyclic Nelore heifers, resulting similar rates of estrus and conception.