Ciclicity induction protocols in Nelore zebu heifers using injectable long-acting progesterone

The puberty induction (PI) in Zebu-heifers using an intravaginal progesterone (P4) device associated with an estradiol administration increase the cyclicity and conception rate at Timed Artificial Insemination (TAI; Sa Filho, et al., 2015, doi:10.1016/j.anireprosci.2015.06.024). However, there is little information about the use of injectable long-action progesterone in PI protocols. Thus, this work aim to evaluate the efficacy of PI protocols using injectable long-acting progesterone (Sincrogest® Injetavel, Ourofino Saude Animal, SP, Brazil) or an intravaginal P4 device (Sincrogest®, Ourofino). The experiment 1 was conducted at three different farms at southeast of Mato Grasso state in Brazil. About 557 Nelore heifers (BCS: 3.42 ± 0,15) aged 24.0 ± 3.10 months and without corpus luteum (CL) at D–24 were randomized in two experimental groups: 1) P4 Device group (N = 281) and 2) Injectable long-action P4 group (N = 276). At D–24, cows from P4 Device group received a Sincrogest® previously used for 24 days (4th use) and the Injectable long-action P4 group received 150 mg IM of injectable P4 (Sincrogest® Injetavel). At D–12 the P4 devices were removed and all the heifers from both groups received 1 mg IM of estradiol cypionate (SincroCP, Ourofino). After 12 days (D0) all the heifers received the same TAI protocol [D0 = 2mg estradiol benzoate (Sincrodiol, Ourofino) and insertion of the Sincrogest®; D8 = Sincrogest® were removed, 530 ug of cloprostenol sodium (Sincrocio, Ourofino), 1 mg of SincroCP and 300 IU of eCG (SincroeCG, Ourofino)]. All the timed inseminations were performed 48h after the Sincrogest® has been removed. At D–24 and D0 the presence of CL, as well as at D40 the pregnancy, was evaluated by ultrasonography. The statistical analyses were performed using the GLIMMIX procedure of SAS® (version 9.3). There was no difference on the presence of CL between the groups [P4 device group: 80.8% (227/281) and Injectable long-action P4 group: 82.6% (228/276); P = 0.34]. Also, the conception rate was similar in both groups [P4 device group: 50.2% (141/281) and long-action P4 group: 51.4% (142/276); P = 0.75]. In Experiment 2, 617 heifers in two different farms with unknown ciclicity status at D–24 were evaluated with the same experimental design of experiment 1. There was a treatment*farm interaction (P = 0.04) but no difference on presence of CL at D0 [P4 device group: 83.0% (258/311) and Injectable long-action P4 group: 75.8% (232/306); P = 0.10] and conception rate [P4 device group: 39.5% (123/311) Injectable long-action P4 group: 33.0% (101/306); P = 0.48] were found between the experimental groups. In conclusion, the PI protocol using Sincrogest® Injetavel has the same efficacy of PI protocol using P4 device previously used for 24 days and could be strategically adopted at heifer’s breeding programs.