17 MANIPULATION OF PROESTRUS PERIOD BY EXOGENOUS GONADOTROPIN AND ESTRADIOL DURING TIMED ARTIFICIAL INSEMINATION PROTOCOL IN SUCKLED BEEF COWS

Abstract

The objective of this study was to evaluate the effect of eCG or estradiol cypionate (ECP) during the proestrus period on estrus occurrence, ovarian responses, and pregnancy per AI (P/AI) in suckled Bos indicus beef cows subjected to timed AI (TAI) protocols. A total of 393 cows in random stages of estrus (Day 0), received an intravaginal progesterone (P4) device (1.9 g of P4; CIDR®, Pfizer Animal Health, New York, NY, USA) and 2.0 mg of estradiol benzoate IM (EB; Gonadiol®, MDS Animal Health). Eight days later, the P4 devices were removed, and cows were given 0.15 mg of d-cloprostenol (Prostaglandina Tortuga®, Tortuga Companhia Zootécnica Agrária, São Paulo, Brazil). At this time, cows were randomly assigned to 1 of 3 treatments: 300 IU of eCG (Group eCG; n = 138), 300 IU of eCG plus 1 mg of ECP IM (Group eCG+ECP; n = 124), or no additional treatment (control; n = 131). Cows were timed inseminated 48 h after P4 device removal and were administrated simultaneously 100 µg of gonadorelin IM (Profertil®, Tortuga Companhia Zootécnica Agrária). A subset of cows (n = 98) were evaluated according to the occurrence of estrus between the P4 device removal and TAI and their ovarian follicles were evaluated by ultrasound at P4 device removal and corpus luteum (5 days after TAI). The data were analyzed using the GLIMMIX procedure of SAS (SAS Institute Inc., Cary, NC, USA) and differences with P < 0.05 were considered statistically significant. A greater pregnancy rate (P/AI; P = 0.04) was observed in cows receiving the eCG treatment at P4 device removal [eCG = 42% (58/138) and eCG+ECP = 50.8% (63/124)] than cows from the control group [29.8% (39/131)]. There was no additive effect of ECP supplementation on P/AI. Cows that received ECP [eCG+ECP = 56.3% (18/32)] displayed more estrus (P = 0.002) compared with those receiving eCG [eCG = 23.5% (8/34)] or only GnRH at TAI [control = 15.6% (5/32)]. In addition, regardless of the ECP supplementation, cows receiving the eCG treatment at P4 device removal [eCG = 85.3% (29/34) and eCG+ECP = 90.1% (29/32)] presented a greater ovulation rate than cows from the control group [65.6% (21/32)]. In conclusion, exogenous estradiol administrated at device removal increased the proportion of suckled Bos indicus cows that displayed estrus. Cows receiving eCG treatment (with or without estradiol supplementation) had greater ovulatory and pregnancy responses after the estradiol/P4-based synchronization protocol.