Diferentes vias e momentos de aplicação de gonadotrofina coriônica equina em protocolo de inseminação artificial em tempo fixo para vacas

Abstract

The study aimed to evaluate different routes and times of application of equine chorionic gonadotropin (eCG) in Fixed-Time Artificial Insemination (FTAI) protocols for cows. Two experiments were carried out: in experiment I, 70 Nellore cows received, on day zero of the protocol (D0), intravaginal progesterone devices (PRIMER®) and 3mg of estradiol benzoate (EB); on D9 of the protocol the devices were removed, then 150μg of a synthetic analogue of prostaglandin F2α (PGF2α) and the d-cloprostenol were applied, and the animals were randomly distributed in three treatments (T), as follows: T1 (n=22): application of 300IU of eCG (100% of dose) by intramuscular route (IM); T2 (n=23): application of 90UI (30% of dose) of eCG in acupoint Hou Hai and T3 (n=25): application of 90UI (30% of dose) of eCG in false acupoint (IM). On D10 all animals received 1mg of gonadotropin-releasing hormone (GnRH) by intramuscular route (IM) and the FTAI was carried out, 52 hours after the removal of the PRIMER®. The evaluations of follicular growth and ovulation time were carried out in seven, seven, and eight animals in T1, T2 and T3 respectively, in intervals of 24 hours, by ultrasonography, beginning immediately after the removal of devices and ended 24 hours after ovulation. The corpus luteum (CL) evaluations were made nine days after the removal of PRIMER®, by ultrasonographic evaluation. The pregnancy diagnosis was carried out 30 days after FTAI in all animals. The completely randomized design was used, the data was assessed according to normality by Shapiro-Wilk test. For the quantitative variables that presented normal distribution, ANOVA was used, at probability of 5%. For the variables that did not present normal distribution, Kruskal-Wallis test was used, at probability of 5%. There was no difference (P>0.05) to: the interval from device removal to ovulation (T1=72.36±13.62; T2=51.35±35.08 and T3=51.03±32,55h); diameter of the largest follicle on D9 (T1=12.5±0.40; T2=8.5±0.59 and T3=8.7±0,57mm); diameter of ovulatory follicle (T1=15.8±0.33; T2=10.2±0.72 and T3=10.8±0,70mm) and the second largest follicle (T1=9.1±0.32; T2=6.0±0.55 and T3=5.0±0,46mm); follicle growth rate (T1=1.20±0.80; T2=0.50±0.50 and T3=0.80±0,80mm/day); ovulation rate (%) (T1=100; T2=71 and T3=75%); corpus luteum area (T1=2.66±1.45; T2=2.34±1.35 and T3=1.96±1,75cm2) and pregnancy rate (68; 52 and 56% for T1, T2 and T3, respectively). The cost of the protocol in dollars, per animal, was USD 10.67 (T1) and USD 8.50 (T2 and T3). In experiment II, 76 Girolando cows received, on day zero of the protocol (D0), intravaginal progesterone devices (PRIMER®) and 3mg of estradiol benzoate (EB), by IM route. On D9 the devices were removed, then 150μg of d-cloprostenol were applied, and the animals were distributed in three treatments (T), as follows: T1 (n=25): application of 400IU of eCG at the time of removal of PRIMER®; T2 (n=23): application of 400UI of eCG, 48 hours before the removal of PRIMER® and T3 (n=25): application of 400UI of eCG, 24 hours before the removal of PRIMER®. On D10 of the protocol all animals received 1mg of GnRH, all hormones were administrated by IM route. The animals were inseminated 52 hours after the removal of the device. The parameters of follicular growth and ovulation time were evaluated in 10 animals per treatment. The corpus luteum area and pregnancy rates were evaluated in all the animals as described in the previous experiment. The completely randomized design was used, the variables with normal distribution were evaluated by Analysis of Variance at significance of 5% and for the variables that did not present normal distribution, Kruskal-Wallis test was used, at probability of 5%. There were no differences (P> 0.05) among T1, T2 and T3 respectively, for the interval from device removal to ovulation (77.05±10.06; 70.81±11.58; 69.83±0.95h); diameter of the largest follicle on D9 (9.17±2.41; 11.88±2.82; 11.58±2.46mm); diameters of the ovulatory follicle (13.82±2.11; 15.95±2.40; 15.67±2.02mm) and the second largest follicle (8.07±1.54; 7.35±1.94; 7.05±1.54mm); follicle growth rate (1.40±0.07; 1.32±0.04; 1.40±0.06 mm/day); ovulation rate (100; 100 and 90%); corpus luteum area (1.78±1.19; 2.44 ± 1.20; 2.58±1,42cm2) and pregnancy rate (40, 24 and 36%). The use of 90UI of eCG, corresponding to 30% of the total dose used for cattle in synchronization protocols, applied in acupoint Hou Hai or in false acupoint intramuscular, were efficient in the estrus synchronization. Thus, it is possible to reduce the dose, providing a reduction in the cost of the protocol as well as a lower effective dose. The application of eCG 24 hours or 48 hours prior to the removal of the implant did not improve protocol efficiency and it can be carried out at the time of removal of the progesterone device, with less handling of animals.