Reproductive performance of Bos indicus beef cows treated with different doses of equine chorionic gonadotropin at the end of a progesterone-estrogen based protocol for fixed-time artificial insemination

• Published in: Theriogenology Vol. 118; pp. 150 - 156
• Main Authors: Alvarez, Rafael Herrera, Pugliesi, Guilherme, Nogueira Natal, Fabio Luis, Rocha, Cecilia Constantino, Ataide Júnior, Gilmar Arantes, Ferreira Melo, Alfredo José, Otzuk, Ivani Posar, Alvarenga de Oliveira, Claudio, Humblot, Patrice
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-09-2018
• Subjects: Clinical Science; eCG; Fertility; Klinisk vetenskap; Nelore cows; TAI; Twin; eCG; Nelore cows; Fertility; TAI; Twin
• ISSN: 0093-691X; 1879-3231; 1879-3231
• DOI: 10.1016/j.theriogenology.2018.06.003

Two experiments were performed to evaluate the reproductive performance of zebu beef cows treated with different doses of eCG at the end of a progesterone (P4)/estrogen based protocol for timed artificial insemination (TAI). In Experiment 1, suckling Bos indicus Nelore cows (n = 261) received, on day 0, a progesterone (P4) intravaginal device (PD) and an injection of 1 mg estradiol benzoate (EB). On day 8, the PD was removed, 500 μg of cloprostenol was injected, and cows were assigned to one of the following groups: Control (no treatment), 300 (300 IU of eCG), 600 (600 IU of eCG), and 900 (900 IU of eCG). On day 9, all cows received 1 mg EB and TAI performed 54–56 h after cloprostenol injection. A pregnancy diagnosis was done by ultrasound scanning 40 days after TAI, and the number of fetuses and calves was recorded at pregnancy diagnosis and at birth. More cows treated with eCG displayed estrus within 48 h after removal of the PD (42.3% vs. 11.6%, P < 0.01), and ovulated more than one follicle (42%, 58/138 vs. 1.8%, 1/54; P < 0.01). This effect on ovulation rate was dose dependent (P < 0.05). The pregnancy rate was affected only by cow parity (primiparous, 25.3% vs. multiparous, 48.9%; P < 0.01). Twin pregnancy was higher (P < 0.01) in cows treated with eCG (42%, 58/138) than controls (0%, 0/54). However, few cows (33.3%) were able to keep both fetuses intact until birth. For evaluation of ovarian characteristics by B-mode and Doppler ultrasonography, 43 Nelore cows were submitted In Experiment 2 to the same four groups described in Experiment 1. Although no difference (P > 0.1) was observed for size and blood perfusion in the pre-ovulatory follicles, corpus luteum was larger and with greater blood perfusion (P < 0.05) in eCG-treated cows. In conclusion, eCG increased the number of double/multiple ovulations in a dose-dependent manner, induced larger and more vascularized corpora lutea, but did not affect the fertility of cyclic or anestrous cows. Although eCG results in twin pregnancies, most of cows underwet embryo/fetus loss and birth a single calf.
•The use of eCG remains controversial for TAI, particularly in cyclic cows.•Due to its FSH and LH activity, eCG could result in the birth of unwanted twin or multiple calves.•The number of ovulations increases as the dose of eCG increases in both, cyclic and anestrus cows eCG.•eCG does not seem to affect the pregnancy rate of cyclic or anestrous cows.•In cows treated wit eCG, less than 35% of twin or multiple pregnancies are preserved intact until calving.