title: The effect of equine chorionic gonadotropin on follicular size, luteal volume, circulating progesterone concentrations, and pregnancy rates in anestrous beef cows treated with a novel fixed-time artificial insemination protocol.
abstract: The objective was to determine the effects of eCG given on the day of, or 2 days before removal of an intravaginal progestin device, on ovarian follicle diameter, luteal volume, serum progesterone (P4) concentrations, and pregnancy per insemination in a fixed-time AI (FTAI) protocol. Lactating, anestrous, multiparous Bos taurus cross beef cows, 40 to 60 days postpartum, were given estradiol benzoate (2 mg im) and a progestin intravaginal device containing 250 mg of medroxyprogesterone acetate on Day 0 and cloprostenol (0.265 mg) on Day 6. Intravaginal devices were removed on Day 8 and GnRH (100 μg im) was given on Day 9, with timed AI 16 hours later. In experiment 1, cows were randomly assigned to receive 400 IU im eCG on Day 6 (eCG6; N = 8) or Day 8 (eCG8; N = 8), or to not receive eCG (control; N = 8). Dominant follicle diameter on Day 9 in the eCG6 group (10.0 ± 0.5 mm) was larger (P < 0.05) than in the eCG8 (8.6 ± 0.2 mm) or control (8.5 ± 0.4 mm) groups. Corpora lutea (CL) in all cows in the control group underwent premature luteolysis within 10 days after ovulation. Luteal volumes and P4 concentrations 10 and 15 days after ovulation were higher (P < 0.05) in the eCG6 group than in the eCG8 group. In experiment 2, the eCG6 (N = 121) and eCG8 (N = 125) protocols were compared in lactating anestrous cows that underwent FTAI. Pregnancy rate was higher (P < 0.05) in the cows that received eCG on Day 6 (27.3%; 33/121) than on Day 8 (16.0%; 20/125). Furthermore, CL volumes and P4 concentrations were higher (P < 0.05) in the eCG6 group (5784.0 ± 857.3 mm(3) and 8.1 ± 1.3 ng/mL, respectively) than in the eCG8 group (3220.9 ± 505.1 mm(3) and 4.5 ± 0.7 ng/mL, respectively). We concluded that eCG given 2 days before progestin removal in this FTAI protocol for anestrous beef cows increased diameter of the dominant follicle, luteal volume, serum P4 concentrations, and pregnancy rates.
authors.affiliation: Programa de Pós-Graduação em Ciência Animal, Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, UnB, Brasília, Distrito Federal, Brazil.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Dorneles Tortorella
authors.forename: Rogério
authors.initials: R
authors.lastname: Ferreira
authors.forename: Joabel
authors.initials: J
authors.lastname: Tonellotto Dos Santos
authors.forename: Olmiro
authors.initials: O
authors.lastname: Silveira de Andrade Neto
authors.forename: Marcos Henrique
authors.initials: MH
authors.lastname: Barreta
authors.forename: João Francisco
authors.initials: JF
authors.lastname: Oliveira
authors.forename: Paulo Bayard
authors.initials: PB
authors.lastname: Gonçalves
authors.forename: Jairo
authors.initials: J
authors.lastname: Pereira Neves
mesh_terms: D000780:Anestrus / Q000097:blood / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D002417:Cattle; D048429:Cell Size / Q000187:drug effects; D003338:Corpus Luteum / Q000033:anatomy & histology / Q000187:drug effects*; D004973:Estrus Synchronization / Q000379:methods / Q000502:physiology; D005260:Female; D006064:Gonadotropins, Equine / Q000494:pharmacology*; D007315:Insemination, Artificial / Q000379:methods* / Q000662:veterinary; D008297:Male; D009929:Organ Size / Q000187:drug effects; D009994:Osmolar Concentration; D006080:Ovarian Follicle / Q000166:cytology / Q000187:drug effects*; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000097:blood*; D013997:Time Factors
chemical_list: D006064:Gonadotropins, Equine; D011374:Progesterone