Reproduction in Domestic Animals - Facultad de Ciencias Veterinarias

16 t h International Congress on Animal Reproduction
32 Poster Abstracts
Nelore cows were subjected to calf removal for 48 h and divided into
2 groups: GPE/eCG group (n=10) and GPG/eCG group (n=10). At
random stages of the estrous cycle (D-8) animals of the GPE/eCG
group were treated with a GnRH agonist (50 μg lecirelin, i.m.). Seven
days later (D-1) they received 400 IU eCG, immediately after PGF 2 α
treatment (250 μg d-cloprostenol, i.m.), and on Day 0 (D0), 1.0 mg
estradiol benzoate (EB). Cows of the GPG/eCG group were similarly
treated as those of the GPE/eCG group, except that EB was replaced
with a second dose of GnRH. Ovarian ultrasonography was performed
and blood samples were collected on days of hormone administration,
to allow retrospective discrimination of cows based on the presence or
absence of P4 priming, prior to induced ovulation. All animals were
challenged with oxytocin (OT, 50 IU; i.v.) 6, 9, 12, 15 and 18 d after
EB (GPE/eCG group) or GnRH (GPG/eCG group) administration and
blood samples were collected before and 30 min after OT. Frequency
distribution of animals, which underwent luteolysis before D18 was
analyzed by the chi-squared test. ANOVA was used to estimate the
effect of treatment, P4 priming and interactions for discrete variables.
Split-plot ANOVA was used to estimate treatment effect, P4 priming,
day of the estrous cycle and interactions for continuous variables. The
mean P4 plasma concentration during synchronization was higher
(p