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Abstract
The objective was to investigate the influence of corpora lutea physical and functional
characteristics on pregnancy rates in bovine recipients synchronized for fixed-time
embryo transfer (FTET). Crossbred (Bos taurus taurus x Bos taurus indicus) nonlactating
cows and heifers (n=259) were treated with the following protocol: 2mg estradiol benzoate
(EB) plus an intravaginal progesterone device (CIDR 1.9g progesterone; Day 0); 400
IU equine chorionic gonadotropin (eCG; Day 5); prostaglandin F(2alpha) (PGF(2alpha))
and CIDR withdrawal (Day 8); and 1mg EB (Day 9). Ovarian ultrasonography and blood
sample collections were performed on Day 17. Of the 259 cattle initially treated,
197 (76.1%) were suitable recipients; they received a single, fresh, quality grade
1 or 2 in vivo-derived (n=90) or in vitro-produced (n=87) embryo on Day 17. Pregnancy
rates (23 d after embryo transfer) were higher for in vivo-derived embryos than for
in vitro-produced embryos (58.8% vs. 31.0%, respectively; P<0.001). Mean (+/-SD) plasma
progesterone (P(4)) concentration was higher in cattle that became pregnant than that
in nonpregnant cattle (5.2+/-5.0 vs. 3.8+/-2.4 ng/mL; P=0.02). Mean pixel values (71.8+/-1.3
vs. 71.2+/-1.1) and pixel heterogeneity (14.8+/-0.3 vs. 14.5+/-0.5) were similar between
pregnant and nonpregnant recipients (P>0.10). No significant relationship was detected
between pregnancy outcome and plasma P(4), corpus luteum area, or corpus luteum echotexture.
Embryo type, however, affected the odds of pregnancy. In conclusion, corpus luteum-related
traits were poor predictors of pregnancy in recipients. The type of embryo, however,
was a major factor affecting pregnancy outcome.