Evaluation of Corpus Luteum and Plasma Progesterone the Day before Embryo Transfer as an Index for Recipient Selection in Dairy Cows

Abstract

The aim of the present study was to evaluate the effects of synchronization method, season, parity, corpus luteum (CL) size, and progesterone (P4) levels on the pregnancy rate after bovine embryo transfer (ET). Among 165 recipient candidates who received 1 of 2s estrus synchronization treatments, 96 heifers and 43 cows were selected through rectal examination and used as recipients. The day before ET, the CL size and plasma P4 concentration were evaluated. The CL sizes and plasma P4 levels were not different between the selected and unselected candidates, and the pregnancy rates with the two synchronization methods were not different. However, the pregnancy rates were higher in heifers than in lactating cows, and also higher after ET performed from September to February than from March to August (p < 0.05). The recipients with a CL larger than 1.5 cm showed statistically higher pregnancy rates, and although there was no statistical significance, the pregnancy rate was higher when the plasma P4 levels were between 2.0 and 4.0 ng/mL. Exposure to a stressful environment and repeated manipulations can reduce the success rate of ET, and recipient selection with an optimal CL size and P4 level can increase the success rate of ET.

Keywords: corpus luteum; embryo transfer; estrus synchronization; pregnancy rate; progesterone.

Figure 1

Diagram of two estrus synchronization protocols for embryo transfer (ET) and recipient evaluation with corpus luteum (CL) sizing and progesterone (P4) measuring; CIDR = insertion of an intravaginal device with 1.38 g of progesterone, EB = injection of estradiol benzoate, PGF2α = injection of prostaglandin F2α, GnRH = injection of gonadotropin-releasing hormone.

Figure 2

Corpus luteum (CL) of unselected, unpregnant, and pregnant recipients. The ultrasound CL images of were recorded the day before ET, and the operator performed ET without any notification of the evaluation results. (A) The candidates with poor ovarian structures palpated by rectal examination were excluded. (B) The representative figures of the selected recipients are shown in each category according to the pregnancy and CL size: CL-1 (≤1.5 cm), CL-2 (>1.5 cm and ≤2.5 cm), and CL-3 (>2.5 cm). White arrows indicate the presence of CLs. (C) Among the selected recipients, two had cavitary CL with high P4 concentrations, but were not pregnant.