Reproduction, Fertility and Development Reproduction, Fertility and Development Society
Vertebrate reproductive science and technology


G. H. M. Araujo A , C. F. Moya-Araujo B , A. N. Rocha C , C. M. Burns C , S. D. Burns C and C. Meira A
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A School of Veterinary Medicine and Animal Science, São Paulo State University, UNESP, Botucatu, São Paulo, Brazil;

B School of Veterinary Medicine, FIO, Ourinhos, São Paulo, Brazil;

C Burns Ranch Inc., Menifee, CA, USA

Reproduction, Fertility and Development 22(1) 227-227
Published: 8 December 2009


The aim of the present study was to determine the effectiveness of the commercial progesterone to maintain the pregnancies in noncyclic recipient mares and if it helps to decrease the early embryonic death when used in cyclic pregnant recipient mares. A total of 199 mares were used during February to April of the 2008 breeding season at Burns Ranch. The mares were assigned to groups according to their reproductive status. Noncyclic (n = 42) mares were prepared as embryo transfer recipients using our standard protocol with estradiol cypionate (3 days, 10/6/4 mg, Wickliffe, USA) and long action progesterone (P4LA, 1500 mg, BET Labs, Lexington, KY, USA), and 157 naturally cyclic mares were used from Day 3 to 8 after ovulation as embryo transfer recipients. After embryo transfer, 134 of the 157 cyclic mares got pregnant at 15 days. Some of the pregnant mares (n = 43) were assigned to a progesterone-supplemented group; these mares were administered P4LA (1500 mg) after the first pregnancy diagnosis at around 15 days and repeated 7 days later. The remaining mares were placed in a control group (n = 91), with no treatment, in order to compare the embryonic loss rates for the 3 groups. Recipients were evaluated for the presence of the embryonic vesicle between 13 and 16 days (embryo age), and pregnancies were monitored at 30 and 45 days to determine the early embryonic loss. Statistical analyzes were performed using the chi-square test with 5% defined as significance. Pregnancy rates at 13 to 16 days were not different (P = 0.336) for noncyclic and cyclic recipients (39/42, 90.7% and 134/157, 85.4%, respectively). The embryonic loss was evaluated in the 3 groups as follows: control group; 7 of 91 pregnancies were lost between 15 and 30 days (7.69%) and 2 of 84 were lost between 30 and 45 days (2.38%); the progesterone-supplemented group had lost 4 of the 43 pregnancies between 15 and 30 days (9.30%); and the noncycling progesterone mares had lost 2 of the 39 between 30 and 45 days (5.13%). Rates of embryo loss before 45 days of gestation were not different for the control mares with no progesterone supplementation (9.89%), progesterone-supplemented cyclic mares (9.3%), and noncyclic recipients (5.13%). The noncyclic recipients maintain gestation with the supplemental progesterone with no influence on embryo loss. These results demonstrate no advantage in the use of exogenous progesterone to supplementation for cyclic embryo recipients.

Burns Ranch Inc., Menifee, California, USA.

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