Effects of breed on kinetics of ovine FSH and ovarian response in superovulated sheep I. Ammoun a , T. Encinas a , A. Veiga-Lopez b , J.M. Ros a , I. Contreras b , P. Gonzalez-An ˜over a , M.J. Cocero b , A.S. McNeilly c , A. Gonzalez-Bulnes a,b, * a Departamento de Toxicologia y Farmacologı ´a, Facultad de Veterinaria, UCM, Avda. Puerta de Hierro s/n, 28040 Madrid, Spain b Departamento de Reproduccion Animal, INIA. Avda. Puerta de Hierro s/n, 28040 Madrid, Spain c MRC Human Reproductive Sciences Unit, Centre for Reproductive Biology, University of Edinburgh, Little France Crescent, Edinburgh EH16 4SB, UK Received 20 October 2005; received in revised form 10 February 2006; accepted 11 February 2006 Abstract Embryo production is a useful tool for ex situ conservation of endangered species and breeds, despite a high variability in the ovarian response to superovulatory treatments. The current study evaluated the incidence and mechanisms of genetic factors in such variability, by determining the pharmacokinetics and pharmacodynamics of a standard treatment with ovine FSH (oFSH) in two endangered Spanish sheep breeds (Rubia del Molar, R, and Negra de Colmenar, N) in comparison to Manchega ewes (M, control group). In the first experiment, pharmacokinetics of an i.m. single dose of 1.32 mg of oFSH was evaluated in seven animals of each breed. Plasma FSH concentrations reached their maximum at 4 h post-administration in all the ewes, but several of the kinetic parameters (plasma FSH concentration at 4 h post-administration, maximum plasma FSH concentration, C max , and both the area under the plasma concentration-time curve extrapolated to the infinite, AUC inf , and to the last moment of sampling, AUC last ) were higher in the N group. In the second trial, 10 animals of each breed were superovulated using eight decreasing doses of oFSH (3 1.32 mg, 2 1.10 mg, and 3 0.88 mg). The R group, when compared to N and M, showed both a higher number of corpora lutea (13.7  0.6 versus 10.0  0.4 in N and 9.8  0.6 in M, P < 0.05 for both) and embryos (7.9  0.8 versus 4.3  0.4 in N, P < 0.05, and 6.7  0.5 in M, n.s.). Evaluation of pharmacokinetic and dynamic parameters showed that, although there was a trend for a higher hormone availability in R sheep, mean FSH plasma concentrations were similar between breeds (0.54  0.08 ng/ml for R, 0.45  0.05 ng/ml for N and 0.35  0.05 ng/ml for M). However, differences were found in the number of preovulatory follicles growing in response to the FSH treatment between R (24.4  2.2), M (18.9  1.5, n.s.) and N sheep (14.1  1.4; P < 0.01). Thus, differences in embryo yields between breeds would be related to differences in the pattern of follicular growth in response to FSH treatment. # 2006 Elsevier Inc. All rights reserved. Keywords: Breed; FSH kinetics; Follicular dynamics; Sheep; Superovulation 1. Introduction Protocols for superovulation and embryo transfer are widely used to increase progeny produced in sheep, like in other ruminants, thereby providing an alter- native tool both for spread of selected animal genetics www.journals.elsevierhealth.com/periodicals/the Theriogenology 66 (2006) 896–905 * Corresponding author. Tel.: +34 91 347 4022; fax: +34 91 347 4014. E-mail address: bulnes@inia.es (A. Gonzalez-Bulnes). 0093-691X/$ – see front matter # 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2006.02.024