152 FACTORS AFFECTING FERTILITY ON AN EQUINE EMBRYO TRANSFER PROGRAM

Abstract

Assisted reproduction through embryo transfer (ET) increases the chances, within a limited group of genetically superior mares, producing a greater number of desirable offspring. Several variables, however, are involved in the process and may impact or even limit the potential of ET to increase a single mare´s foal production within a given breeding season. The objective was to analyse information on variables related to an ET operation carried over 10 years by a single veterinarian in different reproduction centers or directly from the database of all breeders. General management and reproductive data from 150 embryo donor mares, 362 recipient mares and 73 stallions were submitted to statistical analysis by the GENMOD procedure using SAS^® (SAS Institute Inc., Cary, NC, USA). The proportion of positive recoveries (in which one or more embryos were actually recovered) and of pregnant recipients were dependent variables and donor breed (Campolina, Mangalarga, Thoroughbred, Haflinger and Brasileiro de Hipismo), donor (3–18 years old) and stallion age (3–20 years old) type of semen, hormonal ovulation induction (1000–2500 IU of hCG when dominant follicles reached at least 30 mm in diameter), diameter of the dominant follicles at the time of induction in donors and recipients as independent variables. Gestation rate was greater (P < 0.05) for embryos produced by donors of the Campolina breed compared to all others (74.0 v. 57.6%). The positive flush rates of donor age classes ≤7 (50.2%), >7 and <12 (60.0%) and ≥12 (53.2%) years old were similar (P = 0.45). Gestation rates were similar (P = 0.43) between stallions <6 (70.3%) and ≥6 (75.8%) years-old. The proportion of positive flushes was greater (P = 0.01) for fresh semen (59.9%) compared to those of natural service, cooled and frozen-thawed semen (54.8, 51.5 and 28.6%, respectively). Pregnancy rates were similar (P > 0.05) between recipient mares hCG-induced (70.6%) and not induced (73.3%) to ovulate. In conclusion, we confirmed that donor breed and type of semen are influential over pregnancy and positive flush rates in the present study. Stallion or donor mare age did not influence fertility traits in this study, which indicates that animals were well managed and used within appropriate age limits. More relevant data may be gathered from the field work of veterinarians in order to enhance the knowledge that supports managing decisions in assisted reproduction techniques.