151 REPRODUCTIVE PARAMETERS OF MINI-HORSE MARES

Abstract

The Mini-horse is a new equine breed that is on the rise in Brazil. These are animals with a maximum adult height of 98 cm for females and 93 cm for males, with a well-proportioned body. Those animals are easily handled by children and require small spaces with low maintenance costs. The Mini-horse is under constant genetic selection that is aimed mainly at decreasing its height. For this reason, mares of low stature are required, justifying their use in assisted reproduction programs. Reproductive data of these animals are not available in the literature. Only data of full-size mares are referenced, not taking into account the particularities of this breed. Therefore, the aim of this study was to describe one technique of embryo transfer (ET) for Mini-horse mares. Reproductive rates obtained during the 2012/2013 Brazilian breeding season are presented. Thirteen Mini-horse donor mares were monitored daily by transrectal ultrasonography and ovulation induction was performed with injection of deslorelin acetate or hCG, along with natural breeding using the same stallion for all mares. Eight days after detection of ovulation, flushing for embryo collection was performed. The recipient mares were also monitored daily to detect ovulation and those selected ovulated in the range of up to four days after the donor mare. In order to prevent cervical injuries, the large catheter traditionally employed in uterine washing of large mares was replaced by a Foley catheter (24 Fr in diameter). A range of 50 to 250 mL of Ringer's lactate solution was used to fill the uterus up to 5 times or until the embryo was observed in the collector filter. After the embryo collection, the donor mare received a dose of luteinizing drug (sodic cloprostenol – Sincrocio®, Ouro Fino, Brazil). The recipient mare was examined for a corpus luteum, absence of uterine fluid or endometrial oedema, and good cervical and uterine tone. Recipients were also selected by height (similar to donors) so that the newborn foal could reach the recipient mare's udder to nurse. For non-surgical transfer, the embryos were aspirated by an artificial insemination pipette with ~0.5 mL of holding medium interspersed with small columns of air and then inserted into the uterine body of the recipient mares. Daily follicular growth was 2.2 ± 1.0 mm and the size of follicles at ovulation induction was 31.6 ± 2.8 mm. In 57 embryo collections performed, 46 embryos were obtained and transferred into the uteri of recipient mares, resulting in 35 pregnancies. The embryo recovery and pregnancy rate were 80.7% and 76.1% respectively. The relationship between pregnancy and number of embryo flushes performed was 61.4%. The time between two consecutive flushes was 20 ± 4.5 days. The rate of embryonic loss between 20 and 60 days was 20%. The easy handling of the animals and the high rates of ET program success were promising. However, information regarding full-size mares should be used with caution, respecting the specific characteristics of this breed.