Hormonal Strategy for Advance of Mating Season in Mares Scored on Follicular Diameter

Abstract

In Brazil, the productive horse chain has shown significant growth in recent years. Data showed that the annual gross revenues in this chain increased from R$ 7.5 billion in 2006 to R$ 16 billion in 2015 (Lima and Cintra, 2015), as well as being an activity that generates many direct and indirect jobs (MAPA, 2017). This growth happens mainly due to the creation of horses destined to the sports segment. Unlike the animals directed to the labor segment, usually associated with cattle breeding, the sport or recreational horse requires more exceptional care and investments (Lima and Cintra, 2015). In this scenario, the use of the reproductive biotechniques in the equine species becomes essential to reproduce only the best animals (Bortot and Zappa, 2013). Considering the reproductive aspects, it should be regarded as that mares have particular characteristics, such as seasonality, which makes them be considered as not very productive. An alternative to increase the reproductive period of mares is to use artificial cycles, administering exogenous hormones (Jardim et al., 2015). Several techniques have been studied to anticipate the first ovulation of the mating season; among these techniques, the use of progesterone is highlighted (P4) (Rodrigues et al., 2012). The Intravaginal devices of P4 may be efficient in inducing the first ovulation of the year in some mares since, in the equine species, the P4 does not inhibit the folliculogenesis and the ovulation (McKinnon et al., 2011). The use of P4 is based on the hypothesis that the abrupt increase and decrease of P4 levels in anestrus mares can stimulate the production and release of GnRH