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Assisted reproductive technologies in buffaloes: techniques and outcomes
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Buffaloes present reproductive seasonality and become sexually active with decreasing days (short days) during the late summer to early autumn. The use of assisted reproductive technologies (ART) such as artificial insemination (AI) and embryo transfer (ET) are important alternatives for maximizing the genetic gain and productivity of this species. This review aims to elucidate some aspects of the ART and their outcomes in buffalo production system. The use of AI has already proved to be a reliable technology in increasing genetic progress in buffalo herds. However, the low efficiency of traditional estrus detection system makes this biotechnology difficult to be used in this species. Buffaloes present poor manifestation of the symptoms of estrus, mainly due to low frequency of homosexual behavior. The use of hormonal treatments based on GnRH plus PGF2a (Ovsynch protocol) for timed artificial insemination (TAI) present satisfactory results in cycling buffalo. However, studies have shown that anestrous buffaloes synchronized with Ovsynch have a lower P/AI when compared to cycling buffaloes (20.0 vs. 65.3%). In contrast, research carried out by our group showed that the use of protocols based on P4, E2 and eCG can present favorable P/AI both in the non-breeding (high presence of anestrous) and in the breeding season (66.7 vs. 62.7%), enabling the application of AI throughout the year. ET is an effective technique in accelerating maternal and paternal genetic gain with a consequent increase in herd productivity. In buffaloes, however, the production of in vivo-derived (IVD) embryo has low efficiency. Studies carried out by our group show that despite responding to superstimulation (average of 15 follicles > 8 mm at the end of FSH treatment) with a moderate ovulation rate (approximately 60%), the embryo recovery rate (number of embryos and ova recovered per ovulation) is low (34.8%). While IVD present low efficiency in buffalo, in vitro production (IVEP) has been studied as an alternative and positive results have been achieved in recent years. Historically, the association of follicular aspiration (OPU) with IVEP presented low results in buffalo when compared to cattle. However, recent studies show that is possible to select buffalo donors using different technologies to improve the ET efficiency. Antral follicle population (AFP) is directly associated with the number of oocytes recovered by OPU for IVEP and the number of embryos produced per procedure. Furthermore, strong relationship between AFP and anti-Mullerian hormone (AMH) was found in buffalo. Studies carried out by our group suggest that AMH can be considered an endocrine marker to predict the performance of IVEP in buffaloes. Recently, superstimulation with FSH prior to OPU has been used successfully in IVEP programs in buffalo, resulting in the increase of total embryos produced per OPU session. We found that FSH treatment prior to OPU increased the proportion of medium and large diameter follicles available for OPU procedure in all buffalo donor categories (heifers, primiparous and multiparous). Furthermore, FSH treatment increased the proportion of viable oocytes for culture and embryos produced per OPU-IVEP session, suggesting that the use of FSH treatment may be a strategy to improve the efficiency of OPU/IVEP in buffalo. In addition, another fact to be considered when evaluating the efficiency of IVEP is the bull effect. The semen of certain bulls shows high blastocyst rates and improve the efficiency of the ET programs. The use of calves as oocyte donors is an important strategy to accelerate genetic gain by decreasing generation intervals. We compared the embryo production of calves (2 to 4 months) in relation to prepubertal heifers (13 to 15 months) and lactating buffaloes. Although the embryo rate was lower in calves compared to prepubertal heifers and lactating buffaloes, the P/TE was similar between categories (around 35%), which demonstrates the feasibility of this technique for donor buffalo calves. Therefore, synchronization protocols are designed to control both luteal and follicular function and permit fixedtime AI with high pregnancy rates during the buffalo breeding (autumn-winter) and nonbreeding (spring-summer) season. In addition, the application of OPU/IVEP is showing promising results and has become an alternative to superovulation for in vivo embryo production. Therefore, nowadays AI and ET can be implemented commercially in buffalo farm to increase the meat and milk production.
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