The use of FTAI can overcome the negative impact of

The use of FTAI can overcome the negative impact of low estrus detection efficiency, but implies effective synchrony of luteal function as well as synchronous growth and ovulation of a viable carboxypeptidase b follicle. Pregnancy rates obtained with FTAI may be comparable or better than those obtained after AI with estrus detection because all animals are inseminated regardless of whether they displayed estrus [10]. Gonadotropin releasing hormone (GnRH) induces pituitary release of gonadotropins (LH and FSH) and ovulation – an effect that has formed the basis of common synchronization protocols used today. In early studies, a 10-day synchronization program involving a 6-day interval between GnRH and PGF treatment resulted in a pregnancy rate that was similar to controls, and a second GnRH treatment 36–48 h after PGF treatment improved the precision of ovulation and permitted fixed-time insemination without adversely affecting pregnancy rates [11], [12]. The GnRH-PGF-GnRH protocol was coined “Ovsynch” and came into common use for FTAI in dairy [10], [13] and beef cattle [14]. A limitation of GnRH-based protocols, however, is that emergence of a new follicular wave is synchronized only if GnRH treatment causes ovulation [15]. In later studies, the first GnRH treatment was found to induce ovulation in only 44–54% of dairy cows [16], [17], and in only 56% of beef heifers [15] and 60% of beef cows [18]. If the first GnRH does not synchronize follicular wave emergence, ovulation following the second GnRH may be poorly synchronized [19], resulting in disappointing pregnancy rates following FTAI [20]. High progesterone concentration prior to artificial insemination in fixed-time synchronization protocols such as Ovsynch increases pregnancy rates in lactating dairy cows (5–10% improvement) [21], [22], [23]. External sources of progesterone, such as CIDR, Cue-Mate or PRID, are usually used to increase circulating concentrations of the hormone. Although the exact mechanism behind the improved pregnancy outcomes is not fully understood, it may be related to prevention of early ovulations (due to spontaneous CL regression prior to PGF treatment) [23], enhanced oocyte maturation and/or delayed PGF release from the uterus post-breeding [22], [24]. The driving force behind a dramatic increase in the use of AI in Brazil was the adoption of estrogen-based protocols for controlling follicle development and synchronizing ovulation in cattle These protocols have enabled producers to control the timing of ovulation reliably, enabling efficient use of time, labour and resources by allowing pre-scheduled artificial insemination [3], [25], [26], [27], [28]. This method of synchronizing wave emergence is based on the negative feedback effect that estradiol has on FSH secretion during the luteal phase or under the influence of exogenous progesterone [25], [26], [29]. Exogenous progesterone suppresses LH secretion and growth of the dominant follicle in a dose-dependent manner [30]. Demise of the primary source of FSH suppression (i.e., the extant dominant follicle) then allows FSH to surge again which in-turn elicits the emergence of a new wave of follicles beginning about 4 days after estradiol and progesterone treatment [25], [31]. While steroid-based synchronization protocols are effective, increasing consumer sensitivity to the possible deleterious effects of estrogens in food and in the environment [32] has led to new regulations about the use of estrogenic products in livestock. The European Union has already banned the use of estrogenic products in food producing animals [33], [34], [35], [36]. In United States [37] and Canada [38], estrogens cannot be used for synchronization of estrus except by prescription and custom-compounding. In 2007, New Zealand and Australia banned use of estrogens in lactating dairy animals [36]. The ban of the use of estrogens in livestock and lack of commercially availability of estrogenic preparations negatively impacts the implementation of reproductive biotechnologies in cattle production systems, limiting potential reproductive efficiency and genetic improvement provided by the use of AI or multiple ovulation and embryo transfer [36].