Optimizing Ovulation to First GnRH Improved Outcomes to Each Hormonal Injection of Ovsynch in Lactating Dairy Cows

Abstract

Ovulatory response to the first GnRH of Ovsynch is the critical determinant for successful synchronization of ovulation in dairy cows. Our objective in this study was to develop a pre-Ovsynch treatment that increased the percentage of cows that ovulated in response to the first GnRH injection of Ovsynch. To accomplish our goal, we evaluated a hormonal strategy that consisted of PGF2alpha and GnRH before the first GnRH of Ovsynch. Lactating dairy cows (n = 137) were assigned to receive either no treatment before Ovsynch (control) or 25 mg of PGF2alpha (PreP) followed 2 d later by 100 microg of GnRH (PreG), administered 4 (G4G), 5 (G5G), or 6 (G6G) d before initiating the Ovsynch protocol. Transrectal ultrasonography was performed to assess follicular size and resulting ovulation, and blood samples were collected to measure circulating concentrations of progesterone and estradiol immediately before each hormonal injection. Cows were inseminated at a fixed time 16 h after final GnRH of Ovsynch. Pregnancy diagnosis was performed 35 d later by palpation per rectum of uterine contents. Proportion of cows that ovulated to first GnRH of Ovsynch was 56.0, 66.7, 84.6, and 53.8% for G4G, G5G, G6G, and controls, respectively, and was greater for G6G than for control cows. Luteolytic response to PGF2alpha of Ovsynch was greater in all treated than control cows (92.0, 91.7, 96.2, and 69.2% for G4G, G5G, G6G, and control, respectively). Synchronization rate to Ovsynch was greater (92 vs. 69%, respectively) in G6G than in control cows. In addition, cows that ovulated in response to first GnRH of Ovsynch had greater response to PGF2alpha of Ovsynch (92.7 vs. 77.1%, respectively) and greater synchronization rate to the overall protocol (87.9 vs. 62.9%, respectively) than those that did not ovulate. Concentrations of progesterone at PGF2alpha of Ovsynch, and estradiol and follicle size at final GnRH of Ovsynch, were identified as significant predictors of probability of pregnancy 35 d after artificial insemination. In summary, a PGF2alpha-and-GnRH based pre-Ovsynch strategy consisting of a 6-d interval between PreG and first GnRH of Ovsynch resulted in a greater ovulatory and luteolytic response to first GnRH and PGF2alpha of Ovsynch, respectively, compared with control cows. This, in turn, optimized synchronization rate to Ovsynch.

Synchronization of ovulation and fixed-time artificial insemination in beef cattle

“…CO-Synch protocols are more commonly used in beef cattle because cows are FTAI at the time of the second GnRH (Geary et al, 2001). Recent studies have shown that the first GnRH resulted in ovulation in 44% to 54% of dairy cows (Bello et al, 2006;Colazo et al, 2009), 56% of beef heifers (Martinez et al, 1999) and 60% of beef cows (Small et al, 2009), and the emergence of a new follicular wave was synchronized only when treatment caused ovulation (Martinez et al, 1999). If the first GnRH does not synchronize follicular wave emergence, ovulation following the second GnRH may be poorly synchronized (Martinez et al, 2002a), resulting in disappointing pregnancy rates to AI (P/AI; Martinez et al, 2002b).…”

“…These treatments are called Double Ovsynch (Souza et al, 2008) or G6G (Bello et al, 2006) and have been reported to increase P/AI in high-producing dairy cows. Nevertheless, these treatments may be too complicated and too long to implement in pasture-managed beef cattle.…”

Presenkronizasyon İle Östrusu Uyarılan Montofon Irkı İneklerde Seksüel Siklusun Erken Luteal Döneminde Uygulanan Cosynch Protokolünde PGF2α ve GnRH Uygulama Zamanının Değiştirilmesinin Folliküler Dinamik Üzerine Etkisi

“…In that study, follicle diameter was found to be 13.5 mm before ovulation and the ovulation rate was reported to be 100% in the heifers in all groups [17] . In addition, preovulatory follicle diameters of 14.0 mm [15] and 15.7 mm [16] have been reported during the second GnRH injection administered in the Ovsynch protocol with presynchronization. Furthermore, the ovulation rate was found to be 96.2% after the second GnRH injection [15] .…”

“…Presynchronization with PGF 2α prior to starting the Cosynch protocol has been observed to increase the pregnancy rate in multiparous cows [8] . Studies on cows that have been administered presynchronization have reported follicle diameters of 15.5 mm [15] and 14.4 mm [16] during the first GnRH injection administered in the Ovsynch protocol. Furthermore, the ovulation rate was found to be 69.5% after this procedure [15] .…”

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“…In a previous study [16] it was reported that DF diameter was 15.9 mm at 80 h after PGF injection of Ovsynch in lactating dairy cows. Bello, et al [26] reported that the ovulatory follicle diameter was 15.7 ± 0.4 mm at the time of second GnRH injection of Ovsynch. In agreement with previous findings [16,25,26] the present study demonstrated that usage of half dose buserelin acetate for Ovsynch protocol in lactating cows did not have adverse effects on dominant follicle diameters.…”