Pre- and post-synchronization methodologies to enhance the efficiency of fixed timed artificial insemination in pharmacologically-controlled breeding systems with Bos indicus-influenced cattle
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Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the COÃ¢ÂÂSynch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicusÃ¢ÂÂinfluenced cattle; 2) Characterize ovarian events associated with the presynchronization; 3) Evaluate the efficacy of measuring vaginal electrical resistance (VER) to assess follicular maturity at TAI; and 4) Compare serum concentrations of progesterone (P4) in ovariectomized cows bearing new or previously used CIDR devices with or without autoclaving. In Exp. 1 and 2, cattle received either GnRH or saline on day Ã¢ÂÂ7. The COÃ¢ÂÂSynch + CIDR protocol included a CIDR insert and GnRH (GnRHÃ¢ÂÂ1; day 0), removal of CIDR and PGF2ÃÂ± on day 7, and GnRH (GnRHÃ¢ÂÂ2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS Ã¢ÂÂ¥ 5 tended to differ (P=0.085) between Presynch (38%) and COÃ¢ÂÂSynch + CIDR (54%). In Exp. 2, ovulatory response to GnRHÃ¢ÂÂ1 was greater (P<0.01) in the Presynchronization (58%) than in the COÃ¢ÂÂSynch + CIDR (27.1%) group. Emergence of a follicular wave after GnRHÃ¢ÂÂ1 and ovulation rate after GnRHÃ¢ÂÂ2 did not differ between groups. More (P<0.01) females that developed a follicular wave after GnRHÃ¢ÂÂ1 ovulated (82%) after GnRHÃ¢ÂÂ2, compared to those that did not (29%). Mean VER (ohms) was greatest (101.4ÃÂ±0.8) on day 0 and declined (P<0.01) to 95.2ÃÂ±0.8 and 82ÃÂ±0.8, respectively, on days 7 and 10. We observed a low negative but significant relationship (r=0.38; P<0.001) between VER and follicular size on day 0, 7, and 10. VER difference (day 10 minus day 7) did not differ between females with small and large follicles at TAI. Mean concentrations of P4 during the 7Ã¢ÂÂday insertion period were greater (P<0.03) for new (3.7 ng/ml) and reÃ¢ÂÂused autoclaved (3.4 ng/ml) than for reÃ¢ÂÂused disinfected CIDRs (2.8 ng/ml). In summary, Presynch improved ovulation rate after GnRHÃ¢ÂÂ1, but did not improve pregnancy rates compared to COÃ¢ÂÂSynch + CIDR. Follicular maturity estimation was not feasible using VER as applied in this study. Autoclaving may be the best option when reÃ¢ÂÂusing CIDR inserts because it creates greater concentrations of P4 during the first 48 h.
Zuluaga Velez, Juan Federico (2006). Pre- and post-synchronization methodologies to enhance the efficiency of fixed timed artificial insemination in pharmacologically-controlled breeding systems with Bos indicus-influenced cattle. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from