Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the COâÂÂSynch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicusâÂÂinfluenced 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 âÂÂ7. The COâÂÂSynch + CIDR protocol included a CIDR insert and GnRH (GnRHâÂÂ1; day 0), removal of CIDR and PGF2ñ on day 7, and GnRH (GnRHâÂÂ2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS âÂÂ¥ 5 tended to differ (P=0.085) between Presynch (38%) and COâÂÂSynch + CIDR (54%). In Exp. 2, ovulatory response to GnRHâÂÂ1 was greater (P<0.01) in the Presynchronization (58%) than in the COâÂÂSynch + CIDR (27.1%) group. Emergence of a follicular wave after GnRHâÂÂ1 and ovulation rate after GnRHâÂÂ2 did not differ between groups. More (P<0.01) females that developed a follicular wave after GnRHâÂÂ1 ovulated (82%) after GnRHâÂÂ2, compared to those that did not (29%). Mean VER (ohms) was greatest (101.4ñ0.8) on day 0 and declined (P<0.01) to 95.2ñ0.8 and 82ñ0.8, 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 7âÂÂday insertion period were greater (P<0.03) for new (3.7 ng/ml) and reâÂÂused autoclaved (3.4 ng/ml) than for reâÂÂused disinfected CIDRs (2.8 ng/ml). In summary, Presynch improved ovulation rate after GnRHâÂÂ1, but did not improve pregnancy rates compared to COâÂÂSynch + CIDR. Follicular maturity estimation was not feasible using VER as applied in this study. Autoclaving may be the best option when reâÂÂusing CIDR inserts because it creates greater concentrations of P4 during the first 48 h.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4812 |
| Date | 25 April 2007 |
| Creators | Zuluaga Velez, Juan Federico |
| Contributors | Williams, Gary L. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1111228 bytes, electronic, application/pdf, born digital |
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