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- Title
Comparison of long-term progestin-based protocols to synchronize estrus before fixed-time artificial insemination in beef heifers.
- Authors
Mallory, D. A.; Nash, J. M.; Ellersieck, M. R.; Smith, M. F.; Patterson, D. J.
- Abstract
Two experiments were conducted to compare pregnancy rates resulting from fixed-time AT (FTAI) after administration of 1 of 2 long-term controlled internal drug release (CTDR)-based protocols. Heifers were assigned to treatment by age, BW, and pubertal status. The CTDR Select-treated heifers (Exp. 1, n = 37; Exp. 2, n = 192) received a CIDR (1.38 g of progesterone) from d 0 to 14, followed by 100 ig of GnRH, intramuscularly (i.m.) 9 d after CIDR removal (d 23) and PGF20 (25 mg, i.m.) 7 d after GnRH treatment (d 30). Heifers assigned to the Show-Me-Synch protocol (Exp. 1, n = 40; Exp. 2, n = 200) received a CTDR from d 0 to 14, followed by PGF2c. 16 d later (d 30). Artificial insemination was performed at 72 or 66 h after PGF2a treatment for the CIDR Selectand Show-Me-Synch-treated heifers, respectively, and each heifer was given GnRH (100 ig, i.m.) at the time of AT. In Exp. 1, ovaries of each heifer were examined by transrectal ultrasonography on d 23 and 30 to characterize follicular dynamics. Follicles ⩾ 5 mm and the presence of corpora lutea were recorded. On d 25, ovaries of each heifer were examined to characterize the status of dominant follicles recorded on d 23. Heifers were fitted with HeatWatch (DDx Inc., Denver, GO) estrus-detection transmitters at PGF2, to characterize estrus distribution up to FTAI. The diameter of dominant follicles on d 23 at PGF2 and on d 30, and the estrous response after PGF2 treatment up to the point of FTAT did not differ between CIDR Selectand Show-Me-Synch-treated heifers. Goncentrations of progesterone in serum at PGF2 were greater (P = 0.07) in Show-Me-Synchthan CIDR Select-treated heifers (6.0 vs. 4.8 ng/mL, respectively). Pregnancy rates of heifers resulting from FTAI did not differ (P =` 0.33) between CIDR Selectand Show-Me-Synch-treated heifers (CTDR Select, 59%; Show-Me-Synch, 70%). In Exp. 2, FTAI pregnancy rates tended (P = 0.07) to be greater in Show-Me-Synch-treated (62%) than in CIDR Selecttreated (51%) heifers. Pregnancy rates at the end of the breeding season did not differ (P = 0.72; CIDR Select, 85%; Show-Me-Synch, 83%) between treatments. In summary, pregnancy rates resulting from FTAI were comparable for heifers assigned to each of the 2 longterm progestin-based protocols. The reduced treatment cost and animal handling associated with administration of the Show-Me-Synch protocol offer distinct advantages over the CIDR Select protocol despite similarities in pregnancy rates resulting from FTAI.
- Subjects
HEIFERS; ARTIFICIAL insemination of cattle; PROGESTATIONAL hormones; ESTRUS; ULTRASONIC imaging
- Publication
Journal of Animal Science, 2011, Vol 89, Issue 5, p1358
- ISSN
0021-8812
- Publication type
Article
- DOI
10.2527/jas.2010-3694