Fixed-time artificial insemination in replacement beef heifers after estrus synchronization with human chorionic gonadotropin or gonadotropin-releasing hormone

• Published in: Journal of animal science Vol. 89; no. 9; pp. 2750 - 2758
• Main Authors: Dahlen, C. R, Marquezini, G. H. L, Larson, J. E, Lamb, G. C
• Format: Journal Article
• Language: English
• Published: Champaign, IL American Society of Animal Science 01-09-2011
• Subjects: animal ovaries; Animal productions; Animals; artificial insemination; beef; Biological and medical sciences; blood; Cattle; Chorionic Gonadotropin - pharmacology; controlled internal drug release devices; estrus synchronization; Estrus Synchronization - drug effects; Female; Fertility - drug effects; Food industries; Fundamental and applied biological sciences. Psychology; gonadotropin-releasing hormone; Gonadotropin-Releasing Hormone - pharmacology; heifers; human chorionic gonadotropin; Humans; Insemination, Artificial - methods; Insemination, Artificial - veterinary; Meat and meat product industries; Ovary - diagnostic imaging; Ovary - drug effects; Ovulation - drug effects; pregnancy; progesterone; Progesterone - blood; Terrestrial animal productions; Ultrasonography; Vertebrates; Human; Hormone; Estrus; Bovine; Meat product; Ox; Replacement; Synchronization; Ovulation; Reproduction; Vertebrata; Mammalia; estrus synchronization; human chorionic gonadotropin; Artificial insemination; Chorionic gonadotrophin; Heifer; Artiodactyla; Beef; Ungulata; beef heifer
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2010-3824

We determined the effects of hCG on ovarian response, concentration of progesterone, and fertility in a fixed-time AI (TAI) protocol. Four hundred forty-four crossbred beef heifers were synchronized with the CO-Synch + CIDR (controlled internal drug-releasing insert) protocol. In addition, heifers were randomly assigned to 1 of 4 treatments in a 2 x 2 factorial arrangement of treatments with main factors being 1) pretreatment, no treatment (control), or treatment with 1,000 IU of hCG 14 d before the initiation of the CO-Synch + CIDR protocol and 2) treatment, administration of 1,000 IU of hCG or 100 µg of GnRH at CIDR insertion of the CO-Synch + CIDR protocol. Blood samples were collected from all heifers on d –21, –14, –7, 0, and 2 relative to PGF2α injection. Transrectal ultrasonography was used to examine ovaries in a subset of heifers (n = 362) on d –7 and 0 relative to PGF2α, and to determine pregnancy status of all heifers on d 33 and 82 relative to AI. Pregnancy rates were similar for heifers pretreated with control (33.0%) or hCG (36.4%), whereas pregnancy rates were greater (P < 0.01) for heifers treated with GnRH (40.1%) compared with hCG (29.0%) at CIDR insertion. Heifers pretreated with hCG had more (P < 0.01) corpora lutea present on the day of CIDR insertion and the day of CIDR removal compared with untreated heifers. A greater proportion (P < 0.01) of heifers ovulated as a result of administration of hCG at the time of CIDR insertion (59.0%) compared with GnRH (38.7%). Heifers treated with hCG at CIDR insertion had greater (P < 0.01) concentrations of progesterone compared with those receiving GnRH at the time of CIDR removal (2.42 ± 0.13 vs. 1.74 ± 0.13 ng/mL; P < 0.01) and at fixed-time AI (0.52 ± 0.03 vs. 0.39 ± 0.03 ng/mL; P < 0.01). Therefore, hCG was more effective than GnRH in its ability to ovulate follicles and to increase concentrations of progesterone in beef heifers. Presynchronization with hCG 14 d before CIDR insertion did not alter pregnancy rates, whereas replacing GnRH with hCG at CIDR insertion decreased pregnancy rates.