Document Detail

Fixed-time artificial insemination in replacement beef heifers after estrus synchronization with human chorionic gonadotropin or gonadotropin-releasing hormone.
MedLine Citation:
PMID:  21512119     Owner:  NLM     Status:  Publisher    
We determined the effects of hCG on ovarian response, concentration of progesterone, and fertility in a fixed-timed AI (TAI) protocol. Four hundred and 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 × 2 factorial arrangement of treatments with main factors being: 1) Pretreatment; no treatment or treatment with 1,000 IU hCG 14 d prior to the initiation of the CO-Synch + CIDR protocol; and 2) Treatment; administration of 1,000 IU hCG or 100 µg 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 PGF(2α) injection. Transrectal ultrasonography was used to examine ovaries in a subset of heifers (n = 362) on d -7 and d 0 relative to PGF(2α), and to determine pregnancy status of all heifers on d 33 and d 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 (CL) 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 TAI (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 prior to CIDR insertion did not alter pregnancy rates, whereas replacing GnRH with hCG at CIDR insertion decreased pregnancy rates.
C R Dahlen; G H L Marquezini; J E Larson; G C Lamb
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-4-21
Journal Detail:
Title:  Journal of animal science     Volume:  -     ISSN:  1525-3163     ISO Abbreviation:  -     Publication Date:  2011 Apr 
Date Detail:
Created Date:  2011-4-22     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8003002     Medline TA:  J Anim Sci     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Department of Animal Sciences, North Dakota State University, Fargo 58108.
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