Document Detail

Timed insemination of beef heifers using the 7-11 Synch protocol.
MedLine Citation:
PMID:  23230105     Owner:  NLM     Status:  Publisher    
Two experiments were conducted over 3 yr to determine pregnancy rates in beef heifers after a timed artificial insemination (AI) in response to the 7-11 Synch protocol. In Exp. 1, 179 heifers were either fed melengestrol acetate (MGA; 7-11 Synch) or given an intravaginal progesterone (P4)-releasing insert (CIDR; 7-11 CIDR) for 7 d. Prostaglandin F(2α) (PG) was administered on the last day of MGA feeding or at CIDR removal followed by the CO-Synch protocol (GnRH - PG - GnRH) beginning 4 d after MGA withdrawal or 2 d after CIDR removal. Heifers received a timed AI with GnRH beginning 48 h after the second PG. Blood samples were collected at d -10, 0 (start of MGA feeding) and d 18 (second PG injection). In Exp. 2, 298 beef heifers were treated with the 7-11 Synch protocol with (7-11 Synch) or without (7 Synch) the first GnRH injection. Fixed time-AI and GnRH was given 54 h after PG. Blood samples were collected at d -10 and 0 in yr 1 and d -10, 0, 18 and at AI in yr 2. In Exp. 1, no differences were detected between 7-11 Synch and 7-11 CIDR for attainment of puberty in non-cyclic heifers (94 vs. 78%; P = 0.21), the proportion of heifers that had luteal tissue on d 18 (87 vs. 83%; P = 0.41), or pregnancy rates after timed AI (47 vs. 46%; P = 0.99). In Exp. 2, administration of GnRH 4 d after the last MGA (7-11 Synch) feeding tended (P = 0.07) to induce more prepubertal heifers to cycle (88 vs. 61%) and increased (P < 0.01) the proportion of heifers with luteal tissue on d 18 (88 vs. 72%) compared to heifers in the 7 Synch treatment. Pregnancy rates after the 54 h timed AI were greater (P < 0.01) in the 7-11 Synch treatment (55%) than in the 7 Synch (38%). We conclude that heifer pregnancy rates did not differ whether feeding MGA for 7 d or applying a CIDR insert for 7 d before a CO-Synch protocol. In contrast, use of GnRH at the beginning of the CO-Synch protocol improved pregnancy rates after a timed AI by inducing more prepubertal heifers to ovulate and increasing the proportion of heifers with luteal tissue at the PG injection.
D R Eborn; D M Grieger
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-12-10
Journal Detail:
Title:  Journal of animal science     Volume:  -     ISSN:  1525-3163     ISO Abbreviation:  J. Anim. Sci.     Publication Date:  2012 Dec 
Date Detail:
Created Date:  2012-12-11     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 and Industry, Kansas State University, Manhattan 66506-0201.
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