Document Detail

Delayed insemination of non-estrous heifers and cows when using conventional semen in timed artificial insemination.
MedLine Citation:
PMID:  25023797     Owner:  NLM     Status:  Publisher    
Two experiments were designed to test the hypothesis that pregnancy rates after fixed-time artificial insemination (FTAI) in beef heifers and cows may be improved by delaying insemination of females that have not expressed estrus prior to FTAI. In Exp. 1, estrus was synchronized for 931 heifers across three locations using the 14-d CIDR-PG protocol (CIDR insert [1.38 gm progesterone] on d 0 with removal of CIDR on d 14; 25 mg PGF2α 16 d after CIDR removal on d 30; and 100 μg GnRH on d 33, 66 h after PGF2α). Estrous detection aids (Estrotect) were applied at PGF2α on d 30, and estrous expression was recorded at GnRH on d 33. Heifers within each location were randomly assigned to one of two treatments based on weight and reproductive tract score (RTS): (1) FTAI (concurrent with GnRH, 66 h after PGF2α) regardless of estrous expression or (2) FTAI for heifers expressing estrus, and delayed AI (20 h after GnRH) for heifers failing to express estrus. Heifers assigned to treatment 2 achieved a higher AI pregnancy rate than heifers assigned to treatment 1 (54% versus 46%, P = .01). The observed increase in AI pregnancy rate is attributed to the delayed AI of non-estrous heifers in treatment 2, as AI pregnancy rates for non-estrous heifers were significantly higher for treatment 2 (49% versus 34%, P = .02), while AI pregnancy rates of estrous heifers did not differ by treatment (P = .24). In Exp. 2, estrus was synchronized for 951 mature, suckled cows across 9 locations using the 7-d CO-Synch + CIDR protocol (100 μg GnRH + CIDR [1.38 gm progesterone] on d 0; 25 mg PGF2α at CIDR removal on d 7; and 100 μg GnRH on d 10, 66 h after CIDR removal). Estrus detection aids (Estrotect) were applied at PGF2α and CIDR removal on d 7, and estrous expression was recorded at GnRH on d 10. Cows within each location were assigned to one of two treatments based on age, days postpartum (DPP), and body condition score (BCS): (1) FTAI (concurrent with GnRH, 66 h after PGF2α) regardless of estrous expression or (2) FTAI for cows expressing estrus, and delayed AI (20 h after GnRH) for cows failing to express estrus. No significant effect of treatment was found on AI pregnancy rate (P = .76). In summary, FTAI pregnancy rates in heifers can be improved through a strategy of "split- time" AI. However, a statistically significant increase was not observed in the pregnancy rates of mature suckled cows when using a similar strategy.
J M Thomas; S E Poock; M R Ellersieck; M F Smith; D J Patterson
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-7-14
Journal Detail:
Title:  Journal of animal science     Volume:  -     ISSN:  1525-3163     ISO Abbreviation:  J. Anim. Sci.     Publication Date:  2014 Jul 
Date Detail:
Created Date:  2014-7-15     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8003002     Medline TA:  J Anim Sci     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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