Effect of Interval from Melengestrol Acetate to Prostaglandin F on Timed and Synchronized Pregnancy Rates of Beef Heifers and Cows

D. J. Kesler, D. B. Faulkner, R. B. Shirley, T. S. Dyson, F. A. Ireland, R. S. Ott

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

The objective of this experiment was to determine the optimal interval from the last day of melengestrol acetate (MGA) feeding to prostaglandin F (PGF) treatment on pregnancy rates of beef heifers and cows. All females (149 heifers and 399 postpartum cows) were fed MGA (.5 mg) daily for 14 d and then administered PGF (25 mg Lutalyse®) 13, 15, and 17 d (Groups 1, 2, and 3, respectively) after the last day of MGA feeding. Females not in estrus the first 52 h after PGF treatment were artificially inseminated 72 h after PGF treatment. Females in estrus 0 to 52 h and 78 h to 6 d after PGF treatment were inseminated at estrus. Blood sera (collected immediately before and 3 d after PGF treatment) were assayed for progesterone concentrations. Pregnancy was determined 44 to 47 d after the 72-h AI by rectal examination. The intervals from MGA feeding to PGF that had the highest 72-h AI pregnancy rates were 17 d for heifers (43%) and 15 d for cows (43%). Heifers with a 17-d interval had a higher (P < .05) 72-h AI pregnancy rate than heifers with 13-d and 15-d intervals, and cows with a 15-d interval had a higher (P < .05) 72-h AI pregnancy rate than cows with a 17-d interval. The 4-d synchronized pregnancy rates (the 72-h AI and the succeeding 3 d inseminations) for both heifers (44%) and cows (53%) were not different (P > .05) among groups. Fewer (P < .05) cows with a 17-d interval from MGA to PGF had corpora lutea regression (by 72 h) after PGF treatment than cows with 13-d and 15-d intervals. We interpret the results to indicate that the interval from MGA to PGF treatment may influence 72-h AI pregnancy rates, that optimal intervals are 17 d for heifers and 15 d for cows, and that pregnancy rates are improved by insemination for 3 d after the 72-h AI.

Original languageEnglish (US)
Pages (from-to)2885-2890
Number of pages6
JournalJournal of animal science
Volume74
Issue number12
DOIs
StatePublished - Dec 1996

Keywords

  • Artificial Insemination
  • Beef Cattle
  • Estrus
  • Melengestrol Acetate
  • Pregnancy Rate
  • Prostaglandins

ASJC Scopus subject areas

  • Food Science
  • Animal Science and Zoology
  • Genetics

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