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Journal of Animal Science, Vol 77, Issue 3 715-723, Copyright © 1999 by American Society of Animal Science

JOURNAL ARTICLE

Estrus synchronization of beef cattle with a combination of melengestrol acetate and an injection of progesterone and 17beta-estradiol

K. E. Fike, M. E. Wehrman, B. R. Lindsey, E. G. Bergfeld, E. J. Melvin, J. A. Quintal, E. L. Zanella, F. N. Kojima and J. E. Kinder
Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.

Our hypothesis was that estrus synchronization in beef cattle using melengestrol acetate (MGA) and an injection of progesterone (P4) and 17beta-estradiol (E2) to regress dominant ovarian follicles would improve pregnancy rate (number conceived/number in group) to AI compared with feeding only MGA or injecting PGF2alpha. During 2 yr, peripubertal heifers (n = 52) and cows (n = 327) received either 1) MGA for 18 d (d 0 = 1st d of MGA) plus an injection of P4 and E2 in sesame oil (vehicle) on d 11 to regress persistent ovarian follicles (MGA+P4), 2) MGA for 18 d plus vehicle on d 11 (MGA), or 3) two injections of PGF2alpha 10 d apart (d 7 and 17, PG). Concentration of P4 was assessed in blood samples obtained on d 0, 7, and 17 to indicate estrual status (anestrual or estrual) during treatment to induce estrus synchrony. Observations for detection of estrus occurred every 6 h for 180 h following treatment cessation. Females showing estrus were inseminated 6 to 12 h after estrus detection. Conception to AI was determined by ultrasonography 35 to 40 d later. Conception rate was greater (P < .05) in females in the PG than in those in the MGA group but did not differ from conception rate of females in the MGA+P4 group. Among anestrual females, estrus synchrony rates were greatest (P < .10) among females treated with MGA+P4. Among females that were estrual before treatment cessation, estrus synchrony rates were greater (P < .10) among females treated with MGA+P4 or PG than among those given MGA. Pregnancy rates were greater (P < .05) among females that were anestrual before treatment cessation and treated with MGA or MGA+P4 than among those treated with PG. Estrus synchronization using MGA+P4 and E2 differentially improves estrus synchronization and pregnancy rates among anestrual and estrual beef cattle while maintaining conception rates similar to those of PGF2alpha-treated females.


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H. Rivera, H. Lopez, and P. M. Fricke
Use of Intravaginal Progesterone-Releasing Inserts in a Synchronization Protocol before Timed AI and for Synchronizing Return to Estrus in Holstein Heifers
J Dairy Sci, March 1, 2005; 88(3): 957 - 968.
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Copyright © 1999 by the American Society of Animal Science.