| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Kansas State University,3, Manhattan 66506
Abstract
Expanded use of artificial insemination in the beef cattle industry depends on successful application of treatments designed to synchronize estrus. Regulation of estrous cycles is associated with control of the corpus luteum (CL), whose life span and secretory activity are subject to trophic and lytic mechanisms. The advantages of melengestrol acetate (MGA) in estrous synchronization incorporate ease of administration, lower cost relative to other estrous synchronization products, and potential for use to induce estrus in prepubertal heifers. Treatments first designed to synchronize estrous cycles of normally cycling heifers by feeding MGA were imposed daily for 14 to 18 d at levels of .5 to 1 mg. The minimal daily effective dose required to inhibit ovulation was .42 mg. Longer feeding periods of MGA were associated with low fertility at the first synchronized estrus, but at the second estrus, conception was normal. Low fertility at the synchronized estrus resulted in development of alternative treatment practices, which combined feeding of MGA with injections or implants of estradiol-17ß estradiol cypionate, luteinizing hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, or oxytocin. Estrus was synchronized after MGA and estradiol-17ß or estradiol cypionate treatments, but fertility was low. Short-term feeding of MGA (5 to 7 d) combined with prostaglandin F2
or its analogs (PGF) on the last day of MGA reduced fertility at the synchronized estrus. The reduced conception at first service occurred in animals that began treatment after d 12 of the estrous cycle. However, feeding MGA for 14 d and then injecting PGF 17 d later avoided problems with reduced conception. Fertility of animals after this treatment was similar to that of contemporaries synchronized with Syncro-Mate-B. However, the length of the treatment period creates a need for increased management and may extend management beyond practical limits. Further research is warranted to address problems associated with reduced fertility after short-term treatment with MGA.
1 Contribution no. 89-15-J from Kansas Agric. Exp. Sta., Manhattan 66506.
2 Dept. of Anim. Sci., Univ. of KY, Lexington 40546.
3 Dept. of Anim. Sci. and Ind.
This article has been cited by other articles:
|
|
 |
|
  G. A. Perry, M. F. Smith, and D. J. Patterson Evaluation of a fixed-time artificial insemination protocol for postpartum suckled beef cows J Anim Sci, December 1, 2002; 80(12): 3060 - 3064. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. F. Martinez, J. P. Kastelic, G. P. Adams, and R. J. Mapletoft The use of a progesterone-releasing device (CIDR-B) or melengestrol acetate with GnRH, LH, or estradiol benzoate for fixed-time AI in beef heifers J Anim Sci, July 1, 2002; 80(7): 1746 - 1751. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
