| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
* Institute of Animal Science, Agricultural Research Organization, the Volcani Center, Bet Dagan 50250, Israel
Department of Animal Science, and
# Department of Agricultural Economics and Management, Faculty of Agricultural, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem, Rehovot 76100, Israel
Corresponding author:
D. Wolfenson; e-mail:
wolf{at}agri.huji.ac.il.
Two experiments examined effects of GnRH administered within 3 h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250 µg of GnRH, or 10 µg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of 
30 h and 24% had intervals > 30 h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated 30 h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.
Key Words: GnRH • ovulation • conception • cows
Abbreviation key: OE = onset of estrus, CR = conception rate(s)
This article has been cited by other articles:
|
|
 |
|
  G. E. Schrock, A. M. Saxton, F. N. Schrick, and J. L. Edwards Early In Vitro Fertilization Improves Development of Bovine Ova Heat Stressed During In Vitro Maturation J Dairy Sci, September 1, 2007; 90(9): 4297 - 4303. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Bloch, Y. Folman, M. Kaim, Z. Roth, R. Braw-Tal, and D. Wolfenson Endocrine Alterations Associated with Extended Time Interval Between Estrus and Ovulation in High-Yield Dairy Cows J Dairy Sci, December 1, 2006; 89(12): 4694 - 4702. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. L. Edwards, A. M. Saxton, J. L. Lawrence, R. R. Payton, and J. R. Dunlap Exposure to a Physiologically Relevant Elevated Temperature Hastens In Vitro Maturation in Bovine Oocytes J Dairy Sci, December 1, 2005; 88(12): 4326 - 4333. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Portaluppi and J. S. Stevenson Pregnancy Rates in Lactating Dairy Cows After Presynchronization of Estrous Cycles and Variations of the Ovsynch Protocol J Dairy Sci, March 1, 2005; 88(3): 914 - 921. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
