Postinsemination administration of receptal: follicular dynamics, duration of cycle, hormonal responses, and pregnancy rates.
In experiment 1, concentrations of LH, FSH, and progesterone, but not estradiol-17 beta, in blood serum were increased during 6 to 12 h after injection of 8 micrograms of receptal (GnRH agonist) administered on d 11 to 14 after estrus (d 0) and at first AI compared with saline treatment in lactating Holstein cows. Beginning 2 to 3 d after injection of receptal, concentrations of progesterone were increased for 3 d in nonpregnant cows and for 12 d in pregnant cows compared with controls of similar pregnancy status. Number of ovarian follicles determined by ultrasonography during 10 d after receptal was reduced, specifically those with antral diameters of > or = 10 mm. The dominant follicle in both groups began to decrease in diameter on the day following treatment, but the next dominant follicle began to increase in diameter 2.3 +/- .7 d later in receptal-treated cows than in controls, accounting for an increase in cycle duration of 2.5 +/- .8 d. In Experiment 2, a double-blinded study was conducted in eight herds in which cows (n = 1013) were AI at first detected estrus after 50 d postpartum and assigned randomly to receive either saline or 4, 8, or 12 micrograms of receptal on d 11 to 14 after first AI. Pregnancy rates were improved in one herd at all doses of receptal, but dose responses were inconsistent in remaining herds. A greater proportion of cows given receptal than controls returned to estrus after 24 d. Administration of a potent GnRH agonist altered number and distribution of ovarian follicles, increased cycle duration, and increased concentrations of progesterone without a consistent increase in pregnancy rates.
Stevenson
J S
JS
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201.
Phatak
A P
AP
Rettmer
I
I
Stewart
R E
RE
D000818:Animals; D002064:Buserelin / Q000494:pharmacology*; D002417:Cattle / Q000502:physiology*; D003338:Corpus Luteum / Q000033:anatomy & histology; D004958:Estradiol / Q000097:blood; D004971:Estrus / Q000187:drug effects* / Q000502:physiology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood
D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D002064:Buserelin