Changes in hormone secretion and follicular development in postpartum cows

مرکز و کتابخانه مطالعات اسلامی به زبان های اروپایی

منو

" Changes in hormone secretion and follicular development in postpartum cows "
M. A. Bhatti D. R. Deaver

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112940
Doc. No	:	TLpq304091128
Main Entry	:	D. R. Deaver
	:	M. A. Bhatti
Title & Author	:	Changes in hormone secretion and follicular development in postpartum cows\ M. A. BhattiD. R. Deaver
College	:	The Pennsylvania State University
Date	:	1993
student score	:	1993
Degree	:	Ph.D.
Page No	:	184
Abstract	:	Studies of follicular development in cattle may lead to methods for more precise estrous synchronization. Nineteen lactating cows and 20 heifers were used to determine if progesterone results in a persistent dominant follicle. Cows and heifers were assigned (at estrus = d 0) to Growing follicle (GF); or Persistent follicle (PF) groups. All animals received PGF{2\alpha} on d 6 of the estrous cycle. Animals assigned to PF group received CIDR on d 4 which was removed on d 13 of the cycle. Animals were bred 24 h after detection of estrus. Follicular development was monitored with a ultrasound scanner. The dominant follicle was in the PF group but fertility was lower than GF cows. Twenty-four beef cows at 25 d postpartum were used to compare the effects of hCG and GnRH on luteinization of dominant follicles and expression of estrus. All cows received norgestomet at d 0 and PGF{2\alpha} on d 8. Implants were removed at d 9. Cows were assigned to Control (CON); GnRH and hCG groups. Cows from later two groups were injected with GnRH and hCG, at d 0. Five of seven cows from each GnRH and hCG groups luteinized dominant follicles at d 0 of the experiment and initiated a new follicular waves. hCG-treated cows failed to exhibit estrus and ovulate whereas 80% of the cows that received GnRH were cycling within 23 d after implant removal. Eighteen non-lactating cows were used to investigate the failure of estrus and ovulation in hCG-treated cows. Cows were assigned to: (a) Control (CON; at estrus = d 0); (b) Norgestomet (NOR) and (c) Norgestomet + hCG (N + hCG) groups. All cows received PGF{2\alpha} on d 8 of the experiment. The ovary bearing the dominant follicle was removed from each cow at d 10 of the experiment. Follicular fluid were assayed for estradiol. Granulosa homogenate were used to examine specific binding of hCG. The results indicate that exposure of early antral follicles to hCG reduces the number of LH receptor in granulosa. Consequently, this results in lower estradiol secretion and ultimately failure of estrus and ovulation. In summary, the use of GnRH with progestogens in postpartum cows can synchronize follicle development and decrease the time to first postpartum ovulation.
Subject	:	Biological sciences
	:	Livestock
	:	Livestock
	:	Veterinary services