Reproductive performance of early postpartum Holstein cows where oestrus was synchronised following chronic GnRH agonist treatment.
OBJECTIVE
The objectives of this study were: to compare the recovery of follicular development in early postpartum cows that had been treated for 7, 14 or 21 d with implants containing the GnRH agonist deslorelin; to evaluate the effectiveness of human chorionic gonadotrophin (hCG) for the induction of ovulation when a follicle was at least 10 mm in diameter following implant removal; and to compare final pregnancy rates for treated cows and untreated contemporaries.


METHODS
Within 3 d of calving Holstein cows were allocated to receive a single subcutaneous deslorelin implant to be left in place for either 7, 14 or 21 d, or to remain untreated as controls. Every deslorelin treated cow was monitored twice weekly for 35 d to determine the interval from implant removal to resumption of ovulation using serial transrectal ultrasonography and plasma progesterone assay. An injection of 1000 IU hCG was given to induce ovulation when a follicle of at least 10 mm diameter was first observed. Oestrous cycles of every cow were synchronised to facilitate artificial insemination (Al) at the start of the seasonally concentrated Al program and resynchronised for three rounds. Pregnancy testing was performed by ultrasonography 13 weeks after the first round of Al.


RESULTS
Deslorelin implants inhibited ovulation for at least 10 d after they were removed. Ovarian follicles were smaller for the group that had implants for 21 d at the time of implant removal. Eighteen cows selected for treatment with hCG ovulated and formed multiple corpora lutea within 7 d. There was no effect of treatment duration on final pregnancy rates. After three rounds of AI the pooled final pregnancy rate for every cow that had received a deslorelin implant was similar to the rest of the herd (67% versus 63%; Deslorelin versus Herd, P > 0.1). The interval from start date of the AI program to conception was also unaffected by treatment (9.6 +/- 3.0 versus 14.8 +/- 1.7 d; Deslorelin versus Herd; P > 0.1).


CONCLUSIONS
No significant effect was detected on the interval from implant removal to first ovulation by altering the duration of deslorelin treatment. Treatment with hCG when a follicle at least 10 mm in diameter was present induced ovulation in most cases. Although no significant improvement in fertility was found, a larger field trial using this model for induced anoestrous is necessary before any effect on fertility could confidently be stated.
Padula
A M
AM
University of Melbourne, Veterinary Clinical Centre, Princes Highway, Werribee, Victoria 3030. andrew.padula@bristol.ac.uk
MacMillan
K L
KL
D000818:Animals; D002417:Cattle / Q000502:physiology*; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D004343:Drug Implants; D004971:Estrus / Q000187:drug effects; D004973:Estrus Synchronization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists; D006080:Ovarian Follicle / Q000187:drug effects; D010060:Ovulation / Q000187:drug effects*; D049590:Postpartum Period; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000097:blood; D011897:Random Allocation; D012098:Reproduction / Q000187:drug effects*; D013997:Time Factors; D017329:Triptorelin Pamoate / Q000031:analogs & derivatives* / Q000494:pharmacology*
D006063:Chorionic Gonadotropin; D004343:Drug Implants; D017329:Triptorelin Pamoate; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; C066438:deslorelin