Lack of luteolytic effect of gonadotropin releasing hormone (GnRH) with therapeutic and repeated doses in dairy cows.
Two experiments were conducted with multiparous cycling dairy cows in the post-partum period. They were assigned randomly to GnRH treatment or to saline injection (control groups) during the mid-luteal phase. In experiment 1, seven cows were treated with five consecutive injections of GnRH (100 micrograms i.m.) at hourly intervals and four controls were similarly treated with saline. In experiment 2, (seven treated and three control cows) treatment consisted of 10 i.m. injections of 500 micrograms GnRH or saline twice a day (8 h and 18 h) over a period of 120 h (five days). In both experiments injections started on day 12 of the oestrous cycle. LH immediately following treatment and subsequent progesterone concentrations for the next 35 days were assayed in peripheral blood samples. Most of the cows were inseminated at the oestrus following the treatment period. Profiles of progesterone after GnRH-treatment varied slightly but transiently between days two and four post-treatment in experiment 1. By contrast in experiment 2, there were no significant changes in the progesterone patterns during that period when compared to controls. Moreover two cows had a prolonged oestrous cycle. There was no difference in the conception rates according to groups and the progesterone patterns of the following cycle in the non-pregnant cows did not seem to be modified. In conclusion, repeated therapeutic doses of GnRH administered in the mid-luteal phase did not induce early luteolysis and appeared not to impair fertility.
D000818:Animals; D002417:Cattle / Q000502:physiology*; D003338:Corpus Luteum / Q000187:drug effects*; D004971:Estrus / Q000187:drug effects; D005260:Female; D007273:Injections, Intramuscular; D007986:Luteinizing Hormone / Q000097:blood; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology* / Q000502:physiology; D011247:Pregnancy; D011374:Progesterone / Q000097:blood
D010906:Pituitary Hormone-Releasing Hormones; D011374:Progesterone; D007986:Luteinizing Hormone