Abstract

A single intramuscular injection of 10g of Buserelin (Bus), a potent analogue of gonadotrophin releasing hormone (GnRH) was administered to non-lactating Holstein cows (Experiment 1) or Brangus cross animals (Experiment 2) on cycle day 12 (oestrus + cycle day 0). This treatment altered normal patterns of ovarian follicle development, causing atresia or premature luteinisation especially in follicles of 6 to 9 mm diameter. Injecting 8 or 10g Bus every third day from cycle day 12 to cycle day 48 (Experiment 3), extended the average inter-oestrous interval to 56.2 days, maintained diaoestrous concentrations of plasma progesterone (5 to 12 ng/ml), and increased corpus luteum lifespan to at least 49 days in 5 of 6 Holstein cows. This 3 day interval was also used with 18 cows and heifers which were embryo recipients when they had been in oestrus from 2.5 to 7.5 days before their contemporary embryo donors (Experiment 4). The average pregnancy rate following these asynchronous transfers was 38.9%, varying from 20% when morulas were transferred to 62.5% with blastocysts. Inserting a CIDR-B into heifers 12h after the onset of oestrus for 3 to 15 days produced alterations in inter-oestrus intervals which indicated that progesterone treatment during metoestrus could potentiate the capacity of the uterus to synthesise and release prostaglandin F2a (Experiment5). The results from these five experiments showed that manipulating ovarian follicle development with Bus, or altering normal follicle-uterine interactions could be utilised as forms of oestrous cycle control which may be applied after insemination or embryo transfer.

DJS, Hetzel

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 53-56, 1989