The Effects of GnRH Injection on Follicular Wave Emergence in Cows Suffering from Cystic Ovaries

The effect of Gonadotropin Releasing Hormone (GnRH) on follicular wave emergence in cows with cystic ovaries was investigated. The estrous cycles of 10 cows were synchronized with 2 im injections of prostaglandin F2? given 11 days apart. The cows were randomly assigned to 1 of 3 treatments. Control cows (n=5) received no injection, whereas GnRH cows (n=5) received a GnRH injection on day 6 of the estrous cycle (day of injection=day 0). In cows with cystic ovaries (n=5), diagnosis of a cyst was based on the palpation per rectum of an abnormally large (> 20 mm) follicle and no corpus luteum with these cows then receiving a GnRH injection. The ovaries were scanned through daily ultrasonography from 4 days before (day -4) the day of GnRH treatment (day 0) until 4 days after GnRH treatment (day 4). Daily ultrasonography confirmed the presence of a cyst for at least 10 days in the ovary of the cystic cows. These cows then received a GnRH injection (day 0). The follicles were classified as 4 to 6 mm (small), or ? 7 mm (large) follicles. Data were analyzed using the GLM procedure of SAS. In control group, the number of small follicles tended to decline until day 2 of the experiment. Following GnRH injection (day 0) in groups GnRH and cystic cows, the number of small follicles increased until day 2. The number of large follicles in control group did not decrease, however, these classes of follicles decreased (P<0.05) until day 2 in the GnRH and cystic cows. An increase in the number of 4 to 6 mm follicles, 2 days following GnRH injection showed that GnRH treatment could promote the emergence of a new follicular wave in cystic cattle similar to the normal cyclic cattle.