Comparisons of several dosages of a GnRH analog with the standard dose of hCG in the treatment of follicular cysts in dairy cows

Two experiments were carried out to examine therapeutic effect of a gonadotropin-releasing hormone analog, buserelin, on ovarian follicular cysts in dairy cows. Follicular cysts were diagnosed by palpation per rectum as well as by milk progesterone assay. Luteinization of the follicular cysts following treatment was judged by an increase in milk progesterone. In Experiment 1, 35 cows were diagnosed to have follicular cysts on the basis of palpations and low milk progesterone concentrations 1 week before treatment. Another 19 cows which were clinically diagnosed with follicular cysts but showed high milk progesterone levels before treatment were excluded. Sixty-two percent (11/18) of cows with follicular cysts treated with 20 microg of buserelin and 82% (14/17) of cows treated with 10,000 IU of human chorionic gonadotropin (hCG) showed luteinization of follicular cysts within 4 to 5 days after the treatments. The percentage of cows conceiving within 100 days after treatment and the average interval in days between treatment and conception were 44% and 42+/-18 (SD) days for the buserelin-treated cows and 47% and 42+/-18 days for the hCG-treated cows. In Experiment 2, the effects of treatment doses (6, 10, 20 and 30 microg of buserelin and 10,000 IU of hCG) on follicular cysts were compared using 103 cows. An additional 23 cows which were clinically diagnosed as having follicular cysts and which were given treatment showed a high milk progesterone concentration on the day of treatment and were therefore excluded. Fifty to 64% of the cows responded with luteinization of follicular cysts after treatment. There was no significant difference in response among cows given either the different dosages of buserelin or the hCG. However, the percentage of the total number of cows that conceived after a single or a repeated treatment with 6 microg buserelin was lower than that of cows after a single or a repeated treatment with 10 microg buserelin (P<0.05). An increase in the dose of buserelin from 10 to 30 microg did not improve the therapeutic effect of the drug. Thus, it is concluded that a single intramuscular injection of buserelin at a dose of 10 microg or higher is as effective as 10,000 IU hCG, and is, therefore, recommended for the treatment of ovarian follicular cysts in cows.