Determination of minimum effective doses of luteinizing hormone and human chorionic gonadotropin for intrafollicular treatment to induce ovulation in dairy heifers.

The aim of this study was to determine the minimum effective intrafollicular doses of luteinizing hormone and human chorionic gonadotropin in order to induce ovulation in cycling dairy heifers that have not yet been adequately established. Application of 10, 5, 1, 0.5, 0.1, 0.01 and 0.001 µg luteinizing hormone as well as 10, 1, 0.1, 0.01 and 0.001 international units (IU) of human chorionic gonadotropin in dominant follicles was performed on day 7 of the oestrous cycle. Control animals were given luteinizing hormone (12.5 mg and 25 mg) or human chorionic gonadotropin (2000 IU) intravenously. Accessory corpus luteum on day 14 of the oestrous cycle was considered as an evidence of ovulation. Ovulation was observed in 2 out of 3 heifers in each treatment group (n = 3) after administration of 10–0.1 µg luteinizing hormone (except for 0.5 µg – ovulation in 3 of 3 heifers), in all heifers after administration of 10–0.01 IU human chorionic gonadotropin as well as in all control heifers. Administration of 0.01 µg and 0.001 µg luteinizing hormone as well as of 0.001 IU human chorionic gonadotropin did not result in ovulation. Higher progesterone concentration on day 14 vs. day 7 of the oestrous cycle was found after all treatments. Nevertheless, the differences were signicant (P < 0.05) only after intrafollicular treatments with 5, 1 and 0.001 µg luteinizing hormone as well as 10, 1 and 0.01 IU human chorionic gonadotropin. In conclusion, minimum efcient doses for intrafollicular treatment of the dominant follicles in cycling heifers capable of inducing ovulation were 0.1 µg of luteinizing hormone and 0.01 IU of human chorionic gonadotropin. This is the rst study describing the intrafollicular luteinizing hormone administration in cycling dairy heifers.