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

Abstract

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 significant (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 efficient 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 first study describing the intrafollicular luteinizing hormone administration in cycling dairy heifers. Intraovarian injection, ovum pick-up, ultrasound-guided transvaginal ovarian puncture, accessory corpus luteumUltrasound-guided transvaginal intrafollicular injection of human chorionic gonadotropin (hCG) in cattle was first reported as a useful research tool by Kot et al. in 1995. Since then, intrafollicular injection of different substances such as phosphate-buffered saline or insulin-like growth factor-I (Bergfelt et al. 1998;Ginther et al. 2004;Shahiduzzaman et al. 2010) as well as intrafollicular insemination (Lopez-Gatius and Hunter 2011) have been described. In our former study, intrafollicular treatment (IFT) with luteinizing hormone (LH) injected in the dominant follicle in heifers previously treated by deslorelin implants was reported. Ovulation was proven after the intrafollicular treatment using various doses of LH . However, minimum effective doses of LH for IFT in comparison with IFT using hCG have not yet been adequately established.The aim of this study was to determine the minimum efficient doses of LH and hCG for intrafollicular treatment to induce ovulation in cycling dairy heifers. Materials and Methods Intrafollicular treatment equipmentIntrafollicular treatment was performed using a newly developed double channel instrument enabling asp...