Abstract
The objective of this study was to determine the effects of different intramuscular dosages of human chorionic gonadotropin (hCG) on ovarian follicular development of dairy cows diagnosed with refractory cystic ovarian follicles (COFs). Cows diagnosed with COFs (≥25 mm in diameter) were allocated to four treatment groups: hCG-1 (n = 3), a single dose of 4,500 IU on day 1; hCG-2 (n = 3), 2,250 IU on days 1 and 3; hCG-3 (n = 3), 1,500 IU on days 1, 3, and 5; and hCG-C (n = 3) received saline on day 1. Blood sampling and ovarian ultrasonographic (US) examinations were performed on days 1, 3, 5, 7, and 14. A progesterone (P4) value < 1 ng/ml was used as an indicator of absence of a functional CL. A significant increase (P < 0.05) in the number of follicles < 4 mm in diameter was observed in the hCG-2 group on day 5. Additionally, there was a significant difference in the number of follicles < 4 mm (P < 0.05) between both the hCG-2 and hCG-3 groups compared to the hCG-C group on day 5, and a tendency (P = 0.08) toward a difference in the number of 5–9 mm follicles in groups hCG-3, hCG-2, and hCG-1, compared with the hCG-C group on day 7. The proportion of cows on days 7 and 14 with P4 > 1 ng/ml was 100% (3/3) and 100% (3/3) in group hCG-1; 100% (3/3) and 67% (2/3) in group hCG-2; 67% (2/3) and 100% (3/3) in group hCG-3; and 33% (1/3) and 33% (1/3) in group hCG-C, respectively. Strong tendencies of P4 increases in group hCG-1 (P = 0.054) and hCG-2 (P = 0.051) were measured after hCG administration. Additionally, P4 values tended to be higher (P = 0.07) for group hCG-1 compared to group hCG-C on day 5. The preliminary findings of this study suggest that multiple smaller doses of hCG might be equally effective as a single large dose of hCG in modulating ovarian follicular development in dairy cows with COFs.
Highlights
Cystic ovarian follicles (COFs) are a common cause of reproductive failure in female cattle [1,2,3,4]
We focused on the effectiveness of alternative methods of administration of human chorionic gonadotropin (hCG), i.e., single or multiple divided doses for cows diagnosed with refractory COFs, to assess ovarian responses and serum P4 concentrations
The number of cows included in the study was small, our results suggest that repeated low doses of hCG over time may enhance the ovarian follicular development of the cows with COFs
Summary
Cystic ovarian follicles (COFs) are a common cause of reproductive failure in female cattle [1,2,3,4]. COFs were defined as non-ovulatory follicular structures measuring greater than or equal to 25 mm that persist for at least 10 days without the presence of a functional corpus luteum (CL) [4, 5]. This definition has been modified to include follicular structures with diameters ranging from 17 to 22 mm and persisting for 7 to 8 days [3, 4]. Previous reports estimate that the incidence of COFs in dairy cattle varies between 6 and 60%. Despite extensive research, the mechanism of COF development is unclear [7,8,9]
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