Comparison of follicular development, timing of ovulation and serum progesterone, estradiol and luteinizing hormone concentrations in dairy heifers treated with 4- or 5-day CoSynch + CIDR protocols

Abstract

The use of 4-day CoSynch + Controlled internal drug release (CIDR) + timed artificial insemination (TAI) in dairy heifers has resulted in adequate pregnancy rates compared with the 5-day CoSynch + CIDR + TAI protocol. The objective of this study was to compare follicular growth, timing of ovulation and serum progesterone (P₄ ), estradiol (E₂ ) and luteinizing hormone (LH) concentrations in dairy heifers treated with modified 4- or 5-day CoSynch + CIDR protocols (CIDR for 4 or 5 days, PGF₂ α at CIDR removal and GnRH + TAI 72 h later). Twelve cycling Holstein heifers were randomly assigned to either the 4- or 5-day Co-Synch+CIDR (n = 6/treatment) to receive an intravaginal insert CIDR^® containing 1.38 g of P₄ for 4 or 5 days, respectively. At CIDR removal, 25 mg of PGF₂ α was injected IM; 72 h after CIDR removal, heifers received 100 μg of GnRH IM and timed artificial insemination (TAI). Follicular growth and timing of ovulation were assessed using transrectal ultrasonography. Blood samples were collected at the time of CIDR insertion and at frequent time points after CIDR removal for determination of P₄ (at TAI), E₂ (every 12 h) and LH (every 6 h during the first and second day and every 2 h on the third day). Heifers in the 4-day group had smaller follicles from CIDR insert removal to ovulation compared with heifers in the 5-day treatment. Five of six heifers (83.3%) in the 4-day treatment ovulated at 90-96 h post CIDR insert removal, whereas most heifers in the 5-day treatment (4/6; 66.6%) ovulated at 84-90 h post CIDR insert withdrawal. Heifers in the 5-day treatment reached greater peak LH concentration between 48 and 72 h after CIDR insert removal and lesser E₂ concentration at TAI than heifers in the 4-day treatment. In conclusion, heifers in the 4-day treatment had smaller follicular diameter at 0, 30, 36, 42 and 48 h after CIDR insert removal, longer interval from CIDR insert removal to ovulation, greater E₂ concentrations at TAI, and lesser peak LH concentration than heifers in the 5-day treatment. These results represent a baseline for further studies to determine if prolonging the interval to TAI by 6 h in the 4-day CoSynch+CIDR would improve pregnancy risk.

Keywords: CIDR; Co-Synch; Dairy heifer; Estradiol; Luteinizing hormone; Ovulation.

Figure 1

Diagrammatic representation of the 4‐ and 5‐day CoSynch + CIDR synchronization protocols. CIDR, controlled internal drug release; TAI, timed artificial insemination.

Figure 2

Diameter (mm) of the dominant follicle (a), serum mean concentration of progesterone (P₄, ng mL⁻¹; b) and estradiol (E_2, pg mL⁻¹; c) in dairy heifers treated with 4‐ or 5‐ day CoSynch + CIDR synchronization protocols. For a: * Significant differences between groups at 0 (P = 0.02), 30 (P = 0.05), 36 (P = 0.02), 42 (P = 0.01) and 48 h (P = 0.001) after CIDR removal. ^ǂGroups tended to be different (P = 0.10). For b: Statistical difference was not observed between groups. For c: ^ǂ Mean E₂ concentration tended to be different at E₂ peak (P = 0.1) and at TAI (72 h after CIDR removal, P = 0.06) between treatments.

Figure 3

LH concentration (ng mL⁻¹) after CIDR insert removal in dairy heifers treated with 4‐ (a) or 5‐ day CoSynch + CIDR (b) synchronization protocols. H: heifer