Effect of treatment with eCG, hCG or both 4 days after TAI on the development of the corpus luteum of dairy buffaloes

This study aimed to evaluate the effects of eCG, hCG, or both given at 4 days after TAI in the development of the corpus luteum (CL) of dairy buffaloes. Thus, 72 dairy buffaloes housed in Sete Barras, Sao Paulo state were used. At random days of the estrous cycle (D-12; 4:00 PM) all buffaloes received a new intravaginal progesterone (P4) releasing device (1 g of P4; Primer®, Tecnopec, Sao Paulo, Brazil) plus 2.0 mg of estradiol benzoate im (Gonadiol®, MSD Animal Health, Sao Paulo, Brazil). In D-3 (4:00 PM), females received 0.53 mg of PGF2α im (Cloprostenol sodium, Ciosin®, MSD Animal Health, Sao Paulo, Brazil) and 400 IU of eCG im (Novormon®, MSD Animal Health, Sao Paulo, Brazil), followed by removal of progesterone device. In D-2 (4:00 PM), 1.0 mg of estradiol benzoate (Gonadiol®, MSD Animal Health, Sao Paulo, Brazil) was administered im. The TAI was performed 40 hours after application of GnRH (D0; 8:00 AM). Four days after TAI (D4) all buffaloes that ovulated (n=60) after the protocol were randomly divided into four groups: buffaloes without treatment (Control, n=14); or treated with 400 IU of eCG i.m. (eCG, n=16; Novormon®, MSD Animal Health, Sao Paulo, Brazil); 1500 IU of hCG i.m. (hCG, n=14; Chorulon®, MSD Animal Health, Sao Paulo, Brazil); or 400 IU of eCG plus 1500 IU hCG (eCG+hCG; n=16). Ultrasound examinations (DP2200Vet Mindray, China) were performed to determine: dominant follicle diameter (oDF) in 3-D and D0; daily growth rate of the DF (GrowthDF; between D-3 and 0); and the diameter of the CL originated after TAI protocol in D4, D8, D12 and D16 (oCL), as well as the total growth of the CL (GrowthCL; between D4 and D16). The comparison between variables was performed through analysis of variance using Glimmix procedure of SAS®. The effects of treatment, day and interaction of these two effects on oCL were analyzed as repeated measures using the Mixed procedure of SAS®. Difference was considered when P<0.05. There was no difference among the respective control, eCG, hCG and eCG+hCG groups for: oDF D-3 - 10.1 ± 0.2 mm; oDF D0 - 12.6 ± 0.3 mm; and GrowthDF - 1.4 ± 0.1 mm/day. However, treatment (P < 0.01), day (P < 0.01) and day*treatment (P < 0.01) effects were detected on the development of the CL respectively for Control, eCG, hCG and eCG+hCG: D4 - 14.7 ± 0.6a ; 13.8 ± 0.5a ; 15.2 ± 0.5a ; 14.1 ± 0.4a mm; D8 - 16.8 ± 0.6b ; 17.1 ± 0.6b ; 20.7 ± 0.7a ; 19.1 ± 0.7ab mm; D12 - 17.4 ± 0.6b ; 18.2 ± 0.5ab; 21.6 ± 0.9a ; 21.1 ± 0.9ab mm; and D16 - 18.4 ± 0.6a ; 19.6 ± 0.6a ; 22.2 ± 0.9a ; and 21.1 ± 0.9a mm. Also detected a difference (P=0.03) for GrowthCL: Control - 4.6 ± 0.6c ; eCG - 5.5 ± 0.6bc; hCG - 7.0 ± 0.7ab; eCG+hCG - 6.9 ± 0.8a mm. It was concluded that administration of hCG 4 days after TAI in dairy buffaloes increases the diameter of the CL that was originated in the protocol of synchronized ovulation. In contrast, eCG treatment given at day 4 after TAI did not affect the development of the CL.