13 USE OF EQUINE CHORIONIC GONADOTROPIN OR FOLLICLE-STIMULATING HORMONE-LUTEINIZING HORMONE AT IMPLANT REMOVAL OR AT FIXED-TIME ARTIFICIAL INSEMINATION TIME IN PREGNANCY RATE OF SUCKLED NELLORE COWS

Abstract

Use of eCG as an inducer of follicular growth has improved the efficacy of fixed-time artificial insemination (FTAI) protocols and increased the ovulatory responses and pregnancy rates in beef cattle with low body condition scores (BCS) or are recently postpartum and anestrous. However, there are other gonadotropins such as FSH in different commercial applications (Pluset® – FSH : LH proportion ~50.0%) that could be potentially used to increase follicular growth but with controversial results. The goal of this trial was to evaluate the effects of replacing eCG with FSH/LH in two moments on the pregnancy rates (PR) of lactating Bos indicus cows raised in native grassland at Pantanal. The cows were subjected to a synchronization-of-ovulation protocol and FTAI based on progesterone, oestradiol benzoate (EB), and prostaglandin F_2α. On Day 0, Nellore multiparous cows (n = 352) at 42 days postpartum with BCS = 4.9 (1–9) were evaluated by transrectal ultrasonography and received progesterone implant (DIB 1.0 g of progesterone) plus 2 mg of EB IM. Devices were removed and prostaglandin F_2α was injected on Day 8 with 1 mg of EB. At the time of implant removal, the animals received T1 – 1 mL of saline solution IM (control; n = 80); T2 – 300 IU IM of eCG (Novormon®; ECG; n = 92); T3 – 40 IU IM of FSH/LH (Pluset®; Pluset; n = 98). The T4-group cows received 40 IU IM of FSH/LH (Pluset®) at FTAI time (Pluset-FTAI; n = 82); cows were timed-AI on Day 10 (44–48 h after implant removal) and evaluated by transrectal ultrasonography to measure the preovulatory follicle (POF) at FTAI and to estimate the pregnancy rate on Day 45. The effects of the treatment, sire, and BCS on pregnancy rate were evaluated using PROC GLIMMIX (SAS Institute Inc., Cary, NC). Because there was no difference between BCS, sire, and PR, they were removed from model. Pregnancy rate was not different between the treatment groups (control: 38.70%; ECG: 51.08%; Pluset: 45.91%, and Pluset-FTAI: 39.02%; P > 0.05), but the difference was found in POF, higher in ECG group – 13.53 mm compared with others (Pluset: 12.79 mm; control: 11.73 mm, and Pluset-FTAI: 12.01 mm; P < 0.05). Although PR was not different between treatments, the data are in agreement with the size of POF, where the largest POF are associated with tendency of higher pregnancy rates in ECG group. In conclusion, commercial FSH solution does not provide increases in PR, and eCG increases the preovulatory follicles in Nellore cows with a low-moderate BCS submitted to a progesterone-based FTAI protocol with EB at implant removal.