PSXII-36 Use of FSH or hCG to enhance follicular growth and pregnancy per artificial insemination during a split-AI program in crossbreed beef heifers

Abstract

Abstract The objective of the study was to compare follicle growth and pregnancy per artificial insemination (P/AI) in crossbreed heifers receiving either a low dose of hCG (150 IU) or a low dose of FSH (20 mg) vs. a control group during the final stage of a split-AI protocol. A total of 387 heifers were enrolled in the trial and were randomly assigned in three treatments (Control n = 134, FSH n = 125, and hCG n =128) within reproductive tract score (RTS; 1 to 5 scale), body condition score (BCS; 1 to 9 scale) and pubertal status. All groups were synchronized with a 7-day CO-Synch + CIDR protocol, at CIDR removal the two treatments were injected, an Estrotect patch was placed, and the diameter of the dominant follicle was assessed through transrectal ultrasonography, at day 9 heifers that presented estrus (> 50% of the Estrotect patch rubbed off) were AI, and those that did not were TAI at day 10. An ultrasound was carried out along with the AI to measure the diameter of the preovulatory follicle and 30 days after for pregnancy check. The data was analyzed using the GLIMMIX procedure (SAS). The diameter of the preovulatory follicle was different among treatments (Control: 11.48 ± 0.21; FSH: 11.48 ± 0.25; hCG; 10.73 ± 0.28; P = 0.01). However, the rate of follicular growth (Control: 4.96 ± 0.37; FSH: 4.59 ± 0.39; hCG: 5.12 ± 0.38; P = 0.64) and P/AI (control: 41.35%; FSH: 35.77%; and hCG: 34.38%; P = 0.47) were not different among groups. There was a significant difference (P < .0001) in P/AI when comparing animals that presented estrous (48.99%) or not (29.27%). In conclusion, the use of low dosed of hCG or FSH at the time of device removal did not increase the proportion of pregnant heifers.