The effect of exogenous follicle stimulating hormone (FSH) and endogenous plasma leptin concentrations on the pregnancy rate of beef heifers subjected to fixed-timed artificial insemination (FTAI)

In this study, 53 crossbred beef heifers were used to test the hypotheses that administration of exogenous FSH 2 days following CIDR insertion and administration of estradiol would increase the pregnancy rate in heifers synchronized for FTAI and that plasma leptin concentrations in beef heifers would be higher for heifers that became pregnant to FTAI. The heifers used in this study had a median age of 440 days, an average weight of 324 kg, an average body condition score of 5.1 and a mean reproductive tract score of 3.1. Heifers were stratified by weight and BCS into two groups and then treatments were randomly allotted to each group: (1) control (n=28) or (2) FSH (n=27). Both groups were administered 200mg estradiol benzoate (EB) and received an intravaginal controlled internal drug-releasing device (CIDR) on day 0. On day 2, females in the FSH treatment group were administered 20 mg of FSH, while the control group received 1 ml of saline. On day 7 all females were administered 25 μg PGF2α and the CIDR was removed. Then 24h following CIDR removal all females were administered 1mg EB and 24h later were subjected to FTAI. Pregnancy diagnosis was performed via transrectal ultrasonography 43 days following insemination. Blood samples were collected via jugular venipuncture on days 2, 6-10, 13 and 52 and plasma leptin concentrations were determined by radioimmunoassay. Pregnancy rates were higher (P=0.01) for FSH-treated females (60%) compared with females not receiving FSH (25%). Circulating plasma leptin concentrations were higher (P=0.0051) for pregnant females compared with females that did not become pregnant following FTAI during the experiment. Mean plasma leptin concentration was also higher (P=0.04) from day 2 to day 9 during the synchronization protocol in heifers that became pregnant compared with heifers that did not become pregnant from FTAI. There was no difference (P=0.38) in reproductive tract scores for heifers that became pregnant compared with heifers that did not become pregnant from FTAI. Circulating leptin concentrations were not different (P=0.11) for females receiving FSH compared with females in the non FSH-treated group. Circulating leptin concentrations were affected by sampling day (P<0.0001). However, there was no interaction between sampling day and pregnancy status (P=0.80), treatment and pregnancy status (P=0.14) or treatment and sampling day (P=0.12). These results indicate that the administration of FSH on day 2 of the synchronization protocol may increase pregnancy rates in beef heifers and that increased circulating concentrations of plasma leptin during the synchronization protocol may be indicative of subsequent pregnancy outcome.