Abstract #T223

# T223
Exogenous estradiol decreases relative endometrial gene expression for ERα and ERβ in pre-pubertal dairy heifers.
Chelsee T.L. Holloway*1, Adam J. Geiger1, Jennifer Malkus1, Alan D. Ealy2, Rebecca R. Cockrum1, Robert M. Akers1, 1Virginia Polytechnic Institute and State University, Department of Dairy Science, Blacksburg, VA, 2Virginia Polytechnic Institute and State University, Department of Animal and Poultry Sciences, Blacksburg, VA.

The objectives of this study were to determine (1) the effect of early nutrition on reproductive development and (2) response of reproductive tissues to estradiol (E2) in pre-pubertal heifers. Holstein heifer calves (n = 23; 7 d of age) were fed either a restricted milk replacer diet (20% CP, 20% fat, 454 g/d) or accelerated diet (28% CP, 25% fat 1,333 g/d) for 8 wks. After the initial 8 wks, heifers were partitioned into a 2 × 2 factorial design and treated for an additional 2 wks accordingly: restricted diet + placebo implant (CON; n = 6), accelerated diet + placebo (ACC; n = 5), restricted diet + E2 implant (CONEST; n = 6) and accelerated diet + E2 (ACCEST; n = 6). Estrogen receptor α (ERα) and β (ERβ) gene expression was determined from RNA isolated from harvested endometrial, ovarian, and hypothalamic tissues using Real-Time qPCR. Fold changes were analyzed using the GLM procedure in SAS with treatment used as a fixed effect and initial body weight used as a covariate. The main effect of diet did not differ (P ≥ 0.127) for any of the tissues. However, E2 treatment differed for the endometrium (P ≤ 0.001), but not for the ovary or hypothalamus (P ≥ 0.528). In the endometrium, ERα was upregulated (P ≤ 0.024) in ACC heifers (8.44 ± 1.21) as compared with ACCEST (2.69 ± 1.43), and CONEST heifers (2.63 ± 1.22). Gene ERβ was also upregulated more (P ≤ 0.052) in ACC heifers (4.16 ± 0.52) than ACCEST (2.11 ± 0.61) or CONEST heifers (1.46 ± 0.52) in the endometrium. Additionally, ERβ was upregulated (P < 0.001) in CON heifers (4.56 ± 0.52) as compared with CONEST heifers, and tended (P = 0.071) to be upregulated in ACCEST heifers. Overall, results indicated that diet alone did not affect expression of ERα or ERβ in reproductive tissues of pre-pubertal heifers. However, treatment with E2 in pre-pubertal heifers affected relative gene expression of key genes within the hypothalamic-gonadal pathway. Determining the effect of estrogen on the development of reproductive tissues is key to understanding signaling pathways that activate the onset of puberty.

Key Words: estradiol, gene expression, nutrition