|Cushman, Robert - Bob|
Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2000
Publication Date: 4/15/2001
Citation: Cushman, R.A., Desouza, J.C., Hedgpeth, V.S., Britt, J.H. 2001. Effect of long-term treatment with recombinant bovine somatotropin and estradiol on hormone concentrations and ovulatory response of superovulated cattle. Theriogenology. 55(7):1533-1547. Interpretive Summary: Because previous work with cattle with increased ovulation rate due to either gonadotropin treatment or selection for increased ovulation rate (MARC Twinners) demonstrated that an increased number of growing microscopic follicles was associated with increased ovulation rate, the objective was to assess the effect of treatment with growth hormone or estradiol on superovulatory response in cattle. Non-lactating Holstein and Jersey cows (Trial 1), and Angus cows and heifers (Trial 2) received two ear implants of estradiol and biweekly injections of growth hormone for 75 days. Cows were stimulated with gonadotropins for 4 days beginning 2 days after removal of estradiol implants. Ovaries were collected to determine the number of CL at 1 to 2 wk after treatment. In Trial 2 only, cattle were inseminated at estrus and embryos were collected 6 to 8 d later. In Trial 1, number of CL was increased by the combination of estradiol and growth hormone. In Trial 2, estradiol increased the number of CL, and growth hormone increased the number of total ova and transferable embryos. We conclude that long-term treatment estradiol and growth hormone may interact to enhance follicular development and ovulatory response to gonadotropins.
Technical Abstract: The objective was to assess effects of long-term treatment with recombinant bovine somatotropin (bST) and estradiol-17beta (E2) on the number of follicles that ovulated in response to FSH. Non-lactating Holstein and Jersey cows (Trial 1, n = 27) and Angus cows and heifers (Trial 2, n = 35) received two ear implants of E2 and biweekly injections of bST in a 2 x 2 arrangement of treatments. Estradiol implants were removed 74.6 +/ 1.1 d after insertion and 18.1 +/ 0.9 d after the last biweekly injection of bST. Cows were stimulated with FSH-P beginning 2 d after removal of E2 implants, and PGF2alpha (PGF) was given on the third day of FSH treatment. Ovaries were collected to determine the number of CL at 1 to 2 wk after treatment with PGF. In Trial 2 only, cattle were inseminated at estrus and embryos were collected 6 to 8 d later. Implants or E2 increased (P < 0.01) serum E2 8-fold initially and E2 was still elevated 5-fold at removal of implants. Injections of bST increased (P < 0.01) serum growth hormone (GH) 15-fold and insulin-like growth factor-I (IGF-I) 3-fold. In Trial 1, number of CL was increased by the combination of bST + E2 (P < 0.01). In Trial 2, E2 increased the number of CL (P < 0.05), and bST increased the number of total ova and transferable embryos (P < 0.01). We conclude that long-term treatment with bST and E2 may interact to enhance follicular development and ovulatory response to FSH.