Effect of long-term treatment with recombinant bovine somatotropin and estradiol on hormone concentrations and ovulatory response of superovulated cattle

The objective was to assess effects of long-term treatment with recombinant bovine somatotropin (bST) and estradiol-17 beta (E2) on the number of foll icles that ovulated in response to FSH. Non-lactating Holstein and Jersey c ows (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 o f treatments. Estradiol implants were removed 74.6 +/- 1.1 d after insertio n and 18.1 +/- 0.9 d after the last biweekly injection of bST. Cows were st imulated with FSH-P beginning 2 d after removal of E2 implants, and PGF2alp ha (PGF) was given on the third day of FSH treatment. Ovaries were collecte d to determine the number of CL at 1 to 2 wk after treatment with PGF. In T rial 2 only, cattle were inseminated at estrus and embryos were collected 6 to 8 d later. Implants of E2 increased (P < 0.01) serum E2 8-fold initiall y and E2 was still elevated 5-fold at removal of implants. Injections of bS T increased (P < 0.01) serum growth hormone (GH) 15-fold and insulin-like g rowth factor-I (IGF-I) 3-fold. In Trial 1, number of CL was increased by th e 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 e mbryos (P < 0.01). We conclude that long-term treatment with bST and E2 may interact to enhance follicular development and ovulatory response to FSH. (C) 2001 by Elsevier Science Inc.