Effects of recombinant bovine somatotropin on hypophyseal and ovarian functions of lactating dairy cows

Abstract

1991. Effects of recombinant bovine somatotropin on hypophyseal and ovarian functions of lactating dairy cows. Can. J. Anim. . Three trials were conducted to determine the effects of recombinant bovine somatotropin (rbST) on reproductive functions of lactating Holstein dairy cows. In Trial 1, 49 cows were used to investigate the effects of 0,320 or 640 mg of rbST in a sustained-release formulation injected every 28 d on plasma progesterone (Pa) concentration during estrous cycles. Total P, area and Pa mean were increased (P<0.05) in rbSTtreated cows during the lst and 2nd detected estrous cycle post-rbST injection. Maximum Pa value, slope of the Pa decline and length of cycles were not affected by rbST treatment. In Trial 2, 56 cows were used to investigate the effects of 0, 320, 640 and 960 mg of rbST in a sustained-release preparation injected every 28 d on plasma P4 concentration from weeks 1 to 34 of pregnancy. Mean Po was increased (P:0.08) in rbST-treated cows proportionally to the rbST dose received. In Trial 3, l8 cows were used to investigate the effects of 0 or 25 mg d -' of rbST injected from days 3 to 15 postpartum (pp) on the gonadotropin-releasing hormone (GnRH) induced luteinizing hormone (LH) response curve at 14 d pp. Total area under the LH curve and LH peak value were increased (P < 0.05) in rbST+reated cows, but LH baseline and time to LH peak were not different among groups. Cows receiving rbST were in a more negative energy balance due to higher milk production. In summary, long-term administration of rbST increased the concentration of plasma progesterone during the first two estrous cycles post-treatment and during pregnancy, and enhanced the GnRH-induced LH response at 14 d pp.

Comparative Activities of Growth Hormone and Luteinizing Hormone in the Direct Stimulation of Local Release of Progesterone from Microdialyzed Ovine Corpora Lutea In Vivo.

“…such BST treatments resulted in an increase in plasma concentrations of progesterone (P) [4,5], as well as an increase in the size of the corpus luteum (CL) [6]. The data suggest that BST treatment directly stimulates ovarian function.…”

First lactation ovarian function in dairy heifers in relation to prepubertal metabolic profiles

“…Thus the PCL cows maintained their yield with greater dry matter intake, compared with DOV1 cows, without major adverse consequences for the reproductive system. The endocrine profile of high GH levels may, however, be responsible for the extension of the luteal phase, as GH has been shown to be luteotrophic in vitro (Liebermann & Schams 1994, Wathes et al 1995 and some studies have reported that administration of bovine somatotrophin to lactating cows can prolong the luteal phase (Schemm et al 1990, Gallo & Block 1991, Lucy et al 1994, although this effect was not seen in 1-year-old heifers (Yung et al 1996).…”

A review of bovine growth hormone

“…Schemm et al (1990) then reported positive correlations between rbGH treatment and concentrations of plasma Pa during bovine estrous cycles. Gallo and Block (1991) observed increased P4 secretion during estrous cycles and pregnancy when rbGH was injected and speculated that these effects may have been caused by an increase in IGF-I production stimulated by the rbGH treatment (Spicer et al 1990). However, the length and regularity of estrous cycles were not affected by rbGH treatment in the study by Gallo and Block (1991) (Sirinathsinghji et al 1983).…”

“…Gallo and Block (1991) observed increased P4 secretion during estrous cycles and pregnancy when rbGH was injected and speculated that these effects may have been caused by an increase in IGF-I production stimulated by the rbGH treatment (Spicer et al 1990). However, the length and regularity of estrous cycles were not affected by rbGH treatment in the study by Gallo and Block (1991) (Sirinathsinghji et al 1983). No data are available which demonstrate effects of rbGH or milk yield on p-endorphin production and all of the above listed possibilities require investigation.…”