Effect of daily replacement therapy with recombinant bovine somatotropin on somatotropin, insulin-like growth factor I, and onset of puberty in beef heifers immunized against growth hormone-releasing factor.
Two experiments examined whether replacement therapy with recombinantly derived bovine somatotropin (rbST) would induce puberty in heifers that had been actively immunized at 6 mo of age against growth hormone-releasing factor (GRF). Heifers received daily i.m. injections of 25 mg of rbST (Exp. 1, n = 6; Exp. 2, n = 4) or vehicle (VEH; Exp. 1, n = 6; Exp. 2, n = 4) for 56 d. Serum concentrations of somatotropin (ST, nanograms/milliter) were low in all heifers before first injection in Exp. 1 (1.56 +/- .04) and 2 (.95 +/- .03). During treatment, serum ST was greater (P < .01) in rbST than in VEH heifers (75.4 +/- 4.8 vs 2.8 +/- .1 ng/mL, respectively) in both experiments and remained increased through d 57 (32.2 +/- 6.4 vs .90 +/- .01 ng/mL). IN Exp. 1 and 2, concentrations of serum IGF-I were similar in rbST and VEH heifers before treatment, increased (P < .01) 12 h after first rbST, and remained increased (P < .01) through d 57 in rbST heifers. Concentrations of serum insulin (INS) and plasma glucose (GLU) were similar (P > .10) in rbST and VEH heifers before first injection (Exp. 1 and 2). Serum INS (micro-units/milliliter) was greater (P < .01) in rbST (61.7 +/- 3.7 and 36.0 +/- 2.4) than in VEH (12.4 +/- 1.6 and 8.1 +/- 1.0) heifers on d 1 or 2 only, in Exp. 1 and 2, respectively. In Exp. 1, GLU was increased (P < .05) by rbST on d 2 through 57, but only on d 1 in Exp. 2. Proportion of heifers pubertal by d 21 tended to be greater (P < .07) in rbST (3 of 6) than in VEH (0 of 5) heifers in Exp. 1, but not in Exp. 2 (1 of 4 vs 1 of 4, respectively). All heifers in Exp. 1 and 50% of the heifers in Exp. 2 attained puberty by d 56. Daily rbST increased ST, IGF-I, INS, and GLU but did not hasten onset of puberty in heifers immunized against GRF.
Stanko
R L
RL
Department of Animal Science, North Carolina State University, Raleigh 27695-7621.
Armstrong
J D
JD
Cohick
W S
WS
Harvey
R W
RW
Simpson
R B
RB
Hartnell
G F
GF
Heimer
E P
EP
Campbell
R M
RM
D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D002352:Carrier Proteins / Q000097:blood; D002417:Cattle / Q000276:immunology / Q000502:physiology*; D005260:Female; D013006:Growth Hormone / Q000031:analogs & derivatives* / Q000097:blood* / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000276:immunology*; D006728:Hormones / Q000494:pharmacology; D019382:Human Growth Hormone; D007114:Immunization / Q000662:veterinary; D007328:Insulin / Q000097:blood; D018971:Insulin-Like Growth Factor Binding Protein 2; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D011994:Recombinant Proteins / Q000494:pharmacology; D012741:Sexual Maturation / Q000187:drug effects*
D001786:Blood Glucose; D002352:Carrier Proteins; D006728:Hormones; D007328:Insulin; D018971:Insulin-Like Growth Factor Binding Protein 2; D011994:Recombinant Proteins; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone