Effects of recombinant bovine somatotropin treatment during the transition period on serum growth hormone and insulin-like growth factor 1 concentrations and liver content of lipid, triglyceride, and glycogen

Abstract Text: Objectives were to evaluate the effects of treatment of peripartum Holstein cows with recombinant bovine somatotropin (rbST) on serum growth hormone (GH) and insulin-like growth factor (IGF)-1 concentrations and liver total lipid (TL), triglyceride (TG), and glycogen (GLY) contents. Cows were assigned to one of three treatments at 253±1 d of gestation: CON (0 mg/d rbST,n=53), rbST87.5 (87.5 mg of rbST every 7 d,n=53), or rbST125 (125 mg of rbST every 7 d,n=53). Treatments were given weekly from d -21 to 28 relative to calving. Milk production data was collected weekly until 150 d postpartum. Blood was sampled weekly from d -21 to 21 relative to calving for determination of GH and IGF-1 concentrations. Liver biopsies were performed in a sub-group of cows (n=10/treatment) at -21, -7, and 7 d relative to calving for determination of liver contents of TL, TG, and GLY. Continuous data were analyzed by ANOVA using the MIXED procedure. Treatment did not (P=0.75) affect milk production (CON=45.9±1.3, rbST87.5=45.8±1.4, rbST125=47.1±1.3 kg/d) but there was an interaction between treatment and day (P<0.01). Treatment affected GH concentration (CON=13.0±0.9, rbST87.5=16.1±0.9, rbST125=18.2±0.9 ng/ml; P<0.01). Concentration of GH of rbST125 cows tended to be higher than rbST87.5 cows (P=0.11), and rbST87.5 (P=0.02) and rbST125 (P<0.01) cows had higher GH concentrations than CON cows. Treatment tended (P=0.06) to affect IGF1 concentration (CON=84.6±3.5, rbST87.5=92.9±3.5, rbST125=96.2±3.5 ng/ml). IGF-1 concentration was not (P=0.50) different between rbST87.5 and rbST125 cows but rbST87.5 cows tended to (P=0.10) and rbST125 cows had (P=0.02) greater IGF1 concentration than CON cows. The interaction between treatment and day (P=0.01) demonstrated that the rbST treatment effect on IGF-1 concentration was observed primarily before calving. There was no effect of treatment on TL (P=0.80) and TG (P=0.24) liver content. Although GLY liver content was not (P=0.19) affected by treatment, rbST125 cows tended to have greater GLY liver content compared to rbST87.5 (P=0.10) and CON (P=0.13) cows at -7 and 7 d relative to calving. Peripartum treatment with rbST increased serum GH concentration during the peripartum period and serum IGF1 concentration prepartum. The increased GLY liver content in rbST treated cows may indicate a more efficient use of fatty acids and sparing of glycogen as a consequence of rbST treatment.

Keywords: transition cow, recombinant bovine somatotropin, metabolism