title: Growth rate and changes of the somatotropic axis in beef cattle administered exogenous bovine somatotropin beginning at two hundred, two hundred fifty, and three hundred days of age.
abstract: To determine the effects of bovine somatotropin (bST) treatment beginning at 3 ages on the growth rate and components of the somatotropic axis, 40 beef cattle (200 +/- 21 d of age) were randomly assigned to 1 of 4 treatments (10 animals/treatment). Three of the treatment groups received bST (33 mug/kg of BW) daily beginning at 200, 250, or 300 d of age until all animals reached 400 d of age; the fourth group served as controls (0 bST). Animals were housed in pens (5 animals per pen; 2 pens per treatment) and fed a diet formulated for an ADG of 1.2 kg/d. Feed intake (per pen) was measured daily, and BW was determined weekly. Blood samples (10 mL) and ultrasound measurements were collected at 200, 250, 300, 350, and 400 d of age. Serum concentrations of ST and IGF-I were determined by RIA and IGFBP-2 and -3 by ligand blot procedures. Overall, cattle gained 284.0 +/- 14.7 kg of BW with a treatment x week interaction (P < 0.01), such that during the treatment period ADG was 11.6, 8.7, and 15.8% greater (P < 0.05) in cattle treated with bST beginning at 200, 250, and 300 d, respectively, relative to controls during the same time frame. Average DMI was 13.6% less (P < 0.05) in bST-treated cattle than in controls. Increases in ADG coupled with a reduction in DMI resulted in 11.7, 14.0, and 26.4% increases (P < 0.01) in the efficiency of gain (G:F) in bST-treated cattle beginning at 200, 250, and 300 d of age, respectively, compared with contemporary controls. Backfat thickness increased (P < 0.05) over time, but the magnitude of the increase was less in the bST-treated cattle (treatment x week interaction; P < 0.05). Area of the LM increased (P < 0.05) over time but was similar across treatment groups. Serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05), whereas IGFBP-2 decreased (P < 0.05) over time. The changes in the components of somatotropic axis were more pronounced in bST-treated cattle compared with controls, with the greatest magnitude of response in animals that began bST treatment at 300 d of age. In conclusion, the exogenous bST-induced growth response was greater in animals that began to receive bST administration at 300 d of age and received it for a shorter period (100 d) compared with animals that received bST beginning at 200 or 250 d of age.
authors: Department of Animal Science, University of Connecticut, Storrs 06269, USA.
authors: B T
authors: BT
authors: Velayudhan
authors: K E
authors: KE
authors: Govoni
authors: T A
authors: TA
authors: Hoagland
authors: S A
authors: SA
authors: Zinn
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000367:Age Factors; D000821:Animal Feed; D000818:Animals; D001823:Body Composition / Q000187:drug effects* / Q000502:physiology; D002417:Cattle / Q000097:blood / Q000254:growth & development*; D004435:Eating / Q000187:drug effects* / Q000502:physiology; D002149:Energy Intake; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000494:pharmacology*; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D011897:Random Allocation; D015430:Weight Gain / Q000187:drug effects* / Q000502:physiology
chemical_list: D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; C073294:growth hormone, bovine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone