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

• Published in: Journal of animal science Vol. 85; no. 11; pp. 2866 - 2872
• Main Authors: Velayudhan, B.T, Govoni, K.E, Hoagland, T.A, Zinn, S.A
• Format: Journal Article
• Language: English
• Published: Savoy, IL American Society of Animal Science 01.11.2007; Am Soc Animal Sci
• Subjects: Adipose Tissue - metabolism; Age Factors; Animal Feed; animal growth; Animal productions; Animals; application timing; backfat; beef cattle; Biological and medical sciences; body composition; Body Composition - drug effects; Body Composition - physiology; body weight; carcass composition; Cattle - blood; Cattle - growth & development; cattle feeding; dosage; dry matter intake; Eating - drug effects; Eating - physiology; Energy Intake; feed conversion; feed intake; Female; Fundamental and applied biological sciences. Psychology; Growth Hormone - blood; Growth Hormone - pharmacology; Insulin-Like Growth Factor Binding Protein 2 - blood; Insulin-Like Growth Factor Binding Protein 3 - blood; Insulin-Like Growth Factor I - analysis; Insulin-Like Growth Factor I - metabolism; liveweight gain; Male; medicated feeds; Muscle, Skeletal - metabolism; Random Allocation; somatotropin; temporal variation; Terrestrial animal productions; thickness; Vertebrates; Weight Gain - drug effects; Weight Gain - physiology; Exogenous; Growth rate; Insulin like growth factor binding protein; Vertebrata; Insulin like growth factor; Mammalia; Beef cattle; insulin-like growth factor; Artiodactyla; Day; somatotropin; Ungulata; Age; insulin-like growth factor binding protein
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2007-0281

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 μg/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.