Journal of Animal Science, Vol 78, Issue 11 2913-2918, Copyright © 2000 by American Society of Animal Science

JOURNAL ARTICLE

Predicting growth in angus bulls: the use of GHRH challenge, insulin-like growth factor-I, and insulin-like growth factor binding proteins

E. E. Connor, S. M. Barao, A. S. Kimrey, A. B. Parlier, L. W. Douglass and G. E. Dahl
Department of Animal and Avian Sciences, University of Maryland, College Park 20742-2311, USA.

Plasma IGF-I, IGF binding protein-2 (IGFBP-2), and IGFBP-3 were quantified in growing Angus bulls (n = 56) to determine their relationship with postweaning growth and carcass ultrasound measurements. In addition, GH response to GHRH challenge (area-under-the-curve GH [AUC-GH) was determined for each bull as part of a previous study. Blood was collected by jugular venipuncture at the start of a 140-d postweaning growth performance test and at 28 d intervals for plasma IGF-I determination by RIA. Plasma IGFBP-2 and -3 content was measured at the start of the study, on d 70, and d 140 by Western ligand blotting. Individual weights and hip heights were measured every 28 d during the study and carcass longissimus muscle area, intramuscular fat percentage, and carcass backfat were estimated by ultrasound on d 140. Greater plasma IGF-I at the start of the performance test was associated with reduced postweaning ADG and increased longissimus area. Throughout the performance test period, the correlations between plasma IGF-I and hip height were consistently positive, ranging from 0.10 to 0.38, but the correlations between ADG and IGF-I varied from -0.32 to 0.31. Age-adjusted d-1 plasma IGFBP-2 was related to ADG during the performance test, explaining nearly 30% of the variation in ADG. A model combining weaning age, IGFBP-2, and AUC-GH showed a strong relationship with ADG (R2 = 0.40). Plasma IGFBP-2 and -3 were not related to carcass characteristics, and IGFBP-3 was not related to growth rates. This study provides additional evidence for the variable relationship between plasma IGF-I and growth rates in cattle. A significant positive relationship between plasma IGFBP-2, AUC-GH, and postweaning ADG warrants further investigation.

This article has been cited by other articles:

				M. M. Brandt, D. H. Keisler, D. L. Meyer, T. B. Schmidt, and E. P. Berg Serum hormone concentrations relative to carcass composition of a random allotment of commercial-fed beef cattle J Anim Sci, January 1, 2007; 85(1): 267 - 275. [Abstract] [Full Text] [PDF]

				K. E. Govoni, T. A. Hoagland, and S. A. Zinn The ontogeny of the somatotropic axis in Hereford calves from birth to one year of age and its response to administration of exogenous bovine somatotropin J Anim Sci, June 1, 2004; 82(6): 1646 - 1655. [Abstract] [Full Text] [PDF]

				L. H. Baumgard, W. J. Weber, G. W. Kazmer, S. A. Zinn, L. B. Hansen, H. Chester-Jones, and B. A. Crooker Effects of Selection for Milk Yield on Growth Hormone Response to Growth Hormone Releasing Factor in Growing Holstein Calves J Dairy Sci, October 1, 2002; 85(10): 2529 - 2540. [Abstract] [Full Text] [PDF]

				K. E. Govoni, X. C. Tian, G. W. Kazmer, M. Taneja, B. P. Enright, A. L. Rivard, X. Yang, and S. A. Zinn Age-Related Changes of the Somatotropic Axis in Cloned Holstein Calves Biol Reprod, May 1, 2002; 66(5): 1293 - 1298. [Abstract] [Full Text] [PDF]