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Title: PREDICTING GROWTH IN ANGUS BULLS: USE OF GHRH CHALLENGE, INSULIN-LIKE GROWTH FACTOR I AND INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS

Author
item Connor, Erin
item BARAO, S. - UNIVERSITY OF MARYLAND
item KIMREY, A. - UNIVERSITY OF MARYLAND
item PARLIER, A. - UNIVERSITY OF MARYLAND
item DOUGLASS, L. - UNIVERSITY OF MARYLAND
item DAHL, G. - UNIVERSITY OF MARYLAND

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plasma insulin-like growth factor I (IGF-I), IGF binding protein-2 (IGFBP- 2) and IGFBP-3 were quantified in growing Angus bulls (n=56) to determine their relationships with postweaning growth and carcass ultrasound measurements. In addition, growth hormone response to growth hormone- releasing hormone challenge (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 height were measured every 28 d during the study and carcass ribeye area, intramuscular fat percentage and carcass backfat were estimated by ultrasound on d 140. High plasma IGF-I at the start of the performance test was associated with lower average daily gain (ADG) and increased ribeye area. Throughout the performance test period, the correlations between plasma IGF-I and linear growth were consistently positive ranging from .10 to .38, but the correlations between ADG and IGF-I varied from -.32 to .31. Age-adjusted on-test plasma IGFBP-2 was highly predictive of ADG during the performance test, explaining nearly 30% of the variation in ADG. A model combining weaning age, IGFBP-2 and AUC-GH was highly predictive of ADG (R2 = 0.40). Plasma IGFBP-2 and -3 were poor indicators of carcass characteristics and IGFBP-3 was not related to growth rate. This study provides additional evidence for the variable relationship between plasma IGF-I and growth rate in cattle. A significant positive relationship between IGFBP-2, AUC-GH and postweaning ADG warrants further investigation.

Technical Abstract: 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 (AUC-GH) was determined for each bull as part of a previous study. Blood was collected by jugular venipuncture at the start tof 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 height were measured every 28 d during the study and carcass ribeye area, intramuscular fat percentage and carcass backfat were estimated by ultrasound on d 140. High plasma IGF-I at the start of the performance test was associated with lower postweaning ADG and increased ribeye area. Throughout the performance test period, the ecorrelations between plasma IGF-I and linear growth 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 on-test plasma IGFBP-2 was highly predictive of ADG during the performance test, explaining nearly 30% of the variation in ADG. A model combining weaning age, IGFBP-2 and AUC-GH was highly predictive of ADG (R2 = 0.40). Plasma IGFBP-2 and -3 were poor indicators of 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 on-test plasma IGFBP-2, AUC-GH and postweaning ADG warrants further investigation.