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Title: A TWO-SAMPLE METHOD FOR ASSESSING GROWTH HORMONE RESPONSE TO GROWTH HORMONE-RELEASING HORMONE CHALLENGE: USE AS A PREDICTOR OF GAIN IN BEEF BULLS

Author
item Connor, Erin
item BARAO, S. - UNIVERSITY OF MARYLAND
item RUSSEK-COHEN, E. - UNIVERSITY OF MARYLAND
item DAHL, G. - UNIVERSITY OF MARYLAND

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: In two experiments, Black Angus bulls were challenged at weaning with a growth hormone-releasing hormone (GHRH) analog and evaluated for their growth hormone (GH) response to determine whether GH response is predictive of subsequent growth characteristics. The GH response was determined by measuring GH in blood serum collected 0 and 10 min post-GHRH injection [Experiment 1: 1.5 æg/100 kg BW human GHRH, n = 34; Experiment 2: 1.5 and 4.5 æg/100 kg BW bovine GHRH (treatments LGHRH and HGHRH, respectively) administered 3 h after a 4.5 æg/100 kg BW clearance dose of GHRH (CLEAR), n = 38]. In Experiment 1, GH response was not predictive of growth or carcass measurements. In Experiment 2, GH response to LGHRH was positively related to average daily gain (ADG; R2 = .18; P = .007) during a 112-d controlled feeding trial. In addition, there was a tendency for bulls with a greater GH response to HGHRH to exhibit greater ADG than animals with a low response. However, GH response to GHRH was not related to changes in hip height or carcass ultrasound measurements at Day 112 of the growth performance trial. Response of GH to repeated GHRH challenges was consistent within animal over time = .47; P = .003). The use of a clearance dose 3 h prior to GHRH challenge improved the relationship between GH response and ADG. Results of this study suggest that GH response to GHRH challenge is a useful tool for identifying beef bulls with superior growth potential.

Technical Abstract: In two experiments, Black Angus bulls were challenged at weaning with GHRH analog and evaluated for their GH response to determine whether GH response is predictive of subsequent growth characteristics. The GH response was determined by measuring GH in blood serum collected 0 and 10 min post-GHRH injection [Experiment 1: 1.5 æg/100 kg BW human GHRH, n = 34; Experiment 2: :1.5 and 4.5 æg/100 kg BW bovine GHRH (treatments LGHRH and HGHRH, respectively) administered 3 h after a 4.5 æg/100 kg BW "clearance dose" of GHRH (CLEAR), n = 38]. In Experiment 1, GH response was not predictive of growth or carcass measurements. In Experiment 2, GH response to LGHRH was positively related to ADG (R2 = .18; P = .007) during a 112-d controlled feeding trial. In addition, there was a tendency for bulls with a greater GH response to HGHRH to exhibit greater ADG than animals with a low response. However, GH response to GHRH was not related to changes in hip height (HH) or carcass ultrasound measurements at Day 112 of the growth performance trial. Response of GH to repeated GHRH challenges was consistent within animal over time = .47; P = .003). The use of a clearance dose 3 h prior to GHRH challenge improved the relationship between GH response and ADG. Results of this study suggest that GH response to GHRH challenge is a useful tool for identifying beef bulls with superior growth potential.