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Differential Response to the ß-Adrenergic Agonist Cimaterol in Mice Selected for Rapid Gain and Unselected Controls^1,2,

North Carolina State University, Raleigh 27695-7621

Abstract

Male mice selected for rapid 3 to 6 wk postweaning gain (M16) and unselected controls (ICR) were ad libitum fed a stock diet containing 0, 50 or 200 ppm cimaterol, a ß-agonist, from 4 to 7 or 4 to 10 wk of age. Mortality rate was higher in M16 than in ICR mice fed cimaterol (12.5 vs 1.3%; P<.01). No mortalities occurred in either line fed the control diet. Line M16 exceeded (P<.01) ICR in growth rate, feed intake, feed efficiency and lean index. Line x cimaterol level interactions (P<.01) were found for the first three of these traits, although cimaterol level did not change line ranking. Epididymal fat as a percentage of empty body weight decreased at a faster rate in M16 than in ICR as cimaterol level increased. At 0 and 50 ppm, M16 exceeded ICR (P<.05), but at 200 ppm there was no line difference (P<.05). Line M16 exceeded (P<.05) ICR in blood glucose (5%), nonesterified fatty acids (4%) and lactate at 7 wk (9%), but lactate was higher in ICR at 10 wk (13%). Lines were not different in blood urea-N. Compared to zero cimaterol level, at 50 and 220 ppm glucose decreased (14% and 23%; P<.05), nonesterified fatty acids decreased (3% and 29%; P<.05), lactate increased (9% and 11%; P<.05) and blood urea-N increased (3% and 16%; P<.05). There were no line x cimaterol level interactions for blood metabolites. Differences in mortality rate, growth, feed consumption, feed efficiency and epididymal fat pad percentage between the high-growth and control lines in response to cimaterol may reflect genetic differences in mechanisms of metabolic regulation.

¹ Paper no. 11056 of the journal series of the North Carolina Agric. Res. Serv., Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Serv. of the products named nor criticism of similar ones not mentioned.

² The authors acknowledge R. H. Dalrymple of American Cyanamid Co., Princeton, NJ for supplying the cimaterol. The technical assistance of Helen Bartlett and Derick Davis is acknowledged.

³ Dept. Anim. Sci.

⁴ Animal-Forage Metabolism Complex.

⁵ Present address: 303 Tate St., Cary, NC 27511.