PSIII-A-8 - Daily Clenbuterol Administration to Lambs Born with Low Birthweight Due to Intrauterine Growth Restriction Recovered Growth Rates and Improved Body Composition at 60 D of Age

Abstract: Low birthweight due to intrauterine growth restriction (IUGR) results from unfavorable in utero conditions (i.e., hypoxemia, hypoglycemia) that impairs growth capacity for muscle and other tissues. This programming effect reduces growth efficiency in IUGR offspring below their genetic potential. Specific programming mechanisms are not known, but recent evidence indicates reduced β2 adrenergic regulation of IUGR muscle. Thus, our objective was to determine if early-life growth deficits in IUGR juvenile lambs are improved by manipulating β2 adrenergic activity with daily IM administration of the β2 agonist, clenbuterol (Clen), from birth to 60 d of age. Maternal heat stress-induced IUGR (n=10) and IUGR+Clen (n=9) lambs were smaller (P< 0.05) than controls (n=11) at birth, weighed 18% and 11% less (P< 0.05), respectively, than controls at 30 d of age, and weighed 16% and 13% less (P< 0.05), respectively, at 60 d of age. Average daily gain at 30 and 60 d of age was reduced (P≤0.05) for IUGR but not IUGR+Clen lambs compared to controls. Bioelectrical impedance analysis was used to estimate body composition in live lambs at 58 d of age. Estimated fat-free lean mass and estimated muscle mass were less (P≤0.05) for IUGR but not IUGR+Clen lambs compared to controls. Estimated protein and fat content as well as protein:fat were likewise reduced (P< 0.05) for IUGR but not IUGR+Clen lambs. At necropsy, whole hindlimbs tended to be lighter (P≤0.09) and flexor digitorum superficialis muscle was lighter (P< 0.05) for IUGR but not IUGR+Clen lambs compared to controls. Loin-eye areas measured in chilled carcasses were 15% smaller (P< 0.05) for IUGR lambs and 19% larger (P< 0.05) for IUGR+Clen lambs compared to controls. From this study, we conclude that poor postnatal growth and body composition observed in IUGR juvenile lambs was improved when clenbuterol was used to target programmed deficits in β2 adrenergic regulation of muscle.