Potential Mechanisms for Repartitioning of Growth by β-Adrenergic Agonists

Abstract

A major goal of meat animal production is to generate efficiently an acceptable meat product as a source of protein for humans. In the last several years, there has been considerable interest in using β-adrenergic agonists to repartition growth in animals raised for meat production (Ricks et al., 1984a); oral administration of the β-adrenergic agonists clenbuterol or cimaterol to growing cattle (Ricks et al., 1984b; Hanrahan et al., 1986; Williams et al., 1986; Miller et al., 1988), chickens (Dalrymple et al., 1984a; Hanrahan et al., 1986), pigs (Dal-rymple et al., 1984b; Ricks et al., 1984a; Jones et al., 1985; Hanrahan et al., 1986; Mosher et al., 1986), and sheep (Baker et al., 1984; Beermann et al., 1985, 1986b; Thorntons et al., 1985; Hamby et al., 1986; Hanrahan et al., 1986; Bohorov et al., 1987) increases carcass muscle mass and decreases carcass fat mass. Nitrogen retention increases in calves fed clenbuterol (Williams et al., 1986). The shift toward more muscle and less fat deposition by clenbuterol led to the description of this phenomenon as repartitioning of growth and the designation of such compounds as repartitioning agents. At this time there is one experiment in very young pigs in which an adrenergic agonist did not change body composition; the reason for the negative result is unknown (Mersmann et al., 1987).