The action of the β-agonist clenbuterol on protein and energy metabolism in fattening wether lambs

Abstract

1. Five Greyface wethers (4245 kg) fed on various fixed amounts of dried grass pellets (either approximately 1.3 times maintenance or 2 times maintenance) by means of belt-type continuous feeders were housed in opencircuit respiration chambers for periods of 45 d. Between days 15 and 35 they received daily oral doses of 1.5 mg of the p-adrenergic agonist clenbuterol (adsorbed on to the feed). Continuous energy and nitrogen balance measurements each of 5 d duration were conducted throughout the chamber confinement. 2.On six occasions (twice during the 15 d pre-clenbuterol period, on days +4, + 11 and + 18 of clenbuterol administration and once during the post-treatment period) animals were infused with [l-14C]leucine to determine the rates of leucine oxidation and the amounts of leucine available for protein synthesis. 4. During clenbuterol treatment leucine oxidation was reduced ( P < 001). However, values for the amounts of leucine available for protein synthesis were equivocal, with an increase (P < 0.001) on day 11 of treatment, but no change on days 4 and 18.5. Withdrawal of the clenbuterol resulted in rapid alterations of N and energy metabolism towards those expected of control animals of that weight.The assertion that over-consumption of animal fat is detrimental to human health (National Advisory Committee on Nutrition Edwation, 1983 ; Department of Health and Social Security, 1984) has intensified the interest in methods which induce a leaner carcass conformation in growing animals. Some manipulation can be achieved by nutritional means (Turgeon et al. 1986) but economic considerations limit the extent of such applications. Within the genetic constraints of any particular breed, alternative ways of decreasing the ratio of fat gain:protein gain in growing and fattening animals usually involve the administration of exogenous compounds, e.g. ionophores, anabolic steroids, growth hormone, etc.The phasing-out, within the European Economic Community at least, of the use of anabolic steroids has given added impetus to the search for alternative manipulators of the growth process. Recent interest has focussed on the range of /3-adrenergic agonists, e.g. clenbuterol and cimaterol, which in growth trials involving poultry, pigs, sheep and cattle have been shown markedly to increase the areas of specific muscles, while concomitantly reducing body fat Dalrymple et al. 1984a, b ;Beerman et al. 1986).At present the majority of metabolic studies on the action of the P-agonists have been confined to rats where, for muscle protein metabolism at least, the evidence as to their mode of action is contradictory, with reports of both increases in protein synthesis (Emery et al. 1984) and decreases in protein degradation (Reeds et al. 1986). The present study represents the first stage in an examination of the action of clenbuterol on protein and energy metabolism in sheep. The protocol involved determination of the kinetics of energy https://www.cambridge.org/core/terms. https://doi

Effects of a beta-adrenergic agonist (L-644,969) on performance and carcass traits of growing lambs in a cold environment

“…This result was unexpected and discordant with most previous studies in which nitrogen retention was increased for BAA-treated animals (MacRae et al 1988;Kim et al 1989;Wenk et al 1989). However, carcass analysis in the present study showed that accretion in muscle tissues was enhanced in BAA-treated animals, as indicated by increased ribeye area and biceps femoris weight.…”

“…Under normal conditions, heart rate is closely related to metabolic rate (Yamamoto 1989). Higher heart rate may indicate a higher metabolic heat production, as other researchers have reported that BAA increased fasting heat production and maintenance requirements for energy (Kim et al 1989) and total energy expenditure (MacRae et al 1988).…”

Metabolic responses of the whole body, portal-drained viscera and hindquarter to adrenaline infusion: Effects of nonselective and selective β-adrenoceptor blockade

“…β-adrenoceptor processes mediate protein accretion in animals (Choo et al 1992). Simulation by β-adrenergic agonists results in increased thermogenesis and protein accretion in ruminants (MacRae et al 1988). The blockade of β-adrenergic receptors may reduce metabolic rate and, therefore, maintenance energy requirements, which would be beneficial for energetic efficiency.…”

Effect of dietary cimaterol on performance and carcass traits in bulls and on aspects of digestion in cattle and sheep

“…Obviously, other mechanisms adversely affect feed conversion. A higher energy requirement for maintenance due to an increased heat production has been reported for (3-agonist-treated rats (Sainz and Wolff, 1988), lambs (MacRae et al, 1988) and calves (Williams et al, 1987). If this mechanism affects the efficiency of energy utilization, then there is no reason to suppose that it is more important towards the end of the experiment, on the contrary.…”

“…The higher protein deposition in cimaterol-treated bulls and the accompanying deposition of water (van Es, 1977;Robelin and Geay, 1978) suggest a lower energy requirement per unit of tissue. Furthermore, the decreased protein turnover in cimateroltreated animals (Williams et al, 1987;MacRae et al, 1988;Fiems et al, 1990) is another argument for an improved feed conversion. Obviously, other mechanisms adversely affect feed conversion.…”