Nutritional and endocrinological manipulation of lean deposition in forage-fed steers

Abstract

The effect of supplementing grass silage with fishmeal on growth, muscle composition and the rate of muscle protein synthesis was investigated in young Friesian steers with and without oestradiol implants. The effect of the P-adrenergic agonist cimaterol was simultaneously investigated in animals fed on silage alone. Treatments lasted for 9 or 10 weeks. Fishmeal supplementation significantly increased animal growth rates (P < 0.001) and the weights of three dissected muscles (P < 0.001) compared with the silage-fed controls. These effects were further enhanced in animals also implanted with oestradiol. Muscle weights expressed as a proportion of body-weight were increased by fishmeal, suggesting that protein deposition had been enhanced. No further increase in the proportional muscle weights was obtained with oestradiol. Muscle dry matter content tended to be increased in both implanted and nonimplanted animals receiving fishmeal compared with controls, but the proportions of protein, fat and ash were relatively constant. The intramuscular lipid composition was slightly altered by fishmeal. Muscle protein fractional synthetic rates (FSR), measured by continuous infusion of [3H]tyrosine, were increased by fishmeal in all three muscles of both implanted and non-implanted animals. There were no differences, however, due to oestradiol, over non-implanted fishmeal animals. This suggests that oestradiol may increase muscle accretion by reducing protein degradation rate. Cimaterol significantly increased longissimus dorsi (P < 0.05) and vastus lateralis (P < 0.01) muscle weights but had no effect on semitendinosus muscle weight or live-weight gain. The proportion of protein was increased (P < 0.001) and the fat content reduced (P < 0.05) in all three muscles but intramuscular lipid composition was not markedly affected. Whilst methylhistidine : creatinine excretion was reduced by cimaterol, FSR were increased in the 1. dorsi and v. lateralis muscles suggesting P-agonists have effects on both protein synthesis and protein degradation.

Nutritional and hormonal control of skeletal-muscle cell growth and differentiation

“…Indeed, muscle DNA concentration (pg/g protein) is sometimes less in treated muscles than in control muscles (Kim et al 1987). The predominant mechanism of action of these agents is thus believed to be a reduction in protein degradation, although protein synthesis has also been shown to be stimulated in some studies (Dawson et al 1991). This is supported by the observation that translational efficiency (i.e.…”

“…the amount of protein synthesized per unit RNA) is increased by Padrenergic agonists . All muscles do not respond equally to treatment with P-adrenergic agonists (Dawson et al 1991) and this is probably related to different fibre-type content of different muscles. The crosssectional area of type I1 (fast-contracting, mixed glycolytic-oxidative) fibres tends to be increased more consistently than type I (slow contracting, oxidative) fibres (see Yang & McElligott, 1989).…”

“…The mode of action of these agents differs depending on the compound; testosterone increases both protein synthesis and degradation rates, with a greater effect on the former (Martinez et al 1984), while trenbolone acetate increases muscle mass predominantly by reducing protein degradation, with a lesser effect on protein synthesis (Vernon & Buttery, 1976). The mode of action of oestradiol is believed to involve enhancement of endogenous GH secretion (Gopinath & Kitts, 1984;Breier et al 1988) although measurable increases in protein synthetic rate are not always observed in treated animals (Dawson et al 1991). The response to anabolic agents, however, is clearly dependent on nutritional status (Gill et al 1987).…”

The effect of immunization against somatostatin and β-agonist administration alone and in combination on growth and carcass composition in young steers

“…Plasma IGF-1 concentrations were also reduced in these animals compared with animals receiving either treatment alone in agreement with the suggestion of Beermann et al (1987) that IGF-1 concentrations are influenced by insulin secretion rates. It would thus appear that the small additional increase in muscle accretion observed in immunized animals receiving cimaterol was not mediated through the GH-IGF-1 axis, but through an enhancement of the P-agonist effect, p-agonists are believed to increase muscle protein accretion through a reduction in the rate of protein degradation and an increase in the rate of protein synthesis (Dawson et al, 1991b;NRC, 1994). Both processes are regulated separately and alteration in the rate of either process will result in increased protein accretion.…”

Effects of ractopamine hydrochloride are not confined to mammalian tissue: Evidence for direct effects of ractopamine hydrochloride supplementation on fermentation by ruminal microorganisms1

“…Beta-adrenergic agonists have direct effects on muscle tissue in cattle (Byrem et al, 1998), binding to β2 and β1 receptors located on the tissue, thereby stimulating muscle accretion (Smith et al, 1989) and possibly decreasing protein degradation (Dawson et al, 1988). Byrem et al (1998) observed increases in amino acid uptake by muscle tissue in steers treated with cimaterol, which is associated with the increased protein accretion.…”