The effects of in utero exposure of lambs to a beta-adrenergic agonist on prenatal and postnatal muscle growth, carcass cutability, and meat tenderness.

Abstract

The objectives of the present experiment were to examine the effects of in utero exposure to a beta-adrenergic agonist (L644,969) on prenatal and postnatal muscle growth and meat tenderness of lambs. Thirty twin-pregnant Composite IV (1/2 Finnsheep, 1/8 Dorset, 1/8 Rambouillet, 1/8 Targhee, 1/8 Suffolk) ewe lambs were used for this experiment. All ewes were fed an alfalfa hay-corn-based diet throughout gestation and lactation. From d 25 to 95 of gestation, the diet of one-half of the ewes contained 2 ppm of L644,969 on an as-fed basis. Treatment did not ( P > .05) affect lamb weights at any point in the growth cycle (birth to 43 kg). Heart weights of neonatal and market lambs were increased ( P < .05) by in utero exposure to L644,969. However, weights of lamb carcass components and weights of individual muscles were not affected by treatment (P > .05). Additionally, treatment did not alter the activities of any of the components of the calpain proteolytic system in neonatal or market lambs. Concomitantly, there was no effect of treatment on myofibril fragmentation index or Warner-Bratzler shear force. Moreover, there was no effect of treatment on muscle fiber type distributions, fiber sizes, or apparent fiber number. It seems that the lack of an effect of treatment on apparent fiber number would explain the lack of an effect on muscle weight. Thus, in utero exposure to L644,969 does not seem to have promise as a method for improving lamb carcass cutability. Other methods of improving the rate and composition of lamb carcass growth while maintaining acceptable meat tenderness must be developed.

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

“…In rats exposed to clenbuterol from day 10 of-gestation and throughout lactation, total fibre number was reduced in the soleus muscle but there was an increase in fibre cross-sectional area, particularly in the type I1 fibres, and altered proportions of the different fibre types (Maltin et al 1990). Fibre type was not altered in the muscles of the lambs exposed to a-adrenergic agonist (Shackelford et al 1995), but Kim et al (1994) suggested that in utero exposure to salbutamol increased the proportion of type I fibres in the semitendinosus muscle of pigs compared with untreated controls, in agreement with the results of Maltin et al (1990). Differences between these studies may be related to the timing of /I-adrenergic agonist administration, as was demonstrated for GH administration in pigs (Rehfeldt et al 1993).…”

Responses to maternal GH or ractopamine during early–mid pregnancy are similar in primiparous and multiparous pregnant pigs

“…Mixed effects of in utero exposure to b-agonists have been reported previously in the pig, with no change in total fiber numbers or muscle cross-sectional areas reported in progeny of sows treated with ractopamine (Hoshi et al 2005a), but increased muscle size and the proportion of type 1 muscle fibers in progeny of sows treated with salbutamol (Kim et al 1994). In lambs, in utero exposure to the b 2 -adrenergic agonist L 644,969 from day 25 to 95 of pregnancy also did not alter fiber type proportion or size in young adult offspring (Shackelford et al 1995). In contrast, feeding rats the b 2 -adrenergic agonist clenbuterol throughout most of pregnancy and through lactation increased muscle fiber size but decreased muscle weights and secondary:primary fiber ratios in fetuses (Maltin et al 1990, Downie et al 2008.…”

“…. 63 gestation, term w150 days) did not increase weight or alter body composition of neonatal twin lambs, with the exception of increased heart weight (Shackelford et al 1995). Similarly in rats, fetal weight in late pregnancy and weight of neonatal pups were not changed by feeding pregnant dams the b 2 -adrenergic agonist clenbuterol from day 4 after mating and throughout pregnancy, although neonatal cardiac hypertrophy was also reported in this species (Maltin et al 1990, Downie et al 2008.…”

Role of β-Adrenoceptor Signaling in Skeletal Muscle: Implications for Muscle Wasting and Disease

“…In fact, studies on cattle, sheep, and pigs have shown that the mechanism controlling tissue responsiveness to ␤-agonists varies from species to species, and even among different tissues within a species, primarily because of differences in the densities of each of the receptor subtypes (185,407). Considerable knowledge about the effects of ␤-agonists on skeletal muscle mass has come from the many studies examining the use of these compounds in livestock, especially with respect to their potential to improve meat quantity and to a lesser extent, quality (29,30,34,93,165,235,304,306,373,398). For a comprehensive analysis of technologies for controlling fat and lean deposition in livestock, including the use of ␤-agonists, the reader is referred to the review of Sillence (406).…”