Sixty pigs were used to investigate the effects of two levels of dietary ractopamine (RAC; 0 and 20 mg/kg) and three sex types (SEX; boars, gilts, and barrows) on performance over the live weight range 60 to 90 kg. Pigs were housed in individual pens and allowed ad libitum access to a diet containing 3.466 Mcal of DE and 10.7 g of lysine/kg. Control boars exhibited faster and more efficient growth and deposited more protein and less fat than gilts or barrows. The RAC increased ADG by 17 and 21% in gilts and barrows but not in boars. Feed intake was not altered by dietary RAC. Dietary RAC increased the rate of protein deposition by 15, 42, and 41% in boars, gilts, and barrows, respectively. Nevertheless, the daily rate of protein deposition was greatest in RAC-treated boars. The RAC tended to reduce the daily rate of fat deposition by 21% in boars but not in gilts or barrows. Carcass protein content increased by 5% and fat content decreased by 8% in response to RAC. These improvements in carcass composition occurred without compromising meat quality. Results show that RAC is a potent stimulator of protein deposition in finishing pigs. However, increased protein deposition is not necessarily at the expense of fat deposition.

Interactions between the beta-adrenoceptor agonist cimaterol and beta-adrenoceptors on rat skeletal muscle membranes were examined in two studies. In Exp. 1, muscle samples from eight Sprague-Dawley rats (female, approximately 200 g) were used for competition binding and autoradiographic studies using [125I]cyanopindolol (ICYP) as a radioligand. The affinities or dissociation constants for binding (KD values) for cimaterol in plantaris and soleus muscles were .68 and .92 microM, respectively. Muscle areas stained for succinic dehydrogenase had propranolol-resistant ICYP binding sites; cimaterol did not seem to compete for these sites. In Exp. 2, 60 Sprague-Dawley rats (female, approximately 218 g) were fed 0 or 10 ppm of cimaterol in rat diet that was ground. Groups were killed after 1, 3, 7, 14, or 28 d of treatment. Cimaterol increased BW gain up to 14 d after commencement of treatment, with little or no improvement thereafter. Enhanced weight gain in skeletal muscles also occurred up to 14 d of cimaterol treatment. Densities of beta-adrenoceptors in plantaris and soleus muscle membrane homogenates were estimated using a radioligand binding assay with ICYP. A significant reduction in the number of binding sites (Bmax) was observed after 3 d of cimaterol treatment in plantaris muscle without a change in the KD of ICYP binding. The percentage reductions in Bmax were 26.8, 42.2, 37.7, and 37.8% at 3, 7, 14, and 28 d after cimaterol administration, respectively. In the soleus muscle, significant reductions (44.1 and 29.8%) in Bmax were observed after 3 and 14 d of cimaterol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The chapter elaborates on the factors that affect the efficiency of feed utilization by lambs, their body composition in terms of lean and fat content, and aspects of carcass quality including fat content and meat yield. Predictive mathematical models that would aid in making decisions in relation to nutritional management for sheepmeat production are presented. Aspects of growth and metabolism, the influence of genotype, and the effects of diet on composition of gain are discussed.

The goal of this modelling exercise was to evaluate genetic, nutritional and other factors affecting the distribution of fat in growing and finishing beef cattle. The model had the following objectives: (i) to predict the accretion of total body fat as a function of genotype, sex, implant status and nutrition; (ii) to predict the partition of fat in different depots throughout the animal's lifetime; and (iii) to examine the possible mechanisms for genetic and nutritional differences in fat distribution. This model appears to adequately describe normal growth and accretion fat in the whole body and in the four main depots. It represents a first step in the development of an analytical tool for the study of factors affecting fat deposition and distribution.

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The effects of salbutamol administration to pregnant sows on post-natal growth and carcass characteristics of the progeny were investigated. Salbutamol (4 mg/kg diet) was fed to sows during the first (0 to 38 days, TI), second (39 to 78 days, T2) or third (79 days to term, T3) trimester of pregnancy. At birth, maternal administration of salbutamol had no effect on body weight, dressing percentage or weights of liver, heart, semimembranosus and semitendinosus muscle in proportion to body weight in the progeny. No significant effects of maternal treatment with salbutamol on body weight, dressing percentage, semitendinosus muscle weight in proportion to body weight and loin eye area were observed in the progeny at 21 days. P2 fat depth at 21 days was greater (P < 0-05) in TI than in controls. The percentage of type I fibres in the deep portion of semitendinosus muscle was higher (P < 0.05) in treatment groups as compared with controls: 27.4, 42.8, 36.9 and 36.0% in control, TI, T2 and T3 respectively. At slaughter (90 kg), carcass and meat parameters including length, P2 fat depth, meat colour and drip loss were not affected by maternal administration of salbutamol. However, loin eye areas were larger in T1 than in controls. Larger loin eye areas, coupled with numerically (but not statistically) significant heavier carcasses and lower backfats, resulted in greater estimates of carcass protein mass in TI pigs as compared with controls (P = 0.06).

1. Male Sprague-Dawley rats weighing 146.5 (SE 4.3) g were fed on a semi-synthetic diet containing 0, 25 or 150 mg cimaterol/kg for 12 d. Net changes in weight and composition of carcass, liver, heart, gastrointestinal tract, gastrocnemius plus plantaris muscles, skin and remainder were estimated by comparative slaughter.2. Cimaterol increased protein gains in gastrocnemius plus plantaris muscles from 0.09 g in controls to 0 14 and 012 g in 25 and 150 mg cimaterol/kg groups respectively. Carcass protein gains increased from 6.27 g in controls to 8.00 and 7.05 g in 25 and 150 mg cimaterol/kg groups respectively.3. Rats treated with cimaterol either gained less fat or actually lost fat from all tissues studied, whilst control rats gained fat. These changes were reflected in lower energy retention in cimaterol-fed rats.4. Energy intake was not affected by treatment. Cimaterol increased heat production from 776 kJ/kg bodyweight' 75 in controls to 863 kJ/kg body-weight' 75 in both treated groups. Gross efficiency was reduced from 17.4% in controls to 8.0 and 7.7% in rats fed on 25 and 150 mg cimaterol/kg diets respectively.5. These results indicate that cimaterol increases protein gain at the expense of fat in rats. In addition, subcutaneous adipose tissue appears to be more sensitive than abdominal fat, whilst protein gains are particularly enhanced in skeletal muscle relative to other body tissues.Some P-adrenergic agonists have the ability to increase lean gain at the expense of fat, which has led to the use of the term repartitioning agents (Asato et al. 1984). Clenbuterol (4-amino-cr-(t-butylamino-methyl)-3,5-dichlorobenzyl alcohol) and cimaterol (5-(l-hydroxy-2-(isopropylamino)-ethyl)anthranilonitrile) were identified by their ability to increase body-weight gain and decrease uterine fat pad weight in mice (Asato et al. 1984). Both compounds have been shown to increase carcass protein and decrease fat in sheep Thornton et al. 1985;Wolff et al. 1987), cattle (Ricks et al. 1984, poultry (Asato et al. 1984;Dalrymple et al. 1984) and pigs (Jones et al. 1985). These changes are desirable in view of consumer demand for leaner meat. In addition, P-agonists provide a powerful tool for understanding the factors determining body composition in general and muscle growth in particular. Accordingly, several studies have been aimed at elucidating the mechanism of action of these compounds (Emery et al. 1984;Thornton et al. 1985;Reeds et al. 1986;Bohorov et al. 1987). However, none of the studies to date have included detailed information on initial and final weights of body components, as well as feed intakes. Here we report on quantitative effects of cimaterol on changes in the weight and composition of various tissues in growing rats and on feed intake and energetic efficiency. MATERIALS A N D METHODSMale Sprague-Dawley rats, 6 7 weeks of age and mean body-weight 146.5 (SE 4.3) g, were housed in individual stainless-steel cages and fed on a semi-synthetic diet (obtained from