Muscle growth, myofibre number, type and morphometry were studied in large hindlimb muscles of single and twin fetal lambs during mid to late gestation. Placental insufficiency, evident by lower total placentome weight and number per fetus, resulted in reduced fetal weights from 100 to 140 days gestation in twins compared with singletons (at 140 days: 5016 108 g v. 5750 246 g, respectively; P<0.05). However, competition between littermates did not consistently reduce muscle mass (15–22%) until 140 days gestation. Apparent myofibre number increased with age, indicating that the full complement of myofibres in some large hindlimb muscles may be achieved during early postnatal life. Litter size did not impact on apparent myofibre number in the semitendinosus, plantaris or gastrocnemius muscles. However, a transient effect on myofibre number in the adductor femoris muscle was observed from 80–120 days gestation. The phenotypic maturation of myofibres was unaffected by increasing litter size. Smaller muscle mass in twins was associated with smaller myofibre cross-sectional area in the semitendinosus, adductor femoris and gastrocnemius muscles at 140 days gestation. A similar trend was observed for the plantaris muscle. These results indicate that while competition between littermates for nutrients in late gestation can impact on both fetal and muscle mass, the fetus has the capacity to buffer against the effects of restricted nutrient supply on myofibre hyperplasia and phenotypic maturation, but myofibre hypertrophy is compromised.

The objective was to examine myogenesis in two situations expected to be characterized by maternal constraint: (i) in fetuses due to be born in spring (n=10) or autumn (n=10); and (ii) in single (n=16) and twin (n=20) fetal lambs. Maternal constraint operating through limitation of placental size, as measured by placentome weight per fetus, was evident in each study. Although a lower placental weight did not influence body and muscle weights of fetuses due to be born in the spring or autumn, twins had lower body and muscle weights than singles. Fibre number and average fibre cross-sectional (CS) area were differentially affected by season and fetal number. The differences in muscle fibre morphology between spring- and autumn-born fetuses suggest that muscle fibre development was influenced by maternal constraint in the absence of an effect on fetal weight. The differences in muscle fibre number and CS area in particular muscles from twin and single fetuses suggest that more severe maternal constraint, reflected in a lower placental size per fetus, not only influences fetal weight but can also affect muscle development.

An arterio-venous preparation was developed which allowed infusion into, and/or sampling from, branches of the deep circumflex iliac artery and vein supplying and draining a discrete area of skin on the abdominal flank of Romney sheep.Measurements of blood flow (using dye dilution techniques), utilization or output of energy metabolites (oxygen, glucose, lactate and acetate) and amino acid metabolism were made in relation to whole body protein and energy metabolism.Measurements on the patch suggested that blood flow to the total skin was about 6% of cardiac output but that only 1-2% of whole body oxygen utilization occurred in the skin. This was partly accounted for by a significant proportion of glucose uptake (1.15 g day-1) being anaerobically oxidized to lactate (0.41 g day-1). Measurements of protein synthesis in the patch showed that between 10 and 16% of whole body protein synthesis occurs in the skin.Results from the preparation demonstrate that it is a useful procedure to study metabolism in a defined patch of skin in the intact animal.

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Infusion of [ 35 S]-labelled cysteine into the jugular of Romney sheep of different ages was used to estimate the extent of combined cysteine and cystine (cyst(e)ine) and glutathione (GSH) interchange in various tissues, including skin, and to measure whole body irreversible loss rates (1LR) for cyst(e)ine. The studies were undertaken at Palmerston North, New Zealand during 1990 and 1991.Reverse phase HPLC using a fluorigenic reagent, 7-fluoro-2,1,3-benzoxadiazole-4-sulphonate (SBD-F) was used for the simultaneous determination of thiols (cysteine and GSH) in whole blood (bound and free fractions), liver, kidney, small intestine, muscle, pancreas and skin. The appearance of [ 35 S]-label in thiol compounds and their oxidation products was determined by ion-exchange HPLC. Specific radioactivities (SRA) for cyst(e)ine and GSH derived from this data showed equivalence for cysteine and GSH SRAs in all tissues, except for whole blood, indicating rapid withintissue interconversion between these thiols. In whole blood, however, the very low SRA for GSH (< 4 DPM/nmol) compared to cyst(e)ine (250 DPM/nmol) indicated markedly slower or negligible exchange with red blood cell GSH, and hence little inter-organ transport of [ 35 S]-label as GSH.Close infusion of [ 35 S]cysteine into a defined patch of skin and collection of the venous outflow permitted direct in vivo measurement of the proportional uptake of cysteine by the skin. Results indicated considerable variation in the uptake of cysteine per se (20-40 %) but no, or very little, oxidation of cysteine in the skin and no net export of GSH.The combination of whole body, tissue and skin specific studies of [ 35 S]-labelled cysteine metabolism quantitatively confirmed the very high proportion of circulating cyst(e)ine in sheep which is directed to skin and wool protein synthesis alone, and highlighted those aspects of this metabolism which are of most importance to wool production.