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Intravenous infusion of ~-1~HjphenyIalanine (Phe) was carried out for 8 h in dry, non-pregnant and lactating dairy goats. Nitrogen balance was positive in the dry group and negative in the lactating group.Whole-body Phe flux was 50 % greater in lactating goats (P < 0.01). Fractional synthesis rates (K,) of tissue proteins were estimated from plasma-(K,) and tissue-(KJ specific radioactivities of Phe. In lactating goats, K , for mammary gland, duodenum and diaphragm was increased (P < 0.05). K, also tended to increase in liver, kidney and rumen (P < 0.08) of lactating goats, but was not different in uterus, spleen, caecum or heart. Values of Ksh were higher than Ksp; however, these measures agreed qualitatively. When absolute rates of protein synthesis were calculated, an increased contribution of mammary and visceral organs was seen in lactating goats. K, and absolute rates of protein synthesis of hind-limb skin were less in lactating goats (P < 0.05). A decreased proportion of skeletal muscle (P < 0.01) and decreased K, resulted in lower absolute synthesis of hind-limb muscle protein in lactating animals (P < 0.05). Decreased rates of muscle and skin protein synthesis would appear to participate in alterations of protein metabolism, permitting lactation to occur a t the expense of body reserves.Lactation : Phenylalanine flux : Protein synthesis : GoatIn high-producing dairy ruminants, early lactation is recognized as a period of negative nitrogen balance (Brun-Bellut et al. 1984). In order to maintain milk output, a utilization of maternal sources of protein and energy is necessary to supplement the dietary supply (Brun-Bellut et al. 1984;Giger, 1987;Barnes & Brown, 1990). Dairy goats have attracted some attention for studies of this phenomenon, because of their high milk output per unit body-weight and small body size (Wilkinson & Stark, 1987).Net body protein loss may result from an increase in protein degradation, a decrease in body synthesis, or both. However, the changes in protein metabolism which take place to permit high rates of milk synthesis in the face of negative N balance over-all remain to be fully characterized. Few studies of whole-body or tissue protein metabolism have been performed on ruminants early in lactation (Bryant & Smith 1982;Vincent & Lindsay, 1984;Oddy et al. 1988;Riis, 1988). Some attention has been paid to skeletal muscle (Smith et al. 1981;Bryant & Smith, 1982;Vincent & Lindsay, 1984; MiHican et al. 1987) because it is viewed as a primary site of protein mobilization. At the same time, the nature of any alterations of muscle protein content and metabolism occurring during lactation is not a topic of general agreement amongst these reports.There is little information concerning how the over-all flux of amino acids available for protein synthesis is divided amongst tissues and organs in large animals. Lobley et al.(1 980) characterized the percentage contribution of muscle, carcass, gastrointestinal tract, liver and skin to total protein synthesis in cattle. In lactation the dist...

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The effects of season, geographic source (Lake Geneva, Rhine River), and rearing system (extensive, semiextensive, and intensive systems) on the lipid content and FA composition of fillets of Perca fluviatilis were studied. Significant differences in the total lipid content were found between fish coming from the Rhine River and Lake Geneva (1.21 and 1.48%, respectively). Seasonal effects were investigated quarterly for perch sampled in the Rhine River. Intensively reared perch displayed a higher lipid content (1.48%) than the other farmed perch, i.e., 1.26% for a semiextensive system and 1.16% for an extensive system. No significant difference in lipid content was found (i) between lacustrine fish and intensively reared fish or (ii) among fish from the Rhine River and the semiextensive or extensive rearing systems. The main FA were 22:6n-3 (DHA, 21.3-37.1% of total FA), 16:0 (17.7-20.2%), 20:5n-3 (EPA, 9.2-13.2%), 18:1 (8.0-11.5%), 20:4n-6 [arachidonic acid (ARA), 1.9-10.7%], 16:1 (4.3-6.0%), and 18:2n-6 (2.1-6.0%). In comparison with perch coming from the Rhine River, the lacustrine fish were characterized by higher total n-6 PUFA and a lower proportion of both total monounsaturated FA (MUFA) and total n-3 PUFA. Among rearing systems, extensively farmed fish had higher n-6 PUFA and lower n-3 PUFA contents. Wild fish showed higher ARA and 18:2n-6 than farmed fish. They also had significantly more EPA (12.5-13.2%) than farmed perch (9.2-10.9%). For DHA, no difference existed between (i) the lacustrine fish (31.9% of total FA) and the intensively reared fish (33.0%) and (ii) the Rhine (37.1%) and semiextensively reared fish (36%). Effects of size, diet composition, and environmental conditions on the total lipid contents and FA composition are discussed.