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The level of the essential amino acid lysine is of concern in trout feed. The objective of this study was to investigate the response of different families of fish to lysine-deficient ( LD) versus lysine-adequate ( LA) soy protein-containing diets. For each treatment combination, there were five replicates. As expected, feed efficiency ( p < .0001) and thermal growth coefficient ( TGC, p < .0001) were improved in fish fed the LA compared to the LD diet. Hepatosomatic index ( HSI, p < .01) and whole-body lipid content ( p < .01) were higher for fish consuming the LD compared to the LA diet. There was no effect ( p > .05) of diet on hepatic lysine α-ketoglutarate reductase ( LKR) activity, LKR m RNA abundance or lysine oxidation. There was a family effect on feed efficiency ( p < .0001), TGC ( p < .0001) and condition factor ( p < .05) and there was a trend for differences in oxygen consumption ( p < .07) across families while consuming the LD diet; however, there was no effect on ammonia excretion, HSI, lipid content, efficiency of nitrogen or lysine retention or indices of lysine catabolism. One family, in particular, had more favourable feed efficiency and thermal growth coefficient when fed the LD diet, indicating that it may possess an enhanced genetic potential for performance when consuming LD, soybean meal-containing diets. [ABSTRACT FROM AUTHOR]

Uric acid is an important antioxidant and methods to elevate its plasma concentration may be important in animal health. In a first study, the effect of dietary protein on plasma uric acid (PUA) and glucose concentrations were determined in 3-week-old chicks. Twenty-four broiler chicks were randomly assigned to four diets: a commercial control diet (C, 20% crude protein), low protein (LP) containing 10% casein, medium protein (MP) containing 20% casein or high protein (HP) containing 45% casein for a 3-week experiment. PUA concentration increased (P<0.05) in chicks fed HP diet and declined (P<0.05) in chicks fed LP while plasma glucose concentrations were lower (P<0.05) in chicks fed the LP diet at the end of the study. In a second study, PUA and leukocyte oxidative activity (LOA) were determined in broilers fed C, LP, MP or HP diets for 4 weeks. As in the first study, dietary protein directly affected PUA concentrations. In birds consuming HP diets, PUA was negatively correlated (P=0.06) with lowered LOA. These data support the view that increases in dietary protein can increase PUA concentrations, which can ameliorate oxidative stress. [Copyright &y& Elsevier]