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Department of Animal and Poultry Science, University of Guelph, Guelph, Canada N1G 2W1;
* The Rowett Research Institute, Aberdeen, UK; and
Department of Agricultural, Food and Nutritional Sciences, University of Alberta, Edmonton, Canada
2To whom correspondence should be addressed. E-mail: cdelange{at}uoguelph.ca.
Oxidation contributes to the inefficiency of lysine utilization for protein deposition. The influences of feeding frequency and type of isotope tracer on estimated lysine oxidation were studied in growing pigs fed lysine-limiting diets. Yorkshire gilts (n = 11) weighing 4045 kg were fitted with venous catheters. They were fed, in 3 or 8 equal meals daily, a purified diet based on casein and cornstarch. Lysine intake limited the pigs protein deposition to 70% of their potential. After a 5-d N-balance period, lysine oxidation was estimated by a primed, constant 26-h infusion of [1-14C]L-lysine and [6-3H]L-lysine. Feeding frequency and type of tracer did not affect lysine oxidation (P > 0.1). Increasing feeding frequency from 3 to 8 times daily reduced the variance and fluctuation of lysine oxidation by 46 and 30%, respectively. The mean lysine oxidation, as a fraction of the true ileal digestible lysine intake, was 9.2% based on the free lysine specific radioactivity (SRA) in plasma, 20.1% based on free lysine SRA in liver and 21.8% calculated from N-balance data. On the basis of liver free lysine SRA, tracer dilution methods and N-balance data give similar quantitative estimates of lysine oxidation (P > 0.10). Isotope tracer studies that cover one or more complete feeding cycles, i.e., feeding-to-feeding periods, can be used to obtain valid daily lysine oxidation values.
KEY WORDS: pig lysine oxidation isotope tracers feeding frequency body protein deposition pigs
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