RAPESEED, PEANUT AND SOYBEAN MEALS AS PROTEIN SUPPLEMENTS: PLASMA UREA CONCENTRATIONS OF PIGS ON DIFFERENT FEED INTAKES AS INDICES OF DIETARY PROTEIN QUALITY

Abstract

Plasma urea measurements were taken in an experiment designed to compare rapeseed (RSM), peanut (PNM) and soybean meals (SBM) as protein supplements for growing pigs (5–15 wk of age, 7.0–26.7 kg liveweight). Eight diets were formulated to meet National Academy of Sciences–National Research Council (1973) requirements of 10–20 kg pigs for crude protein and digestible energy. After 8–9 wk on test and following 24 h starvation, plasma urea concentrations of individual pigs were measured at 0, 1, 2, 3, 4, 5 and 7 h postprandial, the 0 h measurements being those taken just before refeeding. Plasma volumes of individual pigs were predicted from an equation. From these volumes and plasma urea concentrations, the increase in plasma urea output was expressed as a percentage of nitrogen (N) ingested on the morning of blood sampling (U/N%) for postprandial intervals of 0–3 h, 0–7 h and 4–7 h. Plasma urea concentration showed no consistent inverse relationship to dietary protein quality. However, U/N% for the period 0–7 h postprandial ranked diets in the same order as average daily liveweight gain. Under conditions of varied feed intake this procedure of relating the increase in plasma urea output to grams N ingested (%) offers a possible method for evaluating protein supplements.