The effects of lysine:energy ratio on the performance of weanling pigs.

In five trials, 382 weaned pigs with an average BW of 9.1 +/- .07 kg were randomly allotted in groups of four to determine the optimum ratio of lysine:energy and the interrelationship between lysine and DE levels. Twelve dietary treatments, three levels of DE (13.3, 14.0, and 14.7 MJ of DE/kg), and four lysine:energy ratios (Lys:DE) of .7, .8, .9, and 1.0 g of lysine/MJ of DE were used in a 3 x 4 factorial arrangement. All diets were formulated to have similar CP levels (19.5%) and were based on wheat, barley, and soybean meal. There was a linear decrease (P < .05) in feed intake as the energy in the diet increased. Feed intake was not affected by Lys:DE. A positive linear effect (P < .001) of Lys:DE on ADG was observed. Also, ADG increased linearly (P < .05) with an increase in DE level. Increases in DE level and Lys:DE resulted in linear (P < .001) improvements in gain to feed. Plasma urea nitrogen (PUN) concentrations decreased (linear, P < .001; quadratic, P < .007) as Lys:DE increased up to .9 g of lysine/MJ of DE. As the level of DE increased, there was a linear decrease in PUN concentration (P < .001). Backfat thickness of pigs increased linearly (P < .003) with an increase in DE level. Ratio of lysine:DE had a quadratic (P < .002) effect on backfat thickness, with an increase up to .9 g of lysine/MJ of DE and a decrease thereafter. The combination of DE level and Lys:DE, based on response surface analysis, that produced maximization of weight gain (612 g/d) was 14.13 MJ of DE/kg and .95 g of lysine/MJ of DE for pigs from 9.1 to 25.7 kg of BW.