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Protein Level, Lysine Level and Source Interaction in Young Pigs¹

North Carolina State University, Raleigh 27607

Abstract

Effects of varying dietary lysine at varying protein levels were studied using 96 crossbred pigs. Corn-soybean meal diets were formulated to contain 20, 18, 16 and 14% protein. L-lysine monohydrochloride (L-lysine HO) was added to the lower protein levels to provide total lysine equal to that contained in the 20% diet (1.08% lysine) less .02% or .04% lysine for each 1% reduction in protein level. No differences in pig performance were noted between the .02% or .04% lysine reduction (P>. 15). Increasing dietary protein level increased average daily gain, the linear, quadratic and cubic compenents were all significant. Feed/gain was improved at the higher protein levels with both the linear and quadratic components being significant. Protein/gain and lysine/gain declined linearly as protein level was reduced from 20 to 16% and then plateaued or increased at the lower protein level, the quadratic component was significant. Maximum performance was attained at the 16% protein level and at the .92% level of dietary lysine.

In a second experiment, performance of pigs fed diets containing 18, 16 and 14% protein and supplemented with L-lysine HC1 (.04% reduction/1% reduction in protein level) was compared with that of pigs fed diets containing 16% protein and equal levels of lysine (1.0, .92 or .84%) (equal to the diets above) obtained by increasing the ratio of soybean meal to corn. The diets were fed to 192 crossbred pigs. Pigs consuming diets in which the soybean meal to corn ratio was adjusted to supply the lysine, grew more rapidly (P<.001), consumed more feed (P<.001), but required more feed per unit of gain (P<.001) than pigs fed diets supplemented with L-lysine HC1. Protein/gain declined linearly (P<.01) in comparing diets 1, 2 and 3. Source of lysine also had an effect (P<.001) on proteins per gain ratio and source of lysine X lysine level interaction was significant. Lysine/gain ratio declined linearly (P<.001) as lysine level was reduced and was also significantly affected by source of lysine.

The four treatments from Experiment 2 which contained .92 and 1.0% lysine were repeated with and without supplemental methionine (.13%). These diets were fed to 96 crossbred pigs. The addition of methionine to the diets tended to increase feed intake and daily gain (differences which approached P=.05%) when soybean meal was the major source of protein. The addition of methionine produced no significant changes in protein/gain or in lysine/gain ratios.

¹ Paper No. 5422 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh.

² Department of Animal Science.