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An experiment was conducted using production and metabolic criteria to estimate the valine requirement of the lactating sow. Ground corn, gelatin, corn sugar, vitamins, minerals and indispensable amino acids were used to formulate a diet containing all the essential nutrients except valine. L-valine was added to provide .23 (basal), .38, .53, .68 and .83% valine. Twenty-five mature Landrace x Yorkshire sows were randomly assigned to the five dietary treatments. Milk production and average pig weight gain increased quadratically (P less than .01) and were maximized at .68% dietary valine. Total solids production (p less than .05) and protein production (P less than .01) increased with increasing level of valine, and both were maximized at .68% dietary valine. Protein content also was maximized (P less than .01) at .68% dietary valine. Fecal (P less than .05) and urinary (P less than .01) nitrogen decreased with increasing valine, yielding greatest (P less than .01) nitrogen retention (excluding milk nitrogen) at .53% dietary valine. Because daily milk nitrogen production also increased (P less than .01) with increasing valine, there were no treatment differences (P greater than .05) in nitrogen balance (including milk nitrogen). Plasma valine concentration increased (P less than .01) gradually until .53% valine was fed, after which there was a rapid increase in concentration. Plasma isoleucine and leucine decreased (P less than .01) with increasing dietary valine. Plasma urea concentration was minimal (P less than .05) with .38% dietary valine. When all the criteria measured are considered, the lactating sow's requirement of valine is between .53 and .68%. The metabolic data support .53% dietary valine for the requirement, although the maximum response in production parameters at .68% dietary valine suggests that the requirement is above .53% dietary valine.

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