Isoleucine Requirement of the Lactating

Twenty-five Landrace • Yorkshire sows (second through seventh parity) were randomly assigned to five dietary treatments in an experiment designed to estimate the isoleucine requirement of the sow during the first 3 weeks of lactation. The basal diet (.20% isoleucine), composed of oat groats, corn sugar, wood cellulose, soybean oil, vitamins, minerals, indispensable amino acids and L-glutamic acid, fulfilled the requirements of the lactating sow for all essential nutrients except isoleucine. L-isoleucine was added to provide levels of .20 (basal), .28, .37, .65 and .92% isoleucine in the five diets. The sows were fed 5.45 kg daily during the 21-day lactation period. The requirement for isoleucine was estimated from the data on milk yield and composition, pig weight gain, nitrogen retention, plasma isoleucine and plasma urea. Milk yield and pig weight gain responded quadratically (P<.05 and P<.08, respectively) to increasing levels of isoleucine and were maximized at .37% isoleucine. Total solids and protein product ion in the milk increased quadratically (P<.005 and P<.05, respectively) with increasing isoleucine. There was a rapid increase from .20 to .28% isoleucine, with a maximum obtained at .65% isoleucine for both parameters. Nitrogen retention was maximized at .37% isoleucine (quadratic component , P<.05). Plasma isoleucine moderately increased to .37% isoleucine, then increased sharply at higher isoleucine levels (linear component , P<.001; quadratic component , P<.05). Plasma urea concentration did not respond significantly to the treatments, but the concentration was minimized a t . 37 % isoleucine. When all parameters are considered, the data