THE LYSINE REQUIREMENT OF LACTATING PRIMIPAROUS SOWS

We conducted an experiment with 289 primiparous sows to evaluate the e ffect of lysine intake on lactation and subsequent reproductive perfor mance. Sows were randomly allotted to one of five experimental corn-so ybean meal lactation diets. The first four diets contained incremental levels of apparently digestible lysine (.67, .86, 1.06, and 1.25%) an d provided digestible lysine intakes of 27, 34, 41, and 48 g/d. All ly sine was derived from intact protein sources. Synthetic valine, threon ine, and methionine were used to maintain ratios to lysine that were e qual to those of the .67% lysine diet. The fifth diet contained 1.06% digestible lysine and provided 43 g/d digestible lysine, but no additi onal synthetic amino acids were added. The average lactation length in this study was 16.9 +/- .2 d. Lysine intake during lactation did not affect number of pigs weaned, litter growth rate, sow backfat loss, or meaning to mating interval. Sow weight loss and loin eye area loss de creased quadratically (P < .05) with increasing lysine intake. These w ere minimized at 45 and 48 g/d digestible lysine, respectively. Removi ng synthetic amino acids from the 1.06% digestible lysine diet resulte d in an increased litter growth rate (1.98 vs 2.15 kg/d, P < .05). Inc reasing dietary lysine intake while maintaining amino acid ratios to l ysine for valine, threonine, and total sulfur amino acids during the f irst lactation resulted in a linear (P < .05) decrease in second litte r total born. However, removal of synthetic amino acids from the 1.06% digestible lysine diet resulted in an increased second litter total b orn (12.9 vs 11.2, P < .05), which tended to be higher compared with t he .67% digestible lysine treatment (12.9 vs 11.7, P = .13). The resul ts suggest that primiparous sows are able to mobilize sufficient body reserves to maintain a high level of milk production at low levels of lysine intake during a 17-d lactation. Higher levels (45 to 48 g/d) of digestible lysine are required to minimize body protein loss. The sou rce or composition of amino acids in the lactation diet may have an ef fect on second litter size.