DIGESTIBLE LYSINE REQUIREMENT OF GILTS WITH HIGH GENETIC POTENTIAL FOR LEAN GAIN, IN RELATION TO THE LEVEL OF ENERGY-INTAKE

One hundred gilts were used to determine the optimal ratio between ile al digestible lysine and digestible energy in the diet, and the effect of energy intake level on this optimal ratio for gilts with high gene tic potential for lean gain, between 20 and 45 kg BW. In a 2 x 15 fact orial arrangement the pigs were fed either 2.5 or 3.0 times the energy requirements for maintenance. Average daily lysine intake in the trea tment period ranged from 6.4 to 18.2 g/d in 15 graduated steps. The fi rst 12 increments were .74 g/d, and the last two increments were 1.48 g/ d. Average daily gain (ADG), gain/feed, and protein deposition incr eased cunilinearly (P < .01) with increasing lysine intake. The ADG wa s maximized at 606 and 768 g/d, gain/feed was maximized at .564 and .6 04 kg/kg, and protein deposition was maximized at 108 and 128 g/d at t he low- and high-energy levels, respectively. The ratio between lipid and protein deposition decreased curvilinearly with increasing lysine intake (P < .01) and reached a minimum of .53 and .75 at the low- and high-energy levels, respectively. The lysine requirements (ileal diges tible lysine/DE, grams/megaJoule), determined with a linear-plateau mo del, were .57 for ADG and gain/feed, and .62 for protein deposition. T hese estimated requirements were similar for the two energy levels. Co nsequently, approximately .60 g of ileal digestible lysine/ MJ of DE w as required to optimize performance in gilts with high genetic potenti al for lean gain, irrespective of the feed intake level. In addition, a factorial model to estimate the lysine/energy requirements is propos ed.