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 ileal digestible lysine and digestible energy in the diet, and the effect of energy intake level on this optimal ratio for gilts with high genetic potential for lean gain, between 20 and 45 kg BW. In a 2 x 15 factorial arrangement the pigs were fed either 2.5 or 3.0 times the energy requirements for maintenance. Average daily lysine intake in the treatment period ranged from 6.4 to 18.2 g/d in 15 graduated steps. The first 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 increased curvilinearly (P < .01) with increasing lysine intake. The ADG was maximized at 606 and 768 g/d, gain/feed was maximized at .564 and .604 kg/kg, and protein deposition was maximized at 108 and 128 g/d at the 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 digestible lysine/DE, grams/megaJoule), determined with a linear-plateau model, were .57 for ADG and gain/feed, and .62 for protein deposition. These estimated requirements were similar for the two energy levels. Consequently, approximately .60 g of ileal digestible lysine/MJ of DE was required to optimize performance in gilts with high genetic potential for lean gain, irrespective of the feed intake level. In addition, a factorial model to estimate the lysine/energy requirements is proposed.