INFLUENCE OF DIETARY LYSINE ON GROWTH AND CARCASS COMPOSITION OF HIGH-LEAN-GROWTH GILTS FED FROM 34 TO 72 KILOGRAMS

One hundred eight high-lean-growth gilts (34.4 kg BW) were used to det ermine the dietary lysine requirement to maximize growth, carcass char acteristics, and protein accretion from 34 to 72.5 kg BW. The experime nt was a randomized complete block design; initial BW served as the bl ocking factor. Six dietary treatments were included, ranging from .54 to 1.04% (.10% increments) digestible lysine (.69 to 1.25% total lysin e). Pigs were housed in pens of three, with six replicate pens per tre atment. Pig weights and feed consumption were collected weekly to calc ulate ADG, ADFI, and gain:feed (G/F). Initially, five pigs were slaugh tered to determine base-line carcass composition. When the mean weight for pigs in a pen reached 55 and 72.5 kg, one pig per pen was randoml y selected and slaughtered for carcass measurements. The right side of each carcass was ground twice and sampled to determine carcass compos ition and tissue accretion rates. Average daily gain was increased by dietary lysine from 34 to 55 kg (linear, P < .01), from 55 to 72.5 kg (linear, P < .10), and from 34 to 72.5 kg (linear, P < .01). Although ADFI from 34 to 55 and from 55 to 72.5 kg was not influenced by dietar y lysine, ADFI for the entire experiment tended to decrease (quadratic , P < .10) as digestible lysine increased. Increased dietary lysine re sulted in improved GIF from 34 to 55 kg (linear, P < .01) and from 55 to 72.5 and 34 to 72.5 kg (quadratic, P < .01). Average backfat thickn ess was not influenced by dietary lysine at 55 kg but decreased (linea r, P < .05) as dietary lysine increased at 72.5 kg. At 55 kg, longissi mus muscle area was larger (linear, P < .05) for gilts fed increased d igestible lysine. However, longissimus muscle area was similar for all treatments at 72.5 kg. Gilts fed increased digestible lysine had grea ter CP accretion from 34 to 55 kg (linear, P < .01), 55 to 72.5 kg (li near, P < .05; quadratic, P < .10), and from 34 to 72.5 kg (quadratic, P < .05). Based on the feed intake observed in this study, the high-l ean-growth gilt requires at least 22 g/d total lysine intake from 34 7 2.5 kg to maximize CP accretion.