THE EFFECT OF DIETARY LYSINE ON GROWTH, CARCASS COMPOSITION, AND LIPID-METABOLISM IN HIGH-LEAN GROWTH GILTS FED FROM 72 TO 136 KILOGRAMS

One hundred fourteen high-lean growth gilts (72.5 kg BW) were used to determine the apparent digestible lysine requirement for maximum growt h performance and carcass protein deposition rate from 72.5 to 136 kg BW. The experiment was a randomized complete block design with initial BW used to establish blocks. Six dietary treatments were included, ra nging from.44 to.94% (.10% increments) apparent digestible lysine (.62 to 1.13% total lysine) with six replicate pens per treatment and thre e pigs per pen. Pig weights and feed consumption were collected weekly to determine ADG, ADFI, and gain: feed ratio (G/F). Six gilts were sl aughtered at 72.5 kg BW to determine initial carcass composition. When the mean weight of pigs in a pen reached 104 or 136 kg, one pig per p en was selected (closest to 104 or 136 kg, respectively) and slaughter ed for determination of carcass measurements and composition. From 72. 5 to 104 kg and from 104 to 136 kg, ADG and G/F increased (linear, P<. 05; quadratic, P<.10, respectively) as apparent digestible lysine incr eased. From 72.5 to 136 kg, G/F increased (quadratic, P < .10) as appa rent digestible lysine increased. Average backfat thickness and longis simus muscle area at 104 kg were not influenced (P >.10) by apparent d igestible lysine. However, average backfat thickness increased (quadra tic, P <.05) with increasing digestible lysine for gilts slaughtered a t 136 kg. Carcass CP accretion was not influenced (P >.10) from 72.5 t o 104 kg but tended to increase (linear, P <.10) from 72.5 to 136 kg a s digestible lysine increased. Plasma and longissimus muscle cholester ol concentrations were unaffected (P >.10) by increasing digestible ly sine. These results suggest that high-lean growth gilts require greate r dietary lysine than current NRC (1988) estimates to maximize ADG, G/ F, and carcass CP accretion from 72.5 to 104 and from 104 to 136 kg.