Effects of lysine : calorie ratio on growth performance of 10-to 25-kilogram pigs

Crossbred barrows (n = 336 Newsham Hybrids) initially 9.9 kg and 31 +/- 2 d of age were used to evaluate the effects of energy density and lysine:calo rie ratio on growth performance. Pigs were allotted by initial weight in a 3 x 4 factorial arrangement of treatments in a randomized complete block de sign with six replicate pens per treatment. Each pen had four or five pigs with an equal number of pigs per pen within replicate. Pigs were fed increa sing dietary energy densities (3.25, 3.38, and 3.51 Mcal ME/kg) and lysine: calorie ratios (3.00, 3.45, 3.90, and 4.35 g lysine/Mcal ME). Energy densit y was changed by levels of choice white grease (0, 3, and 6%), and lysine:c alorie ratio was changed by altering the corn:soybean meal ratio. Over the 21-d trial, an energy density x lysine:calorie ratio interaction was observ ed for ADG (P < .05). Pigs fed diets containing 3.25 or 3.51 Meal ME/kg had increasing ADG with increasing lysine:calorie ratio, whereas ADG of pigs f ed 3.38 Mcal ME/kg was not affected by lysine:calorie ratio. Feed efficienc y (g ain:feed ratio) increased and ADFI decreased as lysine:calorie ratio i ncreased (linear, P < .01) and as energy density increased (quadratic, P < .01 and .10, respectively). On d 21, two pigs per pen were scanned ultrason ically for backfat depth. An energy density x lysine:calorie ratio interact ion (P < .06) was observed. Pigs fed diets containing 3.25 and 3.38 Meal ME /kg had decreasing fat depth as lysine:calorie ratio increased; however, ba ckfat depth was not affected by lysine:calorie ratio and was greatest for p igs fed 3.51 Meal ME/kg. These results suggest that 10- to 25-kg pigs fed d iets containing 3.38 Meal ME/kg had maximum feed efficiency and that they r equired at least 4.35 g lysine/Mcal ME. However, pigs fed 3.51 Meal ME/kg h ad increased fat depth regardless of calorie:lysine ratio.