Effect of high dietary lysine on growth performance and body composition in weaned pigs following a period with dietary protein restriction: A preliminary study

Increasing dietary Lys and remaining essential AA above requirements might counter impaired growth resulting from pigs being fed a low-protein (LP) diet in the early weaning period. It was hypothesized that by increasing dietary Lys and remaining essential AA levels in a 4-week (W) non-reduced period (W5-8) after a 4-W reduced dietary crude protein period (W1-4) would potentially increase growth performance. At weaning, 67 piglets with an ADG of 200-220 g/day during the suckling period were selected based on their weaning weight for the study. On the day of weaning pigs were pre-allocated to 1 of 4 dietary treatments: control (STD-STD), standard (LP-STD), STD+10% Lys (LP-STD10+) and STD+20% Lys (LP-STD20+). From weaning to W4 after weaning LP-STD, LP-STD10+ and LP-STD20+ pigs were fed the same LP starter diet (81/79% total/digestible of CP level in STD diet), whereas STD-STD pigs were fed a diet formulated according to recommendations. From W5 to W8 after weaning LP-STD pigs were fed a diet with standard protein level, and LP-STD10+ and LP-STD20+, respectively, fed a diet with STD protein level plus 10% and 20% Lys including remaining essential AA. One day before weaning, and at W4, and at W8 after weaning, respectively, seven pigs (baseline Dual‑energy X‑ray absorptiometry (DXA) scanning), six STD and six LP pigs, and 12 STD-STD, 12 LP-STD, 12 LP-STD10+ and 12 LP-STD20+ pigs were slaughtered to DXA scan the carcasses. The data were analyzed using ANOVA function in R, with dietary treatment as fixed and pig nested within pen as random effect for BW, ADG and DXA parameters. For ADFI, G:F per pig, G:CP dietary treatment was used as fixed effect. For the fecal scoring the model included dietary treatment and day as fixed and pen as random effect. Results revealed no difference (P > 0.05) in BW, ADG, total feed intake or average daily feed intake between pigs fed STD and LP diet in W1-4, but LP pigs displayed greater (P < 0.01) gain-to-CP-ratio. Furthermore, pigs in the LP compared with STD group tended (P < 0.10) to display greater bone mass deposition, fat mass and fat mass deposition after W4. In W5-8 ADG was similar between STD-STD (0.96 kg/day) and LP-STD20 + (0.90 kg/day), which were both numerically greater than LP-STD (0.83 kg/day) and LP-STD10 + (0.86 kg/day). In conclusion, pigs fed the LP diet did not display expected reduction in ADG but tended to display an altered body composition after W4. This limited the study objective of investigating effect on increasing Lys and remaining essential AA levels, although observed that pigs fed the LP-STD20+ diet maintained an ADG numerically comparable to the STD-STD pigs throughout the non-reduced period in W5-8.