The effects of previous dietary Lys concentration on subsequent growth performance of two different pig genotypes

The aims of this study were to determine whether Lys restriction immediately after weaning could be compensated for when pigs were switched to a high-Lys diet, and to determine whether this may be influenced by genotype. The experiment was a 2×2 factorial arrangement of diets and genotypes with 8 replicate pens per treatment and 8 or 9 mixed sex pigs per pen. Pigs received either a high- (Control; 17.5g/kg of Lys) or a low-Lys (WR; 8.0g/kg of Lys) diet during the first 3 week post-weaning followed by a high-Lys diet (15.5 and 12.0g/kg of Lys during the grower and finisher phases, respectively) to facilitate compensation until slaughter (approximately 101.2 ± 4.9kg). Two hundred and sixty four pigs [132 Hampshire sire×(Large White×Landrace) dam and 132 Large White sire×(Large White× Landrace) dam] were used and are referred to as Hampshire pigs and Large White pigs. Blood samples were collected from 2 selected pigs per pen at 6, 9, and, 15 week of age for blood urea nitrogen (BUN), non-esterified fatty acids (NEFA), and leptin analysis. Throughout the weaner phase, Control pigs gained more (105±1 g/d) than WR pigs (P<0.001). However, once pigs were switched to a high-Lys diet, WR pigs gained more (44±9 kg/d) than Control pigs and utilised their feed more efficiently (P<0.001), and thus compensatory growth was observed. Pigs of both genotypes performed similarly throughout the weaner stage when fed the low-Lys diet, however, when fed the high-Lys diet, Hampshire pigs had a greater rate of gain compared to Large White pigs (308 vs. 296±8 g/d). Throughout the experiment, Hampshire pigs ate more feed (P<0.001), gained more (P<0.001), and had a greater Lys intake (P<0.001) compared to Large White pigs. Lean meat percentage at slaughter was greater for the Large White pigs compared to Hampshire pigs (P<0.05). At 6 week of age NEFA concentrations were greater for Control pigs compared to WR pigs (P<0.05). Hampshire pigs on the WR treatment had lower BUN levels during the weaner period compared to Hampshire pigs on the Control treatment (P<0.10). In conclusion compensatory growth was observed in both genotypes. The fact that Hampshire pigs grew faster when fed a non-limiting diet but grew at a similar rate compared to Large White pigs when fed a limiting Lys diet indicates that limiting dietary Lys level rather than genotype determined growth performance.