Effects of genetic line and dietary crude protein level on growth traits of finishing heavy pigs

This trial was aimed to evaluate the effect on growth performance of restricted diets using conventional (CONV) or low-CP and low-essential amino acid diets (LP) on pigs of 4 genetic lines (GL): Anas (A), DanBred (D), Goland (G) and Topigs (T). In two rounds, 184 pigs (gilts and barrows), born in the same week, were raised on a common feeding regime till 80 kg BW. From 80 kg BW, the pigs were housed in 8 pens (10 to 12 pigs/pen) equipped with feeding station recording individual daily feed intake and received CONV or LP diets. During the early (90 to 120 kg BW) and late (120 to 165 kg BW) finishing periods the CONV diets contained 147 and 132 g CP/kg feed and 50 and 41 g lysine/kg CP, respectively, while LP diets contained 112 and 100 g CP/kg feed and 50 and 41 g lysine/kg CP, respectively. Every three weeks pigs were individually weighted and backfat thickness was ultra-soundly measured at P2 point. Data were subjected to ANOVA and diet was tested on pen within round as line of error. All growth traits were influenced by GL (P<0.001): the D pigs had greatest final BW (172 kg), ADG (0.700 kg/d), gain:feed ratio (0.272) and the lowest final backfat depth (15.9 mm) and backfat gain (+7.5 mm); the A and G pigs exhibited similar final BW (165 kg), average daily gain (ADG, 0.686 kg/d), gain:feed ratio (0.266), final backfat depth (18.6 mm) and backfat depth gain (+8.9 mm); the T pigs had the lowest final BW (159 kg), ADG (0.637), gain:feed ratio (0.248) and final backfat depth (16.2 mm) and backfat depth gain (+7.7 mm). The dietary treatment did not influence final BW and ADG, but LP increased backfat depth gain from +8.0 to +8.6 mm (P=0.013) compared to CONV. The GL × feed interaction was never significant. Differences among GL were more relevant than those due to the reduction of the dietary CP. These results are useful for the Italian Protected Designation of Origin (PDO) dry-cured ham production circuit.