Effect of reducing dietary protein and lysine on growth performance, carcass characteristics, intramuscular fat, and fatty acid profile of finishing barrows

Intramuscular fat is an important quality trait in pork. Lysine and protein have been reported to influence this trait, but most studies have modified both factors simultaneously. In this study, the effects of dietary Lys and protein were investigated in finishing pigs to determine if either of the 2 factors alone or in combination influence the deposition of intramuscular fat. One hundred and four barrows (Landrace x Duroc) were fed 1 of 4 experimental diets, including control protein-control Lys (CPCL), control protein-low Lys (CPLL), low protein-control Lys (LPCL), and low protein-low Lys diets (LPLL) with 10 pens per treatment and 2 or 3 pigs per pen. Pigs fed CPLL showed a trend to decrease feed efficiency (P < 0.10) compared with those fed CPCL, but pigs fed LPLL performed similarly to the CPCL pigs, indicating that CP levels can be reduced to 12% for pigs between 62 and 97 kg and to 9.8% afterward without negative effects on performance. In the longissimus thoracis, intramuscular fat increased in pigs fed LPCL or CPLL (P < 0.05) compared with CPCL. In the semimembranosus muscle, intramuscular fat was reduced in pigs fed LPLL compared with those fed CPLL (P < 0.05), and the same trend was observed in the longissimus thoracis (P < 0.10). Dietary protein reduction tended to increase back fat thickness (P < 0.10) and reduced SFA and MUFA (P < 0.05) and PUFA, particularly in subcutaneous fat (P < 0.05), whereas the effect on MUFA in the longissimus thoracis was less pronounced. A reduction of n-3 FA (P < 0.05) and PUFA (P < 0.01) in the semimembranosus muscle and in the liver, respectively, was observed when the level of dietary protein was reduced. These results indicate that the effect of a reduction of dietary protein and Lys on growth and intramuscular fat is not independent, and reduction of protein, while maintaining Lys, may improve meat quality without impairing performance.