Effect of fatty acids source on growth performance, carcass characteristics, plasma urea nitrogen concentration, and fatty acid profile in meat of pigs fed standard- or low-protein diets

Thirty six Landrace × Yorkshire barrows with 18.6 kg of initial body weight were used to evaluate three sources of fatty acids: crude soybean oil, conjugated linoleic acid (CLA), and soybean soapstock in standard crude protein (CP) and low-protein diets for starter (21 d; 205, 160 g kg-1 CP), growing (28 d; 160, 145 g kg-1 CP), and finishing (29 d; 140, 125 g kg-1 CP) phases. Growth performance, carcass characteristics, plasma urea nitrogen concentration and fatty acid profile in meat were evaluated. The reduction of CP diminished average daily gain, feed:gain ratio, longissimus muscle area and plasma urea nitrogen concentration in nursery pigs; reduced longissimus muscle area and plasma urea nitrogen concentration in growing pigs; increased average daily feed intake, and reduced lean meat percentage and plasma urea nitrogen content in finishing pigs. It also increased c9, t11 and c11, t9 CLA isomers and total lipids and lowered eicosapentaenoic and docosahexaenoic acids concentrations in semimembranosus muscle; linolenic acid decreased with low-protein diets in longissimus and semimembranosus muscles; the oil type affected the concentration of c9, t11 and c11, t9 CLA isomers and total saturated fatty acids in semimembranosus muscle; CLA increased individually and total saturated fatty acids, reduced linoleic and docosapentaenoic acids, and increased total lipids in longissimus muscle. These results indicate that decreasing CP changes the profile of fatty acids. The soybean soapstock can replace crude soybean oil in pig diets; while conjugated linoleic acid does not improve response of pigs fed standard- or low-protein diets.