Effect of early dietary amino acid restrictions on serum metabolites in pigs selected for lean growth efficiency

Thirty-two select line pigs for lean growth efficiency and 32 control line pigs (average 20 kg) were used in each of the two experiments to assess the effect of dietary amino acid restrictions during the grower phase on serum cholesterol, triglycerides, total protein, albumin, and glucose concentrations. In each experiment, 16 pens with two gilts and 16 pens with two castrated males per pen were assigned within the genetic line to grower (6.1 or 11.1 g lysine kg(-1)) and finisher diets (6.1 or 8.9 g lysine kg(-1)) in a 2 x 2 x 2 factorial arrangement in exp. 1, or grower diets (5.0, 7.0, 9.0, or 11.0 g lysine kg(-1)) in a 2 x 4 factorial arrangement of treatments in exp. 2. Pigs were offered common finisher diets in exp. 2. Serial blood samples were collected in both experiments. Serum cholesterol at the end of the grower phase was greater in the select line pigs in exp. 1 (P = 0.009) and pigs fed diets low in amino acids in exp. 2 (P = 0.005, 0.026, and 0.039 for linear, quadratic, and cubic, respectively). Serum cholesterol was correlated negatively with lysine intake (r = -0.38; P = 0.039) and serum urea nitrogen (r = -0.39; P = 0.032) in exp. 1 and positively with ultrasound backfat (r = 0.78; P = 0.001) in exp. 2. Serum cholesterol, however, may not reflect the cholesterol content of tissues or pork, except liver. At the end of the grower phase, pigs fed grower diets high in amino acids had greater serum total protein in exp. 2 (P = 0.040 and 0.093 for linear and quadratic, respectively) and albumin concentrations in exp. 1 (P = 0.001) and exp. 2 (linear, P = 0.001), and, at the end of the finisher phase, they had greater serum albumin in exp. 1 (P = 0.001) and seemed to have more total protein in exp. 2, even though there was a trend for the grower diet x genotype interaction (P = 0.095). The carryover effects of the grower diet during the realimentation phase seem to be contrary to the expected positive metabolite status of pigs exhibiting compensatory growth after a period of early dietary amino acid restrictions. On the other hand, higher serum total protein in exp. 2 (P = 0.041 and 0.001 at the end of the grower and finisher phases, respectively) and albumin concentrations at the end of the finisher phase in exp. 1 (P = 0.016) and exp. 2 (P = 0.059) in pigs selected for lean growth efficiency may be an indication that pigs utilized amino acids more efficiently for growth and protein accretion. Exploring fully the effect of dietary manipulations and genotypes on serum metabolites is obviously important, and the results of the present research may contribute to the development of the environmentally friendly, optimal feeding strategies for successful and sustainable pig production.