The effects of genotype and dietary lysine concentration on the production of weaner pigs

Dietary lysine affects amino acid metabolism and growth performance, which may not involve the GH/IGF-1 axis, in young growing pigs1

Lysine is the first limiting amino acid (AA) in typical swine diets. Our previous research showed that dietary lysine restriction compromised the growth performance of late-stage finishing pigs, which was associated with the changes in plasma concentrations of nutrient metabolites and hormone insulin-like growth factor 1 (IGF-1). This study was conducted to investigate how dietary lysine restriction affects the plasma concentrations of selected metabolites and three anabolic hormones in growing pigs. Twelve individually penned young barrows (Yorkshire × Landrace; 22.6 ± 2.04 kg) were randomly assigned to two dietary treatments (n = 6). Two corn and soybean meal based diets were formulated to contain 0.65% and 0.98% standardized ileal digestible lysine as a lysine-deficient (LDD) and a lysine-adequate (LAD) diets, respectively. During the 8-week feeding trial, pigs had ad libitum access to water and their respective diets, and the growth performance parameters including average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed ratio (G:F) were determined. At the end of the trial, jugular vein blood was collected for plasma preparation. The plasma concentrations of free AA and six metabolites were analyzed with the established chemical methods, and the hormone concentrations were analyzed with the commercial ELISA kits. Data were analyzed with Student's t-test. The ADG of LDD pigs was lower (P < 0.01) than that of LAD pigs, and so was the G:F (P < 0.05) since there was no difference in the ADFI between the two groups of pigs. In terms of free AA, the plasma concentrations of lysine, methionine, leucine, and tyrosine were lower (P < 0.05), while that of β-alanine was higher (P < 0.01), in the LDD pigs. The total plasma protein concentration was lower (P < 0.02) in the LDD pigs, whereas no differences were observed for the other metabolites between the two groups. No differences were observed in the plasma concentrations of growth hormone (GF), insulin, and IGF-1 between the two groups as well. These results indicate that the lack of lysine as a protein building block must be the primary reason for a reduced body protein synthesis and, consequently, the compromised G:F ratio and ADG. The changes in the plasma concentrations of total protein and four AA suggest that the compromised growth performance might be associated with some cell signaling and metabolic pathways that may not involve the GH/IGF-1 axis.

Responses of Pigs of Different Genotypes to a Variation in the Dietary Indispensable Amino Acid Content in Terms of Their Growth and Carcass and Meat Quality Traits

Simple Summary

The aim of the experiment was to study the response of pigs of different genotypes to a variation in their dietary amino acid allowance. Ninety-six crossbred barrows of two lean paternal genetic lines (Hypor Maxter and PIC 337) were housed in eight pens from body weight 60 to 145 kg and fed quasi ad libitum on feeds with either high or low ileal digestible indispensable amino acid contents. The high and low amino acid feeds were formulated to have the same standardized ileal digestible (SID) lysine, methionine, tryptophan and threonine contents per unit of crude protein, but provided 9.4 to 8.0 (assumed to be non-limiting) or 8.5 to 6.5 (close to National Research Council recommendations) g/kg of SID lysine, respectively. The low amino acid feed reduced the estimated N excretion compared with the high, without affecting growth, carcass yield, carcass anatomical composition and meat quality traits. Genetic line had trivial effects and the amino acid level × genotype interaction was never significant. We concluded that the two pig genotypes did not differ sufficiently in growth potential and leanness to respond differently.

Abstract

We studied the response of pigs from two crossbred genetic lines (GL) in the 60 to 145 kg body weight interval to a variation in the indispensable amino acid (AA) content of their feed. Ninety-six barrows of two paternal GLs (Hypor Maxter and PIC 337) were housed in eight pens and fed quasi ad libitum on feeds differing in their standardized ileal digestible (SID) indispensable AA contents. Pigs in four pens received feeds containing 9.4 to 8.0 g/kg of SID Lys (HAA), considered non-limiting, while the others received feeds containing 8.5 to 6.5 g/kg of SID Lys (LAA). The two feeds had identical indispensable lysine, methionine, tryptophan and threonine contents per unit of crude protein (CP). Feed intake, growth, carcass weight, and the weights of the lean and fat cuts were recorded, and samples of longissimus lumborum were analyzed. Data were analyzed using a two-way factorial mixed model. The LAA feed lowered the estimated N excretion (p < 0.001) compared with HAA, without affecting growth, carcass or meat quality traits. Genetic line had trivial effects and the AA level × genotype interaction was never significant. The two pig genotypes did not differ sufficiently in growth potential and leanness to respond differently.