Effects of Dietary Lysine Levels on Apparent Nutrient Digestibility and Serum Amino Acid Absorption Mode in Growing Pigs

Abstract

Two experiments were conducted to determine the effects of different dietary lysine levels on the apparent nutrient digestibility, the serum amino acid (AA) concentration, and the biochemical parameters of the precaval and portal vein blood in growing pigs. In Experiment 1, 15 noncannulated pigs received diets with different lysine densities (0.65%, 0.95%, and 1.25% lysine) for 13 d. A total collection digestion test was performed, and blood samples were collected from the precaval vein at the end of the experiment. In Experiment 2, four cannulated pigs were fed the same diets of Experiment 1. The experiment used a self-control experimental design and was divided into three periods. On d 5 of each period, at 0.5 h before feeding and hourly up to 8 h after feeding, single blood samples were collected from catheters placed in the portal vein. In Experiment 1, some serum AAs (including lysine), serum urinary nitrogen (SUN), and total protein (TP) concentrations were significantly affected by the dietary lysine levels (p<0.05). Moreover, the 0.65% lysine treatment showed a significant lower apparent digestibility of gross energy, dry matter, crude protein, and phosphorus than the other treatments (p<0.05). In Experiment 2, serum lysine, histidine, phenylalanine, threonine, valine, isoleucine (p = 0.0588), triglyceride, and SUN (p = 0.0572) concentrations were significantly affected by the dietary lysine levels (p<0.05). Additionally, almost all of the determined serum AA and total AA concentrations reached their lowest values at 0.5 h before feeding and their highest values at 2 h after feeding (p<0.05). These findings indicate that the greatest absorption of AA occurred at 2 h after feeding and that the dynamic profile of serum AA is affected by the dietary lysine levels. Moreover, when the dietary lysine content was 0.95%, the growing pigs achieved a better nutrient digestibility and serum metabolites levels.

Effects of dietary lysine levels on the concentrations of selected nutrient metabolites in blood plasma of late‐stage finishing pigs

“…(), and Zeng et al. () who found that dietary lysine levels did not affect the plasma concentrations of glucose. The non‐changed glucose concentration among the three dietary treatments of this study may be attributed to the same amounts of metabolizable or net energy provided to all the pigs (Table ), which suggests that when the energy requirement of the pigs is met, the dietary lysine level would not affect or would not significantly affect glucose or energy metabolism.…”

“…(), and Zeng et al. (), who reported decreased plasma UN concentrations with increasing content of dietary lysine up to the level of dietary requirement. Protein synthesis requires a complete set of AAs presented at the synthesis site simultaneously, and when the first‐limiting AA is used up, protein synthesis stops and the remaining free or unbound AAs will be catabolized via deamination (Liao et al., ; NRC, ).…”

“…However, contrasting results were obtained in some previous research. Decreased dietary lysine concentration caused decreased plasma concentration of total protein, and the plasma total protein concentration increased along with increasing dietary lysine levels (Cahilly et al., ; Kamalakar et al., ; Whisenhunt & Carter, ; Yang et al., ; Zeng et al., ). The age differences between the pigs used in this study and those used previously by other researchers may explain the discrepancy in this regard.…”

“…However, this speculation contradicts the fact that there was no difference in total digestible energy content (approximately 14.5 MJ/kg) between the two diets. The pigs fed the two diets should have maintained a constancy of plasma glucose concentration (Zeng et al., ). The reason for the discrepancy between the results of Mule et al.…”

“…In the experiments with growing and finishing pigs (Fuller, Reeds, Cadenhead, Seve, & Preston, ; Roy, Lapierre, & Bernier, ; Shelton et al., ), crystalline lysine supplementation increased nitrogen retention and protein accretion and improved animal growth performance. It has been shown that dietary lysine affects plasma concentrations of nutrient metabolites including total protein, albumin (Kamalakar et al., ; Yang et al., ), urea nitrogen (UN) (Fernández‐Fígares, Lachica, Nieto, Rivera‐Ferre, & Aguilera, ; Zeng et al., ), glucose (Zhang et al., ), triglycerides, and cholesterol (Bouyeh & Gevorgyan, ; Skiba, ). However, results from these previous studies were rather inconsistent, and in many cases the dietary concentrations of other AAs were adjusted to constant ratios to lysine based on the ideal protein concept (Baker, Hahn, Chung, & Hahn, ; NRC, ).…”