Dietary arginine-to-lysine ratio influences nutrient digestibility during early growth without affecting growth performance in growing–finishing pigs

Abstract

The balance of dietary amino acid ratios is an important factor affecting nutrient utilization in pigs. Both arginine and lysine are involved in protein deposition and nitrogen metabolism, and their relative ratio may influence nutrient utilization and metabolic responses. This study evaluated the effects of different dietary arginine-to-lysine ratios (Arg:Lys) on growth performance, fecal characteristics, nutrient digestibility, and serum metabolites in growing–finishing pigs. A total of 165 pigs [Duroc × (Landrace × Yorkshire)] with an initial body weight (BW) of 26.36 ± 3.01 kg were assigned to three dietary treatments in a randomized complete block design based on BW. The CON, TRT1, and TRT2 diets were formulated to provide Arg:Lys ratios of 1.00, 1.10, and 1.20, respectively. Each treatment had 11 replicate pens, with 5 pigs per pen, including 2 gilts and 3 barrows. The experiment lasted 15 weeks. Dietary Arg:Lys ratio did not affect BW, average daily gain, average daily feed intake, or feed conversion ratio during any experimental period (p > 0.05). Fecal score was not affected by dietary treatment throughout the experiment (p > 0.05). Pigs fed the TRT1 diet had greater apparent total tract digestibility (ATTD) of nitrogen (N) (p = 0.0247, p = 0.0361) and gross energy (GE) (p = 0.0402, p = 0.0343) at weeks 2 and 5 than pigs fed the CON diet. At week 12, ATTD of dry matter (DM) showed a significant quadratic response (p = 0.0371). Fecal moisture was not affected at weeks 2, 5, 9, or 12, but showed a significant quadratic response at week 15 (p = 0.0230). Serum homocysteine concentration showed a significant quadratic response at week 5 (p = 0.0334), whereas serum creatine concentration was not affected. Overall, dietary Arg:Lys ratio did not affect growth performance in growing–finishing pigs, but an Arg:Lys ratio of 1.10 improved the ATTD of N and GE during the early growing phase. However, because these digestibility responses were not maintained throughout the entire experimental period and were not accompanied by improvements in growth performance, their practical nutritional significance requires further investigation.