Arginine is the most abundant nitrogen carrier in whole-body proteins and the most abundant amino acid in porcine fetal fluid during early to mid-gestation. Arginine is actively utilized in the body by multiple pathways of enormous biological importance, including protein synthesis and the production of nitric oxide (a major vasodilator) and polyamines. This is consistent with high turnover rates of arginine in pigs during neonatal, growing and gestating periods. Thus, there are particularly high requirements for arginine by both young and gestating pigs for maintenance, health, growth, and reproduction. Recent studies indicate that, for supporting maximal growth and metabolic needs, dietary requirements of arginine by young and gestating pigs (Table 1) are much greater than those currently recommended by National Research Council (NRC, 1998). The current version of NRC (1998) does not provide values for dietary requirements of arginine by 1- to 3-day-old pigs or of glutamine by any age of pigs.
Table 1. Estimated and NRC-recommended dietary requirements of arginine by pigs (% of diet, DM basis)
|Body weight, kg||1-3||3-5||5-10||150 (at breeding)|
|Daily feed intake (g DM/kg BW)||70||65||60||11|
|1 Nutrient Requirements of Swine, National Research Council, 1998|
Dietary supplementation with arginine-family amino acids improves swine nutrition
Arginine content in sow’s milk and conventional corn-soybean meal-based swine diets are 0.76% and 0.78% to 1.0% (DM basis), respectively. Therefore, milk protein-based diet should be supplemented with arginine or an immediate precursor (citrulline) to support maximal growth and reproduction performance of pigs. This notion is supported by compelling experimental evidence.
First, dietary supplementation with 0.2% and 0.4% L-arginine (as L-arginine-HCl) to 7- to 21-d-old milk-fed pigs (artificially reared on a liquid-milk feeding system) dose-dependently increases plasma arginine concentrations (30% and 61%), reduces plasma ammonia levels (20% and 35%), and promotes daily weight gain (28% and 66%). Similar results are be obtained through oral administration of N-carbamoylglutamate (a metabolically stable activator of citrulline and arginine synthesis) to milk-fed piglets (50 mg/kg body wt every 12 h).
Second, dietary supplementation with 1.0% L-arginine-HCl between Days 30 and 114 of gestation increases the number of live-born piglets by 2 and litter birth-weight by 24%. Also, investigators at Nutreco (Boxmeer, Netherlands) have reported that supplementing 1% arginine to the diet for sows between days 14 and 28 of gestation increased the number of live-born piglets by 1 without affecting their average birth weight. The work on arginine nutrition has received worldwide attention and led to the commercial development and availability of feed-grade arginine for improving pig reproductive performance.
Third, supplementing 1.0% arginine-HCl to the diet for sexually active boars for 30 days enhances sperm counts and motility by 18% and 8%, respectively. Fourth, dietary supplementation with 1% L-glutamine prevents jejunal atrophy (a major problem in swine production) during the first week postweaning and increases gain:feed ratio by 25% in the subsequent week. Notably, this finding has led to the commercial development and availability of feed-grade glutamine for use in swine diets.
Practically, large-scale availability of feed-grade arginine and glutamine is expected to improve the efficiency of nutrient utilization by both young and gestating pigs worldwide.
Arginine and glutamine (members of the arginine family of amino acids) are major building blocks for proteins and essential precursors for synthesis of many substances with enormous biological importance. Additionally, they regulate key metabolic pathways that are crucial for maintenance, growth, reproduction, and immune responses in animals. Supplementing arginine to conventional swine diets enhances growth and reproduction performance of pigs. These findings have resulted in a paradigm shift in understanding the role for amino acids in swine nutrition and are transforming the practice of dietary formulation in the pig industry. Large-scale availability of feed-grade arginine and glutamine holds great promise for improving the efficiency of nutrient utilization in pork production worldwide.