# The effects of reduced protein diet supplemented with arginine plus glutamine–glutamate on growth performance, diarrhea incidence, blood metabolites, nutrient digestibility, and nitrogen utilization in nursery pigs

## TL;DR

Reducing protein in pig diets lowers growth and nitrogen waste but increases diarrhea, even with added amino acids.

## Contribution

The study reveals trade-offs between growth, gut health, and sustainability when reducing dietary protein in young pigs.

## Key findings

- Reducing dietary protein compromises growth and nutrient digestibility in nursery pigs.
- Supplementing with arginine and glutamine–glutamate does not fully offset the negative effects of low-protein diets.
- Lower protein diets reduce nitrogen excretion and diarrhea incidence.

## Abstract

This study evaluated the effects of reducing crude protein (CP) and supplementing arginine plus glutamine–glutamate (AGG) on growth performance, diarrhea incidence, blood metabolites, amino acid profiles, nutrient digestibility, and nitrogen (N) utilization in nursery pigs.

A total of 200 entire male and female piglets weaned at 20 d of age (4.8±0.58 kg) were allotted to 5 diets in a randomized block design: 22.5%, 21.0%, 19.5%, or 18.0% CP, and 18.0% CP supplemented with 5 g/kg L-arginine and 10 g/kg L-glutamine+glutamate. Pigs were fed in two phases (20–32 and 32–44 d of age) over a 24-d period.

Reducing dietary CP linearly decreased feed efficiency, with the lowest performance observed in pigs fed the 18.0% CP diet with AGG. Serum urea N and gamma-glutamyl transferase increased linearly with dietary CP level. Plasma arginine and ornithine were elevated by supplementation. Methionine, threonine, and valine were highest in pigs fed the 18.0% CP diets. In contrast, phenylalanine and tyrosine declined with reduced CP. Diarrhea incidence and fecal scores were greater in pigs fed the 22.5% CP, with each 1% CP increase raising diarrhea incidence by 3.55% points. Digestibility of protein and energy improved with increasing dietary CP, and pigs fed 22.5% CP showed the greatest N absorption but also higher fecal N excretion.

Collectively, results indicate that reducing dietary CP from 22.5% to 18.0% compromises growth and nutrient digestibility, even when supplemented with arginine and glutamine–glutamate, but lowers diarrhea incidence and N output. These findings highlight trade-offs between growth efficiency, gut health, and environmental sustainability in nursery pig nutrition.