# The Role of CP Level and Interaction with Antibiotics in the Post-Weaning Piglets’ Diet: Growth Performance, Body Composition, Nutrient Digestion, and Intestinal Health

## TL;DR

This study shows that lower protein diets in young pigs slow initial growth but improve gut health, with later catch-up growth, and antibiotics have limited benefits.

## Contribution

The study reveals that low-protein diets can promote gut microbiota balance in piglets without antibiotics, offering a sustainable alternative.

## Key findings

- Lower protein diets (18% CP) reduced early growth but improved gut microbiota balance in weaned piglets.
- Piglets on low-protein diets showed compensatory growth when protein levels were increased later.
- Antibiotics had no significant effect on growth or nutrient digestion but temporarily altered gut microbiota.

## Abstract

This study highlights the critical interplay between CP levels and antibiotic use in shaping the growth and health of weaned piglets. The findings suggest that lower dietary protein (18% CP) might hinder growth performance temporarily but enables compensatory growth when protein levels are normalized. While the use of antibiotics did not enhance overall performance or body composition, it did modulate gut microbiota transiently. This implies that optimizing dietary protein could be a more sustainable and health-conscious strategy for piglet nutrition, reducing reliance on antibiotics in modern farming practices.

The objective of this study is to evaluate the effects of crude protein (CP) levels and antibiotics in feed on the growth performance, body composition, nutrient digestion and absorption, gut health, and microbiota of weaned piglets. A total of 100 piglets (Duroc × Landrace × Yorkshire, weaned at day 21) with an initial weight of 6.39 ± 0.03 kg were randomly assigned to four treatments and fed with 18% CP antibiotic-free diets, 18% CP with antibiotics diets, 24% CP antibiotic-free diets, and 24% CP with antibiotics diets for 0–14 d (S1). Furthermore, the piglets were fed with an identical diet (19% CP and without antibiotics) starting day 15 until they reached 25 kg (S2). Results indicated that the average daily gain (ADG) and gain feed ratio (G:F) during the S1 phase as well as BW at day 14, were significantly decreased (p < 0.05) in the 18% CP group compared with the 24% CP group. Similarly, piglets in the 18% CP group showed a significantly decreased body protein content and body water, protein deposition rates at the S1 phase, and significantly improved the body lipid content and deposition rate but not (p > 0.05) at the S2 phase. The 18% CP group demonstrated significantly increased (p < 0.05) serum concentrations of Threonine, Valine, Isoleucine, and Lysine in weaned piglets during the S1 phase, while Glycine concentration significantly decreased, and no significant (p > 0.05) effects were observed in the S2 phase. Furthermore, dietary antibiotic supplementation had no effect on (p > 0.05) piglet growth performance, body composition, nutrient digestion, and metabolism throughout the entire trial period. In the absence of antibiotics, compared to the 24% CP diet group, the piglets fed with an 18% CP diet significantly increased the relative abundance of Lactobacillus in the colon of weaned piglets upon reaching 25 kg BW (p < 0.05). Compared to the diet without added antibiotics, the addition of antibiotics to the diet significantly decreased the relative abundance of Pseudoramibacter in the colon of weaned piglets on day 14. No significant (p > 0.05) difference was observed in intestinal morphology or gastrointestinal pH among the groups. In conclusion, lower dietary protein levels in the early post-weaning period reduced growth performance and promoted gut microbiota balance, and compensatory growth occurred after returning to higher protein levels two weeks after weaning.