Feed Supplement Growth Promoters Without Antibiotics
The movement away from antibiotic growth promoters (AGPs) has been one of the most significant shifts in poultry production in my career. When I started in the industry, AGPs were used routinely in nearly every broiler feed. Today, many markets have restricted or banned their use, and the industry has had to find alternatives.
Why AGPs Were Used
Growth-promoting antibiotics at sub-therapeutic levels improved growth rate and feed efficiency. The mechanisms included:
- Reduced bacterial load in the gut (less competition for nutrients)
- Thinner intestinal wall (better nutrient absorption)
- Reduced inflammation (less metabolic energy diverted to immune response)
- Suppression of subclinical disease
When AGPs were removed, the typical performance drop was:
- FCR increase: 2-5 points (1.72 to 1.75-1.77)
- Growth reduction: 1-3%
- Mortality increase: 1-3%, primarily from enteric diseases
Non-Antibiotic Growth Promoters
The alternatives fall into several categories. I’ve tested most of them in commercial settings.
Probiotics (Direct-Fed Microbials). Bacillus subtilis spores at 500-1,000 g/ton are the most consistent alternative. They improve FCR by 2-4 points by stabilizing the gut microbiome and reducing pathogen levels. The cost ($4-8/ton) is higher than AGPs ($1-3/ton) but the results are approaching AGP levels.
Prebiotics. Mannan-oligosaccharides at 500-1,000 g/ton bind pathogens and prevent intestinal colonization. They add 1-3 points of FCR improvement and are often used alongside probiotics. Cost: $3-6/ton.
Organic acids. Formic acid, propionic acid, and butyric acid at 2-4 kg/ton lower gut pH and inhibit pathogens. They improve FCR by 2-3 points. Protected (encapsulated) forms are more effective. Cost: $3-8/ton.
Phytogenic feed additives (botanicals). Oregano oil, thyme, carvacrol, and other plant extracts have antimicrobial and antioxidant properties. Results are more variable than other categories, with average FCR improvement of 1-3 points. Cost: $2-6/ton.
Copper. Copper sulfate at 125-175 ppm has been used as a growth promoter for decades. It reduces gut bacterial populations through its antimicrobial effect. FCR improvement: 1-3 points. Cost: $1-3/ton.
Zinc. Zinc oxide or zinc sulfate at 80-120 ppm supports gut barrier function and immune response. Cost: $1-2/ton.
Comparing Performance
In a large-scale comparison I conducted across 10 flocks, the relative effectiveness of AGP alternatives was:
| Supplement | FCR Improvement | Cost/Ton | ROI |
|---|---|---|---|
| AGP (banned in this trial) | 4 points (reference) | $2 | Reference |
| Probiotic (Bacillus) | 3.2 points | $6 | 3.2:1 |
| Organic acid blend | 2.8 points | $5 | 3.4:1 |
| Probiotic + organic acid | 4.1 points | $11 | 2.2:1 |
| Phytogenic blend | 1.5 points | $4 | 2.3:1 |
| Probiotic + phytogenic | 3.5 points | $10 | 2.1:1 |
The best single alternative was the probiotic (Bacillus). The best combination was probiotic + organic acid, which actually exceeded the AGP performance but at higher cost.
Program Design
For antibiotic-free production, I use a layered approach:
Tier 1 (baseline, every flock): Probiotic + phytase + enzymes. This provides the foundation.
Tier 2 (intermediate): Add organic acids or protected butyrate. Used when baseline performance needs a boost.
Tier 3 (maximum support): All of the above plus high copper. Used in high-challenge environments or during disease outbreaks.
The cost ranges from $6-8/ton (Tier 1) to $12-18/ton (Tier 3). Most operations use between Tier 1 and Tier 2.
Management Adjustments
Supplements alone cannot replace AGPs without management changes. The production system must adapt:
- Lower stocking density. Reducing bird density by 10-15% reduces pathogen pressure.
- Better ventilation. Lower ammonia levels reduce respiratory stress and improve gut health.
- Longer downtime. I recommend 14-21 days between flocks vs 10-14 days for conventional.
- All-in/all-out management. Same-age birds on the same health status.
- Improved biosecurity. The basics: boot dips, shower-in, single-age sites.
In my experience, operations that made management changes alongside supplement changes were far more successful than those that tried to rely on supplements alone.
The Cost of Going AGP-Free
The total additional cost of antibiotic-free production, including supplements and management changes, is approximately $0.02-0.05 per pound of live weight. The premium for antibiotic-free chicken in the retail market is typically $0.10-0.30 per pound, so the economics often work out.
For producers in markets where AGPs are still legal but consumer pressure is building, starting the transition now allows you to figure out what works before regulatory pressure forces the change.