Swine Internal Parasite Control
Internal parasites impose significant but often underestimated costs on swine operations. Subclinical *Ascaris suum* infection — the most common swine parasite — reduces average daily gain by 5–15% and causes "milk spot" liver condemnations at slaughter, both reducing profitability without obvious clinical signs.
The parasitic lifecycle and treatment windows:
*Ascaris suum* eggs passed in feces become infective larvae in soil within 3–4 weeks (under favorable conditions). Larvae are ingested, migrate through the liver and lungs ("swine influenza-like syndrome" in heavy infections), and mature in the small intestine. The prepatent period is 6–8 weeks.
Effective treatment requires reaching migrating larvae *and* adult worms — most anthelmintics target adults; ivermectin and macrocyclic lactones have broader activity against larvae.
Production-stage treatment windows:
| Stage | Recommended timing |
|-------|---------------------|
| Sows | 2–3 weeks pre-farrowing + every 6 months |
| Gilts | 2–4 weeks pre-breeding + pre-farrowing |
| Boars | Every 6–12 months |
| Growers | At placement into grower facility |
| Nursery pigs | If *Strongyloides* is a herd problem |
Designing a Herd Deworming Program
A robust swine parasite control program goes beyond calendar-based deworming. The following framework is recommended by veterinary parasitologists:
1. Baseline assessment:
Run fecal egg counts (McMaster technique) on 10–20 sows and 10 grower pigs twice yearly. Establish your herd's baseline parasite burden by species.
2. Drug selection:
Choose anthelmintics based on your herd's parasite spectrum. *Ascaris* is controlled by all major classes. *Trichuris* requires benzimidazoles or high-dose ivermectin. *Mange* requires ivermectin.
3. Class rotation:
Rotate between macrocyclic lactones (ivermectin, doramectin), benzimidazoles (fenbendazole), and levamisole on annual treatment cycles to delay resistance selection.
4. Efficacy monitoring:
Perform a fecal egg count reduction test (FECRT) at least every 3–5 years: collect pre-treatment samples, treat, re-sample at 14–21 days. Target >95% egg count reduction for effective control.
5. Quarantine protocol:
Treat all incoming animals with two different drug classes before introducing them to the herd. Hold in isolation for 21 days.
