Foal Deworming & Vaccination: Month-by-Month Protocol for the First Year

Foals are born immunologically naive and depend entirely on colostrum-transferred antibodies for the first 4-6 months of life, making your first-year deworming and vaccination schedule one of the most consequential decisions you’ll make as a breeder. Get the timing right and you build a foal with a strong immune foundation; miss a window and you risk gaps in protection during the most vulnerable developmental period.

This guide draws on AAEP guidelines, Merck Veterinary Manual protocols, and University Extension recommendations to give you a practical, month-by-month framework you can act on today.

Why Does the First Year Matter So Much for Foal Immunity?

Foals emerge from the womb with a nearly blank immunological slate. Unlike humans, horses have an epitheliochorial placenta that does not allow immunoglobulin transfer in utero. Every antibody your foal carries in its first months of life arrived via colostrum: the reason colostrum timing is critical.

According to the Clinique Vétérinaire de Grosbois, a 50 kg foal must ingest at least 60 grams of immunoglobulins (roughly 1.5-2 liters of high-quality colostrum) within the first 12 hours of life. The intestinal barrier closes completely by 24 hours, after which no antibody absorption is possible regardless of colostrum volume consumed.

During this time, foals grow rapidly — reaching approximately 80% of their mature height and 50% of their mature weight by 6 months. Weight monitoring every two weeks is recommended to prevent developmental orthopedic disease.

Maternal antibodies wane progressively between 3 and 6 months. This creates an immunity gap. This is a period when maternal protection is too low to defend the foal, but the foal’s own active immunity hasn’t yet been stimulated. Your vaccination schedule exists precisely to close this gap before it becomes dangerous.

What Parasites Threaten Foals in Year One?

Foals face a different parasite landscape than adult horses. The three primary threats are:

• Parascaris equorum (roundworms): The dominant concern in foals under 6 months. Larvae migrate through lungs and liver before maturing in the intestines, causing respiratory signs, poor growth, and potentially fatal impactions.
• Strongyloides westeri (threadworms): Transmitted through the mare’s milk in the first weeks of life. Usually self-limiting but can cause diarrhea in neonates.
• Small strongyles (cyathostomins): Become relevant as foals begin grazing, typically from 3-4 months onward.
• Tapeworms (Anoplocephala perfoliata): Addressed at the end of the first year with praziquantel combination products.

Fecal egg count (FEC) monitoring is the gold standard. Work with your veterinarian to establish a baseline FEC at 8 weeks and use results to guide treatment decisions rather than treating on a fixed calendar.

Month-by-Month Foal Protocol: Complete First-Year Schedule

Important: Benzimidazole resistance in P. equorum is increasingly documented. If you use fenbendazole and FEC remains high at recheck (2 weeks post-treatment), switch anthelmintic class and discuss resistance testing with your veterinarian.

How Should You Manage the Critical Newborn Period (Days 1-7)?

Before any deworming or vaccination enters the picture, the neonatal period establishes the baseline health of everything that follows.

The 1-2-3 Rule is your first checkpoint:

1. Foal stands within 1 hour of birth
2. Foal nurses within 2 hours of birth
3. Mare passes placenta within 3 hours of birth

Any deviation from these benchmarks warrants veterinary contact. A retained placenta beyond 6 hours is a veterinary emergency (occurring in 2-10% of foalings); endotoxemic shock, metritis, laminitis, and septicemia risk escalate sharply after this point.

Normal vital signs for newborn foals provide additional reference points: temperature 99-102°F (37.2-38.9°C), heart rate 80-100 bpm, and respiratory rate 20-40 breaths per minute. Foals should sit sternal within 10-20 minutes before standing within 1 hour.

IgG testing at 12-24 hours is strongly recommended by the Clinique Vétérinaire de Grosbois. Use a Brix refractometer on colostrum to assess quality before the foal nurses: ≥23% Brix generally indicates adequate IgG (>60 g/L). For more precise assessment, research identifies cut-off points of ≤23.75% (digital refractometer) and ≤23.9% (optical refractometer) for detecting IgG <60 g/L, with 93.3% sensitivity and >98% negative predictive value; <15% Brix corresponds to <30 g/L (supplementation required).

If blood IgG testing at 12-24 hours confirms inadequate passive transfer (<400 mg/dL), oral colostrum supplementation is still effective before 24 hours. After 24 hours, intravenous plasma transfusion is the only option.

When Should You Start the Vaccine Series in Foals?

The timing of the primary vaccine series is driven by two competing forces: maternal antibody interference and the immunity gap.

Maternal antibodies suppress vaccine response. If you vaccinate too early, before maternal antibodies have waned, the foal’s immune system won’t mount an adequate response. The colostrum-derived antibodies neutralize the vaccine antigens before the foal’s B-cells can recognize them.

The general consensus from AAEP guidelines:

• Begin primary series at 4-6 months for most core vaccines
• Foals of vaccinated mares should start at 6 months
• Foals of unvaccinated or unknown-status mares may begin at 3-4 months

Core vaccines for foals (AAEP classification):

• Eastern/Western Equine Encephalomyelitis (EEE/WEE)
• Tetanus
• West Nile Virus
• Rabies

Risk-based vaccines to discuss with your veterinarian:

• Equine Influenza
• Equine Herpesvirus (EHV-1/4)
• Strangles (Streptococcus equi)
• Botulism (particularly in high-risk regions)

How Do You Manage Deworming at Weaning?

Weaning is the highest-stress event in a foal’s first year. While conventional practice often targets 5-6 months, natural weaning in wild horses occurs at 9-11 months. Multiple studies document significant stress and behavioral disorders from early weaning at 5-6 months, and breeders should weigh the trade-offs carefully. Research cited by IFCE/INRAE shows that abrupt weaning leads to significantly more behavioral and physiological distress than progressive separation. Progressive separation specifically reduces vocalizations by 50% and trotting by 66% compared to abrupt weaning. Critically, the weaning stress itself directly compromises the foal’s immune response — not just by affecting vaccination timing, but by suppressing the immune system during a period when the foal is already in an immunity gap.

From a parasite management perspective:

• Treat with anthelmintic at weaning regardless of FEC, to reduce the parasite burden during the post-weaning immune dip
• Choose a product effective against P. equorum, fenbendazole or oxibendazole for naive foals, switching to ivermectin if resistance is suspected
• Recheck FEC 10-14 days post-treatment to confirm efficacy
• Move weaned foals to clean pasture where possible, as pastures grazed heavily by young horses carry the highest P. equorum egg counts

Creep feeding should begin at 1-2 months of age (not just at weaning) with 14-16% crude protein feed. Foals should gain 1.25-2 pounds daily for optimal skeletal development, and early creep feeding eases the nutritional transition at weaning
Group weaning in paddocks (ideally ~1,000 m²) is strongly preferred over individual stall confinement, which increases both stress hormones and abnormal repetitive behaviors, both of which can blunt immune response to vaccination. Including familiar adult females in the weaning group also reduces agonistic behaviors. Post-weaning behavioral data is sobering: 10% of foals develop oral stereotypies within one month after weaning, 30% eat wood from stalls within three months, and 10% develop bearing-down tics or pacing within ten months.

Diet matters too: high-fat, high-fiber diets result in calmer post-weaning behavior compared to high-sugar, high-starch diets.

Breedio helps you log deworming treatments, FEC results, and vaccination dates against each mare-foal pair so nothing falls through the cracks at this high-pressure management point. See the Features page for more on tracking tools, or start tracking your mares today.

What Are the Key Deworming Principles for Year One?

Use Fecal Egg Count Monitoring

Blanket calendar-based deworming of all foals is increasingly discouraged. FEC monitoring allows you to:

• Identify high shedders (a minority of animals contribute the majority of pasture contamination)
• Detect anthelmintic resistance early
• Avoid unnecessary drug exposure in low shedders

A threshold of 200-500 eggs per gram (EPG) is typically used to trigger treatment in foals, though many veterinarians recommend treating all foals under 6 months regardless of count given the severity of P. equorum pathology.

Rotate Anthelmintic Classes Strategically

• Benzimidazoles (fenbendazole, oxibendazole): First-line for young foals; P. equorum resistance emerging
• Macrocyclic lactones (ivermectin, moxidectin): Highly effective; moxidectin not recommended under 4 months due to narrow safety margin in foals
• Praziquantel: Required for tapeworm coverage; available in combination products with ivermectin or moxidectin

Pre-Weaning vs. Post-Weaning Parasite Burden

How Should Broodmare Pre-Foaling Vaccination Timing Affect Foal Planning?

Your foal’s colostrum quality depends directly on the mare’s vaccination status in the final weeks of pregnancy.

According to Colorado State University’s Equine Reproduction Laboratory, broodmares should receive boosters 4-6 weeks before foaling for:

• West Nile Virus
• EEE/WEE
• Influenza
• Tetanus
• Rhinopneumonitis (EHV-1)

This timing maximizes the antibody concentration in colostrum, giving your foal the strongest possible passive immunity at birth and the longest effective protection window before active vaccination is required.

If you’re managing multiple mares with different due dates, maintaining a breeding calendar that links foaling dates to pre-foaling vaccine windows is essential. Track your mares with Breedio to automate these reminders across your herd.

What Warning Signs Should Prompt Veterinary Contact?

Even with a perfect schedule in place, monitor foals closely for signs that may indicate parasitic or infectious disease requiring intervention outside your protocol:

In foals under 3 months:

• Pot-bellied appearance with poor growth
• Nasal discharge with cough (may indicate P. equorum larval migration)
• Persistent diarrhea
• Lethargy or failure to nurse

In foals 3-12 months:

• FEC >500 EPG despite recent treatment (suspect resistance)
• Colic signs (can indicate roundworm impaction)
• Respiratory distress
• Fever >38.9°C (102°F) within 24 hours of vaccination

Building Your Year-One Management Calendar

A successful first-year protocol isn’t just about knowing the right products; it’s about execution consistency across a busy breeding season. Key organizational principles:

1. Record everything at the mare level: Link vaccination and deworming events to the dam so you can assess colostrum quality predictions and know when foal active vaccination should begin.
2. Build FEC testing into your calendar at 8 weeks, 4 months, 6 months, and 10 months.
3. Work with a single veterinarian across the season to ensure protocol continuity and drug resistance monitoring.
4. Group foals by age where possible to synchronize deworming and vaccination events; this reduces labor and improves compliance.

Breedio was built for exactly this kind of multi-mare, multi-event tracking. With due-date calculations, foaling alerts, and health event logging, it keeps your breeding operation organized from first cover to foal’s first birthday. Explore the Features or start tracking your mares now.