Study links Parascaris infections to poor outcomes in foal colic surgery
Bottom line
Version 1
A new Scandinavian study in Equine Veterinary Journal highlights how serious Parascaris infections can become in foals and yearlings that need colic surgery. Reviewing records from six equine hospitals over 7 to 15 years, researchers found ascarid impactions in 14 of 233 juvenile horses that underwent surgery for colic, or 6.0% of all cases studied. When the focus narrowed to small-intestinal surgical lesions, Parascaris-associated disease accounted for 26.0% of abnormalities, and short-term survival to discharge was just 38%. The authors also noted that six foals with ascarid impaction had received an anthelmintic within two days before presentation, underscoring the clinical complexity around treatment timing in heavily parasitized young horses. (d197for5662m48.cloudfront.net)
Why it matters: For equine veterinarians, the paper is a reminder that parasite control in juvenile horses is now as much a resistance-management issue as a deworming issue. Current AAEP guidance says fixed-interval, year-round rotational deworming should be abandoned, and notes that Parascaris spp. are widely resistant to macrocyclic lactones, with resistance to other drug classes also emerging. In practice, that means foals and weanlings with colic, recent deworming, or high parasite risk may warrant a higher index of suspicion for ascarid-related small-intestinal disease, along with closer attention to farm-level fecal testing, targeted treatment, and management changes that reduce environmental contamination. (aaep.org)
What to watch: Expect more focus on surveillance, farm-specific parasite protocols, and whether rising multidrug resistance changes how veterinarians triage and prevent surgical colic in young horses. (d197for5662m48.cloudfront.net)
Key facts
- Study type
- Scandinavian retrospective study
- Journal
- Equine Veterinary Journal
- Hospitals
- Six equine hospitals
- Sample size
- 233 juvenile horses, 1 month to under 2 years old
- Ascarid impactions
- 14 cases, 6.0% of juvenile surgical colic cases
- Small-intestinal abnormalities
- Parascaris-associated disease accounted for 26.0%
- Survival to discharge
- 38% among affected horses
- Recent deworming
- Six foals had received an anthelmintic within two days before presentation
Version 2
A new Scandinavian retrospective study is putting numbers behind a long-standing equine health concern: Parascaris infections in young horses can progress to severe small-intestinal lesions that require surgery, and outcomes are often poor. Published in Equine Veterinary Journal, the study reviewed juvenile equine colic surgeries across six Scandinavian hospitals and found that Parascaris-associated lesions made up a substantial share of small-intestinal surgical disease, with survival to discharge of only 38% among affected horses. (d197for5662m48.cloudfront.net)
The backdrop is a parasite-control landscape that has changed sharply over the past two decades. Parascaris spp., the equine roundworm of foals and yearlings, has long been recognized as a cause of pulmonary disease and intestinal impaction in young horses. What is different now is the resistance picture. Earlier work from Sweden documented reduced efficacy of commonly used dewormers in foals, and more recent guidance from the AAEP says Parascaris is widely resistant to macrocyclic lactones, while resistance to other classes is also developing. (pmc.ncbi.nlm.nih.gov)
In the new study, investigators reviewed 233 horses between 1 month and under 2 years of age that underwent surgery for colic over a 7- to 15-year period. Fourteen had ascarid impactions, representing 6.0% of all juvenile surgical colic cases and 11.4% of small-intestinal lesions. Among horses younger than 1 year, the occurrence of ascarid impaction rose to 9.7%. Looking more broadly, the authors found 32 cases of Parascaris-associated intestinal lesions, which accounted for 13.7% of all surgeries reviewed and 26.0% of small-intestinal abnormalities. Only 12 of those 32 horses survived to discharge. (d197for5662m48.cloudfront.net)
One especially notable detail is that six foals with ascarid impaction had been treated with an anthelmintic within two days of presentation. That does not prove deworming caused the lesion, but it aligns with existing guidance that heavily parasitized foals can develop verminous small-intestinal impaction and that treatment decisions in these patients require care. AAEP guidance specifically flags this manifestation of Parascaris infection and advises more strategic, evidence-based parasite control rather than routine blind rotation of products. (d197for5662m48.cloudfront.net)
Industry guidance and review literature point in the same direction. The AAEP’s updated internal parasite control guidelines call for abandoning fixed-interval deworming and instead using age, risk, fecal egg counts, and farm conditions to shape protocols. The Merck Veterinary Manual similarly notes that ascarids are a primary cause of intestinal impaction in foals and weanlings, and that resistance pressure has made historical rotation strategies less reliable. Together, those sources suggest the Scandinavian findings are not an isolated surgical curiosity, but part of a broader shift in how equine practices need to approach parasite prevention in young horses. (aaep.org)
Why it matters: For veterinary professionals, the study reinforces that juvenile equine colic workups should include parasite-related obstruction high on the differential list, especially in foals, recently dewormed patients, and horses from farms with uncertain parasite-control programs. It also strengthens the case for practice-level conversations with breeders and farm managers about fecal monitoring, drug efficacy checks, stocking density, manure management, and targeted treatment plans. In a resistance era, preventing heavy Parascaris burdens may be more clinically important than relying on a deworming schedule alone. (d197for5662m48.cloudfront.net)
What to watch: The next question is whether more hospitals and breeding regions will report similar surgical burdens as multidrug resistance expands. Watch for follow-up surveillance studies, updated regional deworming recommendations, and more emphasis on farm-specific prevention programs aimed at reducing parasite loads before foals present as surgical colic emergencies. (d197for5662m48.cloudfront.net)