Study links Parascaris to poor-outcome surgical colic in young horses
Bottom line
A new Equine Veterinary Journal study from researchers in Sweden, Norway, and Denmark found that Parascaris spp.-related disease accounts for a meaningful share of surgical colic in young horses, and outcomes are often poor. In a retrospective review of 233 juvenile horses under 2 years old that underwent laparotomy at six Scandinavian equine hospitals, 32 cases, or 13.7%, involved Parascaris-associated small intestinal lesions. Fourteen of those were small intestinal ascarid impactions, representing 6% of all colic surgeries in the study group, and only four of the 14 foals with ascarid impactions survived to discharge. The authors link the clinical concern to rising anthelmintic resistance, including reports of reduced drug efficacy and multi-drug-resistant Parascaris populations in Sweden. (beva.onlinelibrary.wiley.com)
Why it matters: For equine veterinarians, the paper is a reminder that Parascaris is no longer just a routine youngstock parasite problem. The study suggests these infections can present as severe surgical disease with a worse-than-average prognosis, especially when obstruction is complicated by rupture or other small intestinal lesions. That makes parasite surveillance, treatment efficacy checks, and barn-level management more important, particularly as current guidance from AAEP and BEVA pushes practices away from fixed-interval deworming and toward evidence-based, veterinary-led control plans. (d197for5662m48.cloudfront.net)
What to watch: Expect more attention on Parascaris monitoring in foals and yearlings, plus growing pressure for stewardship-focused parasite control as resistance data and clinical outcome reports continue to accumulate. (d197for5662m48.cloudfront.net)
Key facts
- Study type
- Retrospective review
- Population
- 233 juvenile horses under 2 years old
- Setting
- Six Scandinavian equine hospitals
- Finding
- 32 cases, or 13.7%, involved Parascaris-associated small intestinal lesions
- Finding
- 14 cases were small intestinal ascarid impactions, or 6% of all colic surgeries
- Outcome
- Only four of 14 foals with ascarid impactions survived to discharge
- Context
- The authors link the concern to rising anthelmintic resistance
- Region
- Sweden, Norway, and Denmark
Parascaris-related colic in juvenile horses may be a bigger surgical problem than many clinicians assume. A newly published Equine Veterinary Journal study examining cases from six Scandinavian equine hospitals found that Parascaris spp.-associated lesions made up 13.7% of intestinal surgical cases in horses under 2 years old, with especially poor outcomes in foals that developed classic ascarid impactions. (beva.onlinelibrary.wiley.com)
The backdrop is familiar, but increasingly urgent. Parascaris commonly infects foals and yearlings, and heavy burdens can obstruct the small intestine. What’s changed is the resistance picture. The study authors frame their findings in the context of progressive anthelmintic resistance, and note published evidence from Sweden showing declining efficacy and emergence of multi-drug-resistant Parascaris populations, while Denmark has documented ivermectin resistance. More broadly, recent international guidance reviews show equine parasite control is shifting toward surveillance-based programs designed to preserve drug efficacy rather than routine calendar deworming. (d197for5662m48.cloudfront.net)
In the Scandinavian study, investigators retrospectively reviewed laparotomy records from hospitals in Denmark, Sweden, and Norway over periods ranging from 7 to 15 years. Among 233 juvenile horses included, 32 had Parascaris-associated small intestinal lesions, accounting for 26% of all small intestinal abnormalities in the cohort. Fourteen horses had small intestinal ascarid impactions, listed as 6% of the total surgical colic population studied. The short-term survival rate for all Parascaris-associated lesions was 38% overall, and only four of 14 foals with ascarid impactions survived to discharge. The paper also notes that secondary lesions, including intestinal rupture, likely worsened prognosis. (d197for5662m48.cloudfront.net)
The management signal in the paper is just as important as the surgical one. The authors conclude that Parascaris-related disease represents a substantial share of small intestinal surgical lesions in juvenile horses and argue that management practices to reduce infection burdens are increasingly important as resistance expands. That aligns with current AAEP guidance, revised in May 2024, which advises clinicians to stop blindly rotating anthelmintic classes and to discontinue fixed-interval deworming year-round. BEVA’s ProtectMEtoo toolkit makes a similar case for veterinary-led, evidence-based parasite control, with management and husbandry treated as central, not secondary, tools. (d197for5662m48.cloudfront.net)
Industry commentary around equine parasite control has been moving in the same direction. BEVA says equine vets are uniquely placed to tailor advice using diagnostic results, management, husbandry, and environmental factors, and its stewardship materials explicitly warn that unnecessary or repeated use of the same drug class accelerates resistance. AAEP’s current guidelines likewise position Parascaris as a key target in foals and young horses while emphasizing that no dewormer will eliminate every parasitic stage. Taken together, that reaction suggests this paper will likely reinforce, rather than radically change, the current clinical conversation: better diagnostics, better stewardship, and fewer assumptions that a deworming history equals protection. (beva.org.uk)
Why it matters: For veterinary professionals, the study helps connect two issues that are often discussed separately: parasite control and emergency surgery. If Parascaris-associated lesions are accounting for a notable share of laparotomy cases in juvenile horses, then resistance isn’t just a parasitology concern, it’s a case outcome concern. Practices advising breeders, referral hospitals managing foal colic, and ambulatory equine veterinarians working on prevention may all need tighter protocols around fecal monitoring, treatment efficacy assessment, and environmental control. The paper’s low survival figures also offer a practical point for conversations with pet parents and breeders about prognosis, timing of referral, and the limits of relying on dewormers alone. (d197for5662m48.cloudfront.net)
What to watch: The next questions are whether similar rates are being seen outside Scandinavia, how quickly multi-drug resistance is spreading, and whether updated field guidance for foals and yearlings becomes more specific on Parascaris surveillance and post-treatment efficacy testing. Expect future work to focus on region-specific control plans, not one-size-fits-all deworming schedules. (d197for5662m48.cloudfront.net)