Study clarifies postoperative monitoring after equine colic surgery
Bottom line
A new prospective study in Animals tracked serial bloodwork, peritoneal fluid findings, and abdominal ultrasound changes in 36 client-owned horses recovering from ventral midline exploratory celiotomy for colic, aiming to show what “expected” postoperative changes look like in the first five days after surgery. The Ohio State-led team found that peritoneal L-lactate stayed higher than blood L-lactate even in horses without complications, while blood L-lactate was consistently higher at all measured timepoints in horses that did develop complications. Ultrasound showed postoperative small-intestinal diameter generally normalized over time in both groups, suggesting it may be less useful as a stand-alone early warning marker than clinicians might hope. Of 32 horses discharged, 25 experienced postoperative complications, most commonly postoperative colic. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For equine veterinarians, the study adds practical reference points for interpreting repeat abdominocentesis and ultrasound after colic surgery, when normal postoperative inflammation can blur the line between recovery and deterioration. That fits with broader expert guidance that peritoneal fluid findings, including color, protein, cell counts, cytology, and lactate, should help direct treatment decisions rather than serve as definitive diagnostic tests on their own. The work also lands in a field still looking for better complication predictors after colic surgery, with related research efforts exploring peritoneal fluid protein and transcript markers. (onlinelibrary.wiley.com)
What to watch: Expect follow-up studies to test whether combining serial blood lactate, peritoneal fluid trends, and imaging can produce more reliable postoperative risk tools for horses after colic surgery. (pubmed.ncbi.nlm.nih.gov)
Key facts
- Study type
- Prospective cohort study
- Sample size
- 36 client-owned horses
- Procedure
- Ventral midline exploratory celiotomy for colic
- Monitoring window
- Before surgery, and at 48, 72, and 120 hours after surgery
- Main finding
- Peritoneal L-lactate stayed higher than blood L-lactate in horses without complications
- Complication finding
- Blood L-lactate was higher at every timepoint in horses that developed complications
- Ultrasound finding
- Postoperative small-intestinal diameter generally normalized over time in both groups
- Discharge and complications
- 32 horses were discharged, and 25 had postoperative complications
- Most common complication
- Postoperative colic
A new Animals study offers a clearer look at what postoperative monitoring data actually mean in horses recovering from colic surgery. In a prospective cohort of 36 client-owned horses undergoing ventral midline exploratory celiotomy, investigators tracked serial venous blood, peritoneal fluid, and abdominal ultrasound findings before surgery and at 48, 72, and 120 hours afterward. Their central message: some abnormalities clinicians may worry about, especially in peritoneal fluid, can persist even in horses recovering as expected. (pubmed.ncbi.nlm.nih.gov)
That question matters because repeat peritoneal fluid sampling and ultrasound are widely used after equine colic surgery, but reference data for normal early postoperative change have been limited. Existing expert guidance already emphasizes that abdominal fluid interpretation is useful, but context-dependent: changes in color, turbidity, protein, cell counts, cytology, and L-lactate can reflect intestinal injury, ischemia, inflammation, or contamination, and should guide treatment rather than act as a single definitive test. (onlinelibrary.wiley.com)
The new paper, published September 1, 2026, in Animals, found that peripheral blood L-lactate declined after surgery overall, averaging 1.9 mmol/L preoperatively and then 0.9, 0.8, and 0.9 mmol/L at the postoperative sampling points. Peritoneal fluid L-lactate also fell over time, from 3.8 mmol/L preoperatively to 2.8 and then 1.1 mmol/L, although the final 120-hour peritoneal timepoint could not be assessed because there was not enough fluid to sample. Importantly, postoperative peritoneal L-lactate remained higher than blood L-lactate even in horses without complications, while blood L-lactate was higher at every timepoint in horses that did experience complications. Ultrasound suggested postoperative normalization of small-intestinal diameter in both horses with and without complications. (pubmed.ncbi.nlm.nih.gov)
Complication burden remained high, which is consistent with the broader colic surgery literature. In this study, 32 horses survived to discharge, and 25 of those 32 had postoperative complications, with postoperative colic the most common. A recent multicenter study and a scoping review likewise describe postoperative complications after equine colic surgery as common and clinically significant, with implications for survival, welfare, cost, and future athletic use. (pubmed.ncbi.nlm.nih.gov)
Industry and research commentary around the paper has framed the findings as a needed calibration tool rather than a practice-changing single test. The Herd previously noted that the practical challenge is separating expected postoperative inflammation from early signs of reflux, peritonitis, hemoperitoneum, or incisional complications. That framing also aligns with ongoing Morris Animal Foundation-backed work at the University of Illinois, where researchers are studying peritoneal fluid transcript and protein patterns in hopes of building a more predictive test for surgical colic complications. (theherd.news)
Why it matters: For veterinary professionals, the study reinforces a familiar but important point: postoperative surveillance after equine colic surgery works best when markers are interpreted as trends, not absolutes. A persistently higher peritoneal fluid lactate concentration after surgery may not, by itself, signal deterioration, whereas comparatively higher blood lactate across serial checks may deserve closer attention. In practice, that could support more measured decision-making around repeat sampling, escalation of monitoring, and conversations with pet parents about expected recovery versus warning signs. (pubmed.ncbi.nlm.nih.gov)
The findings also underscore the limits of ultrasound as a lone predictor in this setting. If bowel diameter can normalize in both uncomplicated and complicated recoveries, then imaging still matters, but likely as one piece of a broader postoperative picture that includes physical examination, reflux status, pain, hematology, chemistry, and peritoneal fluid interpretation. That is especially relevant in referral hospitals trying to catch deterioration early without over-calling expected inflammatory change. This is an inference based on the study’s reported trends and the broader expert literature. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next step is likely multimodal prediction, combining serial biomarkers with imaging and clinical signs, rather than relying on any single postoperative measurement. Watch for larger validation studies, and for results from ongoing biomarker programs focused on whether peritoneal fluid can help identify which horses are most likely to develop complications after colic surgery. (morrisanimalfoundation.org)