CyberKnife stereotactic radiotherapy for treatment of primary intracranial tumors in dogs.

BACKGROUND: Limited data exist about the use, efficacy, and prognostic factors influencing outcome when CyberKnife is used to treat dogs with intracranial neoplasia. OBJECTIVES: To determine the prognosis and associated prognostic factors for dogs that were imaged, determined to have primary intracranial tumors, and treated with CyberKnife radiotherapy. ANIMALS: Fifty-nine dogs treated with CyberKnife radiotherapy for primary intracranial tumors. METHODS: Retrospective medical record review of cases from January 2010 to June 2016. Data extracted from medical records included signalment, weight, seizure history, tumor location, tumor type (based on imaging), gross tumor volume, planned tumor volume, treatment dates, radiation dose, recurrence, date of death, and cause of death. RESULTS: The median progression-free interval (PFI) was 347 days (range 47 to 1529 days), and the median survival time (MST) was 738 days (range 4 to 2079 days). Tumor location was significantly associated with PFI when comparing cerebrum (median PFI 357 days; range 47-1529 days) versus cerebellum (median PFI 97 days; range 97-168 days) versus brainstem (median PFI 266 days; range 30-1484 days), P = .03. Additionally, the presumed tumor type was significantly associated with MST (P < .001). CONCLUSIONS AND CLINICAL IMPORTANCE: Use of Cyberknife and SRT might improve MST, compared with RT, in dogs with intracranial neoplasia.

Evaluation of novel serological markers and autoantibodies in dogs with inflammatory bowel disease.

BACKGROUND: The use of serological markers to diagnose inflammatory bowel disease (IBD) in humans is well-established. Because of the frequency of IBD in dogs and resources required for its diagnosis with current methods, new approaches are desired. OBJECTIVE: The goal is to evaluate novel serologic markers to differentiate clinical cohorts in dogs with gastrointestinal (GI) disease and assess their potential to develop a serum-based IBD diagnostic test. ANIMALS: Seventy dogs diagnosed with biopsy-confirmed IBD, 23 dogs with non-IBD predominantly acute GI diseases, and 58 normal dogs. METHODS: Prospective control study. ELISA methods were developed to detect autoantibodies to polymorphonuclear leukocytes (APMNA) and calprotectin (ACNA), antibodies against gliadins (AGA), microbial outer membrane porin C (ACA), and flagellins (AFA) isolated from diseased dogs based on clinical and histopathological scoring. RESULTS: IBD dogs displayed a 39%-76% prevalence of seropositivity against selected serologic markers that markedly decreased to 0%-13% in non-IBD and normal dogs. ROC analysis showed statistical significance in differentiating the cohorts, with seropositivity against OmpC being the highest single performance marker. The combination of markers such as OmpC and APMNA reached specificities of 93%-99% and 79%-98% and sensitivities of 76%-97% and 66%-86% when comparing IBD versus normal cohorts and non-IBD cohorts, respectively. CONCLUSION AND CLINICAL IMPORTANCE: Seropositivity of canine immunoglobulins A against selected serologic markers in dogs appears promising in the detection and differentiation of IBD versus other acute GI conditions. Among them, antibody reactivity to Escherichia coli OmpC and canine autoantibodies against polymorphonuclear leukocytes displayed the highest single marker discriminating performance.

Ex vivo evaluation of imatinib mesylate for induction of cell death on canine neoplastic mast cells with mutations in c-Kit exon 11 via apoptosis.

Several studies of canine spontaneous mast cell tumours have described mutations in the c-kit proto-oncogene. These mutations produce a constitutively activated product and have been suggested to play a role in the malignant transformation of mast cells. We hypothesize that the selective tyrosine kinase inhibitor imatinib mesylate inhibits signal transduction and induces apoptosis when tested in cutaneous canine mast cell tumour samples positive for mutation in c-kit exon 11. Three-dimensional ex vivo cultures of canine grade II mast cell tumour treated with STI-571 at 48, 72, and 96 h and tested for signal transduction and apoptosis using appropriate assays were used. There was a progressive and significant increase in caspase-3 and TUNEL-positive mast cells compared to the untreated cultures. Additionally, a concurrent reduced expression of Ki67 and BCL-2 was observed. Furthermore, the treated cultures showed a marked reduction of Kit expression. Our results demonstrate that STI-571 induces Caspase-dependent apoptosis in a canine neoplastic mast cells possessing mutations in c-kit exon 11.

Characterization and evaluation of a new oncolytic vaccinia virus strain LIVP6.1.1 for canine cancer therapy.

Virotherapy on the basis of oncolytic vaccinia virus (VACV) strains is one novel approach for canine cancer therapy. In this study we described for the first time the characterization and the use of new VACV strain LIVP6.1.1 as an oncolytic agent against canine cancer in a panel of four canine cancer cell lines including: soft tissue sarcoma (STSA-1), melanoma (CHAS), osteosarcoma (D-17) and prostate carcinoma (DT08/40). Cell culture data demonstrated that LIVP6.1.1 efficiently infected and destroyed all four tested canine cancer cell lines. In two different xenograft models on the basis of the canine soft tissue sarcoma STSA-1 and the prostate carcinoma DT08/40 cell lines, a systemic administration of the LIVP6.1.1 virus was found to be safe and led to anti-tumor and immunological effects resulting in the significant reduction of tumor growth in comparison to untreated control mice. In summary, the pre-clinical evaluation has demonstrated the efficacy of LIVP6.1.1 for canine cancer therapy. Furthermore, a clinical trial with canine cancer patients has already been started.

Oncolytic virotherapy in veterinary medicine: current status and future prospects for canine patients.

Oncolytic viruses refer to those that are able to eliminate malignancies by direct targeting and lysis of cancer cells, leaving non-cancerous tissues unharmed. Several oncolytic viruses including adenovirus strains, canine distemper virus and vaccinia virus strains have been used for canine cancer therapy in preclinical studies. However, in contrast to human studies, clinical trials with oncolytic viruses for canine cancer patients have not been reported. An 'ideal' virus has yet to be identified. This review is focused on the prospective use of oncolytic viruses in the treatment of canine tumors - a knowledge that will undoubtedly contribute to the development of oncolytic viral agents for canine cancer therapy in the future.

Menhaden oil administration to dogs treated with radiation for nasal tumors demonstrates lower levels of tissue eicosanoids.

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) or menhaden oil may reduce inflammatory eicosanoids (prostaglandin E2, thromboxane B2, leukotriene B4, and 11-dehydro thromboxane B2), matrix metalloproteinases (MMPs), and blood lactate in dogs with nasal carcinomas receiving radiation therapy. We hypothesized that menhaden oil would reduce inflammation from radiation damage and lower blood lactate levels in dogs with nasal carcinoma. In a randomized, double-blind, placebo-controlled clinical study, 12 dogs with malignant carcinomas of the nasal cavity were given dietary menhaden oil (DHA and EPA) or soybean oil (control) and then received radiation therapy. Megavoltage radiation was delivered in 18 fractions to a total dose of 56 Gy. Blood levels of DHA, EPA, insulin, glucose, lactic acid, and MMPs 2 and 9; resting energy expenditure; and inflammatory eicosanoids from nasal biopsies were measured throughout radiation therapy. Samples were obtained from each patient 1 week before the start of radiation therapy, at start of radiation, and 7, 18 (end of radiation therapy), and 42 days after radiation was initiated. Dogs that are fed with menhaden oil had significantly (P < .05) higher plasma concentration of DHA by 500% and EPA by 200% and had significantly lower tissue inflammatory eicosanoids and decreased resting energy expenditure by 20% when compared with controls. Increased plasma DHA was significantly associated (P < .05) with decreased plasma lactic acid and MMPs. These data may suggest that dietary fish oil could reduce some detrimental inflammatory eicosanoids and metabolic consequences of radiation therapy.

Evaluation of 12- and 24-month survival rates after treatment with masitinib in dogs with nonresectable mast cell tumors.

OBJECTIVE: To evaluate the effectiveness of masitinib for the treatment of nonresectable mast cell tumors (MCTs) in dogs at 12 and 24 months after onset of treatment. ANIMALS: 132 dogs with nonresectable grade 2 or 3 MCTs. PROCEDURES: Dogs received masitinib (12.5 mg/kg/d, PO; n = 106) or a placebo (26). After 6 months, treatment was extended with tumor assessments at 3-month intervals until detection of disease progression. Endpoints were tumor response and overall survival rate and time. RESULTS: In dogs with nonresectable MCTs, masitinib significantly improved survival rate, compared with results for the placebo, with 59 of 95 (62.1%) and 9 of 25 (36.0%) dogs alive at 12 months and 33 of 83 (39.8%) and 3 of 20 (15.0%) dogs alive at 24 months, respectively. Median overall survival time was 617 and 322 days, respectively. Tumor control at 6 months had a high predictive value for 24-month survival, with high specificity (88%) and sensitivity (76%), whereas short-term tumor response (within 6 weeks) had a poor predictive value. Complete responses at 24 months were observed in 6 of 67 (9.0%) dogs with nonresectable MCTs treated with masitinib. CONCLUSIONS AND CLINICAL RELEVANCE: Masitinib significantly increased survival rates at 12 and 24 months in dogs with nonresectable MCTs. Control of disease at 6 months, but not best response at 6 weeks, was predictive of long-term survival in dogs treated with masitinib, which suggested that short-term response may be irrelevant for assessing clinical efficacy of tyrosine kinase inhibitors for treatment of MCTs.

Polyunsaturated Fatty Acid dietary supplementation induces lipid peroxidation in normal dogs.

Polyunsaturated fatty acids (PUFAs) have anti-inflammatory effects at low concentrations; however increased dietary consumption may conversely increase susceptibility to oxidation by free radicals. The objective of this study was to determine the effects of PUFAs on selective oxidative injury and inflammatory biomarkers in canine urine and serum. Dogs (n = 54) consumed a diet supplemented with 0.5% conjugated linoleic acid/dry matter, 1.0% conjugated linoleic acid/dry matter, or 200 mg/kg docosahexaenoic acid/eicosapentaenoic acid for 21 days. All dogs exhibited significantly increased plasma PUFA concentrations. All dogs had significant elevations in urinary F(2a) isoprostane concentration, though dogs consuming a diet containing 1.0% conjugated linoleic acid/dry matter had the highest increase (P = .0052). Reduced glutathione concentrations within erythrocytes decreased significantly in all three dietary treatment groups (P = .0108). Treatment with diets containing 1.0% conjugated linoleic acid/dry matter resulted in the greatest increase in oxidant injury. Caution should be exercised when supplementing PUFAs as some types may increase oxidation.

Fish oil decreases matrix metalloproteinases in knee synovia of dogs with inflammatory joint disease.

This study was designed to determine whether dietary fish oil affects the expression and activity of matrix metalloproteinases (MMP), tissue inhibitors of MMP-2 (TIMP-2) and urokinase plasminogen activator (uPA) in synovial fluid from dogs with spontaneously occurring stifle (knee) instability in a single hind limb resulting from acute cranial cruciate ligament (CCL) injury. Two groups of 12 dogs were fed diets from 1 week prior to surgery on the affected knee to 56 days post-surgery. The fish oil and control diets provided 90 and 4.5 mg, respectively, of combined eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)/kg body weight per day. Plasma and synovial fluid, from both surgical and nonsurgical knee joints, were obtained at start of the diet (-7), surgery day (0) and 7, 14, 28 and 56 days post-surgery. Plasma total EPA and DHA were significantly increased, and plasma total arachidonic acid (AA) was significantly decreased by the fish oil diet. In synovial fluid from the nonsurgical knee, fish oil treatment significantly decreased proMMP-2 expression at Days 7 and 14, and proMMP-9 expression at Day 56, and uPA activity at 28 days and significantly increased TIMP-2 expression at Days 7 and 28. There were no differences in MMP expression or activity, TIMP-2 expression and uPA activity in the surgical joint synovial fluid at any time throughout the study. These results suggest that dietary fish oil may exert beneficial effects on synovial fluid MMP and TIMP-2 equilibrium in the uninjured stifle of dogs with unilateral CCL injury.

Doxorubicin and BAY 12-9566 for the treatment of osteosarcoma in dogs: a randomized, double-blind, placebo-controlled study.

BACKGROUND: This study was designed to assess the efficacy of a matrix metalloproteinase inhibitor in prolonging posttreatment survival for dogs with appendicular osteosarcoma after treatment with amputation and doxorubicin chemotherapy. HYPOTHESIS: Survival will be prolonged in dogs receiving BAY 12-9566. ANIMALS: The study included 303 dogs with appendicular osteosarcoma. METHODS: Dogs were treated with doxorubicin (30 mg/m2) every 2 weeks for 5 treatments starting 2 weeks after amputation. Dogs were randomly allocated to receive a novel nonpeptidic biphenyl inhibitor of matrix metalloproteinases (MMPs, BAY 12-9566; 4-[4-4-(chlorophenyl)phenyl]-4-oxo-2S-(phenylthiomethyl) butanoic acid) or placebo after doxorubicin chemotherapy. RESULTS: Median survival for all 303 dogs was 8 months; and 1-year, 2-year, and 3-year survival rates were 35%, 17%, and 9%, respectively. Treatment with BAY 12-9566 did not influence survival. Multivariate analysis revealed that increasing age (P = .004), increasing weight (P = .006), high serum alkaline phosphatase (ALP) (P = .012) and high bone ALP (P < .001) were independently associated with shorter median survival times. Additional analyses on available data indicated that as the number of mitotic figures in the biopsy increased (P = .013), and as plasma active MMP-2 concentrations increased (P = .027), the risk of dying increased. CONCLUSIONS AND CLINICAL IMPORTANCE: Doxorubicin is an effective adjuvant to amputation in prolonging survival for dogs with appendicular osteosarcoma.

Dietary long-chain n-3 fatty acids modify blood and cardiac phospholipids and reduce protein kinase-C-delta and protein kinase-C-epsilon translocation.

The effects of an n-3 PUFA-enriched diet on cardiac cell membrane phospholipid fraction compositions and associated protein kinase-C (PKC) translocation modification have never been studied in higher mammals. This is of importance since membrane fatty acid composition has been shown to influence PKC signalling pathways. In the present study, we have tested whether the incorporation of n-3 PUFA in cardiac membrane phospholipids correlated with changes in the fatty acid composition of diacylglycerols (DAG) and led to a differential translocation of PKC isoforms. Two groups of five dogs were fed the standard diet supplemented with palm oil or fish oil for 8 weeks. Dogs fed a fish oil-enriched diet showed a preferential incorporation of EPA and, to a lesser extent, of DHA, at the expense of arachidonic acid, in the circulating TAG, plasma phospholipids, erythrocyte phospholipids and cardiomyocyte phospholipid fractions. Analysis of 1,2-DAG fatty acid composition also indicated a preferential enrichment of EPA compared with DHA. Associated with these results, a reduction in the expression of PKC-delta and PKC-epsilon isoforms in the particulate fractions was observed whereas no effect was seen for PKC-alpha and PKC-zeta. We conclude that a fish oil-enriched diet induces a modification in fatty acid composition of cardiac membrane phospholipids, associated with a differential translocation of PKC isoforms. These results can be explained by the production of structurally different DAG that may participate in some of the protective effects of n-3 PUFA against various chronic diseases.

Evaluation of the effects of dietary n-3 fatty acid supplementation on the pharmacokinetics of doxorubicin in dogs with lymphoma.

OBJECTIVE: To determine the effect of dietary n-3 fatty acids on the pharmacokinetics of doxorubicin in dogs with lymphoma. ANIMALS: 23 dogs with lymphoma in stages IIIa, IVa, and Va. PROCEDURE: Dogs receiving doxorubicin chemotherapy were randomly allocated to receive food with a high (test group) or low (control group) content of n-3 fatty acids. Serum doxorubicin and doxorubicinol concentrations were measured via high-performance liquid chromatography before and 6 to 9 weeks after initiation of the diets. Lymph node concentrations of doxorubicin were assessed 6 hours after the initial treatment. Dogs' body composition was assessed by means of dual-energy x-ray absorptiometry scans. RESULTS: No significant differences in doxorubicin pharmacokinetics were detected between treatment groups. Significant differences existed between the first and second sampling times among all dogs for area under the curve, maximum serum concentration, and clearance. Differences in body composition did not affect measured pharmacokinetic variables. The terminal elimination half-life was longer in dogs in which a long-term remission was achieved than in dogs that did not have remission. CONCLUSIONS AND CLINICAL RELEVANCE: Dietary supplementation of n-3 fatty acids is common in veterinary patients with neoplasia, but supplementation did not affect doxorubicin pharmacokinetics in this population of dogs. Explanations for the beneficial effects of n-3 fatty acids other than alterations in the pharmacokinetics of chemotherapy drugs should be investigated. Dogs may metabolize drugs differently prior to remission of lymphoma than when in remission. The pharmacokinetics of doxorubicin at the time of the first administration may predict response to treatment.

Canine digital tumors: a veterinary cooperative oncology group retrospective study of 64 dogs.

We compared clinical characteristics and outcomes for dogs with various digital tumors. Medical records and histology specimens of affected dogs from 9 veterinary institutions were reviewed. Risk factors examined included age, weight, sex, tumor site (hindlimb or forelimb), local tumor (T) stage, metastases, tumor type, and treatment modality. The Kaplan-Meier product limit method was used to determine the effect of postulated risk factors on local disease-free interval (LDFI), metastasis-free interval (MFI), and survival time (ST). Outcomes were thought to differ significantly between groups when P < or = .003. Sixty-four dogs were included. Squamous cell carcinoma (SCC) accounted for 33 (51.6%) of the tumors. Three dogs presented with or developed multiple digital SCC. Other diagnoses included malignant melanoma (MM) (n = 10; 15.6%), osteosarcoma (OSA) (n = 4; 6.3%), hemangiopericytoma (n = 3; 4.7%), benign soft tissue tumors (n = 5; 7.8%), and malignant soft tissue tumors (n = 9; 14%). Fourteen dogs with malignancies had black hair coats, including 5 of the 10 dogs with MM. Surgery was the most common treatment and, regardless of the procedure, had a positive impact on survival. None of the patient variables assessed, including age, sex, tumor type, site, and stage, had a significant impact on ST. Both LDFI and MFI were negatively affected by higher T stage, but not by type of malignancy. Although metastasis at diagnosis correlated with a shorter LDFI, it did not have a significant impact on ST. On the basis of these findings, early surgical intervention is advised for the treatment of dogs with digital tumors, regardless of tumor type or the presence of metastatic disease.

Plasma and skin concentrations of polyunsaturated fatty acids before and after supplementation with n-3 fatty acids in dogs with atopic dermatitis.

OBJECTIVE: To determine essential fatty acid concentrations in plasma and tissue before and after supplementation with n-3 fatty acids in dogs with atopic dermatitis. ANIMALS: 30 dogs with atopic dermatitis. PROCEDURE: Dogs received supplemental flaxseed oil (200 mg/kg/d), eicosapentaenoic acid (EPA; 50 mg/kg/d)-docosahexaenoic acid (DHA; 35 mg/kg/d), or mineral oil as a placebo in a double-blind, placebo-controlled, randomized trial. Clinical scores and plasma and cutaneous concentrations of linoleic acid, arachidonic acid, alpha-linolenic acid (alpha-LLA), EPA, DHA, prostaglandin E2, and leukotriene B4 were determined. RESULTS: Total plasma concentrations of alpha-LLA and EPA increased and those of arachidonic acid decreased significantly with administration of EPA-DHA, and concentrations of alpha-LLA increased with flaxseed oil supplementation; nevertheless, there was no significant change in the concentrations of these fatty acids or eicosanoids in the skin. There was no correlation between clinical scores and plasma or cutaneous concentrations for any of the measured fatty acids or eicosanoids. CONCLUSION AND CLINICAL RELEVANCE: Results indicated that at the dose used, neither the concentrations of fatty acids in skin or plasma nor a decrease in the production of inflammatory eicosanoids was a major factor involved in the mechanism of action in dogs with atopy that responded to fatty acid supplementation.

Enhanced radiosensitivity of rat autochthonous mammary tumors by dietary docosahexaenoic acid.

Dietary docosahexaenoic acid (DHA), which integrates into tumor cell membranes, has been reported to enhance the efficacy against tumors of cytotoxic drugs that induce reactive oxygen species (ROS). Because ionizing radiation also generate ROS, we initiated a study to determine whether dietary DHA might sensitize mammary tumors to irradiation. Mammary tumors were induced by N-methylnitrosourea (NMU) in Sprague-Dawley rats. The optimal dose of radiation to examine the effect of DHA on tumor response to irradiation was determined to be 18 grays (Gy) using a 4-6 MeV electron beam (according to the depth of the target volume) delivered in a single fraction from a linear accelerator. Two groups of rats were fed a basal diet containing 7% of a mixture of peanut and rapeseed oils enriched with 8% of an oil containing either a low (palm oil) or high (DHASCO oil containing 40% DHA) DHA content. DHA group was equally subdivided into 2 groups without or with addition of vitamin E (100 IU/kg diet). Irradiation was carried out when the first tumor in each rat reached 1.5 cm2 and subsequent change in tumor size was documented over time. DHA level in adipose tissue, taken as a biomarker, was higher in the DHA supplemented group compared to the control group. Vitamin E level in liver, the best storage for this compound, was higher in the vitamin E supplemented DHA group compared to the DHA group. Tumor size decreased by 60% at 12 days after irradiation in the DHA group vs. 31% in the control group (p = 0.03) and 36% in the DHA plus vitamin E group. Therefore, dietary DHA sensitized mammary tumors to radiation. The addition of vitamin E inhibited the beneficial effect of DHA, suggesting that this effect might be mediated by oxidative damage to the peroxidizable lipids.

Cyclooxygenase-2 expression in canine appendicular osteosarcomas.

Osteosarcoma is the most common primary bone tumor in dogs and it has a high mortality rate from distant metastatic disease. Targeted adjuvant therapies are needed to prolong currently achievable survival times. The role of cyclooxygenase-2 (COX-2) in carcinogenesis has been attributed to the production of prostaglandins and involvement in apoptosis, immune surveillance, and angiogenesis. COX-2 is up-regulated in a number of different human and animal epithelial tumors, but data about its function in mesenchymal tumors is lacking. The purpose of this study was to evaluate COX-2 expression in canine appendicular osteosarcomas and to identify if a relationship exists between the intensity of COX-2 expression and clinicopathologic outcome. Of 44 osteosarcomas analyzed, 34 (77.3%) were positive for COX-2 expression. Most of the positive cases (88%) had poor to moderate COX-2 staining. Dogs that had strong COX-2 expression had significantly decreased overall survival time (P = .0107). The median survival times for dogs with negative (n = 10), poor (n = 19), moderate (n = 11), and strong (n = 4) expression were 423, 399, 370, and 86 days, respectively. Additional studies are warranted to further evaluate COX-2 in osteosarcoma for its prognostic value and as a target for adjuvant therapy.

Streptozocin for treatment of pancreatic islet cell tumors in dogs: 17 cases (1989-1999).

OBJECTIVE: To determine toxic effects of streptozocin given in combination with a diuresis protocol in dogs and establish whether streptozocin is efficacious in treatment of pancreatic islet cell tumors in dogs. DESIGN: Retrospective study. ANIMALS: 17 dogs. PROCEDURE: Medical records were reviewed to obtain information regarding signalment, tumor stage and staging tests performed, number of streptozocin treatments, adverse effects, results of biochemical and hematologic monitoring during streptozocin treatment, tumor dimensions, duration of normoglycemia, and date of death, when applicable. Dogs were compared with a historical control group of 15 dogs treated surgically and medically. RESULTS: 58 treatments were administered to the 17 dogs. Only 1 dog developed azotemia. Serum alanine aminotransferase activity increased in some dogs but decreased when treatment was discontinued. Hematologic toxicoses were rare. Vomiting during administration was uncommon but occasionally severe. Two dogs developed diabetes mellitus after receiving 5 doses. Median duration of normoglycemia for 14 dogs with stage-II or -III insulinoma treated with streptozocin was 163 days (95% confidence interval, 16 to 309 days), which was not significantly different from that for the control dogs (90 days; 95% confidence interval, 0 to 426 days). Two dogs had rapid resolution of paraneoplastic peripheral neuropathy, and 2 others had measurable reductions in tumor size. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that streptozocin can be administered safely to dogs at a dosage of 500 mg/m2, IV, every 3 weeks when combined with a protocol for induction of diuresis and may be efficacious in the treatment of dogs with metastatic pancreatic islet cell tumors.

Effects of dietary flaxseed oil supplementation on equine plasma fatty acid concentrations and whole blood platelet aggregation.

An 18-week feeding trial was performed to investigate the effects of an omega-3 (n-3) fatty acid-enriched ration on plasma fatty acid concentrations and platelet aggregation in healthy horses. Flaxseed oil served as the source of the n-3 fatty acid alpha-linolenic acid (ALA). Twelve horses were fed dietary maintenance requirements using a complete pelleted ration (80%) and timothy grass hay (20%) for a 2-week acclimation period before being randomly assigned either to a treatment (group 1) or control (group 2) group. Group 2 horses (n = 6) were fed the diet described in the acclimation period, whereas group I horses (n = 6) were fed a 10% flaxseed oil-enriched complete pellet (80%) and grass hay (20%). Biological samples and physical measurements were collected at one point during the acclimation period (week 0) and every 4 weeks thereafter (weeks 4, 8, 12, and 16). Body weight, CBC (including platelet count), plasma fibrinogen. electrolyte (Na, K, and Cl) concentrations, and biochemical profile enzyme activities (aspartate aminotransferase, alkaline phosphatase, gamma-glutamyltransferase, and creatine kinase) did not change markedly with diet. Platelet aggregation was not altered by the supplementation of flaxseed oil in these healthy horses, although increases in plasma cis-polyunsaturated 18-carbon fatty acids C18:3; n-3 (ALA) and C18:2; n-6 (linoleic acid), biologically active C20:5; n-3 (eicosapentaenoic acid [EPA]), and malondialdehyde (MDA) were evident. There were no marked decreases in C20:4; n-6 (arachidonic acid [AA]) or increases in C22:6; n-3 (docosahexaenoic acid [DHA]), signifying that flaxseed oil may have had a high percentage of omega-6 (n-6) fatty acids as well as n-3 fatty acids, and this relatively high n-6: n-3 fatty acid ratio may have affected the biochemical effect of n-3 fatty acids. In healthy horses supplemented with flaxseed oil, platelet aggregation was not altered, which may have been due to the limited biologic effect in healthy subjects or the inability of flaxseed oil to induce the necessary biochemical effect of replacing n-6 fatty acids with n-3 types.