The present study comprised of a 6-month prospective, randomised, double-blinded, placebo-controlled, cross-over dietary trial comparing the MCTD to a standardised placebo diet for canine epilepsy. Dogs were fed either the MCTD or the placebo diet for 3 months (day 1 to day 90±2 d) followed directly by a subsequent respective switch of diet for a further 3 months (day 90 to day 180±2 d). Relevant data were collected on the following variables at visit 1 (day 2), visit 2 (day 90 (sd 2) d) and visit 3 (day 180 (sd 2) d): seizure frequency (generalised seizures); body weight; measurements of serum phenobarbital (PB) and/or potassium bromide (KBr) concentrations as appropriate; dynamic bile acids; complete blood cell count; standard clinical serum chemistry; adverse events; and visual analogue score (VAS) for ataxia, sedation and QoL.

Participants were recruited through different media in the UK based on the following inclusion criteria that were verified by telephone interviews with owners, followed by physical and laboratory examinations: canine species of mixed or purebred breeds; suspected to have idiopathic epilepsy (unremarkable former MRI scan); aged between 6 months and ≤12 years; weighing between 4 and ≤65 kg; no clinically significant findings on haematology and biochemistry or dynamic bile acid results; have unremarkable interictal neurological examinations for a dog on antiepileptic treatment; only one dog per household enroled to the study; have had at least three seizure episodes in the previous 3 months before the start of this study; on at least one antiepileptic treatment; and no use of drugs that could influence the metabolism of PB and KBr. Dogs intended for breeding in <2 weeks from the start of study; with known cause of epilepsy such as brain neoplasm, brain trauma, encephalitis and meningitis; with chronic or acute renal, hepatic or cardiac failure; with an acute or surgical condition at the time of enrolment; and bitches known or suspected to be pregnant or lactating were all excluded from the study.

Owners of dogs meeting all the above-mentioned criteria received further information, both verbally and in writing, on all aspects of the study, including information about the protocol and explanations about the seizure frequency diary that was to be completed at home. Dogs were enroled as an individual experimental unit and independent of other dogs. A unique study case number, consisting of a two-digit number, ascending in a chronological order of enrolment, was allocated and used to identify each dog on all documents and samples throughout the study. Twenty-one dogs were included in the analysis and all of them completed the study.

VAS was recorded for ataxia, sedation and QoL using a line ranging from 0 to 100 mm. The observer was asked to draw a secondary intersecting line perpendicular to the line of measurement that best represented the subjective severity. A perpendicular line at 0 mm represented ‘asymptomatic/normal’ and at 100 mm represented either ‘ataxia so severe dog is unable to walk’ or ‘sedation to the extent dog only sleeps’ or ‘QoL is so poor euthanasia is requested’, respectively.

The experimental placebo and test formulae were dry extruded kibble (Nestle Purina PetCare) formulated to meet or exceed the nutritional guidelines established by the Association of American Feed Control Officials (AAFCO). Both formulae were of the same ingredient composition, and formulated to contain <10 % moisture, at least 28 % crude protein, at least 15 % crude fat and 50 % carbohydrates with <2 % as crude fibre. The only compositional exception was that zero MCT were added to the placebo formula, and lard was used as fat substitute to ensure that the formulae were isoenergetic (1560·6 kJ/100g (373 kcal/100 g)), whereas the test formula contained 5·5 % MCT. MCT content was about 10 % of the total formula calories (based on fat as 35·6 kJ/g (8·5 kcal/g) and MCT as 28·5 kJ/g (6·8 kcal/g)). Proximate analysis of both formulae indicated that they were of similar composition, with the exception of MCT, as the placebo diet was void of C12, C10 and C8 fatty acids (each <0·100 % of placebo formula). Both formulae exceeded the AAFCO minimum requirements for essential fatty acids. The dogs were housed and fed mainly once or twice daily at home with no restrictions on water consumption. The owners were educated to keep the diet consistent throughout the study period. The amount of food given per day was calculated according to the weight of each dog in order to provide sufficient food to fulfil their nutritional requirements. A deviation of ±10 % food consumption (kg) was allowed to account for the individual needs of each dog, taking into consideration differences in activity level and physical condition. Dogs were restricted to consumption of the study diet, and thus treats or snacks were replaced by the respective placebo or MCTD food.

Three sets of blood samples were collected from the dogs over the duration of the study on the days of visit (baseline – day 2, end of period 1 – day 90 (sd 2) d and end of period 2 – day 180 (sd 2) d). Blood samples were collected 2 h after consumption of the respective diets and routine concomitant AEDs. Blood samples were collected and stored using clotting activator dipotassium EDTA-containing (with serum-separation gel) polypropylene blood-collection tubes and plain polypropylene blood-collection tubes (International Scientific Supplies Ltd). Blood samples were allowed to clot and serum was stored at −80°C. Serum samples were analysed for β-hydroxybutyrate (BHB) concentrations using an enzymatic end point (colorimetric) reaction assay as directed by following the kit manufacturer’s protocol (C444-0A; Catachem Inc.) and using an Olympus AU 640e (Beckman Coulter) chemistry analyser for measurements.

Any abnormal health observation that was unfavourable, unintended and occurred after enrolment, regardless of whether it was considered as an MCTD- or a placebo diet-related event, was reported to the investigator and documented (online Supplementary Table S1). Details of the adverse event include the following: a description of the adverse event; length of the adverse event recorded in days; severity of the adverse event recorded using 1=mild, 2=moderate, 3=severe and 4=serious; frequency of the adverse event measured using 1=once, 2=occasionally, 3=regularly and 4=ongoing; concomitant treatment noted as 1=none and 2=yes; and final outcomes consisted of 1=resolved without further effects, 2=resolved with further effects, 3=unchanged, 4=euthanasia and 5=death. In light of the objectives of this study, seizure occurrences during the study period were not regarded as an adverse event. Any concomitant treatments including routine AED administered during the study period were recorded, detailing indication of treatments, products used and length of treatments (online Supplementary Table S2). To avoid confounding influences, concomitant AED medication and dosages were unchanged throughout the study. Eighteen of the twenty-one dogs were drug-resistant. All twenty-one dogs received PB. Most dogs were treated additionally with KBr (n 18). Some dogs were chronically treated with a third AED, imepitoin (n 1) or levetiracetam (n 4). Twelve owners had rectal diazepam or levetiracetam for pulse therapy at home available for the acute treatment of cluster seizure episodes.

Seizure frequency refers to the number of seizures per month, and seizure day frequency refers to the number of days in a month with seizure occurrence. The severity of seizures was analysed using the McNemar test by comparing the presence of cluster seizures between diet groups. Comparisons between the MCTD and placebo-standardised diet groups were made using match-paired Student’s t tests for parametric data and Wilcoxon matched-pairs signed rank test for non-parametric data. The relationships between two variables, such as seizure frequency and age, were analysed using Pearson’s correlation coefficient analysis. All comparisons were two-sided, and P<0·05 was considered significant. Non-parametric data are presented as median (25th–75th percentile), and parametric data are represented as mean values and standard deviations.

Patterson et al. ^{( 36 )} performed power calculations using the results that were acquired from their study, which showed that twenty-two dogs in each group would be sufficient to show significant differences between diet groups using seizure frequency as the major outcome variable. We report only twenty-one dogs as one dog was excluded due to an error in the diet dispensed, which came to our notice only during data analysis after completion of the study.

This study included twenty-one dogs of seventeen different breeds including the following: American bulldog, two Beagles, two Border Collies, Boxer, Cavalier King Charles Spaniel, English Bull Terrier, English Springer Spaniel, German Shepherd, Golden Retriever, Lhasa Apso, Mastiff, Rhodesian Ridgeback, Saint Bernard, Siberian Husky, Slovakian Rough Haired Pointer, Welsh Springer Spaniel, and three cross breeds (online Supplementary Table S3). The study population consisted of fifteen males, of which ten were neutered and five were intact, and six females, of which four were neutered and two were intact (online Supplementary Table S3). The dogs had a mean of 4·59 (sd 1·73) years of age and weighed a mean of 29·79 (sd 14·73) kg at the start of the trial (online Supplementary Table S3). There were no differences for the acute or chronic treatment regimens between the placebo and MCTD phases.

The results revealed a significantly lower seizure frequency when dogs were fed the MCTD (2·31/month, 1–4·46/month) in comparison with the placebo diet (2·67/month, 0·33–4·91/month, P=0·020; Fig. 1(a)). Three dogs achieved complete seizure freedom (100 % reduction), seven additional dogs had a 50 % or greater reduction in seizure frequency (56·85 %, 50·76–62·8 %) and five dogs had an overall reduction in seizure frequency (38·87 %, 35·68–43·27 %) (online Supplementary Table S4). Six dogs showed no response to the MCTD with an overall increase in seizure frequency. Seizure day frequency was also shown to be significantly lower when dogs were on the MCTD in comparison with the placebo diet (P=0·022), with over 80 % of the trial population achieving reduction in seizure day frequency (Fig. 1(b)) (online Supplementary Table S4). During the MCTD trial phase, three dogs achieved complete seizure freedom (100 % reduction), four dogs had over 50 % reduction in seizure day frequency (67·15 %, 58·25–75·15 %) and ten dogs had <50 % reduction in seizure day frequency (34·10 %, 19·40–43·45 %). Four dogs showed no response to the MCTD with an overall increase in number of seizure day frequency.Fig. 1

Effect of the medium-chain TAG diet (MCTD) on (a) seizure frequencies per month and (b) seizure days per month compared with the placebo-standardised diet (n 21). There were significant reductions in the (a) number of seizures per month (P=0·0195) and (b) seizure days per month (P=0·0216) during the MCTD phase in comparison with the placebo diet. Data are shown as box-and-whisker plots (central lines of the box represent the median, lower and upper limits of the box represent the 25th and 75th percentiles and whiskers represent the minimum and maximum). Two-sided Wilcoxon’s matched-pairs rank tests were used to compare placebo and MCTD groups. * P<0·05.

The MCTD resulted in a shift in the distribution of seizure frequencies per month with higher percentages of the whole population (n 21) experiencing reduced seizure frequencies compared with the placebo-standardised diet (Fig. 2). The total number of seizures that occurred in the study population (n 21) on each day of the MCTD period was also reduced in comparison with the placebo diet (Fig. 3). These results also show a reduction in the number of dogs with seizure occurrences during the MCTD period, with a stable distribution of around three dogs with seizure occurrences per day (Fig. 4). On the other hand, during the standardised placebo diet phase, the distribution was more varied with higher number of dogs with seizure occurrences per day. It is interesting to note that the results suggest a rapid onset of antiseizure efficacy. The total number of seizures (Fig. 3) and the number of dogs with seizure occurrences (Fig. 4) did not seem to gradually reduce throughout the MCTD phase, but instead showed improvements as early as day 1 and persisted throughout the diet period. There were no significant differences in the number of days with cluster seizures between diet groups (P=0·6171). There were also no significant associations between seizure frequency and seizure day frequency reductions with age, weight or BHB concentrations (online Supplementary Table S5).Fig. 2

Effect of the medium-chain TAG diet (MCTD) on seizure frequency distributions compared with the placebo-standardised diet. The figure shows the distribution of the population (n 21) based on seizure frequencies per month, shown in a column bar graph. The MCTD resulted in higher percentages of the population experiencing lower seizure frequencies per month. , Placebo; , MCTD.

There were no significant changes in serum concentrations of PB (26·50, 23·50–34·00 v. 32·50, 25·00–36·75 μg/ml, P=0·423) and KBr (1·23, 1·09–1·89 v. 1·29, 1·02–1·61 mg/ml, P=0·404) or weight (29·79 (sd 15·16) kg v. 29·61 (sd 15·51) kg, P=0·300) between the placebo-standardised diet and MCTD, respectively. There was a significant increase in blood concentrations of BHB when dogs were fed the MCTD (0·041 (sd 0·004) mmol/l) in comparison with the placebo diet (0·031 (sd 0·016) mmol/l, P=0·028) (Fig. 5). There were significant differences between placebo and MCTD groups in creatinine (83·62 (sd 17·08) μmol/l v. 79·67 (sd 15·02) μmol/l, P=0·025) and mean cell Hb concentrations (34·8, 33·5–35·0 v. 34·0, 33·0–34·7 g/dl, P=0·030), both of which were higher in the placebo diet group. All other complete blood count and clinical chemistry results, including glucose, were not significantly different between diet groups. There were no significant differences between diet groups in the VAS scores for ataxia (P=0·742), sedation (P=0·917) and QoL (P=0·568) (online Supplementary Fig. S1).Fig. 5

Effects of the medium-chain TAG diet (MCTD) on concentrations of β-hydroxybutyrate (BHB). BHB concentrations were measured after dogs (n 21) were fed the MCTD for a period 90 (sd 2) d and the placebo diet for a period 90 (sd 2) d. The figure shows a respective increase in BHB levels when dogs were on the MCTD in comparison with the placebo diet (P=0·0280). Data are shown as scatter plot (central line represents the mean values with standard deviations). Two-sided matched paired Student’s t test was used to compare the placebo and MCTD groups (* P<0·05).

All the aforementioned dogs did complete the study protocol. Ten further dogs had been recruited, but did not complete the study, of which five dogs were fed the MCTD and five were fed the placebo-standardised diet at the time of withdrawal. Of the five dogs that withdrew when on the MCTD, two were euthanised before completion of study due to uncontrollable cluster seizures. The remaining three withdrew due to the following reasons: dog becoming lethargic due to the diet; difficulty in feeding exclusively the test diet with a new puppy in the household; and dog not being satisfied with the diet, being constantly hungry and looking for food. Reasons for withdrawal of the five dogs on the placebo diet include the following: the study being too much a hassle; seizure activity increased with frequent cluster seizures; increased seizure frequency; owner unable to commit to the study due to other commitments; and food intolerance causing allergic reaction. One dog completed the study but was excluded from the analysis due to an error in the diet dispensed where the dog was given the same diet for both diet periods.