Plus-Hex CLINICAL
Introduction
Elimination-provocation diet trials( hereafter described in this article as diet trials, for the purposes of brevity) are notoriously challenging to perform well, but are the current best practice for diagnosing cutaneous adverse food reactions( CAFR) in dogs and cats.
They require intense client education, excellent compliance from the client, patient and veterinary team, and an almost Sherlock Holmes-esque approach to interpretation and subsequent diagnosis. Common pitfalls are often evident in the histories of referred patients. These can mean a diet trial has to be repeated by the referral clinician, which can be frustrating for an animal ' s owner.
Learning outcomes
• Identify what constitutes the current best practice diet trial
• Evaluate how, when, why and with what to perform the ideal diet trial
• Discuss how to avoid common pitfalls when performing diet trials
Best practice for diet trials
To understand what a diet trial consists of, it is important to understand why the diet trial is being performed. CAFR, also known as food-induced atopic dermatitis, makes up around 20 % of cases of allergic patients [ 1 ]. Dermatology complaints are the most common reason for a pet to be presented to UK general veterinary practices [ 2 ]. As such, there is scope for CAFR to be a common diagnosis, with impacts on the general health and quality of life of a large number of patients.
Owners may ask if there are alternatives to a diet trial, and blood, hair and saliva tests are marketed to both owners and veterinary practices as suitable options. However, there is debate about the efficiency and accuracy of these tests, with minimal evidence to support their use, none of which seems to demonstrate consistent findings, accurate positive or negative predictive values, or any correlation between positive laboratory results and the presence of clinical disease [ 1 ]. As such, a strict elimination-provocation diet trial is current best practice until an accurate alternative test is devised.
Choosing a diet
The most commonly reported food allergens implicated in canine and feline CAFR are beef, dairy, chicken, lamb, fish and soy [ 1 ]. Due to cross-reactivity between certain allergens, patients may be allergic to one or more of these, and they can be allergic to any allergen to which they have previously been exposed.
In an ideal diet trial, from a scientific point of view, the patient would be starved for 8 weeks and kept free from any exposure to allergens. This clearly is not possible, from an animal welfare and ethical point of view or from a practical point of view, as patients cannot be without access to food for this length of time and will always be exposed to allergens in their home environment. As such, any diet trial that is performed is already a compromise.
To maintain a strict elimination phase, a full dietary history should be taken and a food selected that either avoids all known allergens to which the patient has previously been exposed or is hydrolysed to reduce its allergenicity [ 3, 4 ]. It can help, especially with cats, to choose a formulation they are used to, such as kibble or wet food, as changing the diet can be a source of stress and can lead to food aversion [ 5 ]. The patient ' s life stage should also be taken into consideration, as not all diets are suitable for growing animals or those with concurrent disease.
Home-cooked diets are an option but they need to be nutritionally balanced if fed long-term. Appropriate sources of protein to prepare at home can be difficult to source, as it is important to make sure that no cross-contamination with other protein sources has occurred.
Hydrolysed diets
Hydrolysed feeds are diets in which the proteins have been chemically‘ digested’ to disrupt their structure and make them less likely to trigger an immune response [ 6 ]. To stimulate an immune response, two or more immunoglobulin( Ig) E molecules need to cross-link with an allergen, which means that allergens need to be a certain size. The aim of hydrolysation is to create small protein fragments that are unable to bind to IgE [ 6 ]. There are multiple commercial hydrolysed diets available on the UK market, some with dry and wet options, with varying degrees of hydrolysation and different protein sources( Table 1).
Table 1. Hydrolysed diets available in the UK( not an exhaustive list).
Diet
Royal Canin Hypoallergenic
Royal Canin Anallergenic
Protein source
Soy, poultry liver
Chicken feather
Protein weight
< 3 kDa
0.5 – 1 kDa
Hill ' s z / d Chicken liver < 3 kDa Purina HA Soy < 10 kDa
Dechra Specific Allergen Management Plus
Salmon < 3 kDa
Volume 41( 5) • October 2026
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