Dietary management of skin disease: elimination diets and dietary approach to canine allergic disease
Didier Carlotti (France) gave a brief introduction to the session and acknowledged the help of the session’s sponsors, Proctor and Gamble Pet Care (IAMS). He announced the two topics: the first would be the dietary management of skin disease with emphasis on food allergy and choosing an elimination diet, and the second would address the dietary management of canine allergic disease. There were 34 delegates in the session. Hilary Jackson was identified as the first speaker.
Hilary Jackson (UK) acknowledged that a substantial portion of her presentation was work performed by a former PhD student, Rebecca Ricci, who is currently undertaking a nutrition residency in Europe, and that the work was in press.1 Their study looked at the presence of antigens in pet food and compared 12 commercially produced kibble diets. The diets were of European origin, both novel protein and a hydrolysed soya-based diet. The declared protein sources were rabbit, horse, fish, deer and duck. The fats, when declared by the manufacturer, were of fish and animal origin.
The first part of the study used standardised microscopic techniques to look for mammalian, fish and poultry bone fragments (identification microscopy) within a preparation made from a ground portion of the food treated with tetrachloroethylene. The results were graded positive or negative. The second study utilized polymerase chain reaction (PCR) techniques to look for DNA of mammalian, avian or piscine origin in samples of the food.
Unexpected contamination with bone fragments was found in 10 of the 12 diets; for example, a fish-based diet contained mammalian bone fragments. The PCR confirmed the results in some cases, whereas in other cases there were discordant results between microscopy and PCR. The only fish-based diet tested was free of contamination using PCR, and the hydrolysed soya-based diet was also found to be free of contamination.
Ed Rosser (USA) enquired as to whether the diets were veterinary exclusive (‘prescription only’) or commercially available.
Hilary Jackson confirmed that many of the diets were veterinary exclusive.
The Chairman then introduced Ralf Mueller, who presented his personal approach to the process of conducting an elimination diet study.
Ralf Mueller (Germany) was happy to announce, in the light of the first speaker’s presentation, that his preference to use home-cooked diets for the diagnosis of food allergy makes complete sense. He emphasized that home-cooked diets are used for the diagnosis of food allergy in adult dogs. The diets he subsequently uses for maintenance are essentially whatever can be tolerated by the patient. He said that he had not researched cross-reactivity between ingredients. He advocated feeding the diagnostic diet for 8 weeks and trying to find a novel protein and carbohydrate combination. For example, if the animal was fed ruminant-based food he might advocate poultry and millet. If it was fed a fish-based diet, he would advocate rabbit (or hare, or kangaroo) and sweet potato or pumpkin. If the dog was fed soya-based food then he avoids soya hydrolysates. If the dog had a very varied diet, or refused to eat home-cooked food, then he advocates an appropriate commercially produced selected-protein diet or a hydrolysed protein diet. However, he avoids the commercial chicken hydrolysates in dogs fed poultry, and avoids soya hydrolysate if the dog was fed soya. Otherwise, provided that there was no such protein cross-match, he was happy to use hydrolysates.
In growing dogs, particularly rapidly growing dogs, Ralf Mueller stated that he avoids simple home-cooked diets and hydrolysed diets, preferring to use a commercially produced restricted-protein diet. If he must use home-cooked diets he takes great care to optimize nutrient balance with appropriate supplements, making use of an internet-based diet-balancing tool, whose company would send out an appropriate mineral balance mix (www.ernaehrung.vetmed.uni-muenchen.de/service/ernaehrungsberatung/eb_hunde/index.html).
Ralf Mueller also advocates an 8-week duration for restrictive diet trials in cats. He advises the owner to feed a protein-only diet. In his experience, cats refuse to eat potatoes or rice, and a protein-only diet usually results in better compliance. A problem arises if the clients of the cats are strict vegetarians who refuse to have raw meat in the house, and for those cases a commercial novel-protein or hydrolysed diet might be necessary. Cats frequently have been fed foods with very varied protein content, making a novel protein difficult to identify.
Ralf Mueller reported that he has started to use patch testing in dogs exposed to a very varied diet or in cases where the owner was sceptical of food allergy. He used both cooked and raw samples of feed placed onto the skin. The relevant foods are ground, aliquoted and frozen until needed. He has found a good correlation with a negative cutaneous patch reaction and suitability for the diet. For example, a negative reaction to potato meant it could be used in the diet. He said that a positive reaction was regarded as meaningless for allergen selection, being possibly false-positive or even perhaps irritant. He described this technique as useful to convince sceptical owners that a diet trial is necessary, and in identifying suitable food trial ingredients in dogs fed very varied diets.
In response to a question from the Chairman, Ralf Muller described how he had also back-tested proven food-allergic dogs against a commercial food enzyme-linked immunosorbent assay (ELISA). The likelihood ratio (a statistical technique that is less dependent on the prevalence of the disease in a population) of the results from this study of 23 dogs suggested that ELISA assay for food allergy was not reliable.
Hilary Jackson asked which ELISA was used.
Ralf Mueller replied that he used the Avacta test.
Michael Stephan (USA) asked what the value of patch testing would be if the dog was intolerant, rather than allergic.
Ralf Mueller pointed out that he did not know if the dogs were simply intolerant rather than allergic – they just reliably responded to challenge. Commenting further on patch testing, he pointed out that it was a very time-consuming procedure, taking about 45 minutes to prepare and apply the patches to the dog. The dogs are allowed to return home after the patches are affixed.
Ed Rosser said that in his hands patch testing was a 3-day procedure and that he preferred the dogs to be hospitalized.
Ralf Mueller said that during an in-house study of these 32 dogs they read 132 reactions at 24, 48 and 72 hours. Only one reaction was only positive at 72 hours. Only six were positive only at 24 hours, and that four of these were subsequently judged to be false-positive. All the other reactions were positive at both 24 and 48, or 48 hours only, or 48 and 72 hours, so he now reads these food patch tests at 48 hours.
Ed Rosser, commenting on Ralf Mueller’s 8-week diagnostic protocol, said that he still recommended that food trials be continued for 12 weeks. He could recall dogs, and still sees dogs, that showed no improvement at all at 8 weeks, only to respond by 12 weeks.
Didier Carlotti asked what percentages of dogs do not respond at all at 8 weeks but will by 12 weeks.
Ed Rosser replied that not many, maybe 5% at most.
Ralf Mueller said that he had not had a single dog with demonstrated food allergy that had failed to show some improvement by 8 weeks, over a 2-year period when in practice in Melbourne.
Ed Rosser further added that he had always advocated home-cooked food and would continue to do so, particularly in the light of Hilary’s presentation.
Michael Stephan asked Ralf Mueller if he had ever used pork as it is very rarely included in commercial dog foods.
Ralf Mueller replied that he did use cooked pork if the dog had been fed a fish-based diet. However, in Germany, porcine by-products are present in meat-based dog diets and, therefore, pork was unsuitable for these dogs.
Ed Rosser reminded members of the audience from the USA that the palatability enhancer in heartworm medication was pork. He expressed interest in the assumption by many dermatologists that food allergy was IgE mediated. For example, he said, in all other IgE-mediated diseases, if the allergen was removed from the environment, it only takes 5–7 days for remission to be obtained, not 8 or 12 weeks.
Ralf Mueller said he agrees that food allergies may not be IgE-mediated. He had published a study investigating serum IgE concentrations before and after challenging dogs with proven food allergy, and had found no difference in IgE concentrations.2