Observation about phosphorus and protein supply in cats and dogs prior to the diagnosis of chronic kidney disease.

There is evidence that nutritional phosphorus (P) excess may be a risk factor for chronic kidney disease (CKD) in humans and pets (Advances in Nutrition: An International Review Journal (2014), 5, 104; The American Journal of Clinical Nutrition, (2013), 98, 6; Journal of Feline Medicine and Surgery, (2017); The source of phosphorus influences serum PTH, apparent digestibility and blood levels of calcium and phosphorus in dogs fed high phosphorus diets with balanced Ca/P ratio. Proc. Waltham International Nutritional Sciences Symposium, USA; Clinical aspects of natural and added phosphorus in foods, 2017, Springer Science+Business, Media). A retrospective study was conducted in order to gather data about P and protein intake in the feeding history of dogs and cats prior to the diagnosis of CKD. Cases of 75 dogs and 16 cats with CKD with comprehensive nutritional history presented to the nutrition consultation service of the Chair of Animal Nutrition and Dietetics, Ludwig-Maximilians-University Munich, between October 2009 and March 2016, were evaluated. Cases of age-matched dogs (n = 57) and cats (n = 18) without diagnosed or suspected CKD served as controls. The most frequent type of diet used in the four groups (cats CKD, cats control, dogs CKD and dogs control) was home-made. In all groups, P and protein supply was in excess (>150%) of the recommended daily allowances (RDA; Nutrient requirements of dogs and cats (2006), National Research Council, National Academy Press). Between the dog groups, no differences regarding P and protein intake existed. The P and protein intake relative to the RDA was altogether higher in cats than in dogs. Cats with CKD showed significantly higher P and protein intakes prior to diagnosis than the control cats (170 ± 36 vs. 123 ± 34 mg P/kg BW0.67 ; p < .05). These observations call for further investigations into the long-term effects of P excess.

A comparative meta-analysis on the relationship of faecal calcium and phosphorus excretion in mammals.

To investigate the relationship between faecal calcium (Ca) and phosphorus (P) excretion in different mammalian species, a meta-analysis on digestibility data derived from the literature was conducted. Seventy-three studies on carnivores, omnivores, large and small hindgut fermenters, ruminants and hippos (a total of 21 mammalian species, precondition for inclusion dietary Ca/P ratio 1.5/1 - 3.0/1) were analysed for Ca and P digestibility. Dietary Ca/P ratios were lower than faecal Ca/P ratios in carnivores, omnivores, ruminants and hippos. In hindgut fermenters, dietary Ca/P ratios were higher than faecal Ca/P ratios, indicating higher intestinal Ca absorption in these species. In all species investigated, there was a significant positive relationship between Ca intake and faecal Ca excretion and between P intake and faecal P excretion. In the biologically relevant range, these equations predicted lower faecal Ca losses in hindgut fermenters than ruminants, for faecal P vice versa. In all species, faecal Ca and P excretion correlated significantly. In carnivores, this highly linear correlation was exceptionally strong (R² = .92). Yet, the linearity of the correlation was questionable in omnivores and ruminants. Possibly, the strong linear correlation of faecal Ca and P excretion in carnivores is due to the formation of insoluble Ca/P complexes in their relatively short and simple gastrointestinal tract. Another hypothesis is that in carnivores, Ca homeostasis relies on modifying bone turnover to a higher degree than on changes in intestinal Ca absorption. For the formation of bone matrix, a constant ratio of Ca and P absorption is of advantage.