Although many herbivores and omnivores have been shown to balance their intake of macronutrients when faced with nutritionally variable foods, study of this ability has been relatively neglected in carnivores, largely on the assumption that prey are less variable in nutrient composition than the foods of herbivores and omnivores and such mechanisms therefore unnecessary. We performed diet selection studies in 5 breeds of adult dog (Canis lupus familiaris) to determine whether these domesticated carnivores regulate macronutrient intake. Using nutritional geometry, we show that the macronutrient content of the diet was regulated to a protein:fat:carbohydrate ratio of approximately 30%:63%:7% by energy, a value that was remarkably similar across breeds. These values, which the analysis suggests are dietary target values, are based on intakes of dogs with prior experience of the respective experimental food combinations. On initial exposure to the diets (i.e., when naive), the same dogs self-selected a diet that was marginally but significantly lower in fat, suggesting that learning played a role in macronutrient regulation. In contrast with the tight regulation of macronutrient ratios, the total amount of food and energy eaten was far higher than expected based on calculated maintenance energy requirements. We interpret these results in relation to the evolutionary history of domestic dogs and compare them to equivalent studies on domestic cats.

BACKGROUND: Dual-energy X-ray absorptiometry (DXA) has been used extensively to measure body composition, but has been validated by comparison to chemical analysis on relatively few occasions. Moreover, these previous validation studies have ground up entire carcasses prior to chemical analysis, thus potentially obscuring sources of error in the DXA analysis. OBJECTIVE: The purpose of this study was to validate DXA by comparison to chemical analysis in dogs and cats, performing chemical analysis on dissected rather than ground carcasses to reveal sources of discrepancy between the two methods. DESIGN: Sixteen animals (10 cats and 6 dogs weighing between 1.8 and 22.1 kg) were scanned by DXA post-mortem using a Hologic QDR-1000 W pencil beam machine and then dissected into 22 separate components. Individual tissues were dried and then sub-sampled for analysis of fat content by Soxholet extraction, or ashing in a muf¯e furnace. Body composition by DXA was compared to body composition by chemical analysis and discrepancies between the two correlated with chemical composition of individual tissues. We also explored the capability of the machine to establish the fat contents of mixtures of ground beef, lard and water. RESULTS: DXA estimates were strongly correlated with estimates derived from chemical analysis: total body mass (r 1.00), lean tissue mass (r 0.999), body water content (r 0.992) and fat mass (r 0.982). Across individuals the absolute and percentage discrepancies were also small: total body mass (13.2 g, 1.02%), lean tissue mass (119.4 g, 2.64%), water content (101 g, 1.57%) and fat content (28.5 g, 2.04%), where the percentage error is expressed relative to the average mass of that component across all individuals. Although on average DXA compared very well to chemical analysis, individual errors were much greater. Individual errors in the lean tissue and fat tissue components were strongly correlated with the fat content of skeletal muscle and the lean content of mesenteric fat. The error in the DXA estimate of total fat content was related to skeletal muscle hydration. Experimental studies using mixtures of lean ground beef, water and lard indicated that tissue hydration may have important effects on the perception of tissue fat content by DXA. Bone mineral content by DXA was approximately 30% lower than whole body ash content but only 7.7% lower than ash content of the bones. CONCLUSIONS: On average pencil beam DXA analysis using the Hologic QDR-1000 W machine provides an accurate estimate of body composition in subjects weighing between 1.8 and 22.1 kg. Individual discrepancies, however, can be large and appear to be related to lean tissue hydration.

Limited information is available on what constitutes optimal growth in dogs. The primary aim of this study was to develop evidence-based growth standards for dogs, using retrospective analysis of bodyweight and age data from >6 million young dogs attending a large corporate network of primary care veterinary hospitals across the USA. Electronic medical records were used to generate bodyweight data from immature client-owned dogs, that were healthy and had remained in ideal body condition throughout the first 3 years of life. Growth centile curves were constructed using Generalised Additive Models for Location, Shape and Scale. Curves were displayed graphically as centile charts covering the age range 12 weeks to 2 years. Over 100 growth charts were modelled, specific to different combinations of breed, sex and neuter status. Neutering before 37 weeks was associated with a slight upward shift in growth trajectory, whilst neutering after 37 weeks was associated with a slight downward shift in growth trajectory. However, these shifts were small in comparison to inter-individual variability amongst dogs, suggesting that separate curves for neutered dogs were not needed. Five bodyweight categories were created to cover breeds up to 40kg, using both visual assessment and hierarchical cluster analysis of breed-specific growth curves. For 20/24 of the individual breed centile curves, agreement with curves for the corresponding bodyweight categories was good. For the remaining 4 breed curves, occasional deviation across centile lines was observed, but overall agreement was acceptable. This suggested that growth could be described using size categories rather than requiring curves for specific breeds. In the current study, a series of evidence-based growth standards have been developed to facilitate charting of bodyweight in healthy dogs. Additional studies are required to validate these standards and create a clinical tool for growth monitoring in pet dogs.

These data indicate that L. acidophilus can be successfully incorporated into a dry dog food, survive transit through the canine gastrointestinal tract, and populate the colon and are associated with local and systemic changes. This probiotic bacterium may have the potential to enhance intestinal health and improve immune function in dogs.

Renal disease has a high incidence in cats, and some evidence implicates dietary P as well. To investigate this further, two studies in healthy adult cats were conducted. Study 1 (36 weeks) included forty-eight cats, stratified to control or test diets providing 1·2 or 4·8 g/1000 kcal (4184 kJ) P (0 or approximately 3·6 g/1000 kcal (4184 kJ) inorganic P, Ca:P 1·2, 0·6). Study 2 (29 weeks) included fifty cats, stratified to control or test diets, providing 1·3 or 3·6 g/1000 kcal (4184 kJ) P (0 or approximately 1·5 g/1000 kcal (4184 kJ) inorganic P, Ca:P 1·2, 0·9). Health markers, glomerular filtration rate (GFR) and mineral balance were measured regularly, with abdominal ultrasound. Study 1 was halted after 4 weeks as the test group GFR reduced by 0·4 (95 % CI 0·3, 0·5) ml/min per kg, and ultrasound revealed changes in renal echogenicity. In study 2, at week 28, no change in mean GFR was observed (P >0·05); however, altered renal echogenicity was detected in 36 % of test cats. In agreement with previous studies, feeding a diet with Ca:P <1·0, a high total and inorganic P inclusion resulted in loss of renal function and changes in echogenicity suggestive of renal pathology. Feeding a diet containing lower total and inorganic P with Ca:P close to 1·0 led to more subtle structural changes in a third of test cats; however, nephrolithiasis occurred in both diet groups, complicating data interpretation. We conclude that the no observed adverse effects level for total dietary P in adult cats is lower than 3·6 g/1000 kcal (4184 kJ), however the effect of inorganic P sources and Ca:P require further investigation.