# Epidemiological and clinical profiles of young and senior dogs fed a standard diet

Tiphaine Blanchard, Amélie Mugnier, Fleur Boulet, Annabelle Meynadier, Nathalie Priymenko

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## To cite this version:

Tiphaine Blanchard, Amélie Mugnier, Fleur Boulet, Annabelle Meynadier, Nathalie Priymenko. Epidemiological and clinical profiles of young and senior dogs fed a standard diet. Preventive Veterinary Medicine, 2025, 240, pp.106537. 10.1016/j.prevetmed.2025.106537. hal-05041920

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# Epidemiological and clinical profiles of young and senior dogs fed a standard diet

Tiphaine Blanchard<sup>a,b,*</sup>, Amélie Mugnier<sup>b</sup>, Fleur Boulet<sup>a</sup>, Annabelle Meynadier<sup>a</sup>, Nathalie Priymenko<sup>c</sup>

## ARTICLE INFO

Keywords:

Aging

Canine

Diet

Health

Lifestyle

Nutrition

Omega-3 fatty acids

## ABSTRACT

This study aimed to explore age-related differences in epidemiological and clinical parameters in dogs consuming a standardized diet, focusing on factors relevant to veterinary practitioners. A total of 106 dogs were included, comprising young (2–5 years) and senior (≥8 years) individuals. Epidemiological data were collected through questionnaires and veterinary consultations, while clinical parameters were assessed via physical examinations and blood analyses. Compared to younger dogs, senior dogs were less active, more likely to live in houses, and more frequently received regular deworming. They were also more likely to consume food purchased from pet stores or supermarkets compared to younger dogs. Clinical evaluations revealed that senior dogs had higher plasma globulin and platelets and lower albumin, consistent with chronic low-grade inflammation associated with aging. Muscle loss, poor coat quality, and reduced lymphocyte counts were also prominent in senior dogs, potentially reflecting sarcopenia, malnutrition, and immunosenescence, respectively. Notably, dogs previously fed diets lacking a source of omega-3 fatty acids exhibited elevated plasma triglycerides even after transitioning for four weeks to a premium diet containing fish oil, underscoring the lasting impact of long-term dietary habits. These findings highlight the importance of regular veterinary follow-ups for senior dogs and the role of high-quality nutrition, including sources of omega-3 fatty acids. By identifying key epidemiological and clinical differences, this study offers valuable insights to help veterinary practitioners distinguish between healthy and pathological aging.

## 1. Introduction

In recent decades, advancements in veterinary care, improved nutrition, and heightened owner awareness have contributed to an increase in canine life expectancy (FACCO, 2023; Kraft, 1998; Montoya et al., 2023). For instance, in France, the average lifespan of dogs reached 12.5 years in 2022, marking a one-year increase compared to 2003 (FACCO, 2023). As a result, senior dogs now represent a growing proportion of patients in veterinary practice. This demographic shift presents unique challenges for veterinarians, who must navigate the complexities of geriatric care (Dhaliwal et al., 2023; McKenzie et al., 2022). A critical aspect of this care involves distinguishing age-related physiological changes from pathological conditions, enabling timely diagnosis and appropriate treatment (Bellows et al., 2015).

Studies exploring age-related changes in dogs have been conducted on both laboratory (Lee et al., 2020; Lowseth et al., 1990; Strasser et al., 1993) and pet populations (Alilovic et al., 2022; Chang et al., 2016; Kusaba et al., 2024; Radakovich et al., 2017; Vikartovska et al., 2020; Willems et al., 2017). Laboratory studies, while valuable for generating data under controlled conditions, often fail to account for the diverse environmental, genetic, and lifestyle factors that influence the health of pet dogs (Schulte and Arlt, 2022). Meanwhile, studies on pet dogs, although more clinically relevant, have always lacked standardization in key areas, such as diet (Sargeant and O'Connor, 2014). This dietary variability introduces a significant confounding factor that may partly explain the inconsistent findings in the literature, as diet given by the owner differ between young and senior dogs (Wallis et al., 2018). For instance, while Lowseth et al. (1990) and Strasser et al. (1993) reported

<footnote><sup>a</sup> GenPhySE, Université de Toulouse, INRAE, ENVT, Castanet Tolosan 31326, France</footnote>

<footnote><sup>b</sup> Lallemand SAS, 19 rue des Briquetiers, Blagnac, France</footnote>

<footnote><sup>c</sup> Toxalim, Université de Toulouse, INRAE, ENVT, Toulouse 31300, France</footnote>

<footnote>* Corresponding author at: GenPhySE, Université de Toulouse, INRAE, ENVT, Castanet Tolosan 31326, France.</footnote>

<footnote>E-mail addresses: tiphaine.blanchard@envt.fr (T. Blanchard), ameliemugnier@lallemand.com (A. Mugnier), fleur.boulet_20@envt.fr (F. Boulet), annabelle.meynadier@envt.fr (A. Meynadier), nathalie.priymenko@envt.fr (N. Priymenko).</footnote>
a decrease of plasmatic urea with age in laboratory and police dogs, Radakovich et al. (2017) and Kusaba et al. (2024) found an increase of plasma urea with age in pet dogs, underscoring the need to clarify these conflicting results.

Moreover, previous studies have largely overlooked important epidemiological factors that may differ between young and senior dogs. For instance, senior dogs are less active, have less interactions with their owners (Wallis et al., 2018), and receive less frequent veterinary care than younger dogs (Marinelli et al., 2007), all of which could contribute to differences in their health profiles. Failing to account for these factors limits the applicability of previous findings to real-world clinical practice (Skelly et al., 2012; Wallis et al., 2018).

This study aimed to address existing gaps through two key objectives. First, it sought to identify epidemiological factors that significantly differ between young and senior dogs. Second, it aimed to explore age-related changes in clinical parameters commonly assessed in routine practice, while accounting for the confounding effects of the identified epidemiological variables. By standardizing diet and examining real-world epidemiological differences, this research offers a unique opportunity to isolate age-related trends and their implications for veterinary care.

## 2. Material and methods

This study has received approval from the Animal Ethical Committee "SCIENCE ET SANTE ANIMALES N°115" in Toulouse, France, under the reference number SSA_2022_014. For the owners' questionnaires, this study received approval from the Research Ethical Committee "Comité d'éthique et de la recherche – CER" in Toulouse, France, under the reference number 2023_719. Prior to providing consent, dog owners received an initial email with general information about the project. At the beginning of the consultation, they discussed the study in detail with the veterinarian before signing the consent form. The information sheet was included at the beginning of the consent form to ensure transparency and informed decision-making.

### 2.1. Animals

Dogs were recruited for the study on a voluntary basis through a multi-channel approach. Recruitment efforts included the social media platforms of the Veterinary School of Toulouse, email invitations sent to dog owners who had previously visited the school and consented to receive communications, and articles published in both an online Toulouse city news outlet and a local printed newspaper. Veterinary students at the Veterinary School of Toulouse were also informed about the study.

The recruitment campaign specifically targeted two groups of dogs: those aged between 2 and 5 years, and those 8 years and older (the latter group had also been included in a previously published study (Blanchard et al., 2024a)). All participating dogs needed to weigh more than 20 kg and be in apparently good health with no ongoing treatments or chronic illnesses. To encourage participation, the campaign emphasized several incentives, including two free veterinary consultations, with the second consultation including blood tests. Additionally, participants received free premium dog food sufficient for at least four weeks of their dog's diet.

### 2.2. Questionnaires

Questionnaires were distributed at two times during the study: prior to the first consultation and during the consultation itself. The pre-consultation questionnaire was sent by email at least 24 hours before the first visit, allowing owners sufficient time to respond thoughtfully without fatigue (Adams and Cox, 2008). This questionnaire collected detailed information about the dog's dietary habits using the World Small Animal Veterinary Association (WSAVA) diet history form

(WSAVA, 2020). It also included questions about the veterinary care the dog had received, encompassing medical treatments and preventive care. Dogs were classified as "regularly dewormed" if antiparasitic treatment was administered at least every three months, following the European Scientific Counsel for Companion Animal Parasites (ESCCAP) recommendations for groups B and C, which correspond to slight and moderate risk of endoparasites (ESCCAP, 2021). Similarly, dogs were considered "regularly treated against ectoparasites" if the treatment frequency aligned with the efficacy duration of the product used.

During the consultation, owners completed additional questionnaires to provide comprehensive information about both their dog and themselves. These included the Big Five Inventory (BFI) for assessing the owners' personalities (Plaisant et al., 2010), and the succinct Monash Canine Personality Questionnaire (MCPQ-R) for evaluating their dogs' personalities (Ley et al., 2009). The BFI is a 45-item self-report questionnaire where individuals rate themselves on short descriptive phrases, and five core traits are scored: extraversion, agreeableness, conscientiousness, neuroticism, and openness. The MCPQ-R assesses canine personality through a 26-item owner-reported questionnaire that evaluates five dimensions: extraversion, motivation, motivation at training, agreeableness, and neuroticism, using adjective-based ratings. Additionally, the Lexington Attachment to Pet Scale (LAPS), a 23-item questionnaire on general attachment, people substituting, and animal rights/welfare attitudes, was used to measure the attachment of owners to their dogs (Blanchard et al., 2024b; Johnson et al., 1992). Owners also answered questions regarding their personal circumstances and the dog's living environment. To assess the dog's activity level, a scale ranging from 1 (very inactive) to 4 (highly active) was employed.

### 2.3. Veterinary consultation

Two veterinary consultations were conducted during the study. The first consultation served as a general health check to confirm that the dog was physically healthy and eligible for the study. Dogs with a body condition score (BCS) of 3, 6, and 7/9 were nonetheless accepted to ensure sample size, as they were equally distributed between young and senior dogs. This consultation was conducted by one of two veterinarians (Vet 1 or Vet 2). If the dog was deemed healthy, it received sufficient Purina ProPlan® All Sizes Light Adult dog food for a four-week period, with instructions for a gradual one-week transition to the new diet. The feeding quantity was calculated by a third-year ECVCN resident to match the dog's previous energy intake at a stable weight, ensuring that no weight loss or gain occurred during the study period. This food was selected to meet the nutritional requirements for both young and senior dogs (Churchill and Eirmann, 2021; National Research Council, 2006).

After at least three weeks exclusively on the diet (range 21 days – 31 days), the second consultation was conducted. Owners were instructed to ensure that their dogs had fasted for at least eight hours prior to the visit. This consultation, lasting one hour, was carried out exclusively by the same veterinarian (Vet 1) to ensure consistency. The examination followed a standardized protocol and included a comprehensive assessment of the dog's health. Measurements included body weight, recorded using a standardized scale (Precia Molen – Access, France, max 150 kg, accuracy 50 g); a 9-point BCS, with 1 extremely thin and 9 obese (Laflamme, 1997) and a 4-point muscle condition score (MCS) (WSAVA et al., 2011). The MCS was analyzed as a score of 1 indicating good muscle condition, 2 slight muscle loss, 3 moderate muscle loss, and 4 severe muscle loss. A detailed dermatological examination was also performed, using a published skin scoring system (Devriendt et al., 2021). For statistical analysis, individual scores for partial alopecia, glossiness, greasiness, softness, scaliness, and overall coat quality were combined into a composite “hair quality score.” This score was calculated out of 30 points (5 points per item), with higher scores indicating lower coat quality.
## 2.4. Sampling and analysis

At the start of the second consultation, blood samples were collected from the cephalic vein into both a 3 mL lithium heparin tube and a 3 mL EDTA tube. Blood from the heparinized tube was centrifuged (2000 RCF for 10 minutes) at room temperature (22°C) to isolate the plasma. Eighteen biochemical parameters were analyzed using the same automated chemistry analyzer (Ikems; MS Labos, Osny, France); albumin (ALB), total proteins (TP), alkaline phosphatase (ALP), gamma glutamyl transferase (GGT), alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), phosphates (PHOS), uric acid (UA), blood urea nitrogen (BUN), creatinine (CR), amylase (AMY), creatine kinase (CK), lactate dehydrogenase (LDH), total calcium (CA), glucose (GLU), total cholesterol (TC), and triglycerides (TG).

Plasmatic isoprostanes (8-isoprostane, 8-epi PGF2α) were measured using the ELISA method by Lara Spiral Laboratoires (Couternon, France). Plasmatic vitamin E (α-tocopherol) was determined by chromatography according to (Lyan et al., 2001) using HPLCapp (N,V,P).

For hematological analysis, EDTA tubes were kept at room temperature (22°C) on an agitator (Specie Mix, Drew Scientific Inc, Florida, United States) for 20 minutes and were gently inverted to ensure homogenization. Samples with visible or microscopic clots were excluded. Hematological measurements were performed within two hours of

sampling using the Sysmex XN-V (Sysmex Corporation, Kobe, Hyogo, Japan) analyzer with settings “dogs.” The parameters analyzed included red blood cell counts (RBC), hematocrit (HCT), hemoglobin (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), fluorescence platelet counts (PLT), reticulocyte count (RET), white blood cell count (WBC), neutrophils (NEUT), lymphocytes (LYMPH), monocytes (MONO), eosinophils (EO), and basophils (BASO) counts.

## 2.5. Statistical analysis

The statistical analysis was divided into two parts to answer the two objectives of this study (Fig. 1). The first focused on identifying epidemiological differences between young and senior dogs. The second examining age-related changes in clinical parameters, while accounting for potential confounding variables.

### 2.5.1. Exploration of epidemiological differences between young and senior dogs

To minimize bias, dogs owned by veterinary students were excluded from the epidemiological analysis. This decision was made because veterinary students owned 26 % of the young dogs but none of the senior

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Workflow of the statistical analysis designed to explore differences between young and senior dogs in this study.</figcaption></figure>
dogs

Considering the high number of epidemiological variables (23 categorical and 15 numerical), the exploration of association with the dog's life stage (young vs. senior) was conducted in two main steps: variable selection and modeling using binary logistic regression. All statistical analyses were performed using R (version 4.2.2) (R Core Team, 2021).

For variable selection, categorical variables were first converted into dummy variables using the FastDummies package (Kaplan, 2017). All the dataset was then transformed using a centered log-ratio (CLR) transformation. To identify the most relevant variables, a Partial Least Squares Discriminant Analysis (PLS-DA) was performed using the MixOmics package (Rohart et al., 2017), with the dog's life stage (young or senior) as the discriminant factor. The number of components in the PLS-DA was determined based on the minimum number of components required to achieve an area under the receiver operating characteristic curve (AUROC) greater than 0.9, ensuring outstanding discrimination between young and senior dogs (Mandrekar, 2010). Variable selection was based on Variable Importance in Projection (VIP) scores, which indicate the contribution of each variable to the model. Only variables with a VIP score > 1, indicating a contribution greater than the average to differentiation, were retained for the next step.

The selected variables were incorporated as explanatory variables into a full binary logistic regression model, with life stage (young = reference group) as the dependent variable. To address potential multicollinearity among the explanatory variables, Variance Inflation Factor (VIF) values were calculated. Variables were excluded iteratively until all VIF values were < 2, ensuring minimal multicollinearity. Following this, a stepwise selection procedure combining forward and backward approaches was applied on the model using Akaike Information Criterion (AIC) to identify the most parsimonious final model. VIF values were rechecked in the final model to confirm multicollinearity was adequately addressed. A Type III ANOVA was performed to obtain p-values in the final model. Statistical significance was defined as p < 0.05. Variables with p-values between 0.05 and 0.10 were interpreted as indicating a trend that may warrant further investigation.

### 2.5.2. Exploration of differences in clinical parameters between young and senior dogs

Dogs owned by veterinary students were included in this analysis. However, dogs that were apparently healthy but not classified as healthy based on their hematological and biochemical test results, following the criteria outlined by Schooley et al. (2024), were excluded.

For each parameter, distribution normality was assessed using the Shapiro-Wilk test. Variables with a normal distribution were compared between young and senior dogs using Student's t-tests. For variables that did not follow a normal distribution, Wilcoxon rank-sum tests were applied. To account for multiple comparisons, p-values were adjusted using the Benjamini-Hochberg correction. Statistical significance was defined as an adjusted p-value (="q-value") < 0.05.

In order to evaluate differences between young and senior dogs while considering relevant epidemiological parameters, linear regression models were applied to clinical parameters with q-values lower than 0.1, in order to minimize unnecessary multiple testing. Each model included life stage as primary explanatory variable, and epidemiological parameters identified in the first part of the analysis and "owner being a veterinary student" as co-variables.

## 3. Results

### 3.1. Study participation and follow-up

On a total of 155 submissions, 55 young dogs and 89 old dogs were selected to attend the first consultation. All young dogs were deemed eligible for the study, while 69 old dogs qualified (20 old dogs were excluded due to physical health issues).

After one month on the diet, 50 young dogs and 56 old dogs returned for follow-up consultations (respectively, 91 % and 63 % of study populations). The primary reasons for non-return included a lack of response from owners (n = 4 for young dogs, n = 8 for old dogs, representing 9.7 % of all owners), reluctance from owners to change their dog's food (n = 3 for old dogs), and intolerance to the new kibble (n = 1 for young dogs, n = 2 for old dogs, representing 2.5 % of all dogs). Among the returning participants, all owners declared that their dog had been exclusively eating the provided diet for at least three weeks.

### 3.2. Population description

The study population included young dogs (median age: 3 years, range 2–5) and senior dogs (median age: 9 years, range 8–14), with the same median weight for these two groups (29 kg, IQR 26–34). Females represented 52 % of the total population, and neutered dogs 75 %, these proportions did not vary according to life stage. Purebred dogs made up 56 % of the population, with the most represented breeds being Golden Retrievers (15 %), Australian Shepherds (14 %), and Labrador Retrievers (8.5 %). These breed distributions were consistent across both young and senior dogs (chi-square p-value > 0.9 for each breed).

Dog owners were predominantly women (72 %), with no variation between dogs' life stages. The age of senior dog owners was most frequently between 41 and 60 years (46 %), while young dog owners were most often aged 18–25 years (34 %). Among senior dogs, 29 % were "rarely" walked, compared to 0 % of young dogs. Outdoor access was reported for 95 % of senior dogs and 80 % of young dogs.

All the young dogs and 89 % of senior dogs received yearly veterinary visits. The main reasons for the last veterinary visit were similar between groups: vaccination (64 % of all dogs) and check-ups (8.6 %). Additional reasons in senior dogs included digestive problems (n = 4), injuries (n = 3), lameness, otitis, skin lumps, and other skin issues (n = 2 each), as well as abscesses, dentistry, and neutering (n = 1 each). For young dogs, additional reasons included injuries (n = 4), nutrition (n = 2), digestive problems, lameness, otitis, behavioral issues, and coughing (n = 1 each). Insurance was reported for 16 % of dogs, with 20 % in young dogs and 12 % in senior dogs. Preventive care measures included regular deworming (55 % of all dogs) and regular ectoparasite treatments (50 % of all dogs). Clinical abnormalities were identified in 20 % of the total population, with 34 % in senior dogs and 4 % in young dogs. The most common abnormality in senior dogs was skin lumps (n = 17), followed by skin erythema, alopecia, and polypnea (1 case each). In young dogs, skin erythema was the only abnormality, noted in 2 cases.

According to the criteria of Schooley et al. (2024), 4 senior dogs and 3 young dogs were classified as not clinically healthy and thus excluded for the exploration of clinical differences between young and senior dogs.

A detailed description of the study population is available in Additional File 1.

### 3.3. Epidemiological differences between young and senior dogs

The performance of the PLS-DA with three components was very good with an AUROC value of 0.91. Most contributing variables (VIP > 1), are presented in Fig. 2. The inclusion of the variables into the full binary logistic regression stopped at the "dwelling" variable as inclusion of the next one increased VIF values over 2.

So, 13 variables were initially included in the full logistic regression model, and after the stepwise backward and forward selection process, 6 variables remained (Table 1). Senior dogs were associated with lower activity score (OR: 0.28, p = 0.004), higher motivation at training score (OR: 1.08, p = 0.006), living in house (OR: 6.81, p = 0.009), regular deworming (OR: 6.43, p = 0.006), and buying food from pet stores (OR: 5.78, p = 0.020) and supermarkets (OR: 13.8, p = 0.016).
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Variables contributing most to the differentiation between young and senior dogs (VIP > 1) identified via PLS-DA, presented in decreasing order. In red variables associated with senior dogs and in blue variables associated with young dogs. LAPS = Lexington Attachment to Pet Scale. VIP = Variable Importance in Projection.</figcaption></figure>

<caption>**Table 1**</caption>

Results of the binomial logistic regression on dog life stage (reference = "young") following stepwise selection (n = 93).

<table><thead><tr><th>Variable</th><th>N</th><th>Odds Ratio</th><th>95 % CI</th><th>p-value<sup>a</sup></th></tr></thead><tbody><tr><td>Activity</td><td>93</td><td>0.28</td><td>[0.11,0.63]</td><td>0.004 *</td></tr><tr><td>Motivation at training score (dog)</td><td>93</td><td>1.08</td><td>[1.03, 1.15]</td><td>0.006 *</td></tr><tr><td>Dwelling</td><td></td><td></td><td></td><td></td></tr><tr><td>Flat</td><td>18</td><td>-</td><td>-</td><td></td></tr><tr><td>House</td><td>75</td><td>6.81</td><td>[1.73, 32.6]</td><td>0.009 *</td></tr><tr><td>Regular deworming</td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>47</td><td>-</td><td>-</td><td></td></tr><tr><td>Yes</td><td>46</td><td>6.43</td><td>[1.89, 27.1]</td><td>0.006 *</td></tr><tr><td>Regular ectoparasites treatment</td><td></td><td></td><td></td><td></td></tr><tr><td>No</td><td>52</td><td>-</td><td>-</td><td></td></tr><tr><td>Yes</td><td>41</td><td>0.42</td><td>[0.12, 1.39]</td><td>0.2</td></tr><tr><td>Place of purchase of the food<sup>b</sup></td><td></td><td></td><td></td><td></td></tr><tr><td>Veterinary clinic</td><td>24</td><td>-</td><td>-</td><td></td></tr><tr><td>Pet store</td><td>56</td><td>5.78</td><td>[1.41, 27.9]</td><td>0.020 *</td></tr><tr><td>Supermarket</td><td>13</td><td>13.8</td><td>[1.94, 151]</td><td>0.016 *</td></tr></tbody></table>

N: number of dogs; 95 %CI = 95 % binomial confidence intervals.

<sup>a</sup>Type III ANOVA p-values.

<sup>b</sup>Prior to the 1-month period on the study diet.

*Values < 0.05

### 3.4. Clinical differences between young and senior dogs

All clinical variables, except plasmatic globulin, were not normally distributed. Compared to young dogs, senior dogs exhibited significantly higher heart rate (q = 0.015), muscle condition score (q < 0.001), hair quality score (q < 0.001), plasmatic globulin (q < 0.001), and platelet count (q < 0.001). Conversely, senior dogs had significantly lower

plasmatic albumin (q = 0.034), albumin-to-globulin ratio (q < 0.001), AST (q = 0.009), phosphorus (q < 0.001), white blood cell count (q = 0.009), lymphocytes count (q < 0.001), monocytes count (q = 0.003), eosinophils count (q = 0.002), and basophils count (q < 0.001). Additionally, senior dogs demonstrated non-significant trends toward higher plasma total protein (q = 0.066), plasma triglycerides (q = 0.057), and isoprostanes (q = 0.060), as well as lower blood urea nitrogen (q = 0.060) and hematocrit (q = 0.069). Full details of the median values for each clinical parameter are provided in Table 2.

#### 3.4.1. Age-related changes in clinical parameters including confounding epidemiological variables

The effect of life stage considering preselected epidemiological parameters was evaluated on 18 clinical variables (q-value < 0.1): MCS, hair quality score, albumin, TP, globulin, A:G ratio, AST, PHOS, BUN, TG, isoprostanes, WBC, HCT, PLT, lymphocytes, monocytes, eosinophils, and basophils. The following epidemiological factors were retained as confounding variables in the regression models: activity, motivation at training score, dwelling, regular deworming, place of food purchase and owner being a veterinary student. Additionally, plasma triglycerides were included as a confounding variable for hair quality score, as plasma lipids have been shown to influence skin quality (Franco et al., 2021). Similarly, BCS was included as a confounder in the analysis of plasma triglycerides, given the established positive association between BCS and plasma triglycerides (Floerchinger et al., 2015).

Among the 14 clinical parameters identified as significantly different between young and senior dogs, 13 remained significantly associated with the dog's life stage after adjusting for confounding variables. Senior dogs showed significantly higher values for heart rate (β = 11, p < 0.029), MCS (β = 1.0, p < 0.001), hair quality score (β = 1.9, p = 0.029), plasma triglycerides (β = 18, p < 0.022), globulin (β = 0.36,
<table><caption>**Table 2**
Median values and interquartile range for each measured clinical parameter for young and senior dogs.</caption><thead><tr><th>Variable</th><th>Young, N = 47<sup>a</sup></th><th>Senior, N = 52<sup>a</sup></th><th>p-value<sup>b</sup></th><th>q-value<sup>c</sup></th></tr></thead><tbody><tr><td>Heart rate (bpm)</td><td>87 (80, 96)</td><td>98 (84, 112)</td><td>0.005 *</td><td>0.015 *</td></tr><tr><td>MCS</td><td>1 (1.00, 1.00)</td><td>2 (2.00, 3.00)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td>Hair quality score<sup>d</sup></td><td>7.0 (6.0, 10.0)</td><td>10.0 (8.0, 13.2)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td><em>Plasmatic biochemistry</em></td><td></td><td></td><td></td><td></td></tr><tr><td>Albumin (g/dL)</td><td>3.20 (3.00, 3.30)</td><td>3.00 (2.90, 3.20)</td><td>0.012 *</td><td>0.034 *</td></tr><tr><td>Total proteins (g/dL)</td><td>6.40 (6.10, 6.75)</td><td>6.70 (6.30, 6.90)</td><td>0.031 *</td><td>0.066</td></tr><tr><td>Globulin (g/dL)</td><td>3.30 (3.00, 3.50)</td><td>3.50 (3.40, 3.80)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td>Albumin:Globulin</td><td>1.00 (0.90, 1.00)</td><td>0.90 (0.80, 0.90)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td>ALP (U/L)</td><td>44 (36, 61)</td><td>48 (34, 68)</td><td>0.351</td><td>0.431</td></tr><tr><td>GGT (U/L)</td><td>7.00 (5.00, 9.00)</td><td>8.00 (6.75, 9.00)</td><td>0.095</td><td>0.152</td></tr><tr><td>ALT (U/L)</td><td>44 (38, 55)</td><td>49 (41, 67)</td><td>0.096</td><td>0.152</td></tr><tr><td>AST (U/L)</td><td>36 (31, 42)</td><td>32 (28, 36)</td><td>0.003 *</td><td>0.009 *</td></tr><tr><td>Total bilirubin (mg/dL)</td><td>0.20 (0.10, 0.20)</td><td>0.20 (0.20, 0.23)</td><td>0.087</td><td>0.152</td></tr><tr><td>Phosphorus (mg/dL)</td><td>5.36 (4.71, 5.64)</td><td>4.53 (3.96, 5.05)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td>Uric acid (mg/dL)</td><td>0.10 (0.00, 0.10)</td><td>0.10 (0.00, 0.10)</td><td>0.752</td><td>0.841</td></tr><tr><td>BUN (mg/dL)</td><td>14.3 (12.2, 17.0)</td><td>12.0 (10.5, 15.7)</td><td>0.027 *</td><td>0.060</td></tr><tr><td>Creatinine (mg/dL)</td><td>0.80 (0.70, 0.80)</td><td>0.70 (0.60, 0.80)</td><td>0.327</td><td>0.414</td></tr><tr><td>Amylase (U/L)</td><td>781 (644, 964)</td><td>835 (735, 1008)</td><td>0.224</td><td>0.304</td></tr><tr><td>Creatine kinase (U/L)</td><td>68 (58, 78)</td><td>65 (55, 82)</td><td>0.641</td><td>0.738</td></tr><tr><td>LDH (U/L)</td><td>47 (41, 56)</td><td>46 (38, 66)</td><td>0.933</td><td>0.950</td></tr><tr><td>Total calcium (mg/dL)</td><td>10.60 (10.40, 10.90)</td><td>10.60 (10.40, 10.80)</td><td>0.838</td><td>0.908</td></tr><tr><td>Glucose (mg/dL)</td><td>104 (98, 113)</td><td>104 (101, 110)</td><td>0.861</td><td>0.908</td></tr><tr><td>Total cholesterol (mg/dL)</td><td>178 (151, 201)</td><td>184 (155, 213)</td><td>0.301</td><td>0.394</td></tr><tr><td>Triglycerides (mg/dL)</td><td>65 (58, 73)</td><td>73 (58, 97)</td><td>0.023 *</td><td>0.057</td></tr><tr><td>Isoprostanes</td><td>25 (18, 38)</td><td>34 (23, 70)</td><td>0.025 *</td><td>0.060</td></tr><tr><td>Vitamin E (µg/mL)</td><td>21 (18, 23)</td><td>23 (20, 28)</td><td>0.096</td><td>0.152</td></tr><tr><td><em>Hematology</em></td><td></td><td></td><td></td><td></td></tr><tr><td>WBC (10<sup>3</sup>/uL)</td><td>8.53 (7.30, 10.28)</td><td>7.32 (6.69, 8.77)</td><td>0.003 *</td><td>0.009 *</td></tr><tr><td>RBC (10<sup>6</sup>/uL)</td><td>7.08 (6.68, 7.53)</td><td>6.81 (6.54, 7.37)</td><td>0.150</td><td>0.216</td></tr><tr><td>Hemoglobin (g/dL)</td><td>17.20 (16.15, 18.00)</td><td>16.50 (15.73, 17.83)</td><td>0.113</td><td>0.172</td></tr><tr><td>Hematocrite (%)</td><td>48.3 (46.3, 51.3)</td><td>46.5 (44.2, 49.1)</td><td>0.035 *</td><td>0.069</td></tr><tr><td>MCV (fL)</td><td>68.40 (66.70, 69.75)</td><td>67.45 (66.10, 68.93)</td><td>0.062</td><td>0.118</td></tr><tr><td>MCH (pg)</td><td>24.20 (23.40, 24.90)</td><td>24.00 (23.48, 25.00)</td><td>0.517</td><td>0.613</td></tr><tr><td>Platelets (10<sup>3</sup>/uL)</td><td>230 (188, 250)</td><td>285 (241, 346)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td>Reticulocytes (%)</td><td>0.49 (0.35, 0.77)</td><td>0.55 (0.43, 0.83)</td><td>0.154</td><td>0.216</td></tr><tr><td>Neutrophils (10<sup>3</sup>/uL)</td><td>4.68 (3.88, 5.70)</td><td>4.89 (3.94, 5.74)</td><td>0.950</td><td>0.950</td></tr><tr><td>Lymphocytes (10<sup>3</sup>/uL)</td><td>2.50 (2.24, 2.85)</td><td>1.86 (1.40, 2.23)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr><tr><td>Monocytes (10<sup>3</sup>/uL)</td><td>0.54 (0.43, 0.64)</td><td>0.41 (0.36, 0.52)</td><td>0.001 *</td><td>0.003 *</td></tr><tr><td>Eosinophils (10<sup>3</sup>/uL)</td><td>0.60 (0.41, 0.77)</td><td>0.41 (0.28, 0.56)</td><td>&lt; 0.001 *</td><td>0.002 *</td></tr><tr><td>Basophils (10<sup>3</sup>/uL)</td><td>0.020 (0.010, 0.030)</td><td>0.010 (0.010, 0.010)</td><td>&lt; 0.001 *</td><td>&lt; 0.001 *</td></tr></tbody></table>

N: number of dogs; MCS: muscle condition score; ALP: alkaline phosphatase; GGT: gamma-glutamyl transpeptidase; ALT: alanine aminotransferase; AST: aspartate aminotransferase; BUN: blood urea nitrogen; LDH: lactate dehydrogenase; WBC: white blood cells; RBC: red blood cells; MCV: mean corpuscular volume; MCH: mean corpuscular hemoglobin.

<sup>a</sup>Median (25 % quantile, 75 % quantile).

<sup>b</sup>Wilcoxon rank sum test, except for globulin, Students' t test.

<sup>c</sup>Adjusted p-value with Benjamini Hochberg correction.

<sup>d</sup>The score increases as the quality decreases

*Values < 0.05.

p < 0.001) and platelet count (β = 72, p < 0.001), and significantly lower values for albumin (β = -0.14, p = 0.026), A:G ratio (β = -0.13, p < 0.001), PHOS (β = -0.58, p = 0.007), AST (β = -5.5, p = 0.031), WBC (β = -1.1, p = 0.042), lymphocytes (β = -0.81, p < 0.001), monocytes (β = -0.11, p = 0.026), and basophils (β = -0.01, p < 0.001).

Some parameters showed non-significant trends toward association with life stage. Senior dogs tended to have higher TP (β = 0.22, p = 0.090), and lower hematocrit (β = -1.9, p = 0.065) and eosinophils (β = -0.14, p = 0.078). No significant association was found for isoprostanes. These results are presented in Table 3.

Some parameters were also associated with each other. Activity was positively associated with BUN (β = 1.3, p = 0.033). Plasma triglycerides were significantly associated with BCS (β = 9.7, p = 0.020) and tended to be associated with food purchased at a supermarket (β = 22, p = 0.055). Hair quality score was associated with plasma triglycerides (β = 0.02, p = 0.042). These results can be found in Table 4.

## 4. Discussion

This study aimed to explore differences between young and senior pet dogs consuming a standardized diet in several epidemiological and clinical parameters. Four epidemiological characteristics were found significantly different between young and senior dogs of our study population: senior dogs were less active, more frequently lived in houses, received more regular deworming treatments, and were more likely to consume diets purchased from pet stores, with an even stronger likelihood for diets purchased from supermarkets. In contrast, younger dogs were more likely to consume diets purchased from veterinary clinics.

Here, senior dogs were less active than younger dogs, consistent with previous research (Lee et al., 2022). Several factors may contribute to this decline. While osteoarthritis is a common cause of reduced activity in aging dogs (Anderson et al., 2018; Runge et al., 2010; Smith et al., 2001), the dogs in this study were confirmed to be healthy, meaning no clinical sign of osteoarthritis was detected. However, chronic subclinical pain, which may not be easily diagnosed by owners or veterinarians, could still play a role in reduced activity levels. Additionally, behavioral
<caption>**Table 3**</caption>

Multivariable linear regression results for variables associated with dog life stage, with young dogs as the reference.

<table><thead><tr><th>Dependent variable</th><th>Beta coefficient for life stage</th><th>95 % CI</th><th>p-value<sup>a</sup></th></tr></thead><tbody><tr><td colspan="4"><em>Significant associations</em></td></tr><tr><td>Heart rate</td><td>11</td><td>[1.1, 20]</td><td>0.029 *</td></tr><tr><td>MCS</td><td>1.0</td><td>[0.72, 1.3]</td><td>&lt; 0.001 *</td></tr><tr><td>Hair quality score<sup>b</sup></td><td>1.9</td><td>[0.20, 3.6]</td><td>0.029 *</td></tr><tr><td>Albumin</td><td>-0.14</td><td>[-0.27, -0.02]</td><td>0.026 *</td></tr><tr><td>Globulin</td><td>0.36</td><td>[0.17, 0.55]</td><td>&lt; 0.001 *</td></tr><tr><td>Albumin:Globulin</td><td>-0.13</td><td>[-0.19, -0.07]</td><td>&lt; 0.001 *</td></tr><tr><td>AST</td><td>-5.5</td><td>[-10, -0.52]</td><td>0.031 *</td></tr><tr><td>Phosphorus</td><td>-0.58</td><td>[-1.0, -0.16]</td><td>0.007 *</td></tr><tr><td>Triglycerides</td><td>18</td><td>[2.7, 34]</td><td>0.022</td></tr><tr><td>WBC</td><td>-1.1</td><td>[-2.1, -0.04]</td><td>0.042 *</td></tr><tr><td>Platelets</td><td>72</td><td>[38,106]</td><td>&lt; 0.001 *</td></tr><tr><td>Lymphocytes</td><td>-0.81</td><td>[-1.1, -0.48]</td><td>&lt; 0.001 *</td></tr><tr><td>Monocytes</td><td>-0.11</td><td>[-0.20, -0.01]</td><td>0.026 *</td></tr><tr><td>Basophils</td><td>-0.01</td><td>[-0.02, -0.01]</td><td>&lt; 0.001 *</td></tr><tr><td colspan="4"><em>Trends toward significance</em></td></tr><tr><td>Total proteins</td><td>0.22</td><td>[-0.03, 0.47]</td><td>0.090</td></tr><tr><td>Hematocrit</td><td>-1.9</td><td>[-3.9, 0.12]</td><td>0.065</td></tr><tr><td>Eosinophils</td><td>-0.14</td><td>[-0.29, 0.02]</td><td>0.078</td></tr></tbody></table>

CI: Confidence interval; MCS: Muscle condition score; AST: Aspartate aminotransferase; WBC: White blood cells

<sup>a</sup>Type III ANOVA p-values.

<sup>b</sup>The score increases as the quality decreases

* Value < 0.05.

<caption>**Table 4**</caption>

Associations between clinical parameters and other parameters than age.

<table><thead><tr><th>Dependent variable</th><th>Explicative factor</th><th>Beta coefficient</th><th>95 % CI</th><th>p-value<sup>a</sup></th></tr></thead><tbody><tr><td colspan="5"><em>Significant associations</em></td></tr><tr><td>BUN</td><td>Activity</td><td>1.3</td><td>[0.11, 2.4]</td><td>0.033 *</td></tr><tr><td>Triglycerides</td><td>BCS</td><td>9.7</td><td>[1.5, 18]</td><td>0.020 *</td></tr><tr><td>Hair quality score</td><td>Triglycerides</td><td>0.02</td><td>[0.00, 0.05]</td><td>0.042 *</td></tr><tr><td colspan="5"><em>Trends toward significance</em></td></tr><tr><td>Triglycerides</td><td>Food purchased at supermarket<sup>b</sup></td><td>22</td><td>[-0.51, 45]</td><td>0.055</td></tr></tbody></table>

CI: Confidence interval; BUN: Blood urea nitrogen.

<sup>a</sup>Type III ANOVA p-values.

<sup>b</sup>Prior to the 1-month period on the study diet.

* Value < 0.05.

changes may play a role, as older dogs tend to be less active in familiar environments compared to younger dogs (Siwak et al., 2002). This is particularly relevant as owners typically assess their dogs' activity levels within the context of their home environment, which is familiar to the dog. Such behavioral shifts may be linked to age-related changes in the dopamine system, which regulates motivation for locomotion (Sallis, 2000). Housing type may also play a role, as senior dogs were more likely to live in houses, while younger dogs were often in flats, where owners may feel a greater need to ensure regular exercise (Marinelli et al., 2007; Wallis et al., 2018). It is also important to acknowledge that owners may perceive older dogs as less active simply due to their age, rather than actual activity levels. Similarly, the measurement of dog activity relied on subjective, owner-reported questionnaires, which could have been influenced by the owners' perceptions and even their own activity levels, potentially introducing bias (Lee et al., 2022). Maintaining physical activity in senior dogs is crucial, as it supports cognitive function (Bray et al., 2022) and combats frailty, which is linked to increased comorbidities and reduced healthspan (Gonçalves et al., 2022; Hua et al., 2016), while promoting better overall health (McCoy et al., 2023).

Senior dogs in this study were more regularly dewormed than young

dogs, a finding that was unexpected given that previous research has shown senior dogs often receive less veterinary care from their owners compared to younger dogs (Marinelli et al., 2007). However, this higher rate of regular deworming in senior dogs is a positive observation, as a prior study demonstrated that regular deworming is associated with greater robustness in senior dogs (Blanchard et al., 2024a).

Senior dogs were also more likely to be fed food purchased from pet stores and supermarkets compared to dogs aged 2–5 years. This may reflect differences in habits between long-term dog owners and newer ones, who could be more influenced by recent marketing and nutritional communications. In France, a shift has been observed in cat food purchasing, with a decline in supermarket sales and an increase in purchases from veterinary clinics (Blanchard et al., 2025; Colliard et al., 2009). Although comparable data for dogs are unavailable, a similar trend is plausible, particularly among new dog owners, as long-term owners may be less inclined to alter their established purchasing habits. The quality of a senior dog's diet plays a pivotal role in maintaining their overall health and mitigating age-related metabolic changes (Churchill and Eirmann, 2021; Laflamme, 2012). A table comparing some characteristics of the diets previously eaten by the dogs according to the place of purchase is available in Additional File 2. While all dog diets in France must adhere to FEDIAF guidelines, which ensure that analytical constituents meet specific standards, these guidelines do not regulate ingredient quality. Furthermore, no specific guidelines exist for omega-3 fatty acids in adult dogs.

Interestingly, this study revealed that dogs previously fed supermarket-purchased food tended to exhibit higher plasma triglycerides, even after transitioning to a premium diet for four weeks. In fact, when the variable "place of purchase of food" is replaced with "clear indication of a source of omega-3 fatty acids in the previous diet," plasma triglycerides remain significantly associated with age and BCS, and are also significantly associated with the absence of omega-3 in the previous diet (β = 17, p = 0.045). These findings underscore the lasting impact of diet on canine health. Elevated triglycerides have been associated with increased circulating insulin and fructosamine, potentially indicating early-phase glucose intolerance (Gomez-Fernandez-Blanco et al., 2024). This is particularly concerning, as aging in dogs is already linked to increased insulin resistance, glucose intolerance, and a higher risk of diabetes mellitus (Catchpole et al., 2005). A diet with no clear indication of a source of omega-3 fatty acids in its ingredients may further exacerbate these risks.

Moreover, senior dogs exhibited poorer hair quality, potentially indicating low quality diet (Connolly and Wu, 2024; Hua et al., 2016). This was supported by its association with elevated triglycerides, which were linked to previous diets without a clear indication of a source of omega-3 fatty acids. Poor coat quality may also reflect reduced owner care, such as less frequent grooming. Improving coat and skin health in senior dogs requires nutritional optimization and better owner education on grooming and care. These findings highlight the critical need for improved owner education about the importance of high-quality nutrition, particularly for aging dogs, to support healthier aging and reduce the risk of metabolic complications associated with poor dietary habits.

Compared to young dogs, senior dogs showed lower muscle condition, consistent with previous findings (Freeman et al., 2018; Hutchinson et al., 2012). While reduced activity may partly explain the loss of lean body mass (LBM) (Harper, 1998), MCS in this study was not significantly associated with activity scores, aligning with prior research (Hutchinson et al., 2012). In humans, age-related LBM loss is linked to chronic inflammation, reduced hormone levels (growth hormone, testosterone, IGF-1), motor-unit remodeling, and decreased protein synthesis (Hutchinson et al., 2012), mechanisms that may similarly affect dogs. LBM loss is a hallmark of sarcopenia, the age-related decline in muscle mass and function, which increases the risk of weakness, immobility, and injury in elderly individuals (Larsson et al., 2019). In dogs, sarcopenia could similarly reduce quality of life and increase injury risk emphasizing the importance of routine muscle condition
scoring in senior dogs by veterinarians. While MCS and skin scoring relied on subjective assessments, these evaluations were conducted by the same trained veterinarian. Even mild muscle loss can be easily identified by experienced clinicians, and our findings of reduced muscle mass in senior dogs are consistent with prior studies using ultrasonography and CT scans to assess changes in epaxial muscles in older dogs (Hutchinson et al., 2012).

Several blood parameters were impacted by age category in our study. In line with previous studies, senior dogs exhibited an increase in globulins and a decrease in albumin compared to younger dogs (Alilovic et al., 2022; Chang et al., 2016; Lowseth et al., 1990; Radakovich et al., 2017; Strasser et al., 1993), a pattern consistent with chronic inflammation (Radakovich et al., 2017). This inflammatory profile aligns with the concept of “inflammating,” a state of low-grade, chronic, systemic inflammation that develops with aging in the absence of infection, driven by accumulated cellular damage and the upregulation of pro-inflammatory cytokines (Jiménez, 2023). The observed increase in platelet count in senior dogs may indicate reactive thrombocytosis secondary to inflammation (Radakovich et al., 2017). Additionally, the higher heart rate observed in senior dogs, corroborated by a previous study (Hezzell et al., 2013), has been associated to subclinical inflammation in aging humans (Sajadieh et al., 2004), further supporting the inflammatiging hypothesis. The decrease in plasmatic albumin observed in senior dogs may also be attributed to reduced hepatic synthesis, as well as subclinical renal and intestinal losses (Chang et al., 2016). Additionally, the increase in globulin could act as a compensatory mechanism to maintain osmotic pressure in response to the decline in plasmatic albumin (Lowseth et al., 1990). In parallel, senior dogs showed a decrease in lymphocyte counts compared to younger dogs, in line with previous studies (Alilovic et al., 2022; Radakovich et al., 2017; Strasser et al., 1993), a hallmark of immunosenescence (Radakovich et al., 2017). Immunosenescence refers to the age-related decline in immune system function, which reduces the host's ability to mount effective defenses against pathogens (Aw et al., 2007). This decline in lymphocytes is primarily attributed to the loss of CD4⁺T cells with age (Blount et al., 2005) and may be linked to the involution of the red bone marrow (Strasser et al., 1993). Both inflammatiging and immunosenescence are recognized as key contributors to age-related diseases (Santoro et al., 2021). Prebiotics and yeast derivatives have been shown to counteract immunosenescence in healthy senior dogs (Wambacq et al., 2024), while anti-inflammatory dietary ingredients can attenuate markers of chronic low-grade inflammation associated with aging (Panickar and Jewell, 2015). Such ingredients are typically found in higher-quality diets, highlighting the critical role of nutrition in promoting healthier aging in senior dogs.

Senior dogs exhibited lower AST compared to younger dogs. Although this difference was statistically significant, its clinical relevance appears minimal, with median values of 36 U/L (IQR: 31–42) in young dogs and 32 U/L (IQR: 28–36) in senior dogs, both well within the reference range of 10–50 U/L. Nevertheless, this finding aligns with a previous study (Connolly et al., 2020) and may be attributed to age-related muscle mass loss (Kaspar and Norris, 1977), which was notably more prevalent among the senior dogs in our cohort. However, this relationship could not be directly confirmed in our data, as none of the young dogs in the study exhibited a muscle loss classified as moderate or severe.

We observed lower phosphorus in senior dogs compared to younger dogs, while plasma total calcium remained consistent across age groups. A reduction in circulating phosphorus with age has only been reported when comparing puppies to senior dogs, likely due to the increased bone metabolism in growing animals (Alilovic et al., 2022; Chang et al., 2016; Connolly et al., 2020; Vajdovich et al., 1997). Previous comparisons between adult and senior dogs, however, have not shown similar reductions in phosphorus (Alilovic et al., 2022). In humans, circulating phosphorus tend to decrease with age after 60 years in both men and women (Fujisawa et al., 1984; Kelly et al., 1979). This age-related

decline in phosphorus might be explained by renal parenchymal changes that occur with aging, potentially leading to a decrease in renal tubular phosphate reabsorption (Kelly et al., 1979; Yoo et al., 2016). Additionally, increased parathyroid hormone activity with age (Insogna et al., 1981) has been linked to lower circulating phosphorus, stable total calcium, and higher ionized calcium (Wiske et al., 1979). Unfortunately, ionized calcium was not measured in the current study, which limits the exploration of this mechanism in our findings.

Previous studies on the relationship between age and BUN have reported conflicting results, with some showing an increase (Kusaba et al., 2024; Radakovich et al., 2017), others no change (Lee et al., 2020; Vikartovska et al., 2020), and still others a decrease (Lowseth et al., 1990; Strasser et al., 1993) with age. In the present study, we found that, after controlling for confounding variables, BUN was positively associated with activity scores, but not with the dog's life stage. The variability in findings reported in the literature may stem from a failure to account for such epidemiological factors. BUN is produced from ammonia via the urea cycle, with ammonia originating from dietary amino acids, glutamine catabolism by enterocytes, or the breakdown of peripheral tissues like skeletal muscle, a process intensified by exercise (Dimski, 1994; Wakshlag et al., 2002). This mechanism may explain the positive association between higher activity levels and increased BUN.

This study has several limitations that should be considered when interpreting the results. One limitation is that the study took place in a Veterinary Teaching Hospital. Dogs owned by veterinary students, who primarily had young dogs, were excluded from the epidemiological analysis to avoid bias related to their specific care and knowledge of veterinary practices. Since the study relied on voluntary participation, the sample may not fully represent the general population. However, this group likely reflects owners more invested in their dogs' health, making the findings particularly relevant to this demographic. While the study standardized the dogs' diet for four weeks before data collection, the observed impact of previous diet on plasma triglycerides suggests that the washout period may not have been sufficient to entirely eliminate the long-term effects of prior diets, particularly on circulating levels of lipophilic molecules. However, previous diet was incorporated as confounding variable in statistical analysis and this finding permitted to highlight the lasting influence of diet on health markers, reinforcing the importance of long-term nutritional choices for canine health. This study focused on dogs weighing more than 20 kg, meaning the findings cannot be directly extrapolated to the entire dog population, particularly smaller breeds. However, this specific focus provides valuable insights into the aging of large-breed dogs and sets the groundwork for future research that could extend these findings to smaller breeds.

Despite these limitations, the study highlights important associations between age, diet, and key health parameters in dogs, emphasizing the critical role of dietary and lifestyle management for promoting healthy aging. Future research could incorporate more objective measures of activity, such as pedometers (Warren et al., 2011), and recruit a broader range of dog sizes and breeds. Longitudinal studies spanning longer durations could provide further insights into the lasting impacts of diet and lifestyle on canine health and the aging process.

## 5. Conclusion

This study reveals key epidemiological and clinical differences between young and senior dogs. These findings will provide veterinary practitioners with clinically relevant data to better anticipate physiological changes associated with aging, distinguish these from pathological conditions, and deliver data-driven recommendations to pet owners, ultimately enhancing the quality of life for senior dogs. Moreover, the long-lasting impact of diet, particularly the inclusion of omega-3 fatty acids, highlights the importance of nutrition in managing aging-related changes.
## Ethics statement

This study has received approval from the Animal Ethical Committee "SCIENCE ET SANTE ANIMALES CEEA N°115" (ANIMAL SCIENCE AND HEALTH CEEA N°115) in Toulouse, National Veterinary School of Toulouse, France, under the reference number SSA 2022.014. During the study, AMe and NP were members of this committee but the conflict of interest was properly declared. This study also received approval from the Human Research Ethical Committee "Comité d'éthique et de la recherche - CER" (Ethics and Research Committee - CER) in Toulouse, Toulouse Midi Pyrénées Federal University, France, under the reference number 2023.719. The authors of the study do not have any link with this committee. Informed consent was obtained from all the dog owners.

## Funding sources

This study was partially funded by Lallemand SAS (Blagnac, France) and supported by Melet Schloesing Laboratories Inc (Osny, France), which provided all the resources needed for biochemistry measurements. The food was generously provided by the PROPLAN France team, which had no involvement in the conceptualization or interpretation of the data for this study.

## CRediT authorship contribution statement

**Boulet Fleur:** Investigation, Data curation. **Mugnier Amélie:** Validation, Resources, Conceptualization. **Blanchard Tiphaine:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Priymenko Nathalie:** Supervision, Methodology, Conceptualization. **Meynadier Annabelle:** Supervision, Methodology, Conceptualization.

## Declaration of Competing Interest

TB and AMu were employed by Lallemand SAS and participated in the analyses of the data, in the methodology and in the reviewing of the paper. The commercial affiliation did not interfere with the full and objective presentation of the results of this work. The authors declare that the research was conducted without any commercial or financial relationships that could be perceived as potential conflicts of interest.

## Acknowledgements

The authors sincerely thank all the dog owners who generously brought their pets, making the completion of this study possible. The authors also extend their gratitude to the PROPLAN France team for generously providing the food (Proplan All Sizes Light) free of charge for this study. The authors also gratefully thank the Comparative Medical Biology and Histology team of CREFRE, Université de Toulouse, Inserm, UPS, ENVT, Toulouse, France and acknowledge the financial support of Melet Schloesing Laboratories Inc (Osny, France).

## Additional files

Additional File 1: Full description of the studied dog population.

Additional File 2: Characteristics of the diets previously eaten by the dogs, according to their place of purchase.

## Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.prevetmed.2025.106537.

## Data availability

The datasets used and analysed during the current study are

available from the corresponding author on reasonable request.

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