The protocols employed for supplementation with collagen peptides and vitamin C (PolyPet) in this study were efficient in determining the changes generated in the urine of canines with a standardized diet and consistent environmental management [19]. The distribution of this research was similar to other studies, such as those conducted by Santos et al, recording data such as breed, sex, age [20], and body weight of each animal [21]. Pathological processes or induced changes (sexual alteration, neutering, or ovariohysterectomy) that could affect the results were ruled out through comprehensive medical examination. Additionally, an assessment of urinary pathways was conducted through ultrasonography, which provided support for cystocentesis. This ultrasound process enables precise characterization of urinary tract disorders with a success rate of 95.4% [22].
The importance of urine analysis in canines in veterinary clinical practice is second only to findings from blood chemistry and a complete blood count [13]. Thus, the product of urinary system function directly reflects the increase or decrease of substances that may arise due to the use of nutraceuticals, which, in animals, aim to reduce the degree of urine oversaturation and thereby lessen the predisposition to accumulate harmful substances in the body [23].
A trend was observed across the three studied groups, wherein negative results were evident in relation to protein detection in the urine. This might suggest that the study population did not exhibit elevated protein excretion through urine, even with the supplementation of collagen peptides and vitamin C (PolyPet). For positive values of 1+, 2+, and 3 + based on studies related to proteinuria in healthy dogs, factors like stress during sample collection, diet, physical activity, and hydration should be considered [24]. It is relevant to note that none of the investigated dogs displayed clinical signs indicative of renal disease, as noted by Tvedten et al., which should be taken into consideration when defining inclusion criteria for classifying dogs as healthy but with apparent proteinuria [25].
Regarding the decrease in urinary protein in the supplemented canine group, the results show similarity with findings from other studies that have explored the effects of nutraceutical supplementation on renal and urinary function [26]. Likewise, some research addresses renal glomerular hyperfiltration caused by high-protein diets as a normal adaptive physiological response, while others indicate the possibility of an increased risk of developing renal conditions [27]. Broader and controlled research is needed to precisely determine the impact of these substances on urine protein levels [28].
The urine protein-to-creatinine ratio in dogs allows for an evaluation of health and the early detection of potential renal conditions, such as the presence of proteinuria [29]. In this context, it is crucial to consider patient staging based on the UP/UC ratio to clearly distinguish the contribution of proteinuria from other components related to renal function. The results highlighted that groups receiving supplementation with collagen peptides and vitamin C (PolyPet®) experienced an increase in the UP/UC ratio compared to the control group. This finding reinforces the significance of the protein-to-creatinine ratio as a sensitive indicator of changes in renal function in response to supplementation with diets rich in animal-origin protein and determines the effectiveness of sample processing and analysis [13, 30].
No significant differences were found in the concentration of crystals in the urine of supplemented canines compared to the control group. This finding contrasts with research results supporting the notion that supplementation may play a role in urinary stone prevention [11]. However, it's important to consider that other dietary and environmental factors might have influenced these results, as well as the duration of supplementation [31].
The observation of a higher presence of amorphous urate crystals 1 + in the analyzed samples, especially in group 2 and to a lesser extent in the control group, highlights a potential relationship between the intake of collagen peptides and vitamin C (PolyPet®) and the formation of these crystals in the urine. This is reminiscent of previous studies that have indicated the influence of diet on urinary crystal composition, as reported by Lulich et al, who found a link between protein intake and the formation of amorphous urate crystals [32].
The presence of triple phosphate (struvite) crystals in canine urine is directly related to alkaline urinary pH according to Okafor et al, a situation congruent with the observed pH values in the study canines [33]. These crystals, mostly composed of ammonium and magnesium phosphate, have a characteristic crystalline structure and can develop in urine under favorable conditions, including bladder infections and high mineral concentration. Moreover, the presence of these crystals can be observed in canines that are in good health [33].
The weight of the canines included in the study decreased over the follow-up period; therefore, it was affected by the supplementation with collagen peptides and vitamin C (PolyPet®). This indicates a favorable reduction for the variable, as different studies indicate that peptides promote cholesterol reduction, in addition to having anti-inflammatory effects in chronic diseases, immunomodulatory effects, control of oxidative stress, being antioxidants, antihypertensive, antidiabetic, and anticancer agents [3, 7, 34, 35]. It is emphasized that proper nutritional management of a pet is a central component in current medical care, being an integral part of the longevity and quality of life of each individual, promoting the prevention of diseases such as chronic kidney disease, diabetes mellitus, and osteoarthritis [36].
The pH values found in this study were contrary to expectations and what has been reported by other authors like Beerepoot and Geerlings, who indicate that orally supplemented ascorbic acid has a very mild acidifying effect on urine pH. It's worth noting that ascorbic acid has promising health effects, as it acts as an antioxidant, prevents DNA damage [37], and destroys cancer cells, reducing the risk of metastasis [9]. These qualities complement the positive effects of peptides, including their cancer-preventive properties, reduction of metastasis, antioxidant properties, and reduction of the effects of chemotherapy treatments [3, 7]. However, the present study indicates that peptides can lead to urine alkalization over extended treatment periods.
Regarding specific gravity, differences were observed over the follow-up days, which decreased over time [12]. However, compared to the normal ranges reported by Sharma et al, and Yadav et al (2020), the changes in specific gravity in the different groups of the current study apparently do not indicate a positive or negative impact on the renal filtration rate induced by the supplementation of collagen peptides and vitamin C (PolyPet®), considering that specific gravity highlights the valuable kidney capacity to concentrate and dilute urine [12, 38].
Considering that urinary calcium levels can be directly or indirectly affected by its supply in the diet or dietary supplements, it will be related to the metabolism of vitamin C, which, together with glycine, will result in the presence of oxalates, concentrations that can directly affect urinary calcium levels, predisposing to the formation of mineral uroliths or not [39]. However, for the current study, the levels of ascorbic acid supplied in the supplement apparently are not sufficient to stimulate crystal formation. Therefore, it would be pertinent to conduct studies with a longer duration [40].
The present study recommends that future researchers extend the duration of supplementation and measurement of creatinuria or advise clinical veterinarians who have patients supplemented with nutraceuticals to keep a close watch on the chemical levels in urine. Since canines are carnivores and receive protein supply along with ascorbic acid supplementation [20], this could lead to an increase in creatinuria due to normal metabolism, muscle wear and tear, or repair, eventually leading to a slow presentation of acute or chronic renal failure in individuals. This makes frequent urine chemical analysis very useful in both healthy and sick dogs [38].
Supplementation with collagen peptides and vitamin C (PolyPet®) generated significant changes in the amount of urate crystals in urine and in the weight reduction of supplemented patients. This supplement is considered safe for healthy canines. However, it is advisable to take into account the need to monitor renal function in patients with a history of urinary disease who may be more susceptible to diets with high protein and ascorbic acid content.