Comparative study of the digestibility of dry and raw food in dogs

The present study aims to determine the digestibility of raw and dry food in pitbull dogs.The study involved 10 clinically healthy male dogs, matched in age and weight.Two digestibility experiments were performed, the first of which tested the digestibility of dry food, and the second experiment, the digestibility of raw food, which underwent HPP processing.To determine the digestibility coefficients of the two types of food during the experiments, the amount of food and excreted feces were daily controlled.We found significant differences in the chemical composition of the two types of food, as well as a higher digestibility coefficient of raw food.

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Introduction

Food digestibility indicated the amount of nutrients that are available to the dog for absorption from the intestine into the bloodstream. Foods with better digestibility provided more absorbed nutrients than those with less digestibility. For this reason, digestibility was a criterion for the nutritional value and quality of food (Cargo-Froom et al. 2019) [5] . According to Khan et. al (2003) [16] the digestibility of food could be influenced by various factors, such as the type of food consumed, the composition, and the amount of different raw materials. Heat treatment was one of the factors that negatively affect digestibility. The low digestibility of dry extruded foods was one of the reasons why proponents of raw food eating in dogs recommend the raw foods because of their better digestibility (Freeman et al. 2013) [10] . A number of studies with carnivores had supported the claim of higher digestibility in raw foods (Kerr et al., 2013; Hamper et al., 2015; Iske et al., 2016) [14,11,13] . Other authors found low digestibility of dry foods of low price range compared to high class (Huber et al. 1986) [12] . According to Brambillasca et al. (2010) [3] the type of food consumed also determined the consistency of the excreted feces. Their results showed that the frequency of feeding did not affect the digestibility of nutrients, as well as the composition of the excreted feces. However, the quality of food had a beneficial effect on digestibility and the amount of feces excreted. The authors observed, the higher the quality of the food, the better the digestibility and the less the amount of feces. The digestibility and consistency of the excrements could be affected by the amount of fiber in the diet. Some authors have found an inverse proportionality between the amount of fiber and digestibility, namely with an increasing amount of fiber there was a decrease in digestibility. (Earle at al. 1998, Castrillo et al. 2001) [8,7] . Swanson et al. (2004) [19] investigated the relationship between digestibility and the type of raw materials. Foods with predominant raw materials of animal origin showed much better digestibility compared to those in which the amount of plant raw materials was higher. Also, dogs fed foods rich in animal raw materials showed better absorption of fats and proteins and excrete fewer feces compared to those fed foods produced mainly from plant products. The literature showed that animals fed raw foods usually excreted less feces than those that eat extruded foods (Kerr et al., 2012) [15] . The aim of present study was to compare dry extruded and raw food underwent HPP processing, in regard to their digestibility.

Material and Methods

For this purpose, we used 10 pitbull dogs that had completed their growth. The animals were matched by age, 3.5 ± 0.5 years, and body weight 21.04 ± 1.39 kg. All of them were regularly vaccinated and dewormed for internal and external parasites, but nevertheless, the feces of each of them were examined by the Füleborn method for the presence of nematodes and cestodes. At the beginning of the study, the health status of all dogs was determined by the methods of propaedeutics, and it was established that they were clinically healthy. During the experiments, the dogs were placed in individual cages, fed alone twice daily, and water was provided ad libitum. We performed the technical manipulations (clinical examinations) in accordance with the good clinical practice and in accordance with Ordinance № 20 of 01.11.2012 on the minimum requirements for protection and welfare of experimental animals and the requirements for the sites for their use, breeding and/or delivery [18] . Two in vivo digestibility experiments were performed. The first with dry extruded food low price range and the second experiment with raw food underwent HPP processing based on chicken meat, using only raw materials suitable for human consumption. The second experiment was conducted in two stages after the start of the fed raw food diet, on the 15th day and the 45th day, respectively. Food processing was performed with "AVURE AV-20M high pressure processing equipment" for microbiological reduction of food, with the following parameters cycle time for 3 minutes and a pressure of 6000 bar. Throughout the experiment, the raw food was stored from 0 to 4 0 C. The amount of dried food consumed was determined according to the recommended data for maintaining live weight, indicated on the label by the manufacturer. And this of raw food was determined based on the energy contained in 0.1 kg of food and the exchange weight of animals, using the formulas: MЕ=460 х W 0,75 MJ/day (Burger 1994) [4] where ME is metabolic energy, W is weight for one dog, and W 0,75 is an exchange weight. Х=ОЕн/ОЕх (Тodorov et al. 2010) [20] where Хthe amount of food in kg ОЕнthe energy needs of the animal in MJ OExthe energy value of food in MJ / kg Fecal samples were collected each day individually from each dog's cage. Gloves and hermetically sealed plastic bags were used for this purpose. After collection, the feces were weighed and the amount recorded in an individual diary for each of the dogs. An average sample of the total amount of faeces was formed, and the chemical analysis of the faeces was performed according to BDS -11374-86 [2] . The digestibility coefficient of food was determined by the difference between the ingested amount of food and the excreted feces, according to the formula (Khan et al. 2003) [16]

Statistical analysis

The data were analyzed using Microsoft Excel for Windows. Confidence between groups was calculated by Student t-test at P < 0.05.

Results and Discussion

The chemical composition of the dry and raw dog food used in the experiment was presented in Table 1. The analytical constituents of the dry extruded food were from the information provided on the label by the manufacturer. The raw food data were based on laboratory chemical analysis for 0.1 kg. food, after that they were recalculated to the dry matter. The table 1. showed that there were differences in the values of quality indicators of the two types of food. The visible difference was in the percentage of dry matter, which was determined by the amount of moisture depending on the technology used. Moisture in most brands of dry extruded foods varied between 6% and 10% (Case et al. 2011; FEDIAF. 2018) [6,9] . Significant differences were also observed in protein and fat content, which could be explained by the fact that the composition of dry foods usually includes a significant amount of cereals, low in protein (Moss, 1996) [17] , and the opposite in raw foods we had a high meat and meat products rich in protein and fat (Freeman et al. 2013) [10] . The values of fiber and ash were similar for both types of food. Table 2 presented the chemical composition of the studied pooled fecal samples of dogs fed dry and raw food. The data showed low levels of dry matter in the faeces of dogs fed dry food. The indicators of protein and fibre in the dry matter of the feces of dogs fed dry extruded food were higher than those fed raw food. These results could once again be explained by the fact that in dry extruded foods, the source of protein was largely of plant origin, which had lower digestibility than the animal protein ( Swanson et al. 2004) [19] . The large amount of raw materials of plant origin could be the reason for lower values of ash and higher content of fibre in the feces of dogs fed dry food.

Type of sample	Dry matter, %	Protein, %	Fats, %	Fibre, %	Ash, %	Са, %	Р, %
Feces of dogs fed raw food	48,43±0.16	19,61 ± 0.23	3,26 ± 0.09	7,23 ± 0.03	41,62 ± 0.01	8.76 ± 0.11	3.77 ± 0.03
Feces of dogs fed dry food	38.96±0.11	27,14 ± 0.35	1,63 ± 0.01	9,01 ± 0.15	31.99 ± 0.51	9.72 ± 0.01	4.53 ± 0.07

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Chemical composition of feces (% in dry matter)

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Chemical composition of dry and raw food converted to

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The food intake and amount of feces were presented in Table 3. On the basis of data, the coefficients of digestibility in absolute values of dry food and raw food were calculated. The obtained results showed that the intake of dry matter (DM) in dry food was 270 grams, and that of raw food -152.05 grams. Regardless of the different amounts of DM, it was seen that the coefficients of digestibility were higher in raw food and on the 15th and 45th day of feeding. We found significant differences in the amount of feces, as on day 15 of the intake of raw food we had a statistically significant difference in the weight of feces, as their amount begins to decrease. This trend is maintained on day 45 of the diet, as we observed almost 6 times less feces excreted compared to day 0 (from 128.7 ± 27.42 to 21.45 ± 5.84). Smaller amounts of excreted feces in animals fed raw food were reported by other authors too (Kerr et al., 2012) [15] . Our results showed significantly higher digestibility of raw food (over 90%), both on day 15 and 45. The coefficient of digestibility of dry food was 57.11 ± 9.14%, and of raw food on day 45 was 95.71 ± 1.16%, which was increased by 67.58%. Our results were analogous to those of Huber et al.

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Food intake, fecal output and coefficient of digestibility of

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(1986) [12] and Algya et al. (2018) [1] , which also established better digestibility in raw foods.

Conclusion

Despite the intake of more dry matter in the dry food, the amount of intake of protein and fats was less than the intake with the raw food. The amount of feces decreased significantly after starting to eat raw food, and this trend kept in dynamics.

The comparative study of the digestibility of dry and raw food showed significantly higher coefficients of digestibility of raw food.

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