assessment of nutrient digestibility in four dry dog foods containing different levels of protein, fat and carbohydrate

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in modern society. Along with appropriate health care and adequate medical attention, nutrition is an important component of pet care. Understanding basic nutrition and the nutrients required by healthy dogs and cats is crucial for understanding practical feeding strategies (Case et al., 2011). According to 20 th livestock census 2019, the dog population of Kerala is 8.36 lakhs, most of which are medium sized dogs (12-20kg). Considering the popularisation of pets across income groups in Kerala, it is becoming imperative to look into the nutritional profile of pet dogs so as to ensure their health and clinical well-being. The commercial pet foods have different levels of protein, fat and carbohydrate with levels of carbohydrates on a higher side in most pet foods. Even though dogs can utilise carbohydrates, the extent of utilisation is limited. Hence this work was undertaken to assess the influence of various levels of nutrients on digestibility in dogs.

Materials and methods
This study was conducted in switch over design at the Animal Nutrition Production Shed, Department of Animal Nutrition, College of Veterinary and Animal Sciences, Mannuthy, Thrissur, Kerala during the period from February, 2022 to June, 2022.

Preparation of dry dog food
Complete dry food for adult medium sized dogs was developed at the first stage. Different combinations of feed items were used for formulating four different dry foods .  The dietary treatments were T1 (40 per cent  CP, 23 per cent fat, 30 per cent carbohydrate  and 3626 kcal ME), T2 (35 per cent CP, 20 per  cent fat, 38 per cent carbohydrate and 3528 kcal ME), T3 (26 per cent CP, 15 per cent fat, 52 per cent carbohydrate and 3475 kcal ME) and T4 (20 per cent CP, 11 per cent fat, 62 per cent carbohydrate and 3370 kcal ME). The fat to protein ratio was made uniform in all these combinations. The ingredient compositions of diets are provided in Table 1.

Feeding trial
Four medium sized, healthy adult dogs between one to two years of age and around 10 to 15kg body weight were selected. They were dewormed and vaccinated against rabies at the beginning of experiment. The experimental animals were housed individually in well ventilated, clean and dry kennel with facilities for feeding and watering and were maintained under uniform management conditions. The dogs were randomly allotted to one of the dietary treatments initially and fed with the corresponding diet for a period of four weeks. Thereafter the animals were switched. One week was given in between treatments to nullify the carry over effect. Subsequent food was given during rest period and the entire feeding trial period was for a period of five months. At the end of each feeding trial, a digestibility trial for 3 days was carried out, by total collection method.

Statistical analysis
As the design adopted was switch over design, variation between treatments were analysed after removing the variation due to period and also variation due to animal. For this, three-way ANOVA without interaction was adopted. When the F-value corresponding to treatment was found to be significant, Duncan Multiple Range Test (DMRT) was used for finding out which treatments are homogenous.

Results and discussion
The data on chemical composition of feed (T1, T2, T3 and T4) and faecal sample of dogs fed with the four experimental diets are presented in Tables 2 and 3.
The mean average daily dry matter intake (DMI) of the experimental animals maintained on T1, T2, T3 andT4 during digestibility trial were 151.23± 4.64, 158.52± 3.73, 164.06 ± 3.48 and 173.02 ± 5.22g, respectively. The mean daily faecal output of the experimental animals maintained on T1, T2, T3 and T4 during digestibility trial were 119.37± 5.62, 137.85 ± 7.92, 171.55 ± 8.02 and 188.06 ± 5.09g, respectively. The faecal output per kg body weight for dogs fed T1, T2, T3 and T4 were 10.17, 11.97, 14.78 and 16.15g, respectively. The faecal volume and faecal volume per kg body weight showed significant difference (p<0.01) between all the four treatment groups with values of animals fed, with T4 value being significantly higher than those of animals in other treatment groups. In accordance with the results of the current study, Sabchuk et al. (2012) reported that mature Beagles confined in metabolic cages and kennels and fed diets containing 92 percent DM and 23 percent CF, respectively, had faecal production of 14.6 and 19.8 g per kg body weight. Similar to the observations made in the present study Abinaya et al. (2020) in their study with adult medium sized non-descript dogs also reported faecal output of 11.86, 16.37 and 19.39g per kg body weight in dogs fed isonitrogenous diets.
The apparent digestibility coefficient of nutrients in the four experimental diets calculated from digestibility trial in dogs belonging to the four dietary treatments is presented in Table 5. The apparent digestibility coefficient for dry matter showed difference (p<0.01) between all the four treatments with digestibility in T1 being significantly higher than that in other treatment groups. Similar apparent DM digestibility coefficient of 79 per cent, 76.1 per cent, 65.8 to 72.9 per cent and 77.41 per cent were observed by Murray et al. (1999), Sa et al. (2013), Abinaya et al. (2020) and Kahraman and Inal (2021).
The data for crude protein digestibility was similar for T1 and T4 diets and was significantly different from T2 and T3 feeds (p<0.01) with T3 values being significantly higher than other treatment groups. In agreement to the results of present study, Madhusudhan (2007) reported mean CP digestibility of 84 per cent in adult dogs. Hervera (2011) observed apparent CP digestibility of 71 to 91 per cent in adult dogs fed an extruded diet with CP ranging from 15.8 to 39.8 per cent (DM basis). Geiger and Weber (2022) based on their study in dogs fed with four dry dog foods containing crude protein ranging from 18 to 38 per cent observed that total tract apparent digestibility (TTAD) of proteins ranged from 69 to 84 per cent.
The calculated ether extract digestibility was similar between T1 and T2 and between T2 and T4 groups and was significantly lower from T3 group (p<0.01). According to Bazolli et al. (2015), mature Beagles given a diet containing 53.3 per cent maize and 4.5 per cent poultry fat had an apparent EE digestibility of 94.1 per cent. Kahraman and Inal (2021) estimated the ether extract digestibility of commercial dry dog diets with or without grains and reported values of 95.14 and 96.96 per cent, respectively.
No difference was recorded between the dietary treatments with regard to the digestibility of crude fibre. Similar to the present study, Brambillasca et al. (2010) reported 44.3 per cent crude fibre digestibility in dogs fed with diet containing 33 per cent crude fibre. Similarly, Kahraman and Inal (2021) observed a crude fibre digestibility of 48 per cent in dogs fed with diets containing grain and lamb meat.
The NFE digestibility was similar between T1, T2 and T3 groups and also between T1 and T4 but digestibility in T4 was significantly lower than that in T2 and T3. Meyer et al. (1999) reported higher digestibility coefficient for NFE at 66.5 per cent in ten different breeds of dogs fed diets with CF ranging from 5 to 9 g/kg.

conclusion
From the above results, we can conclude that the levels of nutrients in diet had a significant influence on nutrient digestibility in experimental animals. The dry matter digestibility was higher in high protein and fat diet whereas digestibility of crude protein and ether extract was highest for T3 diet which was having crude protein and ether extract levels less than T1 and T2 diets. The mean daily faecal output was higher for animals fed with high carbohydrate diet when compared with animals in other treatment groups. From the observations made in the study, for efficient protein and energy utilisation in adult dogs, a diet containing 26 per cent protein, 15 per cent fat and 52 per cent carbohydrate is better and can be recommended .