Determining metabolisable energy (ME) requirements of dogs (and cats) is an important topic for pet food brands and manufacturers alike.  Accurate data on ME requirements of pet dogs allows us to ensure that we give accurate feeding recommendations on packaging, ensures we are advising our customers correctly and, given the incidence of obesity in our pets, it also plays a role in animal welfare. Not only that, but the feeding guide and the amount to be fed is key to consumers for whom all they really want to do is to choose a food that’s right for their beloved pet. But does published research suggest that we are getting this right?

It has long been established that energy requirements vary considerably from pet to pet, with factors such as activity level, breed, sex, neuter status, age, health status, temperament, body size, insulation characteristics of skin and coat, in addition to environmental factors such as housing conditions and ambient temperature all having an effect. Energy requirements of animals with differing body weights (BW) are not correlated in a linear way and typically energy requirements are calculated per kg BW0.75 (known as metabolic body weight).  However, the accuracy of even this as a basic principle is in question and a valid alternative (per kg BW0.67) has been proposed as being more accurate in dogs as it is suggested that this is more related to body surface and may therefore be a better reflection of heat production (Finke, 1994, Kienzle et al., 1991, Männer, 1991). Determining energy requirements using a single “one size fits all” equation is therefore not possible and no matter which equation you choose to use, it will only ever predict an average for a specific group of animals.

Therefore, a practical recommendation for ME requirements of adult dogs of 110 kcal ME/ kg BW0.75 is made although ranges from 95 to 130 kcal ME/ kg BW0.75 are identified (FEDIAF, 2018).  Furthermore, different figures are recommended for dogs of different ages, activity level, reproductive state and even a small number of breeds. 

Much of the data used to determine the ME requirement of dogs is based on kennel dogs rather than pet dogs and this may contribute to reports by Männer (1991) and the NRC (2006) that the recommendations may overestimate energy needs of pet dogs by 10 to 60%. Few studies have been conducted in pet animals and this is something that the scientific community and industry are aiming to address over time.

Whilst feeding trials remain the gold standard in determining the ME of a diet, they are expensive and time consuming so predicting the ME of a diet by calculation is more practical in most cases.  Historically, the simplest and most often used method of calculating the predicted ME of processed pet food was by using the modified Atwater equation, which is based on average digestibility for fat, protein and nitrogen free extract (NFE), where kcalME/100g of processed pet food is calculated as (% crude protein x 3.5) + (% crude oils and fats x 8.5) + (% NFE x 3.5).  However, following the publication of the revised FEDIAF Nutritional Guidelines for Cats and Dogs in August 2018, the modified Atwater equation was no longer recognised as an appropriate method for calculating energy requirements in the vast majority of situations. Instead, it has now been suggested that the most appropriate method for calculating ME in prepared pet foods for cats and dogs is to use the 4-step (CEN; EN 16967) method as follows:

STEP 1: CALCULATE GE

GE (kcal) = (5.7 x % protein) + (9.4 x % fat) + [4.1 x (% NFE + % crude fibre)]

GE (KJ)    = (23.85 x % protein) + (39.33 x % fat) + [17.15 x (% NFE + % crude fibre)]

 

STEP 2: CALCULATE ENERGY DIGESTIBILITY (%)

Dogs: % Energy Digestibility = 91.2 – (1.43 x % crude fibre in DM)

Cats:  % Energy Digestibility = 87.9 – (0.88 x % crude fibre in DM)

 

STEP 3: CALCULATE DIGESTIBLE ENERGY

kcal DE = (kcal GE x energy digestibility) / 100

KJ DE    = (KJ GE x energy digestibility) / 100

 

STEP 4: CALCULATE METABOLISABLE ENERGY

Dogs: kcal ME = kcal DE – (1.04 x % crude protein)

           KJ ME    = KJ DE – (4.35 x % crude protein)

 Cats:  kcal ME = kcal DE – (0.77 x % crude protein)

           KJ ME    = KJ DE – (3.22 x % crude protein)

However, it must be noted that this equation is only valid for prepared dog and cat foods (wet and dry) and excludes milk substitutes and liquid preparations for enteral nutrition, which must be highly digestible to fulfil their function. Additionally, in foods with a crude fibre content greater than 8% in DM and a high percentage of non-starch polysaccharide (NSP) in the crude fibre fraction, the 4-step method can underestimate the energy density.

Once the ME of the processed pet food is calculated, this, along with the ME requirement of the pet or pet population, is used to calculate the daily required intake of that particular feed and so the on-pack feeding guide. The owner then should feed their individual pets using the on pack feeding guide as an estimation only, adjusting the amount fed to their own pets body condition. 

Although the labelling of ME of the pet food is not a mandatory requirement on pack in most instances, it does of course play a critical role is calculating the recommended feeding guides which are indeed a mandatory on pack requirement. Additionally, there can be some instances whereby the FEDIAF Code of Good Labelling Practice for Pet Food (2018) advises that the labelling of the ME content of the pet food does become a requirement for example, where increased or reduced energy claims are made Vs a comparable product or where a product is claimed as being “Light”, which without any reference to a specific nutrient or other substance (for example, light in xxx), the term “Light” refers to a reduction in energy content. In such instances, the energy content of the food should be declared, calculated according to the EC-method (generally the 4-step method) if available, or to the respective official national method in the Member State where the feed is placed on the market (if available) and must be at least -15% lower in energy content vs a comparable product (FEDIAF Code of Good Labelling Practice for Pet Food, October 2018). ME declarations are also required to be placed on pack for specialised convalescence and obesity diets (Commission Directive 2008/38/EC of 5th March 2008 establishing a list of intended uses of animal feedingstuffs for particular nutritional purposes).

A study published by Thes et al., (2016) determined the ME intake of 586 pet dogs. The study looked at ME intake of these pet dogs and the effect of age, weight, health status, neuter status, sex and breed and compared results to those from previous studies carried out on kennel dogs. The study found that pet dogs have a lower ME requirement than that of kennel dogs and the high incidence of pet obesity that we are seeing amongst the current pet population is an indication that the mean ME intake of dogs should be carefully considered to ensure accurate feeding recommendations on packaging. Furthermore, given the high incidence of pet obesity and the effect of obesity on ME requirements (which can typically be 10–15% less than that of normal healthy weight dogs), then the study does give a recommendation that the labelling of pet foods should give a range of feeding recommendations, starting with the mean calculated within this study (98 kcal/kg BW0.75) as the upper limit and reducing this by approximately 20% for the minimum recommended allowance.

It is clear that determining ME requirements in pets is difficult and can never be 100% accurate for an individual pet . Ongoing research is needed to better establish and perhaps further improve determination of ME requirements to enable manufacturers and brand owners to better inform and advise pet owners of feeding recommendations.

For further information, advice and guidance on this article please contact your Pet Nutrition Account Manager (contact details below), or, alternatively, please e-mail info@premiernutrition.co.uk

Andrew Miller             - Andrew.Miller@premiernutrition.co.uk        +44(0)7969 246642

Sara Rowley               - Sara.Rowley@premiernutrition.co.uk         +44(0)7786 436712

Cara Freeston-Smith- Cara@premiernutrition.co.uk                      +39 345 892 3860

Graham Yeo               - Graham.Yeo@premiernutrition.co.uk         +44(0)7753 796215