Introduction
When we decide to buy or adopt an animal, we are usually aware of the new responsibilities involved. We need to ensure our pet’s safety and well-being. It seems obvious that a dog or cat needs a place in our home, a full food bowl and constant access to clean water. We often spend a great deal of time choosing the right bed, blanket, bowl or toys.
Then comes the question of nutrition. It may seem straightforward: we decide whether to feed dry or wet food or prepare our pet’s meals ourselves. We then serve food once, twice or three times a day.
When thinking about our own nutrition, we are generally aware that an average-sized, moderately active adult requires approximately 2,000 kcal per day. We also know that if we want to lose or gain weight, we need to adjust our calorie intake accordingly.
But what about dogs and cats? There are enormous differences in body size and weight, particularly among dogs. How should we feed a 3 kg Yorkshire Terrier compared with a 50 kg Great Dane?
When choosing commercial pet food, it may seem that the manufacturer has already solved this problem by providing calorie content and feeding guidelines on the packaging. Dry food bags sometimes even include measuring cups, while cans of wet food may provide information on how much food an animal should receive each day.
If feeding companion animals were really that simple, however, we would not currently be facing such high rates of obesity and other diet-related diseases in dogs and cats.
How much should a dog or cat eat?
Every owner should know approximately how much their dog or cat needs to eat.
To determine this accurately, we first need to assess our pet objectively, evaluate their body condition and, importantly, weigh them. Owners often have a distorted perception of their dog’s or cat’s body condition, and the number on the scales can come as a surprise. Age and activity level are also important factors.
Once we have this information, it may seem sufficient to find the appropriate weight range in the feeding table on the food packaging and simply follow the manufacturer’s recommendations.
However, owners should remember that feeding guidelines on packaging are generalised estimates. They do not take into account an individual animal’s health status or activity level.
Recommended portions are also frequently provided for broad weight ranges, even though a 5 kg dog has different energy requirements from an 8 kg dog. Feeding guidelines also do not account for treats and rewards, which can contribute significantly to a dog’s daily calorie intake.
So how can we calculate an animal’s energy requirements more accurately?
Calculating RER
For dogs, the formula is:
RER = 70 × body weight⁰·⁷⁵
For cats:
RER = 70 × body weight⁰·⁶⁷
For example, for a dog weighing 7 kg:
RER = 70 × 7⁰·⁷⁵ = 301.2 kcal
RER, or resting energy requirement, is only one component used to estimate an animal’s daily energy needs.
To determine how many calories an animal requires each day, we need to calculate DER – daily energy requirement.
This requires the RER together with factors such as the animal’s age, activity level, neuter status, pregnancy and other physiological circumstances.
The formula for calculating daily energy requirement is:
DER = k × RER
where k is a factor reflecting the animal’s activity level, age or physiological status.
RER factors for dogs
Adult dogs:
- Entire = 1.8
- Neutered = 1.6
- Overweight and inactive = 1.4
- Weight-loss programme = 1.0
- Nutritional support in intensive care = 1.0
- Weight regain during recovery = 1.2–1.4
Working or training dogs:
- Light activity = 2.0
- Moderate activity = 3.0
- Heavy activity = 4–8
Pregnancy:
- First two trimesters (up to approximately 6 weeks of pregnancy) = 1.8
- Final trimester = 3.0
Lactation – depending on the number of puppies:
- 1 puppy = 3.0
- 2 puppies = 3.5
- 3–4 puppies = 4.0
- 5–6 puppies = 5.0
- 7–8 puppies = 5.5
- 9 puppies or more = 6.0
Growth:
- From 4–5 months of age = 3.0
- From 8–12 months of age = 2.5
- After 8–12 months of age = as for an entire adult dog
We select the factor that most closely reflects the individual animal’s condition and lifestyle.
Returning to our example of a 7 kg dog that is neutered and moderately active, with two short walks and one longer walk per day:
DER = RER × 1.6
DER = 301.2 × 1.6 = 481.92 kcal
The dog therefore requires approximately 482 kcal per day.
RER factors for cats
Adult cats:
- Neutered adult = 1.2
- Entire adult = 1.4
- Obese and inactive = 1.0
- Weight-loss programme = 0.8
- Nutritional support in intensive care = 1.0
- Weight regain during recovery = 1.2–1.4
Oestrus and pregnancy:
- During oestrus = 1.6
- During pregnancy = 2.0 or ad libitum feeding
Lactation – depending on the number of kittens:
- 1 kitten = 2.0
- 2 kittens = 2.5–3.0
- 3–4 kittens = 3.0–4.0
- 5–6 kittens = 5.0
Lactation – depending on the stage of lactation:
- Weeks 1–2 = RER + 30% per kitten
- Week 3 = RER + 45% per kitten
- Week 4 = RER + 55% per kitten
- Week 5 = RER + 65% per kitten
- Week 6 = RER + 90% per kitten
Growth:
- From birth until physical maturity = 2.5 or ad libitum feeding
Senior cats:
- 1.4–1.6
The same principle is used when calculating a cat’s daily energy requirement:
DER = RER × k
Body condition should also be considered when selecting the appropriate k factor, as it helps determine whether the animal is at an ideal weight, overweight or obese.
The Body Condition Score (BCS) is particularly useful for this purpose. It is a multi-point scale using visual and descriptive criteria to assess whether a dog or cat is underweight, at an ideal body condition, overweight or obese.
How much food should a pet receive each day?
Once we know how many kilocalories a dog or cat requires each day, the next step is to determine how much food will provide that amount of energy.
Most manufacturers provide the energy value of their food on the packaging. If this information is available, calculating the daily portion is straightforward.
For example, suppose a food provides 320 kcal per 100 g, while our dog requires approximately 483 kcal per day:
483 ÷ 320 = 1.509 × 100 = 150 g
In this example, the dog should therefore receive approximately 150 g of food per day if the food provides 320 kcal per 100 g.
What if we do not know the calorie content of the food?
Sometimes the energy value is not provided on the packaging. In this situation, we can estimate the amount of energy supplied by the food ourselves.
It is generally assumed that one gram of protein or carbohydrate provides approximately 3.5–4 kcal, while one gram of fat provides approximately 8.5–9 kcal.
Manufacturers are required to declare the amounts of protein, fat, fibre and ash, as well as moisture content. They are not required to declare carbohydrate content, and many manufacturers do not provide this information.
However, we can estimate the carbohydrate content ourselves.
Subtract all of the other declared components from 100, including moisture.
For example, if a food contains:
- 15% moisture,
- 35% protein,
- 20% fat,
- 3% fibre,
- 2% ash,
then:
100 − 15 − 35 − 20 − 3 − 2 = 25
The estimated carbohydrate content of this food is therefore 25%.
To estimate its calorie content, multiply the amount of protein and carbohydrate by 3.5 and the amount of fat by 8.5:
35 × 3.5 + 25 × 3.5 + 20 × 8.5 = 380 kcal
We can use a similar approach to estimate the energy content of home-prepared meals if we know how much protein, fat and carbohydrate the ingredients provide. Applications containing nutritional information for individual foods may also be helpful.
Why can 14% sometimes be more than 34%?
Once we know how many kilocalories our dog or cat requires and how much of a particular food should be provided, we may find that the manufacturer’s feeding recommendations differ considerably from our calculations. This can potentially result in either overfeeding or underfeeding.
So how can we make sense of all the information and tables and choose an appropriate food?
Should we choose the food with the highest calorie content? Or perhaps the one with the most protein? And how can we compare dry food with wet food?
To compare the nutrient content of different foods accurately, we need to calculate their values on a dry matter (DM) basis.
Suppose we have a dry food containing 18% moisture and 34% protein and a wet food containing 78% moisture and 14% protein. How can we determine which contains more protein?
Although 34% appears to be considerably higher than 14%, converting the values to dry matter can produce a very different result.
How do we calculate it?
Subtract the moisture percentage from 100 to determine the dry matter content.
Dry food:
100 − 18 = 82% DM
Wet food:
100 − 78 = 22% DM
Protein content of the dry food on a DM basis:
34 ÷ 82 × 100 = 41% protein DM
Using the 16% protein value in the source example, the wet food calculation is:
16 ÷ 22 × 100 = 72% protein DM
In this example, the wet food contains considerably more protein on a dry matter basis despite appearing to have a lower percentage on the label.
The same method can be used to compare fat, carbohydrates and minerals. This is particularly important when feeding animals whose intake of specific nutrients needs to be carefully controlled.
Weight problems and healthy weight loss
If a dog or cat is overweight, the first step is to calculate its daily energy requirement using the appropriate k factor for weight loss.
However, successful weight management requires consideration not only of calorie intake but also of meal volume.
Wet food or appropriately formulated home-prepared cooked or raw diets may provide a larger volume of food for a given amount of energy than energy-dense dry food, which can help reduce hunger in some animals.
Weight loss is a gradual process requiring consistency and discipline. Excessive calorie restriction may cause discomfort and hunger-related problems and can make an appropriate weight-loss programme more difficult to maintain.
Increasing physical activity is also important, although this may be challenging in some animals, for example those recovering from injuries or affected by orthopaedic conditions. Diet therefore remains a key component of achieving and maintaining an appropriate body weight.
Healthy nutrition for companion animals is similar in some respects to our own nutrition: understanding the theory is often easier than putting it into practice.
While we experience the consequences of our own dietary choices, dogs and cats are entirely dependent on their owners when it comes to nutrition.
Looking after an animal’s well-being means more than providing attention, toys and a comfortable place on the sofa. Appropriate nutrition is one of the foundations of a healthy and happy life.
Unfortunately, we often begin paying close attention to what is in our pets’ bowls only once health problems appear.
Rather than waiting until a health problem forces us to change our animal’s diet, it is worth choosing the most appropriate feeding strategy from the outset. The diet should be nutritionally complete, appropriately balanced and tailored to the individual animal’s requirements.
Making informed nutritional choices is one of the most important things we can do to support the long-term health and well-being of our dogs and cats.
References:
- M. Ceregrzyn, R. Lechowski, B. Barszczewska. Podstawy żywienia psów i kotów.
- W.D. Gram, R.J. Milner, R. Lobetti. Choroby przewlekłe psów i kotów.
- A. Cholewiak-Góralczyk. Psie smaki.
- R.E. Minguez. Otyłość psów i kotów.