If you have ever looked at the back of a pet food bag from a New Zealand supermarket or vet clinic, you have likely seen a feeding guide. These charts provide a broad range of how many grams or cups to feed based on weight. However, these are often just general estimates that do not account for your pet’s unique metabolism. To truly take control of your dog or cat’s health, you need to understand Resting Energy Requirements (RER). This is the baseline number of calories your pet needs to perform essential functions like breathing, digestion, and heart function while at rest. By calculating the Resting Energy Requirements (RER) specifically for your animal, you can prevent common issues like obesity and ensure they are receiving the precise nutrition required for their lifestyle and life stage.
The Flaw in Standard Feeding Guidelines
Most pet owners in New Zealand rely on the feeding tables printed on the back of kibble bags. While these are a helpful starting point, they are designed for the 'average' dog or cat. The problem is that very few pets are truly average. These guidelines often use a one-size-fits-all approach that doesn't account for whether your pet is a high-energy Heading Dog working on a farm or a lazy Ragdoll cat living in a Wellington apartment.
Furthermore, many pet food manufacturers base their recommendations on 'intact' adult animals with high activity levels to ensure they don't under-feed. For the typical desexed pet that enjoys a daily walk around the local park and then sleeps on the sofa, these bag guidelines can lead to overfeeding by as much as 20% to 30%. This excess energy is stored as fat, contributing to the growing pet obesity crisis. Calculating the RER allows you to bypass these generic estimates and start with a scientific baseline tailored to your pet's specific biological needs, ensuring they maintain an ideal body condition score.
Understanding the Science of RER
Resting Energy Requirements (RER) represent the energy expended by a pet at rest in a thermoneutral environment. It is the metabolic cost of staying alive. Unlike 'Maintenance Energy Requirements' (MER), which include the energy needed for exercise and daily activity, RER is the bare minimum. In veterinary medicine, the most accurate way to calculate this is using a power function rather than a linear formula. This accounts for the fact that as an animal's body size increases, its metabolic rate doesn't increase at a 1:1 ratio.
A common mistake is assuming a 20kg dog needs exactly double the food of a 10kg dog. In reality, smaller animals have a higher metabolic rate per kilogram of body weight. The standard formula used by veterinary nutritionists is: RER = 70 * (body weight in kg)^0.75. While the math looks intimidating, it is the gold standard for determining how many calories (kilocalories) a pet's body burns just by existing. Using this metabolic approach ensures that larger breeds aren't overfed and smaller breeds receive enough energy to sustain their higher relative burn rates.
The Step-by-Step Calculation Guide
To calculate your pet's RER, you first need an accurate weight in kilograms. If you only have the weight in pounds, divide it by 2.2. Once you have the weight, apply the formula: 70 times (weight in kg raised to the power of 0.75). For example, a 10kg dog would be calculated as: 70 * (10^0.75) = 393 kcal per day. If you do not have a scientific calculator, you can use a simpler linear approximation for pets between 2kg and 45kg: (30 * weight in kg) + 70. However, the exponential formula is more precise for very small or very large animals.
Once you have the RER, you must apply a 'Maintenance Multiplier' to find the Daily Energy Requirement (DER). For a typical neutered adult dog, the multiplier is usually 1.6. For a neutered adult cat, it is often 1.2 to 1.4. If your pet is highly active or still growing, these numbers will be higher. Conversely, if your pet needs to lose weight, you might feed exactly the RER (a multiplier of 1.0). Always use a kitchen scale to measure food in grams rather than using a measuring cup, as 'cups' can vary significantly in volume depending on how tightly the kibble is packed.
Adjusting for Life Stage and Lifestyle
Calculations provide a theoretical starting point, but the 'real-world' application requires observation. Factors such as age, desexing status, and the New Zealand climate can all influence energy burn. A dog living in the cooler South Island may require slightly more energy in winter to maintain body temperature compared to a dog in subtropical Northland. Additionally, desexed pets generally have a metabolic rate 20% to 30% lower than intact animals, which is why they are more prone to weight gain if fed according to standard bag guidelines.
Age is another critical variable. Senior pets often have slower metabolisms and may lose muscle mass, requiring a higher protein-to-calorie ratio but fewer total calories. Puppies and kittens, on the other hand, are 'energy sponges.' A growing puppy may require a multiplier of 3.0 times their RER during their peak growth phase. As a pet owner, you should evaluate your pet's Body Condition Score (BCS) every two weeks. If you can't easily feel their ribs or if they lose their visible waistline, it is time to reduce the multiplier by 10% regardless of what the initial math suggested.
Troubleshooting Weight Plateaus
Sometimes, even with precise RER calculations, a pet might not lose weight or might continue to gain it. This is often due to 'hidden calories.' In New Zealand households, it is common to share a bit of toast or a piece of cheese with our furry friends. However, for a 5kg cat, a small cube of cheese is metabolically equivalent to a human eating a whole hamburger. Treats should never exceed 10% of the total daily caloric intake.
If the math is correct and there are no extra treats, but the weight isn't budging, consult your veterinarian. Medical conditions like hypothyroidism in dogs or diabetes in cats can significantly alter metabolic rates. Furthermore, as animals lose weight, their RER actually decreases because there is less tissue to maintain. This means you must re-calculate the RER every time your pet loses a significant amount of weight (usually every 1-2kg for dogs) to avoid hitting a plateau. Consistency in measuring and frequent re-evaluation are the only ways to ensure long-term success.
Safety First: When to Seek Professional Advice
While calculating RER at home is an excellent way to take charge of your pet's nutrition, it should never replace professional veterinary advice, especially for pets with underlying health issues. Rapid weight loss can be dangerous, particularly for cats, who are at risk of developing hepatic lipidosis (fatty liver disease) if they go into a severe calorie deficit too quickly. A safe rate of weight loss is generally 1% to 2% of total body weight per week.
You should seek professional help if your pet shows signs of lethargy, refuses to eat the calculated portion, or if you notice sudden weight changes that don't align with their intake. Veterinarians can perform blood tests to rule out metabolic disorders and provide prescription diets that are higher in essential nutrients, allowing for lower calorie intake without causing deficiencies. Always transition to a new feeding amount gradually over 7 to 10 days to avoid gastrointestinal upset, ensuring your pet's digestive system adapts to the change in volume and frequency.
FAQ
Can I use RER for both dogs and cats?
Yes, the basic RER formula (70 * kg^0.75) applies to both dogs and cats. However, the multipliers used to determine the final daily energy requirement (DER) differ between the species, as cats generally have lower maintenance energy needs than dogs of the same weight.
Why is my pet still hungry after feeding the calculated RER?
RER is a measure of energy, not volume. If your pet seems hungry, consider switching to a diet with more fibre or 'air-puffed' kibble that provides more volume for the same calories. Also, ensure they are not just begging out of habit or seeking attention rather than actual hunger.
Do I need to calculate RER for raw diets?
Absolutely. Whether you feed commercial kibble from a store like Animates or a raw diet like K9 Natural, the caloric density matters. You need to know the 'kcal per gram' of the specific food you are using to translate your pet's RER into a physical portion size.
How often should I re-calculate my pet's calories?
You should re-calculate at every major life milestone: after desexing, when they transition from puppy/kitten to adult, when they reach senior age, or if their activity level changes significantly (e.g., moving from a house with a big yard to an apartment).
Conclusion
Taking the time to calculate your pet's Resting Energy Requirements (RER) is one of the most proactive steps you can take as a responsible owner in New Zealand. While the feeding guidelines on food packaging offer a simple starting point, they lack the precision needed to account for individual metabolic differences, desexing, and lifestyle factors. By using the metabolic formulas and life-stage multipliers discussed in this guide, you can provide a bespoke nutrition plan that promotes longevity and prevents the health complications associated with obesity. Remember to monitor your pet’s Body Condition Score regularly and consult with your local veterinarian before making drastic changes to their diet. Accurate measurement, scientific calculation, and consistent monitoring are the keys to a healthy, happy pet.
References & Sources
This article was researched using the following sources:
