A portion starts with energy. Body weight alone is not enough, because two animals with the same weight can have very different needs. In practice, we first calculate RER, then choose a multiplier and get DER — daily energy requirement.
RER — the starting point
RER is the energy the body needs at rest: for breathing, heart function, and maintaining body temperature. It is calculated with this formula:
RER = 70 × body weight (kg)0.75 [kcal/day]
The exponent 0.75 matters: small animals use proportionally more energy per kilogram than large animals. That is why this formula is more accurate than a simple “kcal per kilogram” rule, especially for very small or very large body weights [1].
From RER to MER and DER
RER does not include movement, age, or physiological state. That is what the multiplier is for.
MER applies to maintaining an adult animal at a stable weight. DER is the full daily energy requirement, which is usually the value needed when planning a portion.
In practice: DER = RER × multiplier. The multiplier depends on factors such as species, neuter status, activity, age, growth, pregnancy, lactation, and BCS [2].
Factors
The multiplier is most often changed by activity, neutering or spaying, life stage, and BCS. Growth, pregnancy, and lactation usually increase the result; low activity, senior age, or excess weight may lower it [2].
The calculator above breaks the multiplier into these elements, so the result does not depend on body weight alone.
What the calculator does not replace
The calculation does not replace observation. After introducing a portion, you still need to monitor BCS and body weight over time. If the animal gains or loses weight against the plan, the portion should be adjusted [2].
The “2-3% of body weight” rule is convenient, but it ignores the diet’s calorie density and the animal’s activity. Calculating from energy is safer.
What this means for BARF
Energy sets the portion size first, and only then do we calculate protein, fat, minerals, and vitamins. That is why BARFLAB bases gram amounts on DER, not only on a percentage of body weight.
Sources
- National Research Council (2006). Nutrient Requirements of Dogs and Cats. The National Academies Press. https://doi.org/10.17226/10668
- WSAVA Global Nutrition Committee. Global Nutrition Guidelines & Toolkit. World Small Animal Veterinary Association. https://wsava.org/global-guidelines/global-nutrition-guidelines/