There are many aspects of veterinary diet that affect our patients throughout their lives, including weight loss, weight gain, pregnancy, lactation, newborns, and starvation. Saar presents approaches for all these situations and breaks the mathematics down into manageable parts. Using these formulas allows you to offer your patients more personalized treatment.
The most common math in animal nutrition is calculating the energy requirements for different situations. Resting Energy Demand (RER) is one of the basic calculations used in many applications. The RER is the requirement when the patient is awake but at rest. The formula for calculating the RER is BW0.75 x 70, where BW is the body weight in kilograms. Although there is a linear formula for RER (RER = 70 + (30 x BW)), Saar does not recommend using it as it is not accurate for pets 30kg. Nowadays most smartphone calculators have the xy key (x to the power of y) where you enter the BW, press the xy key and then enter 0.75 and then multiply that result by 70.
To calculate the daily maintenance requirement (MER), we use the RER multiplied by a factor. In her Fetch presentation, Saar presented a detailed table for the appropriate factors to use in calculating the MER based on whether the patient’s activity is light / moderate / active, whether they are prone to obesity, whether the patient is is intact or neutered, whether he needs it to lose weight or gain weight and whether the patient is a dog or a cat. From this table, Saar emphasizes that cats generally have a slightly lower demand than dogs and that neutered pets have a lower energy demand than intact pets.
When calculating the MER for weight loss, the factor is 1.0, which in these cases effectively corresponds to the RER. Saar advises that for weight loss calculations, the BW used in the calculations should be current weight, not ideal or target weight. On the one hand, this is due to the fact that it is difficult to determine the ideal body weight, and on the other hand, because a regular diet for weight loss also leads to a reduction in calories and nutrients. Using the current weight avoids the risk of nutrient deficiency. This formula should be recalculated frequently using updated weights throughout the weight loss process so that MER can be readjusted for the current weight. However, when calculating the MER for weight gain, use the patient’s ideal weight (not their current weight) to ensure that you are getting adequate nutritional needs.
In some cases, you may need to calculate Daily Energy Requirements (DER). DER is slightly different from MER. When using MER, it can be assumed that the energy demand is similar every day. DER is used for specific short-term increases in demand, such as sled dogs on long (100-mile) runs, during pregnancy or lactation, with newborns or children or with certain illnesses. Think of a DER as having a special need for lots of extra calories “that day”. There are simple formulas for this DER calculation (from 16 weeks DER = RER x 3.0; from 17 weeks DER = RER x 2.0); However, there are much more specific methods of calculating the energy requirements for these situations that allow individual care for each patient according to their needs. Saar calls these “Robin’s fun equations”. They are a little more complicated but can still be broken down into manageable steps and offer a very tailored, personalized approach to caring for a patient. She presents these situations in detail in her fetch seminar.
For example, when calculating a puppy’s DER it is much more accurate to use the following equation: DER = 130 x BWC0.75 x 3.2 (2.71828-0.87 (BWC / BWE) – 0.1) where BWC is the current body weight, BWE is the expected adult body weight, and 2.71828 is a constant, simply multiply by a generic factor as the RER. This more complicated formula takes into account that very young newborns have high energy needs but are lighter in body weight, and then as they grow, their energy needs increase and finally, as they approach their adult weight, their energy needs are lower. The formula for a kitten is very similar, but with some minor differences (DER = 100 x BWC0.67 x 6.7 (2.71828-0.189 (BWC / BWE) – 0.66).
Taking current and expected weight into account, the nutritional needs initially increase as you grow and gain weight, and then decrease as you approach your expected adult weight.
Pregnancy is another stage of life where personalized nutrition can help your patients, although the DER does not need to be increased until 5 weeks after breeding. Here, too, there are minor differences between the formulas for dams (DER = 130 x BW0.75 + [26 x BW]) and women (DER = 140 x BW0.67). In dams, this formula corresponds to an increase in MER of around 25 to 60% and in queens by around 40 to 50%. The goal during pregnancy is to maintain a normal body condition throughout pregnancy.
Breastfeeding is another stage of life that requires additional nutrition. Saar describes that lactation is one of the highest energy demands an animal can have. The calculated DER for lactation depends on the number of puppies or kittens that will be breastfed. With 1 puppy DER = 3.0 x RER; for each additional puppy, however, the increase factor is an additional 0.5. For lactating queens, the DER calculates per kitten at weekly intervals. For example, in weeks 1 to 2 of the suckling period, the DER for the queen is RER + 30% per kitten. At week 3 this factor is 45% per kitten, week 4 is 55% per kitten, week 5 is 65% per kitten, and week 6 is 90% per kitten.
As soon as these temporary phases are no longer active, the energy demand returns to the typical MER formulation.
With respect to disease states, tracking weight loss and calculating percent loss over time can be useful as an indicator of the disease. An unexplained weight loss of 5% or more should lead to further review of all known factors or possibly diagnostic tests to determine possible causes. Inexplicable weight loss of more than 10% is worrying. In smaller patients, a small change in body weight can easily be overlooked despite a significant percentage change.
Other disease conditions that require tailored nutrition plans are patients at risk for refeeding syndrome. An example of this would be a pet that was lost and then found thin and dehydrated a week or two later. Blood values may appear normal at first. However, if you offer food after a period of starvation, the compensatory physiological processes of the body that enable you to survive starvation react poorly to the abundance of food and a day or two later lead to electrolyte imbalances and clinical symptoms. Re-feeding, after these compensatory processes have been established and continue, acts as a trigger for the cells to resume those electrolytes and glucose that were previously shifted into the vasculature, and then the blood levels of these substances are depleted. While this sounds quite complex, it is easy to counteract these processes with a strict feeding schedule. Saar presents a nutrition plan that is not only successful in recovering from hunger, but also in diarrhea, diet changes and similar situations.
After calculating all of these detailed energy needs for specific patients in very specific situations, we still need to know how much food we are feeding. This can be calculated on a volume basis using the kcal / cup data of each food or by weight using the kcal / kg data. For foods where the amount of kcal / cup is not available, Saar shows us how to calculate this using the metabolizable energy from the ingredients. NFE (nitrogen-free extracts) are carbohydrates. Proteins contain nitrogen, so nitrogen-free extracts are carbohydrates. NFE = 100% -% crude protein -% crude fat -% crude fiber -% moisture -% ash. Note that ash is usually not listed, but it is 2.5% for canned food and 8% for dry food. Metabolizable Energy (ME) = 10 ([8.5 kcal/g x % crude fat] + [3.5 kcal/g x % crude protein] + [3.5 kcal/g x % crude NFE]). The addition of these components results in kcal per kilogram of food. From here, the owners could weigh the amount of feed given instead of measuring it.
All of these methods of calculating energy needs are very interesting nutritionally and it is great to make such bespoke plans for our patients, but how do we encourage owners to follow them? Saar presents several strategies for building trust and compliance:
- Build up trust. Why do some owners trust a 16-year-old pet dealer more than their veterinarian with years of training and a university degree? We need to build trust, and Saar reminds us that one of the best ways to build trust is to share stories. Share customer stories about the referrals you make. Share the experiences of others so they know there have been others who have had good experiences with the diet you recommend. Then seamlessly transfer that trust and information to the rest of the team. Once you’ve had your conversation and made your recommendation, communicate with the next person in line (the technician, receptionist checking you out, etc.). Customers want to see that we are all a team and organized and that we do not fail to exchange information or express different opinions.
- Understand our customers and listen to them. Sure, we know medicine and clients should know that, but in this day and age they also hear all kinds of third-party information. It helps to be sure to listen to the owners ’requests. When they talk about nibbles and canned foods, be sure to listen. If they talk about having the convenience of getting groceries at the grocery store or having trouble getting to the city pet store, these are the things you should definitely listen to. Are you talking about preferring homemade or fresh food to others? Pay attention to these details and tailor your conversation and recommendations to suit their needs.
- Make 1 clear recommendation. Saar is aware that we may have several options, but if you are already listening to the owners you should have a clear recommendation that suits their needs and preferences. And repeat this out loud for them to hear, “I’ve been thinking about your pet’s needs and the information you told me, and here is what I recommend.”
- Treat it like a prescription. “This will improve your pet’s health, so we recommend it.”
- Be open to one more recommendation, depending on the client’s needs, in case other factors affect your recommendation.
Packer is Associate Professor of Neurology / Neurosurgery at Colorado State University College of Veterinary Medicine and Biomedical Sciences at Fort Collins and certified in Neurology by the American College of Veterinary Internal Medicine. She is active in the clinical and didactic training of undergraduates and interns in veterinary medicine and has developed a comparative neuro-oncological research program at Colorado State University.