Easy nutritional math? It was my understanding that there would be no math

Help conquer your fear of math with these simple yet effective formulas that offer a more personalized approach to a patient’s nutrition plan.

Does math scare you? Do you find nutrition discussions difficult? Speaking at Fetch dvm360® Robin Sarr Conference, RVT, VTS (Nutrition), puts these concerns out by breaking the math and offering strategies for establishing client confidence during nutrition discussions.

There are many aspects of veterinary nutrition that affect our patients throughout their lives, including weight loss, weight gain, pregnancy, lactation, newborns, and starvation states. Sarr provides approaches to all these situations and breaks mathematics down into manageable parts. Applying these formulas will allow you to provide more personalized care to your patients.

The most common mathematics used in veterinary nutrition is to calculate the energy requirements for various situations. Resting Energy Requirement (RER) is one of the basic calculations used in many applications. RER is the condition when a patient is awake but at rest. The formula for calculating the internal rate of return 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 its use, as it is not accurate for pets under 2 kg or >30 kg. These days, most smartphone calculators have the xy button (x to the y power), you enter BW, you press the xy button, you enter 0.75, and that result is multiplied by 70.

To calculate the daily maintenance requirement (MER), we use RER multiplied by a factor. In her Fetch presentation, Saar provides a breakdown of the appropriate factors to use when calculating MER based on whether a patient is light/moderate/active, whether they are obese, whether the patient is healthy or castrated, and whether they need it Losing weight or gaining weight, whether the patient is a dog or a cat. From this chart, Sarr highlights that cats tend to be slightly lower in their requirements than dogs and that neutered pets have lower energy requirements than healthy pets.

When calculating the MER for weight loss, the factor is 1.0, which is effectively equivalent to the RER in these cases. Sarr points out that for weight loss calculations, the weight of the body used in the calculations should be the current weight, not the ideal or target weight. She explained that this is partly because it is difficult to determine an ideal body weight, and partly because when using a regular weight loss diet, reducing calories will also reduce nutrients. Using your current weight avoids the risk of providing too few nutrients. This formula must be recalculated using updated weights frequently throughout the weight loss process, so the market percentage rate for the current weight can be readjusted. However, when calculating the MER for weight gain, you should use the patient’s ideal weight (not the current weight) so you can ensure that you meet the appropriate nutritional requirements.

In some cases, you may find that you need to calculate your daily energy requirement (DER). DER is slightly different from MER. When using MER, the assumption is that energy requirements are the same every day. DER is used when there are specific short-term increases in requirements, such as in the case of sled dogs on long (100 miles) trails, pregnancy, lactation, newborn or child animals, or certain medical conditions. Think of DER as a special need for a lot of extra calories “that day.” There are simple formulas for calculating DER (if 16 weeks or younger, DER = RER x 3.0; if 17 weeks or more, DER = RER x 2.0); However, there are more specific ways to calculate the energy requirements for these positions that provide personalized care to each patient according to their needs. Sarr calls these “fun Robin’s equations.” They are a bit more complex but can still be broken down into manageable steps, and provide a highly personalized and personalized approach to patient care. These positions are presented in detail in her Fetch symposium.

For example, when calculating DER for a puppy, it is 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 weight of the adult body , and 2.71828 is a constant from simply multiplying the RER by a general factor. This more complex formula considers that newborns have high energy requirements but lower body weight, so their energy needs increase as they grow, and then eventually as they approach their adult weight, their energy requirements are lower. The cat formula is very similar, but has some slight differences (DER = 100 x BWC0.67 x 6.7 (2.71828-0.189 (BWC/BWE) – 0.66).

Given current and projected weights, feeding requirements initially increase with growth and weight gain, and then decrease as they approach the expected adult weight.

Pregnancy is another life stage in which personalized nutrition can help your patients, although there is no need to increase DER until 5 weeks after mating. Again, there are slight differences between the formulas for dams (DER = 130 x BW0.75 + [26 x BW]) and queens (DER = 140 x BW0.67). For dams, this formula equates to an increase in the market exchange rate of about 25% to 60%, and about 40% to 50% for queens. The goal during pregnancy is to maintain a normal body condition throughout pregnancy.

Lactation is another stage of life that requires additional feeding. Sarr describes feeding as one of the highest energy requirements an animal can have. The calculated DER for lactation depends on the number of puppies or kittens that are breastfed. With one pup it is DER = 3.0 x RER; However, the factor of increase for each additional puppy is an additional 0.5. For lactating queens, calculate the DER for each kitten at weekly intervals. For example, during weeks 1 to 2 of lactation, a queen’s DER is RER + 30% per kitten. At week 3 this factor is 45% per kitten, week 4 55% per kitten, week 5 65% per kitten, and week 6 90% per kitten.

Once these phases stop working, the power requirements return to the typical MER formula.

In terms of disease states, tracking weight loss and calculating the percentage of loss over time can be useful as an indicator of disease. Unexplained weight loss of 5% or more should lead to further scrutiny of any known factors or possibly diagnostic tests to identify possible causes. An unexplained weight loss of more than 10% is alarming. For smaller patients, a small change in body weight despite being a large percentage change can be easily overlooked, so it is worth returning the weight within a month to see if the trend continues or more diagnostic testing to assess possible causes.

Other disease states that require customized nutritional plans include patients at risk for refeeding syndrome. An example would be a pet that was lost and then found a week or two later, who was thin and dry. Blood work may seem normal at first. But if you provide food after a period of starvation, the compensatory physiological processes of the body that allow you to survive starvation will respond poorly to an abundance of food, and after a day or two it will lead to electrolyte disturbance and clinical signs. Refeeding, after establishing and continuing these compensatory processes, acts as a catalyst for cells to reabsorb these electrolytes and glucose previously diverted to the blood vessels, and then the concentrations of these substances in the blood are depleted. Although this sounds rather complicated, it is easy to combat these processes with a strict nutrition plan. Sar offers a successful nutritional plan not only for re-feeding after starvation, but also for diarrhea, diet changes and other similar conditions.

After calculating all of these detailed energy requirements for specific patients in very specific situations, we still need to know how much food we’re feeding. This can be calculated based on volume using calorie/cup data of each food, or by weight using kcal/kg data. For foods where the calorie/cup amount isn’t available, Sarr shows us how to calculate this using the metabolizable energy from the ingredients. NFE (Nitrogen Free Extract) is a carbohydrate. Proteins contain nitrogen, so nitrogen-free extracts are carbohydrates. Non-food items = 100% – % crude protein – % crude fat – % crude fiber – % moisture – % ash. Note that ash is not usually included but is 2.5% for canned meals and 8% for food. Metabolic Energy (ME) = 10 ([8.5 kcal/g x % crude fat] + [3.5 kcal/g x % crude protein] + [3.5 kcal/g x % crude NFE]). Addition of these ingredients gives calories per kilogram of food. From here owners can weigh the amount of food served rather than measure it.

All of these methods for calculating energy requirements are really interesting from a nutritional standpoint, and it’s great to create plans like these that are tailored to our patients, but how do we encourage owners to follow through? Saar offers several strategies for building trust and compliance:

  • Building confidence. Why do some owners trust a 16-year-old pet store employee more than a vet who has years of training and a degree behind them? We need to build trust, and Sarr reminds us that the best way to develop trust is to share stories. Share customer stories related to the recommendations you make. Talk about other people’s experiences so they know that there are others who have done well and had good experiences with the diet you’re recommending. Then seamlessly convey that trust and information to the rest of the team. Once you have completed your discussion and made your recommendation, reach out to the next person in line (technician, receptionist checking them, etc.). Clients want to see that we are all a team and an organizer, and we never fail to share information or provide different opinions.
  • Understanding and listening to our customers. Sure, we know medicine and clients should know that, but in this day and age, they also hear all kinds of extraneous information. It pays to make sure you listen to what the owners want. If they talk about kibble food versus canned food, be sure to listen. If they talk about needing the convenience of getting food from the grocery store or have a hard time driving to the pet store across town, make sure you listen up. Are they talking about preferring homemade or fresh foods over other foods? Pay attention to these details and adapt your conversation and recommendations to their needs.
  • Make one clear recommendation. Sar realizes that we may have many options, but by actually listening to the owners, you should have a clear recommendation that fits their needs and preferences. Repeat it out loud for him to hear: “I’ve thought about your pet’s needs and the information you told me, and that’s what I recommend.”
  • Treat it as a prescription. “It will improve your pet’s health, so that’s what we recommend.”
  • Be open to making another recommendation based on the client’s needs in case there are other factors influencing your recommendation.

Packer is associate professor of neurology/neurosurgery in the College of Veterinary Medicine and Biomedical Sciences at Colorado State University in Fort Collins and is board certified in neuroscience from the American College of Veterinary Internal Medicine. She is active in clinical and educational training for veterinary students and residents and has developed a comparative neuro-oncology research program at Colorado State University.


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