WildAgain Wildlife Rehabilitation, Inc.


Update on measuring powdered milk replacers - scooping or weighing? 

One method can result in significant underfeeding
 
 

The texture of some of the milk replacer powders is uneven and inconsistent, and the particles have a tendency to clump together. This can make it difficult to accurately measure the powder volume with a scoop. WildAgain's lab tests show a relatively high degree of variability, averaging around +/- 5%, but in some cases as high as almost 20%. The instructions on the packages of milk powder explain how to use a scoop to measure Volume.  However, the inconsistency of the milk powders suggest Weight gives a more accurate measurement - which is important when preparing food for young and compromised wild mammals.

Measuring by volume  (using a scoop)

Many rehabilitators follow the mixing instructions on the label use a scoop to measure milk replacer powder prior to mixing as it is easy and quick. The scoop used can vary in size from the red scoop supplied with PetAg® products, or a teaspoon, tablespoon, a cup, or even larger, depending on how much formula is being prepared at a time.

Measuring by weight  (using a scale)

Examination of powdered milk replacer products from various manufacturers reveals the powders to be more uneven and inconsistent in texture. As a result, using the volume or scooping method can produce considerable error, especially where fine measurements of components, such as proteins and fats, are desired. For these types of products with high variability in texture, measuring by weight will yield a more consistent amount of powder to be mixed into a formula.

 

Why is this an issue? Part 1

The scooped weight of the powdered products varies with successive scoops even when the person measuring is taking time and care to be very accurate. Figures 1 through 4 below illustrate the results of 35 successive trials of scooping the powdered products and then recording the net weight of each scoop. Figures 1 and 2 show the average net weights, as well as the data point for each of the 35 trials (scoops). Figures 3 and 4 show the percentage variation from the average for each trial, as well as the 'expected' variation, defined statistically as one standard deviation, meaning the scoop weight should fall within that range (gray shaded area below) 68% of the time.

What this means is that the higher standard deviation for the product, the higher a single amount of powder measured by using the scoop (rather than weighing) will deviate from the average. This indication of (scooping) measurement error is included for all products evaluated by WildAgain on the individual web page for the test results for each product. This introduced error can cause a much less accurate amount of powder to be used for mixing into formula, and in some  cases, much less powder than expected. This becomes more pronounced when the powder is mixed with water into a wet matter basis, as described in Figure 5, and further highlighted in Figures 6 through 9.

Figure 1. The powder from this lot (H3532E) was scooped 35 times in successive trials and then weighed. The average net weight of the powder was 4.9 grams/TBSP, with a range of 4.1 grams to 5.5 grams. Figure 2. The powder from this lot (10413) was scooped 35 times in successive trials and then weighed. The average net weight of the powder was 6.0 grams/TBSP, with a range of 5.5 grams to 6.5 grams.
Figure 3. This figure shows the percentage variance from the average weight per scoop, ranging at the high end at +13% over the average and -16% at the low end. The statistical expected range of error is +/- 7%, representing one standard deviation (meaning the scooped value would be within this range 68% of the time, and represented by the gray shaded area above. Figure 4. This figure shows the percentage variance from the average weight per scoop, ranging at the high end at +8% over the average and -9% at the low end. The statistical expected range of error is +/- 4%, representing one standard deviation (meaning the scooped value would be within this range 68% of the time, and represented by the gray shaded area above.

 

Figure 5. So why worry about this range or deviation from the average? The picture at the right shows a graphical representation of how this range can effect the nutritional values when the product is mixed with water to make formula. In the picture, the kcal/cc values are shown for a product mixed 1 part with 2 parts of water, where the red letters indicate the following:

A. This is the average kcal/cc value of the 35 trials (scoops), or .84 kcals/cc.

B. This is the high end of the expected range, or .90 kcals/cc.

C. This is the low end of the expected range, or .78 kcals/cc.

D. This is the highest data point seen during the trials, at .96 kcals/cc. Not expected, but possible.

E. This is the lowest data point seen during the trials, at .71 kcals/cc. Not expected, but possible.

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Why is this an issue? Part 2

As shown below in Figures 1 through 4 above, certain of the powdered milk products commonly used by rehabilitators from various manufacturers are showing increased variability and inconsistency over time, especially with the products recently tested in May 2013. Additionally, because of these weight variations, the scooped average weight of recently manufactured lots of the products, when compared to lots of just a couple of years ago, results in a wet matter basis composition (mixed 1:2) has dropped 17-18% in the case of certain PetAg® products, and increased 4-6% in the case of certain Fox Valley® products. The data shows that the Esbilac® and KMR® formula (as shown in Figures 6 and 7) that is prepared by scooping the powder  can result in a 17-18% more dilute mix than 2 years ago. In the case of the Fox Valley powders tested, the formula may be 4-6% richer than may be expected.

Figure 6. Kcal/cc values over time of various lots of the product indicated when the product is mixed at 1 part powder with 2 parts of water. See Figure 5 for an explanation of how to interpret the chart and the associated values and data ranges. Figure 7. Kcal/cc values over time of various lots of the product indicated when the product is mixed at 1 part powder with 2 parts of water. See Figure 5 for an explanation of how to interpret the chart and the associated values and data ranges.

Figure 8. Kcal/cc values over time of various lots of the product indicated when the product is mixed at 1 part powder with 2 parts of water. See Figure 5 for an explanation of how to interpret the chart and the associated values and data ranges. Figure 9. Kcal/cc values over time of various lots of the product indicated when the product is mixed at 1 part powder with 2 parts of water. See Figure 5 for an explanation of how to interpret the chart and the associated values and data ranges.

 

How can this result in possible underfeeding?

Scooping the product introduces 2 different types of error, as discussed above. First, the net weight of the powder in each time scooped is not identical. Second, the net weight of the scooped powder is not identical to prior years. So that successful results seen using a particular product in prior years may not be fully repeatable because of these two types of errors.

The table shown in Figure 10 illustrates this measurement impact, when comparing recently tested lots of Esbilac® (2013) with previous lots tested in 2010. The table highlights this error in 4 situations:

1. When 6.0 grams of powder (measured by weighing) is mixed with 2 parts of water, both current and past lots yield about the same nutritional composition in a prepared and fully rehydrated formula. The difference is essentially zero.

2. However, when measuring by scooping, the current (2013) lots of Esbilac® produce a composite result that is about 16% lower in nutritional value, on average, than lots manufactured in 2010, because the current lots of powder weigh less on average.

3. When considering the expected range of variability (as discussed above), the expected low end of the range can produce a composite result that is about 21% lower in nutritional value, than lots manufactured in 2010.

4. Finally, when considering the lowest test trials observed but outside the expected range of variability (as discussed above), the possible lowest end of the range can produce a composite result that is about 28% lower in nutritional value, than lots manufactured in 2010

Figure 10. Tabulation of the impact of scooping measurement error on nutritional composition when comparing recent lots tested (2013) with lots from prior years.

 

Scales and how to accurately measure by weight

For those not familiar with using a digital scale, the photos below provide an overview of the process.

Figure 11. The powder can be placed on a small piece of wax paper and then weighed on the scale. In this case, the amount of powder on the scale weighs 6.5 grams, which is equal to 1 tablespoon of the powder. Figure 12. If the scoop is to be used in measuring and then using a scale, it is important to know the weight of the scoop. In this case the scoop weighs 3.1 grams. Figure 13. Here the scale has been adjusted, or "tared" to compensate for the weight of the scoop. Once this is done, then the scale will then show only the weight of the powder. In this case, the powder weighs 6.5 grams. Figure 14. If the scale used does not have a tare function, then simply weigh the scoop (as in Fig.2), then weigh the scoop filled with powder, and subtract the weight of the scoop. In this case, 9.6 minus 3.1 equals 6.5 gr.

What should the milk replacer powder weigh?

For products and lots listed on this website. All of the lots tested by WildAgain have 1 tablespoon weights associated with them, as determined by WildAgain's tests. All of the calculated component analysis values presented on this website are based on those weights. So using those same weights of powder and mixing 1:2 are expected to produce the same component values for those lots.

For products and lots not listed on this website. The best suggestion is for the first 2-3 measurements from a can or bag, weigh each of them, try each in a proven formula recipe, and if successful results are seen, then use that weight as the standard for that bag. If successful results are not seen, then add or subtract slightly from the weight and try again to establish a standard weight for that bag or can that produces successful results in a formula. This is especially important for any milk replacer powders that have a pronounced tendency to compact in the bag or can, and having lighter weight volumes at the top and heavier weights at the bottom. For those products with the tendency to compact, such as some lots of PetAg milk powders, the compaction can be somewhat compensated for by turning or rolling the bag or can multiple times between each time the powder is used.

While it clearly takes more time to weigh the milk powder instead of scooping a volume, weighing can help reduce measurement error from mixing and using formula made with a powdered milk replacer.

 

Sources for scales

Accurate and easy to use scales are essential equipment for a wildlife rehabilitation facility, whether a large rehabilitation center or smaller home-based rehabilitation facility. Accurate digital scales have become fairly inexpensive and easily available for purchase at retain establishments or online. In addition, accurate digital scales that weigh smaller amounts (less than 5 pounds) may be available at kitchen supply shops, cooking schools, or even from weight management programs. In some communities, law enforcement agencies and related non-profit groups have donated extremely accurate scales that had been confiscated and were otherwise scheduled to be destroyed.

There are many type of scales available. Scales that measure in grams are preferred since they are able to be more precise. A digital scale is desirable since the amounts can be easily read. It is nice to have a digital scale that measures in precision to tenths of a gram if weighing small amounts, such as milk replacer powders or very small animals. Regardless of type of scale, it is important for it to be accurate.

 

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