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Not the Brix: Refractometers inaccurate at measuring milk replacer solids

Drew A. Vermeire for Progressive Dairyman Published on 29 December 2017

Consistency is a foremost principle for success in raising calves. Unfortunately, calf producers who use a Brix refractometer in an effort to maintain consistent milk replacer concentration are wasting their time.

Research was undertaken to develop a dataset which would enable a milk replacer manufacturer to include Brix readings on their labels as part of their mixing directions. Brix guidelines would have made it easier for calf producers to consistently mix milk replacer.

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Surprisingly, the researcher showed Brix readings are not related to milk replacer solids content. There are better, more reliable methods for accurately and consistently mixing milk replacers to the desired solids content.

Percent solids, Brix and milk replacer

What does the term “percent solids” mean when referring to milk replacer? Does it mean weight per weight, which is what Brix actually measures (gram sucrose per kilogram solution), or does it mean weight per volume, which is what most calf producers need to know (ounces per bottle)? Worldwide, most calf feeders use weight per volume by referencing grams of milk replacer powder per liter of total solution.

This is an accurate description without confusion because it always means weight per volume. A milk replacer solution with 150 grams of milk replacer powder per liter of solution represents 10 ounces of milk replacer powder in a 2-quart bottle (150 grams per liter x 1.9 liter per 2-quart bottle ÷ 453.6 grams per pound x 16 ounces per pound = 10.05 ounces per bottle). For clarity, grams per liter will be used in this article, and in the figures, percent solids means grams per 100 milliliters.

Brix refractometer reliable for colostrum and waste milk

When a stick is put into water, it appears to bend due to the bending of light. We see that air and water have a different “refractive index.” The refractometer measures this bending of light and is a reliable tool for estimating sugar content in making wine, spirits and maple syrup.

Based on limited research, a refractometer can be used for reliably estimating solids content in colostrum or waste milk. As a general rule, (Brix + 2) x 10 = gram solids per liter for waste milk.

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Should we use Brix for milk replacer?

The simple answer is: no. Calf producers who use a Brix refractometer to test milk replacer are under the assumption milk replacers have the same light-bending characteristics as milk which, unfortunately, is not true.

Laboratory testing of individual milk replacer ingredients

Modern milk replacers are made with ingredients such as whey, whey protein concentrate and nonfat dry (skim) milk power. Additionally, non-milk ingredients such as wheat protein, soy protein and blood plasma protein may be used, which can lower cost and improve calf performance.

Do individual milk replacer ingredients have the same effect on Brix readings? Individual ingredients were mixed with distilled water in the laboratory at a concentration of 150 grams per liter and measured using a digital Brix refractometer. Surprisingly, none of the ingredients showed a consistent or accurate relationship between actual solids content and Brix reading, as shown in Figure 1.

Brix of milk replacer ingredients at 150 g/L

Inconsistent and confounded results due to protein and fat levels

Lactose is not listed on the label, yet it is the constituent with highest concentration in milk replacers. A milk replacer with 22 percent protein and 18 percent fat contains about 4 percent moisture, 6 to 12 percent ash, depending on the manufacturer, and lactose varies from 50 to 46 percent, depending on the ash content.

Lactose levels vary inversely with protein, fat and ash levels. Since Brix is a measure of sucrose, and both lactose (glucose + galactose) and sucrose (glucose + fructose) are disaccharide sugars, one would expect Brix to reflect lactose content of milk replacer. Surprisingly, the test results showed this expectation was also incorrect.

Figures 2 and 3 show Brix measurements of milk replacer solutions with different levels of protein and fat.

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Brix vs. protein in milk replacers mixed at 150 g/L

Sample milk replacers were made in the laboratory using combinations of whey, whey protein concentrate and 7/60 dried fat to adjust protein and fat levels. Samples all had a true concentration of 150 grams per liter. Brix was measured using a digital refractometer.

Brix vs. fat in milk replacers mixed at 150 g/L

As protein levels increased (lactose level decreased), Brix actually increased (Figure 2). Figure 3 shows that, as fat level increased, Brix slightly decreased – but not at a rate reflecting the change in lactose, and Brix measurements did not reflect the solids content of any of the solutions tested.

The bottom line: There is no predicable, meaningful or accurate relationship between the Brix reading from the refractometer and actual solids content of milk replacer solutions. The combination of individual ingredients and levels of protein, fat and ash confound Brix.

Even different batches of the same milk replacer could have different Brix readings because different batches of ingredients are often used to manufacture each batch of milk replacer.

How to accurately and consistently mix milk replacer

Imagine an operation with a trailer which holds 504 2-quart bottles and a mixer which holds 300 gallons. To fill the bottles on the trailer, a total volume of 252 gallons is needed, which is about 85 percent of the mixer’s capacity.

There needs to be a balance of feeding rate and protein level. With a feeding rate of 11 ounces per bottle, for example, protein level will need to be approximately 24 percent to meet the growth potential of most young calves.

To calculate the amount of milk replacer to add to the mixer: 11 ounces per bottle x 504 bottles ÷ 16 ounces per pound = 346.5 pounds milk replacer needed. For simplicity, round up to 350 pounds, which is seven bags of milk replacer per batch. This will consistently deliver 11.1 ounces per bottle.

Concentration is: 350 pounds x 453.6 grams per pound / 252 gallons / 3.8 liters per gallon = 165.8 grams per liter.

Be consistent. Mix at the same time, same temperature and same concentration every feeding. To maximize the time between feedings for the most sensitive calves, feed youngest calves first in the morning and reverse order in the afternoon, feeding youngest calves last.  end mark

Drew A. Vermeire
  • Drew A. Vermeire

  • Consulting Calf Nutritionist
  • Nouriche Nutrition Ltd.
  • Email Drew A. Vermeire

Mixing procedure*

  1. Add 50 percent of the total water (126 gallons) needed to mix the milk replacer at the mixing temperature recommended on the milk replacer label + 5ºF because adding the milk replacer powder will cause the temperature to decrease. Read the label and use a thermometer.

  2. Turn on mixer and add milk replacer powder to mixer. Either feed whole-bag amounts or use a scale to weigh milk replacer. Mix for four to seven minutes.

  3. Add water to mixer and adjust temperature to filling temperature and bring volume up to fill level, in this case 252 gallons.

  4. Mix for one minute, then fill bottles.

  5. Measure feeding temperature in last bottles fed. I recommend 113ºF for the last calf, which means filling temperature will likely need to be in the range of 117ºF to 120ºF. Calves readily accept milk replacers at these temperatures with fewer digestive and sanitary problems. For the next batch, adjust filling temperature based on Step 5 results. 

* Example uses 300-gallon batch mixer, filled to 85 percent capacity, to mix 252 gallons of milk replacer. The volume is enough to fill about 504 bottles with 11 ounces of liquid.

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