Consistency is key when mixing milk replacer for calves. Variations in solids percent can have a negative impact on calf health and growth. It is critical to understand how to calculate solids content of milk replacer and to have an easy-to-follow mixing protocol in place for everyone feeding calves, so they receive the nutrition they need to thrive.
Why Milk Replacer Solids Matter for Calf Health and Growth
A “safe” range for milk replacer solids is between 12% to 15%, although aiming for 12.5% to 13% solids is ideal since it closely mimics the composition of whole milk at 12.5% solids. If the solids percent is too low, the calf may suffer from a nutrient deficiency causing decreased growth and immune function; conversely, a solids percent that is too high increases the osmolality of the solution, which can lead to scours, abomasal bloat, and reduced nutrient absorption.
Understanding Osmolality in Calf Milk Replacer
Osmolality is the total number of solute particles dissolved in a liquid. The osmolality of cow’s milk is around 300 mOsm/kg. Milk replacers vary in osmolality because each has its own formulation and includes different concentrations of lactose, minerals, etc. When mixed properly, milk replacers typically range between 300 to 500 mOsm/kg. If osmolality exceeds 600 mOsm/kg, the solution becomes hypertonic pulling water out of the calf’s tissues and into the gut. This shift can cause scours and significant dehydration. Too high osmolality can also delay abomasal emptying, meaning the milk sits in the stomach longer. This provides a perfect environment for rapid bacterial fermentation and gas production, which can lead to bloat. Continual feeding of high osmolality milk replacer has been shown to damage the lining of a calf’s gut and increase intestinal permeability causing “leaky gut”. This can decrease nutrient absorption and increase the risk of pathogens being transferred into the bloodstream. While not a remedy for excessively high osmolality milk replacer, offering free-choice water to calves is extremely important to provide balance.
To ensure proper osmolality of reconstituted milk replacer, solids percent must be calculated correctly. Knowing how to calculate solids content is something many people do not know how to do or think they know how but are actually calculating it incorrectly. One key factor to consider is how the milk replacer is mixed. When milk replacer powder is added to water, it displaces the final volume in the container. In other words, if you add 10 oz of powder to 2 qt of water, the final solution will be more than 2 qt. This differentiation of if the milk replacer powder is being added “into” a final known volume or “onto” the volume is key in mixing milk replacer to a targeted solids content.
If we mix 10 oz of powder “into” 2 qt, so the final volume of reconstituted milk replacer (powder + water) is 2 qt, the solids content would be 14.5%. If we mix 10 oz of powder “onto” 2 qt of premeasured water, the solids content would be 13.0% and the final volume would be slightly above 2 qt. In both cases, the solids percent falls within a “safe” range, although the 13.0% is optimal because it is similar to whole milk. However, there is a problem if the milk replacer is not mixed the same way by everyone. In this example, there is a 1.5% difference in solids depending on if you are mixing “into” or “onto” a volume. This can lead to poor calf health and decreased average daily gains as calves thrive on consistency. Here’s a breakdown of the math:
Pounds of Powder / Pounds of Total Solution * 100 =
Percent Total Solid
16 oz = 1 lb
1 qt of water = 2.085 lb
1 qt of milk = 2.15 lb
“Into”
10 oz / 16 oz = 0.625 lb
0.625 lb / (0.625 lb + (2 qt * 2.085) * 100 =
14.5% Total Solids
“Onto”
10 oz / 16 oz = 0.625 lb
0.625 lb / (0.625 lb + (2 qt * 2.085) * 100 =
13.0% Total Solids
Weigh Milk Replacer for More Consistent Mixing
When mixing milk replacer, always use a scale to weigh the powder. I repeat, always use a scale to weigh the powder. Measuring milk replacer based on volume using a measuring cup is inconsistent because powder density can vary. If your milk replacer comes with a measuring cup, only use it as a tool to transfer the powder to the scale for a precise weight. Scales are inexpensive, Walmart sells food scales for less than $12 and are cheap insurance when it comes to ensuring milk replacer is mixed accurately.
A single case of nutritional scours caused by high solids content can cost between $50-$500. This includes direct treatment costs such as labor and electrolytes as well as indirect costs such as reduced growth, increased mortality risk, and delayed breeding. Weighing milk replacer reduces variation. For many farms, the same person is not always feeding the calves at every feeding. What one person thinks is 10 oz in a measuring cup may not be the same as the next. Even slight variations can cause a big difference in the solids percent. For example, if one person measures 10 oz into 2 qt and the next measures 11 oz into 2 qt, that’s over a 1% difference in solids. These fluctuations day to day and feeding to feeding can adversely impact the calf.
Create a Consistent Calf Milk Replacer Mixing Protocol
It is vital that everyone feeding calves understands how even slight variations in milk replacer concentration can negatively impact calf growth and health. To ensure proper mixing, develop a clear, step-by-step protocol detailing exact powder and water measurements, and post it prominently in the mixing area. Regularly reviewing these steps will prevent protocol drift and ensure your calves, and your future herd, are set up for long-term success. If you need help developing or reviewing mixing protocols, reach out to your KENT Nutrition territory sales manager for guidance.
