Knowing the total solids content of milk replacer fed to calves is critically important, yet few producers or calf managers know their total solids content or how to calculate it.
Total solids content of a milk replacer mix is how “strong” you mix it up. Every farm does it a little different and it is rare to find someone following the directions on the milk replacer bag. Total solids greater than ~17-18 percent presents a risk of disrupting normal cell balance inducing scours in calves. When total solids are too low, calves will be hungry and not consuming enough calories to grow, maintain body temperature, and support the immune system.
Saleable whole milk is about 12.5 percent total solids. Waste milk can vary greatly but is often 11-15 percent solids. My preference is to use a milk replacer concentration of 12-15 percent total solids, and achieve this with specific volume, feeding frequency and average daily gain (ADG) goals for the farm. As total solids increase, the risk of scours increases. Therefore it is imperative that calves have access to clean, fresh water to self-regulate cell osmotic balance and that milk replacer mixing is very consistent.
The formula to calculate total solids is:
- Percent Total Solids = pounds of powder/ pounds of total solution
In order to calculate total solids, we must know the weight of the powder, not volume, so use a scale. To get to the pounds of total solution, we know that milk is 8.6 lbs. / gallon so we can multiply the volume by 8.6 lb. / gallon to get a final weight.
It is all in the details
It is important to use the final volume to calculate total solids, not the amount of water added. This detail often gets missed and leads to mixing and calculation errors. The correct way to mix milk replacer is to start with water, add the powder and then add enough water to bring up to total volume.
Example 1: The directions say: Feed each calf 12 oz. (0.75lb) of milk replacer in a volume of three quarts (0.75 gallons) total solution twice daily. The calculation is:
0.75 lb. powder/ (0.75 gallon * 8.6 lb. / gallon) = 11.63 percent total solids
If the directions are not correctly followed and three quarts (0.75 gallons) of water are added to 12 oz. (0.75 lb.) of powder, the powder displaces the water for a total volume of 0.86 gallons. When feeding three quarts of this mix, the calf will receive less than the desired 0.75 lb. powder. The calculation is:
0.75 lb. powder / (0.86 gal * 8.6 lb. / gallon) = 10.1 percent total solids
How many pounds is she consuming?
For our previous two examples, let’s figure out how many pounds of milk replacer powder each calf is consuming, assuming that milk replacer powder is mixed into a batch and three quarts twice a day is measured out to each calf.
- Example 1: 11.63 percent total solids * (0.75 gallon* 8.6 lb. / gallon) * 2x/day = 1.5 lb. powder per day
- Example 2: 10.1 percent total solids * (0.75 gallon* 8.6 lb. / gallon) * 2x/day = 1.3 lb. powder per day
The difference between these two ways of mixing could be the difference of a calf gaining weight or not, or fighting off disease versus succumbing to it. Before calves are consuming a measurable amount of starter, all of their calories are coming from milk, so it is imperative that we get it right.
Calves grow better when their diet is consistent. A big advantage to feeding milk replacer over waste milk is the consistency of the diet. Refractometers can be used with whole milk to determine total solids, however it is not accurate for milk replacer. A refractometer is very useful for checking consistency in milk replacer mixing. Michigan State University Extension recommends no more than one percent variation day to day in mixing and during feed-out (from the beginning of feeding to the end). If variation is greater than one percent within a feeding, that indicates that the solids are settling. Ensure that proper water temperature is being used, mixing time is long enough to get all product in suspension and the mixed product is not sitting too long before feeding.
Just knowing that calves are being fed three quarts of milk replacer twice a day is not enough information. In order to understand a calf feeding program, we need to know the pounds of milk replacer powder fed, which is based on volume, frequency and total solids of the liquid fed.
If your calves are not meeting the goals you have set, do the calculations and talk to your vet, nutritionist, or Extension Educators about how to meet your goals.