Managing Total Solids in Nonsalable Milk
Posted: August 12, 2009
Research published in the July issue of the Journal of Dairy Science (Moore et al.) investigated the use of a Brix refractometer to manage total solids in nonsaleable milk fed to calves. The study was conducted on a calf ranch where milk was collected from 12 source dairies, pooled, and pasteurized before feeding. Bacteria counts were measured after pasteurization periodically. Drivers picking up milk rejected any that smelled “off,” and the calf ranch manager evaluated odor, color, and consistency to determine if the milk could be fed. This study began because calves looked thin and mortality rates had recently gone up, even though pasteurization appeared to be effective.
Investigators used a Brix refractometer to measure total solids content of milk at each source dairy and before and after pasteurization at the calf ranch. Total solids ranged from 5.1 to 13.5% with an average of 11%. By comparison, 12.5 to 13% solids is the normal value for whole milk. Milk being fed to calves varied quite a bit in the amount of solids it contained, and the researchers concluded that calves were suffering from inadequate and inconsistent nutrition. Once solids were tested, a program was developed to adjust the solids content at each feeding.
Variation in nutrient content of waste milk is to be expected and may be due to changes in the number of cows contributing milk and their stage of lactation, other factors include added water or reduced milk component production due to mastitis. This study and other on-farm observations have shown that considerable changes can occur between sources and even within one herd from day to day. A survey of 31 Wisconsin herds found ranges of 2.8 to 4.7% for fat and 2.9 to 5.1% for protein in waste milk. Nonsalable milk from 3 North Carolina herds contained 1.5 to 4.5% fat and 2.7 to 3.8% protein, and 10 California farms had 1.2 to 12.1% fat and 2.7 to 4.7% protein in calf milk.
Measuring and adjusting fat and protein levels quickly on the farm is not practical, but with the help of a refractometer, total solids are fairly simple to monitor. The Brix refractometer measures the amount of sugar in a sample, so observed values must be converted to estimate total solids in milk. Researchers in the study described above developed a standard curve using milk samples with a known amount of solids and then calculated an equation to convert Brix values to total solids values. Using this equation, the total solids of a batch of milk can be estimated and adjusted appropriately. The study’s authors cautioned that the refractometer prism must be thoroughly cleaned after every milk sample to avoid residue that could affect the next measurement.
The equation developed in this study was total solids = (0.9984 × Brix reading) + 2.077 for a Reichert hand-held model with temperature compensation (Reichert Brix HP35). Using this equation, the total solids of a batch of milk can be estimated and adjusted appropriately. Developing your own standard curve and equation for your particular model may be more accurate and is not difficult. When selecting a Brix refractometer, be sure to choose one that can measure the range of solids you expect. A scale that starts at 0 and goes to approximately 30 should provide a good range for testing waste milk.
Milk replacer or a milk extender can be added to increase the solids content of nonsaleable milk. Another option is to increase the amount of milk fed to compensate for lower solids; however this would not be practical if feeding from bottles and could result in wide variation in the amount of liquid offered to calves every feeding.
When adding solids to nonsaleable milk, the fat and protein content are not considered. However, some contemplation of the typical fat and protein level of waste milk and of the levels in the chosen product is advised when determining what product will be used. A 20% protein, 20% fat milk replacer will change protein and fat in waste milk proportionally, and the final mix will have the same relative amount of protein and fat as the original waste milk. However, other formulations can reduce fat more than protein or reduce both fat and protein to bring the composition of milk closer to the composition of a 20/20 milk replacer. Consider the impact of these options on milk composition before choosing a strategy for increasing the volume of milk.
A milk solids calculator to help you determine how much milk powder to add is available within the pasteurizer spreadsheet developed by Penn State and Virginia Tech. To download this spreadsheet, which now includes the above Brix transformation equation, visit www.das.psu.edu/dairynutrition/calves.
Coleen Jones, Research Associate, and Jud Heinrichs, Professor of Dairy and Animal Science, Department of Dairy and Animal Science