At CRV, we have three guiding principles to help producers succeed. We help to drive efficient production through Better Life Efficiency, build healthier herds with Better Life Health, and produce Premium Milk with milk components and our CRV HerdBuilder traits.

While fluid milk will always be a prominent focus for some, we believe that producing premium milk captures the value of the contents in milk and is one of the best ways to increase profitability of some herds. Specific fat and protein content are main traits of interest when producing premium milk. The gains for these two traits are attainable relatively fast due to the high heritability of fat and protein percentages—which are 58 percent and 51 percent respectively for Holsteins. Fat and protein pounds are also relatively high, at 30 percent for both traits, which is equally as heritable as milk yield itself.


Casein makes up 77 percent of the total weight of proteins in milk, on average. This high concentration is very valuable—as an increase of .1 percent protein correlates to a 3 percent gain in cheese produced per unit of milk. And, the good news is progress on this trait is relatively easy to obtain, with focus, because protein percent is about 51 percent heritable.

Casein proteins are made up of several diverse types of sub-proteins. These are Alpha-S1, Alpha-S2, Beta Casein (A2), and Kappa Casein—and each one of these has their own genetic variations as well as functional properties. Not only are these proteins important as we value the direct protein content of milk, but their chemical structure is what allows for milk to contain a high concentration of calcium, one of milk’s positive attributes.


Beta Casein, or A2 milk, which has been published for a while now, is anecdotally associated with greater digestibility for individuals who are intolerant to dairy products. Beta casein exists in two variants, one having a single amino acid more in the protein structure than the other. Whether an animal produces the A1 or A2 variety of milk is determined by its genotype for a single gene. Genomic testing, using tools such as CRV’s HerdOptimizer, allows animals to be tested for this gene so one can find out whether the milk that is produced is of the A2 variant. There are only three possible genotypes for Beta Casein, A2A2, A1A2, or A1A1.

Approximately 40% of Holstein animals carry the A2A2 genotype which is behind most other breeds. Breeding for A2 milk follows simple genetic principles. An A1A2 cow bred to an A1A2 sire has a 25% chance to produce a A2A2 or A1A1 animal and a 50% chance of producing a calf with a A1A2 genotype. Because of this, by selecting A2A2 bulls, the genotype of the herd can be shifted towards A2A2 relatively quickly.



Starting this August, Kappa Casein will be included in our Holstein and Jersey sire catalogs. Kappa Casein is a milk protein complex that is extremely important in the cheese making process—as it is highly correlated with milk’s ability to clot and form curds. There are three main alleles that determine the Kappa Casein produced by the cow: A, B, and E.

A cow with a BB genotype for Kappa Casein produces milk that clots 25% faster, as well as cheese that is twice as firm as a cow with an AA genotype. A cow with the BB allele would also be able to make 10% more cheese per CWT than an AA allele cow, as the kappa casein gene partly affects the protein percentage in milk. Research suggests that the third allele, E, has unfavorable effects on cheesemaking. Milk with this Kappa Casein structure could be unsuitable for cheese making as it does not clot to produce curds, this includes the AE genotype as well as EE.

Roughly 10% of North American Holsteins currently have the BB genotype while Jerseys are significantly higher, around 30%. Overall there is a 38% B allele frequency in the Holstein breed. The BB allele also correlated with an overall higher percentage of protein in milk. The approximate frequency of the E allele is 2-5%. For phenotypic expression, there is considerable variance as more expression of the B allele leads to more desirable milk while more E allele expression hinders the cheese making quality of the milk, as color coded in the Punnett squares below.



With the August Sire Evaluations, we are excited to introduce CRV’s Casein Percent trait. This proprietary CRV HerdBuilder Trait capitalizes on research CRV has done on the genetic characteristics of milk components, specifically casein, a trait not seen in any other index and another tool for producers to use when looking to increase their milk checks.

Casein Percent is a number that represents a progeny’s expected percent of casein in the protein–thus more casein per pound of protein and more cheese per pound of milk. Casein Percent is a standard trait, so what you see in our catalog for each bull is the expected genetic potential from his daughters. Simply put, the higher the value the more casein per pound of milk and the more valuable the milk for cheesemakers.

The amount of total protein that casein makes up is a topic that CRV has considered extensively, as it is so important for milk processing to make cheese. In 2012, CRV started collecting casein content from milk samples—and over a 2.5 year period studied more than 14.5 million test results from over 1.3 million cows on more than 14,000 herds from more than 2.2 million lactations.

With this extensive dataset of milk records, that continues to grow today, we found that it is indeed possible to increase casein content though genetic selection. Selecting for the casein within protein allows for the selection of animals that produce higher value of protein given high casein content. Thus, the CRV Casein Percent trait serves to help producers genetically select for a higher casein content within their protein, furthering their ability to produce premium milk.


The other 23% of proteins in milk comes from the proteins found in serum, or whey. Approximately 50% of these are Beta-lactoglobulin, 20% are Alpha-Lactoglobulin, and the rest are blood serum albumin, immunoglobulins, and other minor proteins and enzymes. The physical properties of whey proteins allow for more water to be bound to each molecule which is extremely desirable in certain processing situations, such as yogurt manufacturing.

The four specific whey proteins each have a very high heritability and it is likely a topic that will gain attention in the future. The content of these proteins has increased over time but when scaled within total protein content the whey components have a flat to negative trend. This leaves lots of room for easily attainable improvement with moderate genetic selection.


CRV is studying many specific traits that can have a significant impact on the dairy industry. As of August 2017, the Casein Percent helps predict a progeny’s percent of casein versus whey in her milk to benefit milk processing. Recent trends in the dairy industry show processing plants are starting to tailor the milk they buy based on their processing needs—such as making cheese. CRV will play a vital role to ensure that producers stay on top of this by providing specific milk traits. Our protein-specific traits are just a few tools that can help farmers create a cow that produces the desired premium milk to align well with maximizing their paycheck in the near future.

Contact your CRV Genetic Consultant today to learn how to use CRV genetics to produce premium milk on your farm.

–Written by Logan Voigts and Elizabeth Sarbacker, CRV USA Interns