In the current milk market, making money through milk is all about the amount of components produced in a hundredweight.
With fat and protein percent being highly heritable, genetic selection is one of the routes a dairy producer can take to increase a milk check. Selective breeding is about preparing for the future, so it is important to forecast the intricacies of future milk markets and to provide education about how genetics can contribute to the continuing profitability of dairy farmers.
One of those indicators, A2 milk, has been a hot topic for several years now, but only recently has the public been introduced to the product through television commercials. Brought about by a genetic variant that a proportion of animals carry, the A2 commercial business was fueled by the rise of genomic testing of commercial females.
A1 and A2 are variations of a type of protein (generally termed “caseins”) called beta casein, with the A1 variant being the more common type. Global development continues to provide an increased interest in premium food products as well as a demand for more diverse and highly nutritious foods.
If A2 is the beginning of this new era for milk products, then what components could further make up the milk check of the future? And can these components be promoted by selective breeding? This article lists several possible milk components that may become familiar to cattle breeding in the coming years.
1. Casein (kappa casein)
Milk protein consists of about 78 percent casein, the component used for making cheese. Thus, more total milk protein yields more cheese. An increase of 0.1 percent protein in milk translates to about 3 percent more cheese per pound of milk, with casein being a major contributor to cheese production. There are different types of casein proteins, and they can be largely categorized in the following caseins: alpha-S1 casein, alpha-S2 casein, beta casein and kappa casein.
A casein index is the sum of all of these casein proteins divided by total protein in milk. Research has shown there is genetic variation in the production ratio of these proteins. Some cows produce more casein proteins in the total percent protein than others, due to their genetic predisposition.
And therefore, it is feasible to breed for higher casein content, either through selection of bulls or genomic testing of females.
Current commercial genomic tests return the genetic status (genotype) of three genetic markers that each affect the amount of casein within protein in its own specific way. We already mentioned one of them: beta casein. But there are two more that are worth noting: kappa casein and beta lactoglobulin.
The genetic marker we identify as kappa casein is located on chromosome 6 of the bovine genome. Confusingly, this genetic marker is named after the protein it affects, just as beta casein is also named after the gene it influences.
Due to its effect on kappa casein, this genetic marker indirectly affects the percentage of protein in milk. A genomic test will return the status of the animal for kappa casein, and most active A.I. studs have started publishing the kappa casein genotype for their sires as well.
The highest percentage of animals will have either AA, AB or BB for kappa casein. Cows with the BB genotype are genetically predisposed to produce a higher protein content than cows with the AA genotype. In addition, variant B has a positive effect on milk coagulation during cheesemaking.
To potentially add more confusion to the designation, there is also a less frequent kappa casein variant, E. It is possible that an animal has a genotype AE or BE or EE (approximately 2 to 5 percent of the U.S. Holstein population). Although not scientifically proven, the E variant in milk has been anecdotally related to a lower ability of curdling.
2. Whey (beta lactoglobulin)
While casein makes up 78 percent of the total protein in milk, the other protein component, whey, is still important to consider. There are two main whey proteins: beta lactoglobulin and alpha lactalbumin.
Beta lactoglobulin has been gaining attention in the dairy industry due to its considerable effect on the percent of casein in protein through its effect on whey. Its effect is simple: less whey equals more casein. A cow can have the AA, AB or BB genotype for the genetic marker identifying the types of beta lactoglobulin.
About 18 percent of Holstein cows are AA, 49 percent AB and 32 percent BB for beta lactoglobulin. A research study shows that cows with a BB genotype have about 3 percent higher total casein content within their total milk protein than cows with the genotype AA. AB lies between, with a 1.5 percent higher casein-protein ratio than AA animals.
So what does that mean? Suppose the herd has an average of 87 percent casein in the total percent protein. Active selection and pairing for animals with the BB genotype for kappa casein and beta lactoglobulin allows for an increase of casein percent in protein. If the casein percent increases to 89.5 percent, 3 percent more cheese can be made from the same pound of milk, thereby increasing its value to cheesemakers.
Hidden within the category of “other solids,” lactose is often forgotten when we talk about raising components in milk. However, 5.9 percent of the volume of milk is composed of other solids, making them a substantial part of each milk check, and lactose is the largest element of this category. Important for the production of infant formula and pharmaceutical products, lactose is an essential byproduct of the dairy industry.
As lactose is the main sugar present in milk, it is the main regulator of water content in milk and is notoriously difficult to alter. Every pound of milk contains a more or less equivalent amount of lactose: 4.5 percent. This is because lactose is the final piece of milk production.
The amount of lactose a cow produces controls the height of her milk yield (through osmosis). However, the percent of lactose within milk is subject to genetic variation, even when corrected for genetic merit of milk volume. The European Union introduced a breeding value for lactose percent in 2015 that allows dairy producers to breed for higher lactose, alongside fat and protein.
The trait has a heritability of 55 percent, which means it is very much controlled by animal genetics. The average percent lactose in milk is approximately 4.6 percent, and Holstein cows show genetic variation between 4 and 5.5 percent, making this a trait that can be improved through breeding strategies.
4. Milk urea nitrogen
It doesn’t affect milk checks, but milk urea nitrogen (MUN) is a usual parameter on any DHIA report. In the U.S., we are accustomed to MUN being indicative of crude protein utilization. But MUN also has a large genetic component. It measures the amount of urea in the milk, and is therefore indicative of how efficiently a cow synthesizes protein. The heritability of MUN is 65 percent, greater than fat or protein percent, and therefore lends itself perfectly for selective breeding.
As the value of MUN lies primarily in its relationship to feed efficiency in the U.S., other parts of the world have shown that breeding for low MUN may give additional breathing room when environmental regulations on mineral leakages get tightened.
Due to the direct relationship between MUN concentration and the amount of nitrogen excreted by a cow, it is expected that a reduction of MUN concentration through breeding also leads to a reduction of amount of nitrogen excreted in cow urine. To make dairies profitable, a producer needs to reduce all inefficiencies in a system, and MUN can be considered one component that can control multiple inefficiencies in a dairy system.
By Dr. Sophie Eaglen
Published in Progressive Dairyman, 29th of June 2018