Tyler points to Saletan on science.

Researchers are breeding mutant cows that make low-fat milk. After a farm accidentally produced the first such cow, milk-company researchers "bought her from her owner for $300 … and moved her to a secret location for further testing." Then they bred offspring that carry the trait. The milk is 1 percent fat instead of 3.5 percent, and it has omega-3 fatty acids, which are good for your heart. The next step is to identify how the gene causes the milk so this pathway can be directly engineered. Milk-company spin: It's natural! Cynical view: It's the "accidental" product of constant breeding, and now we're going to engineer it worldwide.

All milk has omega-3 fatty acids, but the percentage and balance with omega-6 fats varies depending on the cow's diet as well as genetics. A grass diet yields milk that is much higher in omega-3 than does a grain diet.

The amount of total fat also varies with diet as well as genetics. Different breeds are well known for wide variation and dairymen select both breed and herd sires depending on their objectives. For example, a dairyman that is producing milk for cheese yield will want higher fat milk than one producing for a fluid market. He may use Jersey cows, known for their high butterfat milk, and feed them a diet designed to increase fat percentage.

The idea of breeding for low fat milk, a relatively new market, has long been discussed but there were few if any mechanisms a dairyman could use to profit from such a market, especially given that the processing plants had efficient methods for separating fat from fluid milk to produce low fat milk and the fat coproducts which had a good market too.

It is misleading to call such cattle mutants. It is normal for animals to vary in their genetics, just as people do. Breeders select for desirable traits in that gene pool. Fashions change over time so the "standard" animal has varied significantly over the decades.

I doubt that there is much of a market for low-fat cattle since the product can be so easily made. There is likely a small market among those who have no grasp of the issues but are believers in some flavor of natural theology. It is said that there is one born every minute.