As strange as it may have seemed a decade ago, milk fat is now an acceptable component of milk. Many registered dietitians have approved regular fat dairy instead of pushing for skim. They’re embracing butter instead of artificial margarine as well. With the rejection of dairy fat as a contributor to heart disease, whole milk, butter, full fat yogurt and other full-fat dairy items are now desirable as a source of energy and as part of a wholesome food rich in calcium and protein. As a result, sales for butter, whole milk yogurt and cheese and whole fluid milk have improved.
The problem for dairymen lies in milk fat depression: the condition that causes dairy cows to produce milk that’s naturally lower in fat.
Dale Bauman, PhD and professor emeritus with Cornell University recently spoke on the topic for a webinar through The Nutritionist hosted by Cornell and Agricultural Modeling and Training Systems, LLC.
Bauman said a cow’s mammary gland naturally synthesizes nutrients into milk fat. A key component of milk, fat makes dairy products taste good and is necessary for butter, cream and ice cream.
Bauman described the characteristics of milk fat, “a lipid droplet surrounded by phospholipid membrane with milk fat globular membrane proteins.” Milk fat is about 95 percent triglycerides, representing more than 400 different fatty acids, including trans fatty acids, because of the rumen fermentation.
“Ruminates have saturated fats because of the rumen microbes converting unsaturated fat to saturated,” Bauman explained. “Only about one-half or less of the fat in ruminates is saturated.”
The naturally occurring trans fatty acids in milk are different from those arising from partial hydrogenation, which have “received a lot of publicity because of their association with heart disease,” Bauman said.
He explained that many factors affect milk fat, such as diet, season, temperature, breed, time of lactation, number of lactations. But diet seems to be the most important overall factor and one of the few that farmers can completely control.
Research as early as 1845 indicated that diet influences milk fat depression, reducing it as much as 50 percent, even as other milk components remain unaffected.
When scientifically based rations became popular in the 1940s, milk fat depression became more widespread, yet another indicator that diet plays a large role in milk fat content.
Diets low in fiber, high in grain, and high in oils such as fish oil is “typically where you’ll see milk fat depression,” Bauman said.
He added, “They began to feed cows according to recommendations and that meant types of diets that are associated with milk fat depression.”
The 1939 World’s Fair in New York City presented a “Dairy World of Tomorrow” display that Bauman said helped many recognize the affect the animal’s diet has on milk quality. The pellet diet the animals ate resulted in milk so low in milk fat that producers struggled to make butter from it.
“It caught people’s attention,” Bauman said.
Since commercially-produced diets began to replace grazing in that time period, several theories developed to explain why and how the cow’s diet affects milk fat.
Bauman concluded that bioactive fatty acids that come from ruminal biohydrogenation of dietary unsaturated fatty acids cause milk fat depression.
He believes the rumen environment is very important and is affected by diet, the cow herself, and the animal’s environment in many ways.
Bauman said the mammary glands take the absorbed bioactive fatty acids to control the expressions of genes for important enzymes that regulate milk fat synthesis.
“Not all fatty acids are created equal,” Bauman added. “Location and geometric configuration of double bonds results in market differences in biological effects.”
He thinks that studying diet’s effect on milk fat truly shows the impact of rumen.