Grass matters in cow diets

by Tamara Scully
Today’s conventional dairy farms typically feed a total mixed ration which includes grains and by-products for energy balancing, as well as hay and other forage crops, plus mineral supplements. No longer do most lactating dairy cows graze the pastures, producing milk primarily from the grass and legumes they harvest themselves. Instead, farmers spend time and energy growing feed crops such as small grains, hay, corn and soybeans.
The organic dairy sector has long fought for the requirement that cows must spend their time outside actively grazing, and that a majority of their dry matter intake comes from pasture forages and not grains. Controversy over the amount of pasture forages in organic dairy cow diets, USDA organic standards set this at a minimum of 30 percent DMI from pasture forages, as well as the amount of time spent grazing, a minimum of 120 days or more if the grazing season lasts longer in the region, still remains.
Some producers are turning to alternative labels to differentiate their milk, made from primarily pasture grass and legumes. Organic Valley released its “Grassmilk™” label, from cows fed an almost 100 percent forage-based diet, along with some allowed supplements such as molasses for energy and needed minerals, in 2011. Maple Hill Creamery, established in 2009 in New York, produces 100 percent forage-based, certified organic milk and milk products, sourced from just over 100 small family farms in the region.
A recent study, led by Charles Benbrook, Bloomberg School of Public Health, Johns Hopkins University, and a team of nine other researchers from Australia, the United Kingdom and the United States, demonstrated that milk made under Organic Valley’s “Grassmilk” standards, or nearly identical standards from other brands (known collectively as grassmilk) has different nutritional profiles than that of conventional, or even certified organic, milk.
Milk nutritional value
The research team examined the differences in beneficial fatty acids between milk produced from primarily grass-fed cows, certified organic milk, and milk from conventional dairies. They then examined whether drinking Grassmilk™ or its equivalents could result in positive health benefits. The results of that study, “Enhancing the fatty acid profile of milk through forage-based rations, with nutrition modeling of diet outcomes,” were published in January 2018 Food Science and Nutrition.
The difference in conventional versus organic versus grass-fed herds is “the percent reliance on forage-based feeds… in contrast to grain-based feeds,” as explained in an educational video from the research study.
According to the research paper, the requirements for Organic Valley “Grassmilk™” is that cows graze for a minimum of 150 days, and that 60 percent of their DMI is from pasture forages during the grazing season. In addition, Organic Valley’s “Grassmilk™” farmers “may not feed grain or silage from grain crops harvested from fields that have reached the “boot” stage of development (when seed heads form and start to fill out). Non-grain supplements including molasses, alfalfa pellets, sugar beets (chipped or whole), mineral supplements, and kelp are allowed to meet the energy needs of lactating cows and support animal health.”
On a conventional dairy, forages account for about 50 percent of the diet, with grains making up the remainder, along with dietary supplements and minerals. The milking herd often is confined, with no grazing component. Certified organic farms vary in how much access and forage they feed, and can feed grains, as long as they meet the USDA’s parameters.
The study took place from 2014-2016, with almost 1,200 raw milk samples, and 69 samples of processed grassmilk dairy products tested. The milk came from farms in the Northeast, the Midwest, and California. Milk samples were tested for levels of fatty acids, including omega-6, omega-3, and conjugated linoleic acids (CLAs), which are considered healthy fats.
In the diet of most American’s today, omega-6 is out of balance with omega-3. A one-to-one ratio is ideal for health: 15:1 is what is now typical.
The researchers sought to determine if grassmilk contained different profiles of these important fatty acids. And, if it did, they’d assess if the consumption of grassmilk led to changes in profiles of the fatty acids in humans drinking the grassmilk in place of conventional or organic milk.
While retail samples of milk were utilized in the study when analyzing the conventional and organic milk, grassmilk analysis was taken raw, from the bulk tank. This is due to the fact that approximately 0.5 percent of the fat found in grassmilk is removed during processing for retail sales, in order to meet the fat requirements for whole milk.
Laboratory analysis of the samples found that the average level of total fatty acids in grassmilk is not significantly different than in conventional or organic brands. However, there are significant differences in omega-6, omega-3 and CLA levels.
Levels of omega-6, which is too prevalent in American diets, was reduced in grassmilk by 52 percent from that of conventional milk, and 36 percent from organic milk. Beneficial omega-3 levels were increased in grassmilk 147 percent from levels found in conventional milk, and 52 percent from those in organic milk.
The study found that the fatty acid ratios of omega-6 to omega-3 in grassmilk are close to the ideal 1:1 for human health, compared to ratios of 5.8:1 in conventional milk and 2.3:1 for those raised on certified organic farms that do not meet grazing and forage requirements for grassmilk.
Cows raised on forages consume different diets depending on season and location. Overall, the ratio of omega-6 to omega-3 fatty acids changed seasonally in grassmilk, with differences of about 30 percent seen from July to December.
Total CLA concentration showed the greatest overall changes, with September’s levels being 50 percent higher than those found in April.
California’s samples showed the least amount of variation, due to a temperate climate year-round. In the Midwest and Northeast, where seasonal changes impact grazing time and increase reliance on stored forages, monthly and seasonal composition changes were more pronounced.
Conclusions
The researchers conclude that increasing forages in the dairy cow diet can have significant impacts on the composition of the fatty acid profiles in the milk, enhancing beneficial levels which then can have positive human health impacts on those consuming this milk. They assessed the impact which substituting drinking three glasses of whole grassmilk for three glasses of whole conventional milk per day would have on human subjects. By making this switch, they found that the ratio of omega-6 to omega-3 was reduced by 24 percent.
“Because of often high per-capita dairy consumption relative to most other sources of omega-3 fatty acids and conjugated linoleic acid, these differences in grassmilk can help restore a historical balance of fatty acids and potentially reduce the risk of cardiovascular and other metabolic diseases,” concluded the researchers.
A forage-based diet and dairy grazing brings environmental benefits, including enhanced soil fertility, reduced runoff and less concerns from concentrated manure storage. Herd health concerns are often reduced in non-confinement, grazing dairies. Genetic selection for grazing animals, as well as management strategies to enhance forage production and nutritional content are some challenges conventional dairy farmers would face when implementing a grazing program and enhancing forage-based nutrition.
Although increasing forage-based feeds can negatively impact milk production levels, economic benefits to the dairy farmer can be seen due to pricing premiums, potential reduction in fuel use for crop production, buffering against high feed pricing, benefits to the farm’s soils, and potentially healthier dairy cows. All milk, it seems, is not created equal.

Leave A Comment