Agriculture Reference
In-Depth Information
that fatty acid composition and concentration in milk are dependent on
animal physiology (breed, age, stage of lactation) [62,63] and diet [64,65].
Alpha-linolenic acid (ALA) is the primary dietary precursor of omega-3
fatty acids (FA) and conjugated linoleic acid (CLA) in the milk of cattle,
and can account for as much as 50-70% of the total fatty acids found in
fresh forage [66,67]. Therefore, it is no surprise that milk from cows graz-
ing fresh grass contains greater concentrations of omega-3 FA and CLA
compared to milk from cows consuming conserved forage, corn silage and
high-grain rations [64,68-70]. A recent meta-analysis examining 29 previ-
ously published studies from 12 countries concluded that organic dairy
products contained significantly higher protein, ALA, total omega-3 FAs,
CLA and a more desirable omega-3 to omega-6 ratio compared to dairy
products derived from non-organic systems [71]. Increasing omega-3 FAs
in the human diet is considered beneficial to health and CLAs have been
shown to be a powerful anticarcinogen in animal models [72].
In 2011, milk sold as certifi ed organic in the United States reached
nearly 1.2 billion kg and was valued at 7.6 million US dollars [2], rep-
resenting an ever growing segment of the dairy industry. The implemen-
tation of the pasture rule insures that 30% of dry matter feed intake by
certifi ed organic ruminants will be obtained by grazing certifi ed organic
pasture or rangeland during at least 120 days of the year. Improvements in
the fatty acid profi le of organic dairy products, including greater omega-3
FA and CLA concentrations and more desirable omega-3 to omega-6 FA
ratios will result from the organic grazing requirement. This is evident in
England, where organic dairy production standards require a reliance on
forage, and greater concentrations of omega-3 FA, CLA, and fat-soluble
antioxidants have been found in organic milk compared to milk from dry-
lot systems [73,74]. Seasonal variation in the fatty acid profi le of milk pro-
duced under grazing conditions is a challenge associated with producing
and marketing products that may be considered enriched with benefi cial
fatty acids. Concentrations of nutritionally benefi cial fatty acids have been
found to be greater in raw and retail milk during the grazing season com-
pared to periods when the animals were consuming a greater proportion of
grain and conserved forages [74,75]. Supplementing the diets of milking
cows with oilseeds such as fl ax may be a method of elevating desirable
milk fats when fresh forage is limited by seasonality or drought [69].
