admin@milksa.co.za 
012 460 7312
Brooklyn Court, Block B, First floor,
Background provided by the authors:
Milk has a high lipid content composed of approximately 400 different fatty acids. These are grouped into short to medium chain fatty acids (C4 to C15) derived from synthesis in the udder and long chain fatty acids (C17 to C26) derived from the diet. The medium-chain fatty acid (C16) is derived from both synthesis in the udder and the diet. The proportion in the fat of each fatty acid determines the health impact. Often the whole fat content is linked to the emergence of chronic disorders, such as diabetes and cardiovascular diseases. However, recent research on the effect of different fatty acids on human health indicates that only a few individual fatty acids are responsible for the negative consequences on consumer health. These are some saturated fatty acids such as lauric (C12:0), myristic (C14:0) and palmitic acid (C16:0), and trans-fatty acids, which are associated with increased blood cholesterol concentration and coronary heart disease.
Research, however, has not only focused on the negatives of milk fatty acids. Milk contains a low concentration of beneficial unsaturated fatty acids, including conjugated linoleic acids (CLA), (C18:2c9t11), α-linolenic and oleic acids, which could be improved in milk through pasture feeding. The potential benefits of C18:2c9t11 include lowering of blood total cholesterol content and supporting anti-carcinogenic, anti-diabetic and immuno-modulatory effects. Benefits of omega-3 fatty acid include prevention of heart disease and improved immune response. It is therefore important to compare and quantify the saturated and certain unsaturated fatty acids into an index weighing the positives and negatives. Other ways of classifying milk fatty acids include the so-called desaturase index and the omega-6:omega-3 ratio. The desaturase index estimates the activity of a vital substance in fatty acid metabolism by comparing product-to-precursor fatty acid ratios, whereas it is also important for production of CLA and mono-unsaturated fatty acids. The omega-6:omega-3 ratio measures the balance between these two fatty acids, which have antagonistic physiological functions, but supportive to good health and development.
Many studies have focused on and acknowledged the significance of diet in manipulating and enhancing health-promoting and disease-preventing groups of fatty acids in milk. Milk fatty acid profiles vary due to many other internal and external factors. These include breed, cow individuality, physiology, stage of lactation, locality, feed intake and season. For example, Jersey cows produce milk with a higher fat, lactose and protein content compared to Holstein cows, which on the other hand produce higher milk yields. Feed intake varies according to stage of lactation and pasture fatty acid profiles differ which could reflect in the milk fatty acid profile. It is therefore important to study fatty acid profiles that occur in different breeds, stages of lactation and pasture compositions in the search of a more desirable milk fatty acid profile. Towards this goal, the objectives of the study referenced below were to determine the effects of stage of lactation on milk fatty acid profiles of Holstein, Jersey and Holstein x Jersey cross pasture-based cows.
Results and interpretation:
The results showed substantial differences. Linoleic acid in pastures was highest in the second phase of the study which coincided with mid-lactation. Higher fat content was observed in late lactation than early lactation. Highest butyric, caproic, linoleic, omega-6 and polyunsaturated fatty acids were observed in milk from Holstein cows. The highest conjugated fatty acids, α-linolenic acid, linoleic acid, saturated fatty acids, polyunsaturated fatty acids, omega-6 and omega-3 were observed in early lactation. The weighted index of positives and negatives and the desaturase index were highest in late lactation.
In conclusion, the results showed that the fatty acid composition of milk varies with stage of lactation in pasture-based cows. Saturated fatty acids were only lower in mid-lactation whereas unsaturated fatty acids were lower in late lactation, leading to a high positive-negative index and omega-6:omega-3 ratio in late lactation, which may have an influence on human health and diet fatty acid proportions. In addition, all measures of desaturase activity were significantly highest in late lactation. Variations due to breed and feed changes were observed in short to medium chain fatty acids and linoleic acid. Holstein cows produced the milk with the highest linoleic acid and polyunsaturated fatty acids at the expense of α-linolenic acid. The results furthermore showed that it is imperative to maintain pasture in a good vegetative state as any deviation will reduce overall CLA content in the milk. Obviously, these results merely provide some indicators and will be more useful to the industry when the experiment can be replicated, with the type and amount of pasture, silage and concentrate fed to each cow accurately measured, in order to find the “ideal” fatty acid profile.
Reference:
C.T.W. Nantapo, V. Muchenje & A. Hugo, 2014. Atherogenicity index and health-related fatty acids in different stages of lactation from Friesian, Jersey and Friesian x Jersey cross cow milk under a pasture-based dairy system. Food Chemistry 146, 127–133.