Detailed milk fatty acid profiling of the Danish dairy cattle population

Summary

Abstract
Milk fatty acid (FA) composition can be manipulated through feeding, and especially effects of grazing have been shown to promote a healthier milk FA profile due to increasing contents of beneficial FAs, like conjugated linoleic acid (CLA) and α-linolenic acid (C18:3, the main n3 FA in milk). In addition to diet-based manipulations, selective breeding for specific FA could also be a strategy for altering the FA profile as milk FA display low to moderate heritabilites (0.07-0.34 in Danish Holstein).
Since 2015, milk samples from all Danish dairy cows under yield control have been analyzed using mid infrared spectroscopy. The FOSS Application Note 64 has subsequently been used to predict content of seven FA groups (short-chain FA (SCFA), medium-chain FA (MCFA), long-chain FA (LCFA), saturated FA (SFA), mono-unsaturated FA (MUFA), poly-unsaturated FA (PUFA), and trans FA (TFA)) together with four individual FA (myristic acid (C14:0), palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1)). This access to millions of FA profiles in milk enables large-scale in depth analyses of factors affecting FA profile of milk and accurate genetic parameter estimation. Initially, more than 3.5 million milk samples from three Danish dairy breeds (Holstein, Jersey, Red) and crossbred cows have been analyzed from May 2015 to October 2016.
The results showed significant (P ≤ 0.05) effects of cow breed. As reported earlier, Jersey cows have a higher de novo synthesis, resulting in higher proportions of SFA, MCFA, SCFA and C16:0 compared to the other breeds. For parity (only checked in Holstein), the proportion of SFA and SCFA increased with increasing lactation number, whereas the proportion of MUFA and C16:0 decreased. PUFA had the lowest proportion in 2nd parity and the highest in 1st parity. Also, significant effects of production system (organic vs. conventional) was found, as organic dairy cows due to legislation have to be on pasture during summer. In months, where cows were fed fresh grass, the proportion of unsaturated FA increased, whereas the proportion of saturated FA decreased. This was seen in both organic, and to a lesser extent, in conventional milk. A healthier FA profile can be obtained by increasing MUFA and PUFA in milk. However, health aspects in relation to SFA are more complex, but there seems to be a general agreement that most SFA have neutral or even slightly positive effects, whereas palmitic acid exerts a negative effect on human health due to its role in increased LDL cholesterol. Thus from a consumers perspective, our results suggest that organic summer milk from 1st parity Holstein or Red cows are preferred during the grass season, whereas conventional milk may have a healthier FA profile during winter.
To explore specific seasonal effect in relation to pasture-based diets in more details, milk samples from 160 cows from eight herds are collected to investigate whether bulls with extreme SFA% breeding values are reflected in the FA milk profile from their daughters. The collected milk
samples will be analyzed by AN64 MIR, as well as by gas chromatography, to provide additional information e.g. in relation to CLA and C18:3 and the n3/n6 ratio. So far, milk samples have been collected prior to summer grazing and will be collected again in June 2017, where most cows in the experiment will be on pasture. In conclusion, this study has shown that the choice of breed, parity, lactation stage, season, production system and genetics affect the FA composition of milk. Different strategies may therefore be applied to alter the FA profile, but generally, which could be exploited for product differentiation for e.g. new healthier innovative dairy products.