The objective of this study was to estimate heritability and crossbreeding parameters (breed and heterosis effects) of various fatty acid (FA) concentrations in milk fat of New Zealand dairy cattle. For this purpose, calibration equations to predict concentration of each of the most common FAs were derived with partial least squares (PLS) using mid-infrared (MIR) spectral data from milk samples (n=850) collected in the 2003-04 season from 348 second-parity crossbred cows during peak, mid and late lactation. The milk samples produced both, MIR spectral data and concentration of the most common FAs determined using gas chromatography (GC). The concordance correlation coefficients (CCC) between the concentration of a FA determined by GC and the PLS equation ranged from 0.63 to 0.94, suggesting that some prediction equations can be considered to have substantial predictive ability. The PLS calibration equations were then used to predict the concentration of each of the fatty acids in 26,769 milk samples from 7385 cows that were herd-tested during the 2007-08 season. Data were analysed using a single-trait repeatability animal model. Shorter chain FA (16:0 and below) were significantly higher (P<0.05) in Jersey cows, while longer chain, including unsaturated longer chain FA were higher in Holstein-Friesian cows. The estimates of heritabilities ranged from 0.17 to 0.41 suggesting that selective breeding could be used to ensure milk fat composition stays aligned to consumer, market and manufacturing needs.

Non-protein-bound oligosaccharides are important bioactive components of cow milk, with potential human-health benefits such as stimulation of the growth of beneficial gut bacteria and defense against pathogens. In bovine milk, the majority of oligosaccharides are sialylated; 3'-sialyllactose (3'-N-acetylneuraminyl-D-lactose; 3'-SL) is the predominant sialylated oligosaccharide, followed by 6'-sialyllactose (6'-N-acetylneuraminyl-D-lactose; 6'-SL). Both 3'-SL and 6'-SL have antimicrobial activity. As bovine milk products such as infant formula can be an important component of the human diet, and the concentrations of 3'-SL and 6'-SL are lower in bovine milk compared with human milk, we aimed to identify cows that naturally produce higher concentrations of sialyllactose in their milk. Milk from such cows could be used to produce foods with an increased sialyllactose content, potentially providing increased health benefits. We speculated that cows overexpressing 3'-SL and 6'-SL would exist at low frequency in the population and, to allow their efficient identification, we developed a novel assay for 3'-SL and 6'-SL utilizing flow-injection analysis-mass spectrometry, which could be used for high-throughput analysis of milk samples. We then determined 3'-SL and 6'-SL concentrations in milk samples from 15,507 cows from Friesian, Jersey, and Friesian-Jersey crossbred animals. We found 329 cows with concentrations of 3'-SL or 6'-SL >2-fold higher than the mean, 26 cows with concentrations of 3'-SL or 6'-SL >3-fold higher than the mean, and 1 cow with concentrations of 3'-SL >4-fold higher than the mean. Although these outliers were observed across the 3 groups of cows, breed had a strong effect on mean 3'-SL and 6'-SL concentrations.

The objective of this study was to estimate genetic correlations among milk fatty acid (FA) concentrations in New Zealand dairy cattle. Concentrations of each of the most common FA, expressed as a percentage of the total FA, were determined by gas chromatography on a specific cohort of animals. Using this data set, prediction equations were derived using mid-infrared (MIR) spectroscopy data collected from the same samples. These prediction equations were applied to a large data set of MIR measurements in 34,141 milk samples from 3,445 Holstein-Friesian, 2,935 Jersey, and 3,609 crossbred Holstein-Friesian × Jersey cows, sampled an average of 3.42 times during the 2007-2008 season. Data were analyzed using univariate and bivariate repeatability animal models. Heritability of predicted FA concentration in milk fat ranged from 0.21 to 0.42, indicating that genetic selection could be used to change the FA composition of milk. The de novo synthesized FA (C6:0, C8:0, C10:0, C12:0, and C14:0) showed strong positive genetic correlations with each other, ranging from 0.24 to 0.99. Saturated FA were negatively correlated with unsaturated (−0.93) and polyunsaturated (−0.84) FA. The saturated FA were positively correlated with milk fat yield and fat percentage, whereas the unsaturated FA were negatively associated with fat yield and fat percentage. Our results indicate that bovine milk FA composition can be changed through genetic selection using MIR as a phenotypic proxy.