Effect of milk yield genotype on lipidomic profiles of multiparous Holstein cows during the first 9-weeks of lactation

Abstract Text: The concentrations of individual fatty acids (FAs) are commonly measured to define the chemical composition and nutritional value of cow milk. However, the distribution of FAs in different milk triacylglycerols (TAGs) and the distribution of these TAGs in different cow milks are rarely examined due to the challenges of analyzing numerous TAGs in milk.  In this study, cows (n = 12/genotype) from unselected (stable milk yield since 1964, UH) and contemporary (CH) Holsteins that differed by more than 4,500 kg milk/305-d (UH<CH) were fed the same diet ad libitum and housed together beginning 5 weeks prepartum. Milk samples were collected weekly from each Tuesday pm milking through 9 weeks of lactation. No differences in milk protein and lactose content (PRO%: 3.13% vs. 2.98%, P=0.49; LAC%: 4.69 vs. 4.75, P=0.39) were observed between UH and CH samples. However, compared to UH, CH milk had higher fat content (FAT%: 3.55% vs. 4.33%, P<0.01). Milk TAGs were further examined by high-resolution liquid chromatography and mass spectrometry and multivariate data analysis (MDA). The distribution patterns of weekly UH and CH samples in the MDA model indicated that TAGs profiles of UH and CH differed greatly in early weeks of lactation, but became much more comparable by week 9. The structures of TAGs markers that differed between UH and CH were elucidated by MSMS fragmentation. Hierarchical clustering analysis of these TAGs markers revealed that oleic acid-containing TAGs were enriched in CH milk while the TAGs containing palmitic acid, short-chain and medium-chain FAs existed in much higher abundance in UH milk. Overall, these observations indicated that, in early lactation, CH had greater incorporation of mobilized fatty acids than UH, which led to different milk TAG profiles between two genotypes.

Keywords: triacylglycerol, lipidomics, milk