Search

In the present study, we aimed to investigate the changes in triacylglycerol (TAG) composition as affected by alterations in the cows' diet due to seasonal variations and genetic factors. For this study, 50 milk fat samples in winter and 50 in summer were used from 25 cows with the DGAT1 KK genotype and 25 cows with the DGAT1 AA genotype. The samples were analyzed for milk fat content (%), fat composition, and TAG composition. We found that the content of TAG species CN54 was higher and that of CN34 and CN36 lower in summer than in winter. This seasonal variation in TAG profile was related to seasonal changes in the fatty acids C14:0, C16:0, C18:0, C18:1 cis-9, total unsaturated fatty acids, and total long-chain fatty acids, most likely resulting from dietary differences between seasons. Furthermore, we quantified the effect of DGAT1 K232A polymorphism on TAG profile and detected a significant effect on TAG species CN36, with higher values for the DGAT1 KK genotype. When adjusting for differences in fat content, we found no significant effects of the DGAT1 K232A polymorphism on TAG profile. We detected a significant interaction between DGAT1 K232A polymorphism and season for TAG species CN42 and CN52; in summer, the KK genotype was associated with higher levels for CN42 than the AA genotype, whereas in winter, the difference between the genotypes was small. For CN52, in summer the AA genotype was associated with higher levels than the KK genotype. In winter, the difference between the genotypes was also small. We show that, regardless of preference for DGAT1 genotype (AA or KK) and depending on the availability of FA according to season, UFA (C18:1 cis-9), short-chain FA (C6:0 and C10:0), and medium-chain FA might be esterified on the glycerol backbone of the TAG, keeping the structure characteristics of each TAG species. To our knowledge, this is the first report on the interaction effect of DGAT1 K232A polymorphism and season on the TAG composition in milk fat.

Milk fat (MF) triacylglycerols (TAG) determine the physical and functional properties of butter and products rich in MF. To predict these properties, it is necessary to understand the variability of fatty acids, TAG, their associations, and their effect on milk productive traits, days in milk (DIM), and genes related to fat synthesis. Therefore, the aim of this research was to study the variability of TAG using MF from individual cows and to investigate the effect of fatty acid composition, DGAT1 K232A polymorphism, DIM, and milk production traits (fat content and morning milk yield) on MF TAG profile in the Dutch Holstein-Friesian dairy cattle population. Large differences in MF TAG profiles were seen among cows. We showed that the variability of TAG is highest for low and high molecular weight TAG [TAG with carbon numbers (Cn) 26-30 and Cn52-54, respectively] and lowest for TAG with Cn38, which was the most abundant TAG. Saturation index (saturated fatty acid/unsaturated fatty acid) and the ratio C16:0/C18:1 cis-9 showed significant effects on TAG Cn34, Cn36, Cn52, and Cn54: TAG Cn34 and Cn36 increased as the saturation index and ratio C16:0/C18:1 cis-9 increased, whereas the opposite was seen for TAG Cn52 and Cn54. Moreover, the DGAT1 K232A polymorphism significantly affected TAG Cn38. We showed that the relative concentration of TAG with Cn38 was higher in cows with DGAT1 KK genotype. Production traits (fat content and morning milk yield) and DIM had no significant effect on TAG profile. This is a relevant observation because considerable increases of milk yield and fat content have been seen in the Netherlands over the last 60 yr. The large differences shown between individual cows in MF TAG profile imply differences in physical properties of MF.