Influence of lactation stage, parity, milk yield, and microbiological parameters on milk fatty acid profile

This study investigated the effects of lactation stage (LS), parity (PAR), milk yield (MY), total bacterial count (TBC), and somatic cell count (SCC) on the fatty acid (FA) profile of milk in 173 Holstein-Friesian cows, sampled at the morning milking. Milk fat was predominantly composed of saturated fatty acids (SFA), followed by monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), with palmitic acid (C16:0) as the most abundant individual FA. Among all examined factors, milk yield (MY) showed the most consistent effects, significantly influencing a wide range of short-, medium-, and long-chain FAs, as well as total SFA, MUFA, and PUFA. Higher milk production was associated with shifts in mammary lipid metabolism and FA synthesis pathways. LS also strongly affected FA composition, with early lactation characterized by increased long-chain FA content due to body fat mobilization, while later stages showed higher contents of de novo synthesized shortand medium-chain FAs. PAR had a moderate but significant influence, mainly affecting short-chain FAs and selected PUFAs, reflecting long-term physiological adaptations of the mammary gland. TBC showed selective effects on specific FAs, suggesting a potential link between microbial quality and lipid metabolism, whereas SCC had no significant effect. The R2 values (0.04 to 0.25) suggest a moderate level of variance explained by the model. The results demonstrate that milk FA composition is primarily driven by physiological and production-related factors (MY and LS), while hygiene-related parameters have more limited or selective impacts. The findings confirm the highly dynamic and multifactorial nature of milk fat composition.