Seasonal Variation and Dietary Effects in the Fatty Acid Composition of Bulk Tank Milk in Taiwan

Background: Information about seasonal variation in the fatty acid (FA) composition of bulk tak milk and its relationship with dietary factors in Taiwan remains to be completed. This study aimed to determine the average FA composition of milk in different seasons and collect dietary information to investigate the relationship between dietary characteristics and lactation performance, including FA concentration in bulk tank milk. Methods: Bulk tank milk samples were collected monthly from 90 dairy farms across Taiwan for two years to capture seasonal variations. Additionally, 36 bulk tank milk samples from three farms were collected monthly from August 2022 to July 2023. Result: Milk production (kg/day), fat (%), crude protein (%), true protein (%), lactose (%) and solids-not-fat (%) were significantly higher in the cold season than in the hot and warm seasons (P<0.05) P <0.05) over the studied period. In contrast, somatic cell counts were significantly lower in the cold season than in the hot and warm seasons (P<0.05). P <0.05). Total saturated FA and C14:0 concentrations were significantly higher in the cold season than in the hot and warm seasons (P<0.05). P <0.05). In contrast, the C18:1 concentration was significantly higher in the hot and warm seasons than in the cold season (P<0.05). P <0.05). However, the C18:0 concentration did not differ significantly by season. Fat and FA concentrations varied significantly among three selected dairy farms (P<0.05). P <0.05). Milk fat only differed significantly between the three farms in the hot season, with Farm B having the lowest milk fat concentration (P<0.05). P <0.05). FA concentrations showed significant seasonal effects at all three farms. These results provide an overview of milk FA variation and identify the critical factors influencing variation in bulk tank milk fat and individual farm FA concentrations: dietary ether extract content and forage choice.