Utilising fatty acid prediction equations and mid-infrared spectroscopy to estimate the seasonality changes in bovine milk from pasture-based systems

The aim of this study was to utilise mid-infrared spectroscopy with fatty acid (FA) predictions to characterise the seasonality-associated changes to the FA profile of milk from Irish spring-calving pasture-based dairy cow production systems. A total of 546 454 individual milk records were collected from the Years 2015 to 2020, from 264 003 cows in 2400 commercial dairy farms. Significant changes occur to the predicted FA profile of milk across the year, such as increases in unsaturated FAs including C18:1 n-9 until April. This can be associated with the increasing proportion of fresh pasture in the cows' diet, and a decrease between September and October as the cows begin to transition indoors for the winter period. The opposite trend was noted for saturated FAs and in particular C16:0, where proportions decreased until April and increased between September and November. Milk produced between April and September also coincided with the lowest spreadability index, indicating a more beneficial milk FA profile for more spreadable butter texture during this period. This work provides a valuable reference resource at a national level of the FA profile of milk from pasture-based spring-calving dairy systems.