Milk harvesting and cow factors influencing seasonal variation in the levels of free fatty acids in milk from Waikato dairy herds

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Free fatty acids (FFA) occur naturally in milk and, under certain on‐farm conditions, concentrations increase, affecting the flavour, processing efficiency, and shelf‐life of dairy products. To obtain some understanding of these, FFA concentration was determined in silo milk samples collected from seasonal supply dairy farms in Waikato, New Zealand during the 1997/98 and 1998/99 dairying seasons. Selected farms represented the major dairy systems: 25 farms had continuous (rotary) milking systems and 25 farms had batch (herringbone) milking systems. Four of the herringbone dairies had milk‐harvesting systems that eliminated the air‐milk interface (Ruakura Milk Harvester; RMH). FFA concentrations were assessed every 2 weeks in bulk milk samples collected from the farm silo. Concentrations of FFA were lowest in spring (early‐lactation) and highest in summer and autumn (mid‐late lactation). The type of dairy design (herringbone versus rotary) had no association with FFA concentrations, but the four herds milked by the RMH system tended to produce milk with lower (P < 0.10) FFA concentrations during summer and autumn 1998/99. A number of factors were associated with increased FFA concentrations: type of milking system, milk yield, somatic cell count (SCC), milk composition, and stage of lactation. Bacterial infection as identified by SCC and the elimination of the air‐milk interface during milk harvesting (RMH) had possibly major influences on FFA concentrations.