Milk component, farm, and industry-level factors associated with elevated free fatty acids in bulk tank milk on conventional dairy farms.

Elevated concentrations of free fatty acids (FFA) in bulk tank milk indicate excessive milk fat breakdown. Levels exceeding the sensory threshold of ≥1.20 mmol FFA/100 g of milk fat compromise milk quality. Average FFA levels on Ontario (ON), Canada, conventional (CON) dairy farms are highest in the early fall months, and this study aimed to identify the factors associated with elevated FFA. A subset of milk-recorded ON CON dairy farm bulk tanks (n = 3,009) with FFA data between August 2018 and December 2022 were analyzed in a cross-sectional study. A mixed-effects multivariable logistic regression model was constructed with elevated monthly mean FFA (≥1.2 mmol FFA/100 g of fat) as the outcome. Monthly average milk components, the number of incentive days (a feature of the Canadian supply management system that allows producers to ship more milk when the domestic demand exists), and milking system were fixed effects in the model, and bulk tank was a random effect. The final dataset included 148,965 observations from 3,009 bulk tanks over 53 mo. The average monthly bulk tank FFA was 0.83 mmol/100 g of fat, and 7% (n = 10,016) of monthly average bulk tank FFA concentrations were elevated. Fifty-three percent of samples came from tiestall farms (n = 1,578), 29% from parlor-milked herds (n = 878), and 18% from farms with automated milking systems (AMS; n = 553). The final reduced model indicated that the odds of monthly average elevated FFA were higher for tiestall farms (odds ratios [OR] = 28.6) and AMS farms (OR = 10.9) when compared with parlor farms. Tiestall farms had higher odds of monthly average elevated FFA than AMS farms (OR = 2.6). The odds of monthly average elevated FFA were greater during months with 3 incentive days compared with none (OR = 1.6). Lower milk protein content was associated with increased odds of monthly average elevated FFA (OR = 33.2 per weighted volume percentage of milk protein decrease), and higher BactoScan (BSN) was associated with increased odds of monthly average elevated FFA (OR = 3.0 per unit increase in BSN (1,000 bacteria per mL more). The results demonstrated that nonparlor milking systems, months with 3 production incentive days, lower milk protein levels, and higher BSN were associated with elevated monthly average FFA levels in ON CON dairy herds.