Effect of Time of Onset of Rapid Cooling on Bovine Milk Fat Hydrolysis

Milk samples (n = 1818), collected from 261 cows, were used to evaluate effect of time of onset of rapid cooling on milk fat hydrolysis. Aliquots, either cooled immediately or after 1 h at ambient temperarure, were analyzed for FFA content after storage at 4°C for 48 h. Acid degree values for immediately cooled aliquots were higher than delayed cooled aliquots following adjustment for days in milk, days pregnant, milk yield, and SCC (.76 vs. .71). Correlation of .89 existed between aliquots; however, within a sample, aliquot response on cooling was variable in direction and magnitude. Immediate cooling enhanced lipolysis associated with increased days pregnant, decreased milk yield, and increased SCC. Consequently, effect of immediate cooling on milk fat hydrolysis was greater in milk collected from late lactation cows.