Milk functional characteristics of cows at extended lactation and effects on bulk tank milk traits

We evaluated the effect of including 0, 2, 5, 10, 20, 40 and 100% of individual milk from cows at extended lactation (more than 315 d in milk) on milk ethanol stability (MES), pH, acidity and ionic calcium (iCa) of the bulk tank milk. The study was carried out on commercial dairy farms in Brazil using milk samples of individual cows, bulk tank and their mixtures. Samples of individual cows were classified as low (≤74%), intermediate (76-78%) and high (≥80%) stability classes based on MES. Data were submitted to Anova, multiple linear regression analysis and logistic regression. Low, intermediate and high stability milk had values of 108, 89 and 79 mg/dl for iCa, and 21, 23 and 20 for acidity, respectively, but similar values for pH and DIM. MES increased linearly with pH, while it decreased linearly with iCa. When individual milks presented higher MES than bulk tank milk, MES and pH increased linearly with individual milk inclusion and DIM, while iCa decreased with individual milk inclusion. When individual milks presented lower MES than bulk tank milk, MES decreased, while iCa increased linearly with individual milk inclusion. Inclusion of milk with higher MES than the bulk tank decreased the odds of low stability, while inclusion of individual milk with lower MES than bulk tank increased it. At extended lactation, 73% of cows produced milk with acceptable (intermediate or better) MES, and iCa was the only functional variable related to MES. Effects of the mixture of individual milks into bulk tank milk functional traits depend on whether individual cows present values higher or lower than bulk tank.