Abstract
The objective of this study was to estimate the influence of lactation number, month of milk sampling, lactation stage and herd size on the freezing point of milk of Polish Holstein‑Friesian cows. Data comprised 4,719,787 milk samples from the first seven lactations of 752,770 Polish Holstein- Friesian cows. Milk freezing point (MFP), milk yield, and fat and protein content were analyzed. The mean MFP of milk samples (-0.5326°C) as well as more than 92% of all milk samples did not exceed the quality limit for the freezing point of cows′ raw milk, which, following Polish standards, was taken to be -0.52°C. The freezing point of milk samples, milk yield, fat and protein content were highly significantly affected by all examined factors: month of sampling, successive lactations, stage of lactation, and herd size. MFP was lowest in milk samples taken from January to March, and highest in samples from November to December. MFP increased with lactation number. Mean MFP decreased with time within lactation, except the first stage (5-35 days in milk). Generally, MFP was highest in small herds (up to 9 cows) and lowest in large herds (more than 150 cows).