Variations in the Heat Stability and Composition of Milk from Individual Cows during Lactation

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Abstract
Milk samples from 2 cows were collected at intervals throughout a lactation period and analyzed for heat stability (over a range of pH), various inorganic constituents, and 7 protein constituents (by electrophoresis). With all except a few early-lactation samples, a sharp maximum in heat stability could be demonstrated by adjusting the pH over a narrow range, usually between 6.6 and 6.7. The heat stability of the untreated milk appeared to be determined by the change in acidity (H+ concentration) required to adjust the milk to the pH of maximum heat stability. When the data for both cows are considered, the heat stability of the original milk was not correlated with any constituent(s) of the milk. The maximum heat stability, on the other hand, was significantly correlated with the ratios: Calcium Ion/Soluble Inorganic Phosphorus, Soluble Calcium/Soluble Inorganic Phosphorus, and Soluble Calcium plus Soluble Magnesium/Soluble Inorganic Phosphorus plus Soluble Citrate.