SALTS OF MILK 247 5.5.3 Infection of the udder Milk from cows with mastitic infections contains a low level of total solids, especially lactose, and high levels of sodium and chloride, the concentration of which are directly related(Figure 5.5). The sodium and chloride ions come from the blood to compensate osmotically for the depressed lactose synthesis or vice versa These are related by the Koestler number Koestler number= 100×%Cl which is normally 1.5-3.0 but increases on mastitic infection and has been used as an index of such(better methods are now available, e.g. somatic cell count, activity of certain enzymes, especially catalase and N-acetyl glucosamidase). The pH of milk increases to approach that of blood during mastitic infection 5.5.4 Feed Feed has relatively little effect on the concentration of most elements in milk because the skeleton acts as a reservoir of minerals. the level of citrate in milk decreases on diets very deficient in roughage and results in the ' Utrecht phenomenon, i.e. milk of very low heat stability. Relatively small changes in the concentrations of milk salts, especially of Ca, Pi and citrate, can have very significant effects on the processing characteristics of milk and hence these can be altered by the level and type of feed, but definitive studies or his are lacking 5.6 Interrelations of milk salt constituents Various milk salts are interrelated and the interrelationships are affected by H Table 5.3). Those constituents, the concentrations of which are related to ph in the same way, are also directly related to each other(e.g. the concentrations of total soluble calcium and ionized calcium), while those related to pH in opposite ways are inversely related(e. g. the concentrations of potassium and sodium Relationships between some of the more important ions/molecules are shown in Figure 5.6. Three correlations are noteworthy: The concentration of lactose is inversely related to the concentration of soluble salts expressed as osmolarity. This results from the requirement that milk be isotonic with bloodSALTS OF MILK 247 5.5.3 Infection of the udder Milk from cows with mastitic infections contains a low level of total solids, especially lactose, and high levels of sodium and chloride, the concentration of which are directly related (Figure 5.5). The sodium and chloride ions come from the blood to compensate osmotically for the depressed lactose synthesis or vice versa. These are related by the Koestler number: 100 x %C1 %lactose Koestler number = which is normally 1.5-3.0 but increases on mastitic infection and has been used as an index of such (better methods are now available, e.g. somatic cell count, activity of certain enzymes, especially catalase and N-acetyl￾glucosamidase). The pH of milk increases to approach that of blood during mastitic infection. 5.5.4 Feed Feed has relatively little effect on the concentration of most elements in milk because the skeleton acts as a reservoir of minerals. The level of citrate in milk decreases on diets very deficient in roughage and results in the ‘Utrecht phenomenon’, i.e. milk of very low heat stability. Relatively small changes in the concentrations of milk salts, especially of Ca, Pi and citrate, can have very significant effects on the processing characteristics of milk and hence these can be altered by the level and type of feed, but definitive studies on this are lacking. 5.6 Interrelations of milk salt constituents Various milk salts are interrelated and the interrelationships are affected by pH (Table 5.3). Those constituents, the concentrations of which are related to pH in the same way, are also directly related to each other (e.g. the concentrations of total soluble calcium and ionized calcium), while those related to pH in opposite ways are inversely related (e.g. the concentrations of potassium and sodium). Relationships between some of the more important ions/molecules are shown in Figure 5.6. Three correlations are noteworthy: 1. The concentration of lactose is inversely related to the concentration of soluble salts expressed as osmolarity. This results from the requirement that milk be isotonic with blood