CITRATE, CALCIUM, PHOSPHATE AND MAGNESIUM IN SOWS MILK AT INITIATION OF LACTATION

Colostrum and milk were collected from ten sows at frequent intervals from before farrowing until 9 d after farrowing. Ionized calcium, pH, and total concentrations of citrate, calcium, phosphate and magnesium were measured in whole milk. The diffusible fraction of the mammary se cretion was separated by ultrafiltration and was used for the measurem ent of diffusible citrate, calcium, phosphate and magnesium. The pH be fore farrowing was 5.7, and increased to 6.5 on day 4 as total calcium and phosphate also increased. Before farrowing, total and diffusible citrate were 7.8 and 7.3 mM respectively, while diffusible phosphate w as 11.9 mM, and these concentrations all decreased during the study pe riod. Total magnesium ranged between 3.3 and 4.1. mM, while diffusible magnesium ranged between 2.0 and 3.1 mM. While these concentrations a nd patterns of change of diffusible calcium and citrate are quite diff erent from those of women's milk during the first week after birth, th eoretical physicochemical relationships between diffusible calcium and citrate, and ionized calcium and HPO42- were corroborated by these re sults. We conclude that diffusible citrate plays an important role in the determination of the concentration of diffusible calcium. However, while citrate may be the major determinant of the total concentration of calcium in women's milk, this is not the case in sows' milk.