Progestogen concentration and ionic composition of the mammary secretion of periparturient bitches.

Mammary secretions were collected from nine bitches of various breeds during the periparturient period. Initial mean progestogen concentrations were high and started to decline from 5 days before parturition, in a similar way to changes in plasma progesterone concentration. Values were basal by 3-4 days after parturition. Marked individual and day variations prevented this method from reliably indicating the time of impending parturition. Calcium concentrations in milk increased from 3-5 days after parturition, whereas a decline in magnesium concentration was noted from day 1 postpartum. There was an increase in the Ca:Mg ratio from 1 day after parturition, although this was not significant until day 3, and was therefore not useful for predicting impending parturition. There were no significant changes in sodium concentration in milk.