Mare’s Milk: Watch for White!

Milk will usually start to fill the mare’s udders - often called “bagging up” - a few weeks ahead of foaling. Some mares don’t bag up until very close to foaling.  The fluid starts out rather salty and gritty in texture but will change as she gets closer.

When the milk turns to white colostrum (“first milk” with high protein and antibody content) just prior to foaling, the thicker milk often collects at the end of the nipple with a waxy feel to it ... commonly called waxing. Many mares will show wax, other’s will not. Some show wax in quantity, others in very small amounts. The color of the wax (or milk) is the key issue.

The typical process is for the “milk-to-be” to initially change from salty and gritty to clear and bland. During this period any “wax” looks rather amber in color.  The mare’s milk then changes to looking more “cloudy” or “watery milk” ... more like skim milk. The change from clear to white is sometimes referred to as transitioning, and may take hours or many days.  When thicker and richer white wax or white milk appears, the transition is completed to colostrum.  

Different sources provide milk for each nipple. White wax (or white milk) on both nipples would indicate colostrum is ready for the foal. That status may or may not be obvious. Foaling, or parturition, may occur within hours, during the next foaling window, or wait for a subsequent foaling window.  (See above regarding the foaling window.)

• Some mares will show wax prior to having colostrum, but the color is more amber or yellow in color instead of white. The presence of amber wax means the mare may be days or even a couple of weeks from foaling.
• Sometimes a mare's milk will indicate a change to colostrum, then transition back to a not-quite-colostrum status. Or, one nipple will indicate colostrum while we wait for the other side to complete the transition ... which may take hours or days.  
• Infrequently there are mares who fail to  even “bag up” much less show waxed nipples, but within a few hours that same mare may be fully bagged and pushing her foal out. Sometimes these mares have problems producing adequate colostrum or subsequent nourishing mare milk.
• Some mares will drip or even squirt milk. This status indicates very full bags, with that internal pressure causing the fluid to leak. The key element is still the color of the liquid. If the mare leaks too much white milk, there is potential for the newborn to suckle an inadequate quantity of colostrum, resulting in low antibody protection. (An IGG test several hours after the birth and consumption of the mare’s milk will confirm adequate or inadequate antibodies in the foal.)
  
  

The traditional method to assess the mare's potential for foaling is to note taste, texture and color of the milk - combined with other evaluation of the mare's behavior and physical status. There are contemporary methods to test the mare's milk to help predict foaling by noting when the milk in both nipples is changed to colostrum based on the Ph balance change.