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Colostrum Formation

Colostrum
Formation

Composition of the mammary secretion at the first milking or the first suckling reflects the functional changes that have occurred in the gland up to that time. These functional changes include the secretions resulting from the two stages of lactogenesis (see the Lactogenesis section of this Mother and Neonate Lesson), as well as other functional changes in the epithelial cells occurring in concert with lactogenesis, such as selective transport of immunoglobulins. After repeated milk removal, the composition of the mammary secretions changes rapidly over the initial 2 to 3 days after parturition, so that there is a continuous transition of composition from colostrum to mature milk. All components of the mammary secretion are changing during this transition period.

Study of the hormonal control of mammary differentiation around the time of parturition mostly has focused on lactogenesis, and specifically on the synthesis of lactose and/or the expression of casein and a-lactalbumin genes and secretion of those proteins. However, a great deal is occurring in the mammary gland that ultimately results in the formation of colostrum.

Compositional Changes - Colostrum to Milk

The major compositional changes in cow milk during the first 7 days of lactation have been discussed previously (see Milk Composition in the Introduction Lesson). In sow milk, milk fat percentage generally increases from colostrum to milk, but declines in cow milk after parturition. Milk fat percentage is the most variable component of milk. Lactose concentration generally is lower in colostrum of both species, then increases over the next few hours and days. Protein concentration is highest in colostrum (first milking or first suckling), then declines rapidly over the next day or two. The major proportion of this change in protein concentration is accounted for by the immunoglobulins.

A closer look at the changes in sow colostrum composition (in the Figure to the right) shows that there is little change during the initial 4 to 6 hr after birth of the first piglet (total length of parturition for the sow can be 2 hr), then the composition begins to change. This probably is similar in the cow where the calf suckles every few hours as opposed to the typical 12 hr interval when the cow is milked.