Stage of Lactation

Science Byte

Milk composition changes during a cow's lactation period

I’m stepping out of my comfort zone with this one. I don’t know much about dairy herd management or dairy nutrition. I suggest reading the article linked at the bottom of the post for a good overview of the subject.

When a cow gives birth to a calf, she will begin to produce milk for ~305 days. This is known as the lactation cycle. A normal lactation cycle for a dairy cow usually lasts around 10 months. The remaining two months are known as the “drying off” period. This rest is really important for the cow’s health and happiness. The milk immediately leading up to and following the calf’s birth is known as colostrum. Colostrum is a crucial part of the calf’s nutrition. Colostrum has high levels of fat, protein, minerals, and antibodies. The newly born calf requires an influx of these nutrients as well as protection from diseases. From there, fat and protein levels drop off and milk quantity increases. This is when the majority of the milk is being collected for use by humans. As the lactation cycles continues, milk yield decreases and fat/protein content increase (reverse dilution effect). There are other factors to consider during the lactation cycle, but won’t be discussed here. See link below for much more information.

Graph of milk composition during lactation cycle (cow)
Data taken from Minnesota Dairy Extension - Feeding the dairy herd


There are many factors that effect the composition of milk. Stage of lactation is one such factor, but there are many others including, but not limited to: nutrition, cow-to-cow variability, season, feed, etc. The data shown in the above graph is a general representation of a trend, not a steadfast rule.

For More Information