The mammary gland is an extremely unusual organ because it is undeveloped at birth. The mammary gland is just a collection of cells inside the teat when a dairy calf is born, and only then does its development truly begin.
Over the first two years of the life of a calf, the mammary epithelial cells proliferate and develop in order to prepare for milk production after calving for the first time. In order to achieve appropriate mammary growth and maximize a heifer’s milk production potential, we need to ensure that proper development occurs at each stage and prevent or manage any stress events or diseases that could divert nutrients and energy that would otherwise be used for mammary development.
It is particularly important for dairy producers to prevent first-calf heifers from becoming infected with mastitis before calving for the first time. A heifer only gets one chance to fully develop the mammary gland, so if mastitis occurs while the mammary gland is still developing, it can permanently lower that heifer’s lifetime milk production potential.
In order to fully understand how mastitis can impact lifetime milk production potential, we must first understand what happens during each stage of mammary development.
Growth stages that impact mammary development
The first stage of mammary development takes place in the first two to three months of life. During this time, the mammary gland grows from the size of a twist tie from a bread bag to about the size of a walnut. This may not seem like a lot, but it actually amounts to around a 60-fold increase in size in the first 90 days. During this period, ailments like respiratory or digestive diseases can cause nutrients to be shifted away from mammary development. Therefore, high levels of nutrition, particularly protein and energy, can have a stimulatory effect on mammary development.
The next stage is from 3 months of age until puberty. At this time, mammary growth is accelerated, and the heifer needs to spend time in this period allowing the mammary gland to grow and develop. It’s critical to not feed too much protein and energy, because the calf can grow too fast and push through this critical period before the mammary gland has a chance to optimally develop.
The third stage is from puberty until near the first calving. Generally, nutrition does not impact mammary development significantly during this time. It is, however, a time when the animal is susceptible to mastitis.
The final stage is the “lactation” stage, which includes the last couple of weeks before calving and the first few weeks of the heifer’s first lactation. At this point, the necessary cell population for high levels of milk production is not yet present, so the heifer is going to experience an extreme amount of mammary growth during those first two weeks post-calving.
If a heifer gets mastitis before that first lactation, it causes scar tissue in the mammary gland that can prevent or limit normal development. So if the heifer has scar tissue that develops at that first lactation, we have essentially limited that animal’s lifetime milk production potential because that scar tissue will continue holding her back during subsequent lactations.
Zinc is critical to epithelial cell proliferation
Zinc is involved in more than 300 enzyme functions and plays a key role in keratin formation and the proliferation of mammary epithelial tissue as the mammary gland develops within the heifer. By producing strong teat keratin on the outside of the mammary gland, we can prevent mastitis pathogens from entering and infecting the heifer. If those pathogens do get through the teat keratin, it’s important to have strong epithelial tissue to minimize damage.
Dairy producers can improve mammary development and help prevent their first-calf heifers from being infected with mastitis by supplementing their dairy nutrition program with zinc from performance trace minerals. Performance trace minerals are different from organic and inorganic trace minerals in the sense that they are bound to an amino acid and are therefore able to be absorbed via the amino acid transporter. This results in less excretion and more of the minerals being absorbed and utilized for growth, development and production.
Research shows feeding performance trace minerals can help produce an extra milligram of teat keratin over the course of a day while providing enough nutrition to help the heifer deal with other problems and stressors to which they are susceptible at this time. Additionally, supplementing heifers with zinc from performance trace minerals during the rearing period has shown to be effective in decreasing first-test somatic cell counts and improving first-lactation milk yields. This is likely to be the result of reducing the probability of mastitis and other infections that could damage mammary gland development. Overall, this will help ensure adequate mammary development and improve that heifer’s lifetime milk production potential.
