“Just because an udder is not lactating doesn’t mean it’s not doing anything,” said Ben Enger during the National Mastitis Council Annual Meeting. The mammary physiologist and associate professor at The Ohio State University pointed out that significant udder tissue growth and development is needed for an animal to be ready to enter lactation, and the vast majority of that occurs during a heifer’s first pregnancy.

The parenchyma tissue that a cow needs to produce milk grows upward from the teat into the fat pad of the developing udder, Enger explained. Of course, there is no need for lactation until an animal is pregnant, so that growth really takes off during those nine months of gestation. The cell growth is not linear but exponential as the body prepares to make milk. Enger noted that the last four months of pregnancy is when cell growth is most rapid.

In addition to cell replication, the architecture of the udder must prepare for milk production. At first, udder maturation involves developing connective tissue, but as the process moves forward, more lumen space is needed for milk production and storage. Epithelial cells open up as the udder grows into its secretory capacity.

A vulnerable time

Although it may be hard to physically see, this period of rapid growth and development is also a crucial time for udder health, Enger said. If a heifer develops a mammary infection at this point, the immune factors recruited to fight off the pathogen can damage the developing cells.

He described a study they completed where quarters of heifers were infected with either Staphylococcus aureus or a control saline solution. The infected quarters had fewer epithelial cells, which are responsible for milk production, and more stromal cells, which are components of connective tissue.

The damage of such an infection is exacerbated because heifers are most likely to encounter a pathogen during the last few months of pregnancy — exactly when that udder development is ramping up. Without intervention, these infections interfere with normal udder growth.

So, what can be done? Enger first recognized that there are many ways to do udder health surveillance in first-lactation animals. Whether it is with a California Mastitis Test (CMT), by analyzing first test day somatic cell count (SCC), or with a culture, finding out if your heifers are calving in with infected udders is the first step.

From there, you can determine if environmental pathogens need to be addressed in pregnant heifer or close-up bedding and calving pens. In some cases, antimicrobial treatment and/or a teat sealant may be warranted to control the issue. While these options require additional labor, helping cows biologically prepare for lactation is a benefit that can last for their lifetime.