What would make a young heifer milk bag large and not uniform shape?

It's important to remember that heifers don't have milk bags. They have udders. And the term "milk bag" is usually used to describe the udder of a cow that is lactating.

However, there are a few reasons why a young heifer's udder might appear large and uneven:

* Hormonal Fluctuations: During puberty, heifers experience hormonal fluctuations that can cause the udder to swell and grow. This is a normal part of development.

* Pregnancy: If the heifer is pregnant, her udder will start to develop in preparation for lactation.

* Mastitis: This is an inflammation of the udder, which can cause swelling, redness, and unevenness. It's usually caused by bacterial infection.

* Cystic Ovarian Disease: In some cases, cysts on the ovaries can cause hormonal imbalances that lead to udder enlargement.

* Genetic Predisposition: Some breeds of cattle are more prone to having large, uneven udders.

It's important to note that a large or uneven udder in a young heifer doesn't necessarily mean there's a problem. However, if you are concerned about the appearance of your heifer's udder, it's best to consult with a veterinarian to rule out any underlying medical conditions.