Some cows don't have udder, here is the list:
Auroch cow, angus cow, highland cow and hereford cow, these breed just in third and fourth variants

• Minecraft 1.16.5
• Forge 36.2.39
• HotChicks 1.0.0

known, not a bug or unintentional. many beef breeds do not have a noticeable udder. closed.