What are three undesirable characteristics of a sow's udder?

The three undesirable characteristics of a sow's udder include blunt nipples, pin nipples, and mastitis, making this option the correct choice.

Blunt nipples can be problematic as they may not allow piglets to latch properly, which can hinder their ability to suckle effectively. This can lead to inadequate nutrition for the piglets and impact their growth and health. Pin nipples are similarly problematic; these are underdeveloped or malformed nipples that can also prevent piglets from nursing efficiently.

Mastitis, an infection of the mammary gland, is a serious condition that can lead to reduced milk production and can pose health risks for both the sow and her litter. This condition can also make nursing painful for the sow, further complicating the feeding process for the piglets.

The other options do not correctly reflect undesirable characteristics of a sow's udder. Cleanliness, symmetry, and firmness are characteristics associated with a healthy udder rather than indicators of problems. Soft texture, regular shape, and healthy appearance are also attributes of a desirable udder. Large size and high volume combined with low milk yield do not represent common undesirable characteristics; instead, an effective udder should have a balance of size and functionality with high milk yield.