What is an undesirable trait in a replacement gilt regarding her reproductive tract?

An inverted nipple is considered an undesirable trait in a replacement gilt's reproductive tract because it can lead to difficulties in nursing piglets effectively. Functional reproductive traits are crucial for the success of a gilt's performance as a breeding animal. Inverted nipples do not protrude outward as they should, which can hinder the ability of piglets to latch on and receive adequate nutrition. This can result in poor growth and survival rates among the piglets, ultimately affecting the productivity of the breeding operation.

While functional nipples are beneficial for milk production and successful nursing, a long neck is not directly related to reproductive efficiency and is therefore not a critical concern in this context. Pin nipples, although less desirable than perfectly formed ones, may still allow for sufficient nursing under certain conditions. However, inverted nipples present a more significant problem that can severely impact the overall reproductive success of the gilt.