For purposes of sire evaluation, a female is classified as a first-calf heifer when she is less than how many months of age?

The classification of a female as a first-calf heifer is based on her age and her status in terms of having had her first calf. Generally, a first-calf heifer is defined as a female that has calved for the first time and is typically under 24 months of age. This classification is important in sire evaluation because it helps producers assess the reproductive performance and productivity of young females in their herd.

When a heifer gives birth before reaching 24 months, she is usually still relatively young in terms of breeding and development, which can provide insights into her potential longevity and future productivity. This distinction between first-calf heifers and older cows can significantly influence breeding decisions, management practices, and overall herd health. The other age options mentioned are beyond the typical range used to define first-calf heifers, which is why they do not apply to this classification.