Which factor is NOT typically used when evaluating breeding heifers for volume?

When evaluating breeding heifers for volume, the critical factors generally focus on the animal's capacity to carry and produce offspring efficiently. Factors like breast width, rib shape, and depth of body are all indicative of an animal's overall volume and internal capacity.

Breast width relates to the heifer's heart and lung capacity, which is vital for ensuring proper growth and reproductive performance. Rib shape contributes to the heifer's internal volume, as a well-shaped rib will indicate a more substantial body cavity that can accommodate more room for the digestive system, leading to better nutrient absorption. Depth of body is another significant indicator, as a deeper-bodied heifer typically has a larger capacity for carrying unborn calves and has better overall body condition.

In contrast, roundness of the rump, while it can indicate certain desirable traits in a breeding heifer, does not have a direct relationship with the measurement of volume or internal capacity. The shape of the rump does contribute to conformation and can influence aspects like fertility or muscle development, but it’s not a primary factor in assessing volume when comparing these animals for breeding purposes.