Final answer:
Heifers have a lower dressing percentage than steers because they generally have a higher proportion of body fat compared to muscle, which results in a lighter carcass about live body weight.
Step-by-step explanation:
The reason why heifers have a lower dressing percentage than steers is that heifers generally have a higher proportion of body fat compared to muscle mass. On the other hand, steers are often castrated male cattle that, due to hormonal differences, usually gain muscle mass more efficiently than heifers. Dressing percentage is a measure of the proportion of the live animal that ends up as carcass, and because fat is lighter than muscle, animals with a higher fat content relative to muscle, such as heifers, will typically have a lower dressing percentage.