Why would one sterilize a heifer?

Answer 1

Heifers are not usually sterilized, they are usually kept for breeding purposes. However, in the case that the heifer is mean during heat cycles or has something wrong with her reproductive tracts then the farmer may decide to sterilize the heifer. Normally, they would just be sent for slaughter if this is the case.

Another opinion:

Heifers would be sterilized or spayed (by surgical removal of the ovaries) because they are not conformationally viable to be used in the breeding herd (i.e., too small in size, pelvic area too small, poor conformation, etc.), and because the stocker or backgrounder feeding these heifers before slaughter doesn't want to waste the money to buy drugs to keep the heifers from going into heat all the time. A hormonal drug called MGA is used for this, but can be costly to administer to feeder heifers all the time, and impossible to feed to heifers if they're out on pasture all the time. A spay program is then set up so that all the heifers that are not suitable for breeding and used for beef are spayed, minimizing costs on drugs and feed and allowing the manager/producer more time for other things other than having to worry about when the heifers have to be administered with MGA again.

Spaying unwanted heifers also decreases the issues that may occur if a bull caught the scent of a heifer in heat and wrecked some fences in order to get at her. It also decreases the loss of production and increases weight gain because, when a heifer is in heat, she spends most of her time looking for a mate, pacing around and bawling and getting the other herd members riled up. This tends to, though temporarily, decrease weight gain and feed intake during that time the heifer is in heat.

So it's all down to production costs and intention on increasing weight gain that would give a producer reason to spay stocker/feeder heifers.