A working ram will not last forever. The primary reasons for selecting a ram for culling are its age and reproductive or physical abnormalities.
Culling rams for age
A ram's best days are usually those up to 6 years of age. Older rams often suffer from reduced fertility and/or libido.
As most rams are purchased to be first joined at 12-18 months of age, you should ideally look to cull and replace them after a maximum of 4 years' use. Culling for age and purchasing replacement rams each year means that a good balance of mixed aged rams is maintained.
Studs will also be in a much better position to supply the quantity and type of ram needed if annual replacement numbers are relatively constant. Also, if your stud is making genetic gain, the more rapidly that your ram flock is replaced the closer your flock will be in genetic merit to your stud.
Find out more about improving sheep flocks through genetics.
Culling rams for abnormalities
You should physically examine (palpate) the testes of your rams before annual replacements are ordered so that those with abnormalities can be replaced. You should palpate well before joining, to allow replacements a minimum of 8 weeks after arrival to recover from any stress-related fertility problems arising from their handling, transport and relocation.
Rams of all ages are prone to the development of testicular lesions and abnormalities and need to be examined for reproductive health at least once a year, with defective rams being culled.
You should also check for general physical fitness, and rams with permanent disabilities (e.g. broken mouth) should be culled. You don't need to cull those rams with temporary problems such as lameness and blindness, as they can be put aside for use the following year, providing they are young enough and otherwise healthy enough.