When to 'retire' breeding females?

Is there a 'retirement' age for breeding females. We have a couple of mature girls and are wondering how long we should go on breeding from them. As they get older should we give them a year off for a rest or do we continue the breeding plan. They are strong, fit and healthy girls but we don't want to wear them out and cause them any distress by breeding for too long. Any suggestions?
Vicki

I don't believe there is a particular age at which female llamas should stop being bred. However, I think that the right age to stop will depend on the all round health of the llama concerned. If she is big, stong and fit then I can see no problem, if she is staring to lose weight, look a bit frail etc then it is clearly time to stop breeding her. One thing that many forget is that having a female nurse a cria and be pregnant at the same time can put a hugh strain on the female and as she gets older there are times when this burden can physicaly drain them. I have read on US llama forums of females giving birth to healthy cria at 18 years +.

Hope this helps,

Rgs, Mike L