In strong, healthy females this is not generally a problem as a one off - and some breeders even allow it as a way of obtaining more kits out of a female - but it should not be allowed to take place. As well as causing problems for the female it will often produce weaker kits in following litters.

When a female chinchillas gives birth, she will come into season within 24 hours.  If the male is present then there is a high likelihood that she will conceive and again become pregnant.

At this time the female is feeding milk to her kits, which drains her body of calcium and other essential vitamins and minerals, the growing foetuses within her are also taking additional nutrients from her body. This toll is very intense upon her - and the process will breakdown much of her own body tissue and weaken her skeletal structure as the calcium is used in milk production and foetal kit growth.

I personally will not allow breed backs where they can be prevented by separating the male prior to the birth when you know the expected date (though when your as useless at telling when they are pregnant as I am the long term separation of males is often the only safe option!)

Sometimes a breed back will occur due to many circumstances:

• you may not know she was pregnant,
• a female may birth early whilst you are absent,
• you may have your dates wrong,
• a male may force an insecure pop hole and get into a cage you believed to be closed off.

Where the female has not had kits for at least 12-18 months prior to the birthed litter this should not be a large problem so long as she was well and healthy before she became pregnant the first time.   BUT on these occasions it is best that you immediately separate the male by removing him (or close pop hole if in a polygamous system) and leave the female with her kits.

Keep the female with the kits until weaned and then keep her alone or with other females for at least 6 months recovery time before being reintroduced to any males.  This time limit should be flexible, you should wait until her weight returns to at least the original weight she had been before she initially became pregnant.

The only occasion in which some breeders say that a breed back can be a safe option is where a female has had a long rest after a litter, been healthy and robust, then produced a litter which for some reason is lost at birth.   At this time allowing one breed back so that she can become pregnant - but is not feeding kits - will not drain her body as badly as the above - but upon weaning she should have at least a 6-9 month rest before breeding again.   My personal choice would be not to do this but to rest her after losing the litter.

Breed backs can and will shorten the life expectancy of the female.  They are animals and pets - and not breeding machines!   We all love kits - I don't think any one will deny that - but they should not be produced at the expense of the females long term health and happiness.

Breed backs in young females, as well as reducing life expectancy, can lead to skeletal deformity, teeth misalignment due to calcium deficiency, diabetes and hormonal problems.