People do successfully breed smaller female if they are smart about it, there are many thing to take in consideration.
A good starting point for a female is 18 months to 3 years weighing at 1500 grams (however the bigger the better)
Now while I would breed a 18 months old that is 1500 grams I would not however breed a 18 months old that is 1100/1200 grams but I would breed a female that size if she was 4 years or more.
Breeding is about age, weight, and proportion it is also possible not to breed a 1800 grams females that is 3 years old because her proportions are off.
In the end experience makes the difference.
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