Bitches

do not submit to the male throughout their lives, but
only until they reach a certain maturity of years. As a general
rule, they are sexually receptive and conceptive until they are twelve
years old; although, by the way, cases have been known where dogs
and bitches have been respectively procreative and conceptive to the
ages of eighteen and even of twenty years. But, as a rule, age
diminishes the capability of generation and of conception with these
animals as with all others.