The ferret fits in immediately with its new environment as regards its sexual
cycle, when taken from the northern to the southern hemisphere. The animals
that were in anoestrum in England started breeding shortly after they arrived in
South Africa - the last litters being born the 22nd March, 1938.
Females may be stimulated to show oestrus, even where the light is decreasing,
after the birth of a litter or after they have suckled their young for some time.
A female may even remain in oestrum throughout the winter. There is, however,
a big variation in the reaction of different females. Some females that had litters
during December did not show oestrus again during that season while other
females still came on heat as late as the end of April after their young had been
Fertile matings appeared to occur only until the end of January or the first
week in February. A few matings occurred after this date, but no young were
produced. The earliest that a litter has been produced is the 6th September.
This female was served on the 27th July, 1940, so that litters have been obtained
from September to March inclusive. The breeding season at Onderstepoort, therefore, appears to be about 1 to 2 months longer than in Europe. Young males, born during the previous season, will copulate and are fertile
about a month earlier than older males. When females commence to come on
heat toward the middle of July, only young males will sense them.
The average litter size of those in which one and more have been reared
is 6•0 young per litter and 5•7 in those litters of which all the young were
destroyed. If females are served immediately after their vulvas start to swell,
then the average litter size is only 3, which is half the normal. The average
litter size of the previous litters of these females was 9, so that early service can
reduce the litter size to half or a third the normal size.
Up to the end of November only 10 young out of 177 were reared. From
December there was an improvement. It appears that the months September,
October and November have an adverse influence on the mothers and probably
on the young as well. This is substantiated by the results obtained with rats
over a period of 4 years. During this time of the year the survival rate is the
lowest and those that did survive grew at a slower rate and did not reach the
same mature weights as those born during the favourable time of the year.
Experience during the last two years indicates that there is very little
advantage in breeding ferrets before November, although they commence to come
on heat 3 months earlier. Rats born during June and July have done very well.
Therefore it is intended to try out the practicability of electric lighting for large
scale breeding and probably injecting only the males with pregnant mare serum
after they had been exposed to the extra light for some time.