Rams single

out the oldest ewes for copulation, and show no
regard for the young ones. And, as has been stated, the issue of the
younger ewes is poorer than that of the older ones.

The boar is good for breeding purposes until he is three years
of age; but after that age his issue deteriorates, for after that
age his vigour is on the decline. The boar is most capable after a
good feed, and with the first sow it mounts; if poorly fed or put to
many females, the copulation is abbreviated, and the litter is
comparatively poor. The first litter of the sow is the fewest in
number; at the second litter she is at her prime. The animal, as it
grows old, continues to breed, but the sexual desire abates. When they
reach fifteen years, they become unproductive, and are getting old. If
a sow be highly fed, it is all the more eager for sexual commerce,
whether old or young; but, if it be over-fattened in pregnancy, it
gives the less milk after parturition.