estrus. Three out of the four pigs were killed on the 9th day
after withdrawal of administration so that their ovaries could
be examined. They contained no corpora lutea.

2. Recurrence of estrus following treatment: Recurrence
of estrus after withdrawal of methallibure administration took
place in 1 to 11 days, 6,2 days on average in 133 animals. In
83.5 % of these cases, estrus recurred in 5 to 7 days, indicat-
ing the remarkably high effect on estrus synchronization of this
method. There was no distinct difference in the interval up to
recurrence of estrus between gilts and sows. The duration and
symptoms of estrus hardly differed from those of untreated
controls. In the 17 animals given gonadotropin following meth-
allibure administration, recurrence of estrus was concentrated
on the 5th and 6th day after its withdrawal in 15 animals.
Duration of estrus was two or three days in all animals. Estrus
was generally more conspicuous than in cases without gonadotro-
pin injection. These results, as well as the conception rate
and number of piglings mentioned later, seem to indicate the
effectiveness of gonadotropin injection for synchronization of
estrus.

3. PFertility and duration of pregnancy: Artificial insemi-
nation conducted during the first estrus after withdrawal of
methallibure administration, resulted in a conception rate of
86.0 % in gilts and 77.6 % in sows, and 82.1 % in the total of
106 animals. These results are comparable to the rates in
natural mating. Seventeen pigs given gonadotropin following
methallibure administration all conceived. The duration of
pregnancy was 104 to 120 days, 114.7 days on average.

L. Number of piglings and their development: For the gilts,
the number was 9.3 and for the sows 10.0. These figures are
comparable to those of untreated controls. One gilt, in which
estrus recurred 5 to 6 days after withdrawal of methallibure
administration and which was killed 9 days later, cerried 14
corpora lutea. Birth weight and development of each pigling
observed were not inferior to those of untreated controls.

When gonadotropin injection was used in conjunction with metha-
1libure, the number of piglings ranged from 12 to 16 in gilts;
13.0 on average, and from 7 to 19 in sows, 13.8 on average.
These figures are significantly greater than those of treated
with methallibure alone. On the basis of this result, it may
be said that the number of piglings can be increased over that
of controls by injection of PMS and HCG after withdrawal of
methallibure administration.

5. Side effects: Within the scope of treatment in the
present experiment, no particularly harmful effect of the drug
was observed, except some pigs showed decreased appetite over
several or more days during administration.

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