Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. I

as gilts in Experiment I were used for the study. Five
replicates, three of gilts and two of sows, were used for

the experiment. Each replicate contained approximately
equal numbers. The gilts ranged in weight from 90 to 160 kg.
The sows ranged in weight from 160 to 260 kg.

RESULTS.

Experiment I. Seventy-eight percent of the gilts
expressed estrus on the fifth, sixth, or seventh day after
the end of treatment. The mean number of days required to
return to estrus was 5.4. The conception rate after first
service was 91.6%. The farrowing rate of the first service
gilts was 867%. Litters averaged 9.7 pigs born alive. The
average weight gain of animals on treatment was 4.8 kg. No
gilts expressed estrus while on treatment.

Experiment II. Eighty-three percent of the gilts and
70% of the sows expressed estrus on the fifth, sixth, or
seventh day after the end of treatment. The mean number
of days required to return to estrus after the end of treat-
ment was 5.6 and 5.9 for the gilts and sows, respectively.
Conception rate, based on the first service, for the gilts
and sows was 887% and 90%, respectively. The average litter
size was 9.0 for the gilts and 11.2 for the sows. The
farrowing rate of first service animals was 81% for the
gilts and 76% for the sows. Average weight gain of the
gilts for the 20-day treatment period was 4.0 kg.; average
weight gain for the sows was .5 kg. Two sows in one repli-
cate expressed estrus while on treatment and 18 and 19 days
later.

DISCUSSION.

These data show that ICI 33,828 was effective in altering
the estrous cycle and synchronizing estrus when gilts and sows
were group-fed a dose level of 125 mg. of ICI 33,828 per head
per day. There were no differences between replicates within
year or between years in the time required for the gilts to
return to estrus. The average number of days required to
return to estrus for the sows in Experiment II was different
from that observed for the gilts that were fed the same dose

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