ont éte saillis naturellement. Quatre-vingt-un pour-cent
des animaux présenterent un oestrus cing a sept jours apres
cessation du traitement. Le nombre moyen de jours exige
pour retourner en oestrus fut 5.5. Le taux de conception
aprés le premier service fut 89.6%. Le taux de naissance

du premier service fut 86%. Une moyenne de 9.5 cochons

par couche furent nés viables. On n'observa aucune
différence significative dans le precessus de reproduction
entre les répliques au cours d'une année ou entre les années.

Studies (1) and (2) showed that l-a-methylallylthio-
carbamoyl-2-methylthiocarbamoylhydrazine (ICI 33,828) was
effective in controlling the estrous cycle and synchronizing
estrus of female swine. Studies (3), (4), and (5) demon-
strated that a daily dose of 100 mg.-200 mg. of ICI 33,828
was effective in synchronizing estrus and resulted in no
adverse effects on conception rate, embryo survival, or
litter size. This experiment was designed to determine
the effect of estrous synchronization on the progeny of
gilts that had been synchronized the previous year and if
the estrous synchronization could be used effectively, along
with other production practices, in a swine production unit.

MATERIALS AND METHODS.

General. Two separate experiments were conducted, one
in 1966 and one in 1967. All gilts used in the studies were
at least seven months old. All sows had been synchronized
the previous year and had demonstrated normal reproductive
performance. All animals were group-fed a daily ration of
2.27 kg. containing 125 mg. of ICI 33,828. Treatment was
initiated at unknown stages of the estrous cycle and continued
for 20 days. All animals were bred by natural service.

Experiment I. One hundred seventy-one gilts that were
progeny of gilts that had been synchronized the previous
year were assigned to six replicates. The replicates were
started at seven-day intervals with approximately an equal
number of gilts. The gilts ranged in weight from 85 to 157 kg.

Experiment II. Ninety-two gilts that were offspring of
the gilts in Experiment I and 26 sows that had been synchronized

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