application of hormones ovariotomy was carried out
on a number of sows which were on heat and the ova-
ries were histologically analyzed.

RESULTS AND CONSIDERATIONS.The depo-progesterone
preparation did not entirely prevent the occurrence
of estrus in sows even when it was applied in the
dose of 375 mg.In comparison with the control group
estrus was manifested in a considerably smaller num-
ber of sows,the rate of conception was lower and
the average number of piglets in the litter was con-
siderably reduced(tabs.l).The smaller the used dose
of progesterone the lesser was its inhibitory effect
upon the occurrence of estrus.The dose of 125 mg of
depo-progesterone stimulated the occurrence of es—
trus but the percentage of conception was low.In
sows treated with 375 mg of depo-progesterone the
follicles were tiny and there was a rather large
number of tiny corpora luteaj;the ovaries of sows
treated with 125 mg of depo-progesterone contained
well developed corpora lutea and tiny follicles;in
sows treated with 250 mg of progesterone a conside-
rable number of normal tertiary follicles was found
but there were no corpora lutea,

Depo-progesterone was applied at any time accor-
ding to the plan of mating.In sows a great number
of follicles mature during estrus,which increases
the cencentration of estradiol in the organism of
animals.Owing to this,we believe,even large doses
of depo-progesterone could not entirely prevent the
occurrence of estrus,especially if the drug was
applied in the phase of proestrus.

With the subsequent application of PMS the best
results were obtained in the group previously trea-
ted with 250 mg of depo-progesterone.However,con-
sidering the high percentage of estrus manifested
in the period of the working of progesterone a sa-
tisfactory synchronization of estrus was not achie-
vedeIn the ovaries of these sows the number of nor-
mally developed tertiary follicles was considerab-
ly increased but there were no corpora lutea func-
tioning.In the group of sows to which 375 mg of
depo-progesterone had been previously applied the
number of tertiary follicles on the ovaries was
larger and so was the number of corpora lutea while
the sows previously treated with 125 mg of depo-
progesterone had a considerably smaller number of

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