VIe CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. II

ICI 33828 treatment would have practical advantages.

PMS administration following the suppression of estrus with ICI
33828 was found to provide an improved technique for the synchroniza-
tion of estrus without a detrimental influence on the incidence of
estrus or conception rate. The onset of estrus occurred during a 48-
hr. interval in 93% of 55 gilts and 52 of 53 gilts anestrus during
treatment with ICI 33828 returned to estrus during a 3-day post-
treatment period. A level of 1500 i.u. of PMS was used in the present
experiment to induce superovulation. Previous studies have shown that
a similar improvement in the synchronization of estrus occurs in gilts
treated at a Tower Tevel of PMS following prior treatment with ICI
33828. O0f gilts injected with 1000 i.u. of PMS on the same day or one
day following the withdrawal of ICI 33828 and, in addition, 500 i.u.
of HCG 4 days after PMS treatment, 61% exhibited estrus on the 5th
day after the last feeding of ICI 33828 and estrus was detected in 38
of 40 gilts during a 3-day period (4).

Conflicting results have been reported on the incidence of estrus
in gilts following the injection of PMS during the early follicular
stage of the estrous cycle (5,6). However, both the results of
present study, and those of a previous report (4), show that a high
incidence of estrus occurs in gilts following sequential treatment
with ICI 33828 and exogenous gonadotrophins.

These results, and those of previous studies (7,8), provide
evidence in support of the conclusion that average litter size on the
25th day of gestation is increased significantly in superovulated
gilts and sows which may prove to be an additional advantage to the
use of exogenous gonadotrophins in conjunction with ICI 33828 for the
synchronization of estrus and ovulation in swine.

Table 1. Summary of Reproductive Performance of Gilts Following
Treatment with ICI 33828 or ICI 33828 and PMS.

Group I Group II
Item (ICI 33828)  (ICI 33828 and PMS)
Number of animals:
Total 38 55
Anestrus during ICI 33828
treatment 38 98
Synchronized to 8-day period
and inseminated 35 52
Synchronized to 2-day period 28 50
Pregnant at slaughter2 28 42
Av. duration of estrus, days 2.5 2.0
Conception rate, % 80 81
Av. number of corpora lutea@ |22 23.4
Av. number of normal embryos? 9.3 388

aApproximate]y 26 days after insemination.
(8) P. J. Dziuk, 1968. J. Anim. Sci. 27:673-676.

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