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

which received their sponges between day 1 and day 7 and in j
which the progestational phase was lengthened the least. f
No differences could be demonstrated between the groups that ‘
received their sponges between day 7 and 14 and between day

14 and 17.

Litter size. There was no significant difference in litter

size between the PMS and non-PMS treated animals, being

respectively 1.60 and 1.50 (P=0.46). There asppeared to be

an influence of the day of sponge insertion on litter size. 1
(table 3.)

 

 

 

 

 

 

[ ‘ PMS non-PMS
sponge twins & twins &
insertion singles triplets singles triplets
D 1SN 12 23 nG 14
D 7 -14 22 5 16 2
D 14 - 17 8 12 14 7

P=0.05 P=0.20

tabie 3. Influence of time of sponge insertion on litter size.

The ewes in the PMS treated group that received their
sponges between day 1 aud day 7 of tne oestrual cycle
gave pirth to significantly more twins and triplets than
ewes who received their sponges between day 7 and 14.

In the non-PMS group no differences could be demonstrated.

The decrease of fertility of the synchronized oestrus after
an artificial lengthening of the progestational phase can
be brought about by unfavourable circumstances in the female
genital tract. There are several possibilities: ovulation
can be distwyrved; there may be alterations in the ovulated
eggs so that fertilization is disturbed; the environment in
the fallopian tube may be altered so that the transport of
the fertilized eggs is disturbed and the uterine environment
may be not optimal for implantation.

Further investigations will teach us which of these factors
are responsible for the differences in fertility.

1541

46