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

THE EFFECT OF SUPEROVULATION, SYNCHRONISATION AND |
THE RAM ON EWE LITTER SIZE

J.E. NEWTON and J.E. BETTS |
Grassland Research Institute, Hurley, Berks., England

The object of the work reported here was to
investigate superovulation and synchronisation of sheep |
by hormone treatments during the natural breeding season. 1
This paper deals with two recent experiments in which the
effect of Pregnant Mare Serum (PMS), progestagen sponges
and the ram on the mean litter size of the Scotch Half-
bred ewe have been studied. Mean litter size is defined
here as being the total number of lambs born (live ordead)
per ewe lambhing.

Experiment I was concerned with the effect of 1500 iu.
PMS on mature Scotch Half-bred ewes early in the breeding
season. 65 ewes received 1500 i.u. PMS (Group A). This
was injected subcutaneously during the anticipated
follicular phase of the oestrous cycle, either following
teaser detection of oestrus or oestrus synchronisation
resulting from the use of progestagen sponges. 60 ewes
had no PMS (Group B). The use of progestagen sponges
had no significant effect on the resulting mean litter
size. The number of ewes lambing was 50 and L6 in
Groups A and B (Table 1). In Group B this is the number
of ewes lambing as a result of the first mating after
being put with the rams; it does not include ewes
returning for a second, third or fourth oestrus. For
Group A it is those ewes being mated within 6 days of the
PMS injection. There was no difference between the two
treatments in the proportion of ewes lambing to this
mating: 77% in each case. There was a highly
significant difference between the mean litter size of
the two treatments. This was 1.54 for Group B and 2.40
for Group A, a difference of nearly one lamb for each ewe
lambing. LO% of the ewes given PMS had triplets or more.
The ewes with no PMS had no litter size above 2.

Table 2 shows the overall effect of PMS on lambing
percentage (the number of live lambs born per 100 ewes
put to the ram). The use of 1500 i.u. PMS resulted in a
significantly higher lambing percentage of 198, with 25%
of the ewes having 3 or more live lambs. There was no
difference between treatments in the proportion of ewes
lambing (93% and 97%) . In Table 2 ewes lambing refers
to the total lambing on each treatment, after a possible
L4 oestrus periods. The no PMS ewes had 3% lambs born
dead against 8% for the 'PMS' ewes. This difference was
not significant.

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