Experiment 2 was designed to assess whether the
overall response to PMS was altered by the timing of the

PMS injection in relation to sponge withdrawal. In both
groups a Veramix (medroxy-progesterone acetate - MAP)
sponge was inserted for a period of 14 days. In Group 1,

1500 i.u. PMS was given on sponge withdrawal and the ewes
were put with the ram for mating at the first synchronized
oestrus. In Group 2, 1500 i.u. PMS was given 14 days
af'ter sponge withdrawal and the ewes were put with the
ram for mating at the second synchronized oestrus.

Table 3 shows the results of Experiment 2. The
proportion of ewes lambing to the first synchronised
oestrus was 79%, compared with 92% for ewes lambing after
mating at the second synchronised oestrus: this differ-
ence was not significant, nor was the mean litter size
significantly affected.

Each group of ewes was left with the rams for two
successive oestrus periods. The ewes in Group I that
did not become pregnant at the first mating all lambed to
the mating at the second oestrus period when they would
no longer have been superovulated. There was no
significant difference between the lambing percentages.

The last table (table 4) shows the effect of the ram
on the mean litter size of superovulated ewes. The data
are from a previous paper (Newton and Betts, J. Reprod.
Fert., in press) and from Experiments 1 and 2. One
Suffolk ram, S.81, consistently produced more lambs per
ewe lambing than any of the other five rams used. The
overall mean litter size for S.81 was 2.70, when mated
with 6L superovulated ewes, compared with 2.23 for the
other 5 rams (2 Suffolks, 2 Southdowns and 1 Dorset Horn,
mated with 110 superovulated ewes). At no time was any
ram put with more than 12 synchronised ewes per week.
This outstanding ram produced significantly fewer single
lambs and significantly more triplets and above.

ettt et ettt e ettt et et

TABLE 1 EXPT. 1 The effect of Pregnant Mare Serum
(PMS) on mean litter size
e e R e e T R e W G S S e T sk
Group Number Ewes lambs Mean % of ewes
of ewes lambing born litter with 3 or
size more lambs

A LIR00 K. 0. -+ 65 50 (77%) 120 2.40 40
PMS) 3k 3
B (O PMS) 60 ue (77%) 71 1.54 0