A flock of 100 Scottish Halfbred ewes (lowland bred) have been
kept under the same conditions with the rams introduced on the same
dates. The pattern of first matings is shown in Fig. 2 and can be com-
pared with the results from the Speckledface Welsh ewes. There was a
fairly random pattern of mating during the first 17 days after intro-
duction of the ram; presumably those ewes already cycling at the lst
of October. This was followed by a small peak around the 22nd day
after introduction of the ram; presumably those ewes that were stimu-
lated by the ram,

Introducing the ram long before the start of breeding, which is
equivalent to running a ram with the ewes continuously, had no
apparent synchronising effect. Fig. 3 shows results from a flock of
Merino ewes on the same farm, where the ram was introduced on the lst
or 21st of June.

FIGURE 3

There is thus an optimum date for introducing the ram in order to
obtain this partial synchronisation., This date will depend not only
on the breed of ewe, being earlier for a lowland than for a hill breed,
but probably also on nutrition and latitude and possibly environmental
temperature, Introducing the ram on the lst of October will only have
the synchronising effect in some breeds in some situations.

We must now compare the results of this partial synchronisation
with those achieved using exogenous hormones. The mosgt successful way
of administering progestagens to ewes in order to inhibit oestrus is
to insert progestagen-impregnated intravaginal sponges for a period of
about 15 days (2), and we have used Syncromate pessaries (G.D. Searle
& Co. Ltd.) in the Speckledface Welsh ewes in two years, One ram was
run with 2 ewes. The pattern of first oestrus following withdrawal of
the pessaries is shown in Fig. 4.

FIGURE 4.

Mating occurred in two periods each of 4 days, and spread over 20
days. With the untreated ewes the total mating period was 36 days, but
90% were mated in 16 days and 58% in 5 days, without the expense of
pessaries, extra labour and extra rams.

The conception rate to the first matings in the untreated ewes was
91%, Of the ewes treated with pessaries, 67% were mated within 4 days
of removal of the pessaries, and 73% of these conceived; that is 49%
of the treated ewes were mated successfully at the first ocestrus.
However, the conception rate at the second peak of mating, 16 to 20
days after withdrawal of the pessaries, was 100%. The manufacturers

(2) Robinson, T.J., 1965, Nature, Lond., 206: 39 - 41.

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