Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1948, VOL. Il

PARTIAL SYNCHRONISATION OF OESTRUS IN EWES
RESULTING FROM THE INTRODUCTION OF RAMS

J. M. FORBES
School of Agricultural
Sciences,
Leeds University, England.

The advantages of synchronisation of oestrus in a flock of ewes
are all at or after the end of gestation; for example, a short lamb-
ing season giving even batches of lambs at slaughter., However, the
disadvantages of using hormones for oestrus synchronisation are to be
found at the beginning of gestation; that is, the cost of the hormones
the labour involved in treating the ewes, the extra rams required and
the low conception rate at the first oestrus after the hormone treat-
ment. Oestrus synchronisation without exogenous hormones would,
therefore, result in considerable saving of resources at mating time,

It has been noted by several workers, particularly in Australia,
that the introduction of rams into flocks of Merino ewes just before
the expected start of breeding stimulated oestrus to occur in a large
percentage of ewes. Radford and Watson (1) studied this phenomenon in
detail by inspecting smears of vaginal secretion from ewes in such a
flock for desquamated epithelial cells., They found that most of the
ewes had these cells indicative of ovarian activity, 5 to 6 days after
the introduction of the ram in late Gctober or mid November., Normal
oestrus occurred 16 to 17 days after this 'silent heat'. In groups of
ewes with no rams, or those in which the ram was run all the year,
there was no peak in degquamated epithelial cells at this time.

A flock of 50 Speckledface Welsh ewes (hill bred) at Leeds
University Farm, Yorkshire, were run with an entire ram from about the
1st of October (early autumn) in 4 seasons. It was noted in each year
that there was a marked peak of matings at around 22 to 23 days after
the introduction of the ram,

FIGURE 1
The results are brought together in the upper part of Figure 2.
FIGURE 2

If a teaser ram had been used for the first 14 days, the initial
tail of fertile matings would have been shorter.

(1) 1957. Aust. J. Agric. Res., 8: 460 - 470

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