both cattle (Wiltbank, Shumway, Parker & Zimmerman, 1967) and sheep
(Fletcher, 1968). This is probably a function of inadequacy of
progesterone for priming or of oestrogen for inducing oestrus. A
dose of progestagen adequate to suppress ovulation in the sheep may
be quite inadequate to induce oestrus (Figure 5).

A full oestrous response, identical in duration and intensity
to normal oestrus, is indicative of a normal progesterone-oestrogen
relationship.

v. Sperm transport and survival, Probably the best .

evidence of normality of the female reproductive tract is provided
by a normal pattern of transport and survival of spermatozoa.

There appears to be a clear relationship between the numbers of
tubal spermatozoa at the approximate time of fertilization and the
observed fertility of normal and progestagen treated ewes (Table 5),
The data have the advantage over those for fertilization in that
they are continuous, not quantal, so that valid conclusions can be
drawn from relatively few animals. The technique of recovery from
the tubes is fairly simple although the counting is extremely
tedious, Fortunately the differences observed between treated and
untreated animals are so great that, for routine purposes, simpli-
fied techniques for counting can be used. We have found only a
two-fold increase in accuracy, with no effect on conclusions, for a
six=-fold increase in counting time.

4, Areas for future investigation

To summarise, we have the following physiological indices of
normality following manipulation of the cycle.

(a) Manifestation, duration and intensity of oestrus.

(b) Relationship between time of oestrus and of ovulation.
(c) Rate of tubal transport of eggs.

(d) Rate of transport and survival of spermatozoa.

(e) Percentage of eggs fertilized.

(f) Absence of abnormalities in fertilized eggs.

(g) Percentage survival of fertilized eggs.

Each of these parameters is fairly easily measured and its
importance readily understood. Only the data for (a) and (d) are
not quantal, Hence those for duration of oestrus and number of
services and for numbers of spermatozoa recoverable from the female
tract, while relatively difficult to obtain, are particularly
valuable for comparative purposes. Some of the morphological,
histological and biochemical parameters, including the character-
istics of the cervical mucus, are rather more difficult to measure
and their interpretation is obscure because of our lack of knowledge
of limits of normality. Nonetheless a major expansion in this

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