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

untreated ewes. They appeared on day 3 and persisted until day 15.
By contrast, they were plentiful during early oestrus in treated
ewes.

ii. Enzymology, biochemistry. Murdoch & White (1967)
have shown that the amylase, acid phosphatase and alkaline phospha-
tase content of the sheep endometrium follow the growth and retro-
gression of the corpus luteum. The sheep is thus similar to the
cow (Moss, Wren & Sykes, 1954; Skjervan, 1956) but differs from the
sow in which maximum activity of these enzymes is during the
follicular phase (Atkinson & Engle, 1947; Hall, 1950; Goode,
Warnick & Wallace, 1965).

In the cycle following treatment with intravaginal sponges
containing Cronolone, this activity is higher than normal (Figure 4).
This is attributed by Murdoch & White to a specific effect of
Cronolone on synthesis of the enzymes. Another possibility is the
banking up of LH in the pituitary, as shown by Zimbelman (1966), to
an abnormally high level, followed by its release and the develop-
ment of an excessively active corpus luteum. Data on the activity
of corpora lutea following progestagen treatment are limited.
Hansel (1967) reports that corpora lutea formed in cattle after MAP
or CAP treatment contain normal amounts of progesterone at 3 and 10
days but this does not rule out the possibility of activity at the
upper limits of normality, nor does it preclude the possibility of
sub-normal activity following inadequate suppression.

iii. Cervical mucus. Johnson & Ulberg (1965) and Hansel
(1967) have reported differences between normal and CAP or MAP
treated cows in the viscosity and fern pattern of cervical mucus at
oestrus. The mucus of treated cows was less clear and more viscous,
indicative of the influence of progestagen.

In another context, Zimbelman & Smith (1966) reported develop-
ment of a fern pattern in the cervical mucus of cows under treatment
with MGA following regression of the corpus luteum. This was
interpreted as an indication of oestrogenic activity as a result of
inadequate mimicking by MGA of the pituitary inhibiting action of
the corpus luteum.

iv, Overt oestrus. The occurrence of oestrus and its
duration and intensity are useful indices of endocrine status.
"Silent oestrus'", or ovulation without oestrus, is common following
progestagen treatment of cattle (Carrick & Shelton, 1967; Hansel,
1967) and of sheep particularly at the beginning and end of the
breeding season (Robinson, 1968), or if treated with long acting and
oral progestagens (Lindsay et al, 1967; Shelton & Robinson, 1967).

Oestrus following treatment tends to be shorter than normal in

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