sheep ova. In this connection, Shelton & Moore (1967) found that
ova recovered from progestagen treated ewes following AI tended to
be at an earlier stage of development than those recovered from
normal ewes. This phenomenon was not observed with naturally mated
ewes (P<0.02). The clear inference, subsequently confirmed by
Quinlivan & Robinson (1967), is that the accumulation of spermatozoa
in the tubes of the controlled oestrous ewe, particularly following
AI, is delayed.

3

Delayed fertilization, together with normal degenerative
changes in unfertilized ova recovered 2 or 3 days after ovulation,
could account for the observed abnormalities attributed to faults in
the ova.

Indirect evidence of the normality of ova produced under condi-
tions of control, and of the tract for their reception and develop-
ment, comes from several sources,.

(a) All authors who have recovered ova report a normal
rate of ovum transport.

(b) Fertilized ova from superovulated ewes transferred
to normal animals develop normally.

(c) Such ova transferred to progestagen treated ewes
also develop normally (Shelton & Moore, 1966).

One must agree, therefore, with Schmidt (1961) that lowered
fertility following progesterone treatment is not due to an effect
on the fertilized egg or its environment shortly after fertilization:
Factors responsible for the lowered fertility must operate before or
during the process of fertilization,

This still leaves open the special situation early in lactation,
which will be discussed later.

b. Reasons for failure of fertilization

Of the five possible reasons listed in Table 3, there is good
evidence for only one, namely poor sperm transport and survival
(Quinlivan & Robinson, 1967, 1968). Other factors may be involved,
but the evidence of inadequate accumulation of spermatozoa in the
tubes of the ewe is sufficiently strong to account for all the
observed failure of fertilization. This is illustrated in Figures
1 and 2 and Table 5. Progestagen treated ewes fail to accumulate
the same numbers of spermatozoa as do normal ewes at the expected
time of fertilization some 24 hours after insemination. Maximum
accumulation in treated ewes occurs at 36 hours. This could account
for the relatively early stage of development of ova from such ewes,
reported by Shelton & Moore (1967), and for abnormalities due to
late fertilization.

1354