VIe CONG. INTERN. REPROD. ANIM. INSEM. ARTIF,, PARIS, 1968, VOL. lI

Progesterone treatment alone in late anoestrus, associated with
the introduction of rams on cessation of treatment, may be followed
by ovulation and oestrus and an initiation of cycles (Lishman &
Hunter, 1966; Robinson & Smith, 1967) but the response is not
reliable (Wishart, 1966, 1967; Gordon & Keane, 1967; Gordon, 1968).
Gordon stresses the importance of the introduction of the ram and
the greater reliability of the response if PMSG is used. Proges-
tagen impregnated intravaginal sponges are particularly useful in
this context. If they are used just before the onset of the normal
breeding season, and on their withdrawal the ewes are given a small
dose of PMSG and rams are introduced, the breeding season can be
advanced and whole flocks brought into full synchronized breeding
activity at a time when only sporadic ovulations without oestrus
would be occurring.

The problem of breeding sheep in the depth of anoestrus remains
unsolved due to the inability to produce a series of cycles, coupled
with the low fertility due to poor fertilization at the single
induced oestrous period (Table 4).

IV, EARLY LACTATION

The period of early lactation in the ewe poses special problems.
These are both physical and physiological. Some 16 years ago, I
hysterectomised a number of ewes 3 to 4 weeks after parturition and
found the uteri of a high proportion to contain substantial
quantities of autolysing remnants of pregnancy. There was a
complete physical barrier to conception in these animals. A similar
observation has been made by L. E. A. Rowson (personal communica-
tion). Quantitative studies on the rate of involution of the
uterus are lacking. Foote, Call & Hulet (1967) suggest that it is
completed by 24 days after parturition. However Hafez (1952) found
an interval of 35 days to be necessary for conception in Suffolk
ewes. More recently Newton & Betts (1967) found that although
Dorset Horn ewes exhibited oestrus from 1 to 33 days (mean 18) after
parturition, none conceived within 32 days. Hence in all ewes a
longer interval than 24 days is needed for complete involution and,
in that proportion in which there are retained remnants of pregnancy,
the interval may be considerably longer.

Physiological problems include ovulation without oestrus,
failure of fertilization, and early embryonic mortality. Mauléon &
Dauzier (1965) found that ovarian activity after parturition
commenced well before oestrous activity. Several "silent heats"
occurred after parturition, particularly in ewes which were suckling
their lambs. A similar phenomenon was observed by Fletcher (1968).
In two of three experiments, both of which used Merino cross bred
ewes (Table 8), the incidence of oestrus in lactating ewes treated

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