VIe CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. Ii
THE FERTILITY OF SHEEP INDUCED TO BREED DURING LACTATION

SANDRA MOSELEY and G. E. LAMMING
Nottingham University, School of Agriculture,
Sutton Bonington, Loughborough, Leics., U.K.

Lactation is associated with a reduction in reproductive
efficiency in most species and this is certainly the case in
sheep. In temperate climates ewes which lamb in the Spring
normally do not exhibit a post-partu— lactational oestrus and
attempts to use hormone treatment to induce fertile oestrus and
ovulation in lactating sheep have been singularly unsuccessful,
when compared to the use of a similar treatment to synchronise
oestrus in non-lactating ewes during the normal breeding
season, In ewes that do lamb during the breeding season that
is in the Autumm, the interval from parturition to oestrus
depends on the date of lambing within the season, However
the conception rate in lactating animals at the first post-
partum oestrus is low. In those animals failing to conceive,
oestrous cycles are of normal length indicating that reprod-
uctive failure probably occurs early in the cycle. We
decided therefore to study the causes of failure soon after
mating paying attention to fertilisation rate and ovum trans-
port in the oviduct.

MATERIALS AND METHODS A total of 137 half-bred ewes, both dry
and lactating were used for the study of fertility. Compar-
isons were made both in and out of the breeding season.

The hormone treatment used for the induction and synchron-
isation of oestrus was the same throughout the experiment.
Sponges impregneted with 30 mg. fluorogestone acetate (GeDs
Searle & Co, 17 acetoxy 9 fluoro 11 hydroxy pregn-4-ene-3, 20-
dione) were inserted into the vagina for 12 days. A subcuten-
eous injection of 750 i.u. P.M.S. was given at sponge removal.
Al1] ewes were mated to a fertile ram.

Lactating ewes induced to oestrus were treated from 5-7
weeks after parturition so that they mated at about the same
time as ewes allowed to return naturally to cestrus after
lambing during the breeding season.

The onset of oestrus was accurately timed by close
observation of the ewes used for ova recovery., Ova were
flushed from the uterine tubes of ewes under nembutal and
fluorothane asnaesthesia 36 hours or 72 hours after the onset
of oestrus.

Ova recovered were examined by phase-contrast microscopy.
Evidence of cleavage and the presence of sperm in the zona
pellucida were taken as criteria for fertilisation.

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