although at later stages of lactation the treatment was more
effective. A third technique, that of separating sow and

litter for a period of 12 hours each day has met with some
success on a small scale (10),(11). It has been suggested

that the period of separation may be quite critical, since

sows separated for 8 hours each day failed to show oestrus (10).

It seemed that the second and third methods both separat-
ely and in combination were worthy of further investigation(12).

MATERTALS AND METHODS. The investigation was carried out in 2
stages, stage 1 in which the results from 3 methods of
inducing oestrus and ovulation during lactation were compared
with those from control lactating sows and stage 2 in which
one of the induction methods was further compared with controls
and this data and the relevant results from stage 1 were
incorporated together to allow an evaluation of the method to
be made,

Stage 1, A total of 24 Essex sows was divided at random into

4 groups as follows:

Group 1. Control lactating sows

Group 2. Lactating sows separated from their litters for 12
hr. each day beginning on day 21 of lactation and
continued until oestrus was induced or 10 days had
elapsed.

Group 3. Lactating sows injected with 1500 i.u. PHSG on day
21 of lactation.

Group 4. Lactating sows separated from their litters for 12
hr. each day on days 21,22 and 23 of lactation and
injected with 1500 i.u. PMSG at the end of the period
of separation on day 23 of lactation.

Stage 2, The numbers of sows in Groups 1 and 4 were increased

to make a total for these two groups of 29 sows.

Throughout the investigation, sows were tested for
oestrus daily with a boar from day 10 of lactation to day 10
post-weaning. Weaning was carried out on day 49 of lactation.
Sows which came on oestrus during this period were mated on
two successive days whenever possible and, if lactating, were
returned to their litters to continue lactation until weaning.
Growth data were recorded on all litters.

RESULTS.

Stage 1, The oestrus response and pregnancy response data are

shown in Table 1. The data showed that while none of the

control sows exhibited oestrus during lactation, lactational
oestrus could result from each of the three treatments, and
pregnancies could result from lactational matings. The treat-
ment applied to Group 4 was the most successful.

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