RESULTS AND DISCUSSION a) Oestrous response and conception
rate. The results of using hormone treatment during the breed-
ing season to synchronise oestrus in non-lactating sheep have
been extensively described; conception rates usually exceeding
70%. By contrast TABLE I contains the results of our most
recent study with lactating ewes and shows that although lact-
ating ewes were capable of exhibiting a high oestrous response
(74.0% and 75,8%) conception rates were generally low (22,7%
and 13,6%). The difference between conception rates in lact-

ating ewes in and out of the breeding season was not signif-
icant,

TABLE T
Qestrus and conception in lactating ewes

   
 

  

%

mated ewes with
live lambs

   

 
    
 
 

No., ewes %
ocestrus
29 75.8
60 7440

Date during the breeding season refers to the first post-
partum oestrus.

Breeding season

  
   

  

Out of season

b) Ova recovery and fertilisation., The results of ova recovery
experiments are given in TABLE 2a, At 36 hours after the onset
of oestrus in treated lactating sheep 70,0% of the ova were
recovered and their stage of development would suggest that the
time of ovulation in relation to oestrus is normal and in
agreement with other authors. At 72 hours after the onset of
oestrus in treated lactating sheep only 56.2% of the ova were
recovered, There was a significant seasonal difference (P &
.005) in the number of ewes with a complete loss of ova at 72
hours thus treatment or lactation does not appear to influence
the tubal transport of ova.

The results of ova fertilisation are given in TABLE 2b.
Lactation leads to a reduction in fertilisation, 87,0% of all
ova from non-lactating sheep were fertilised compared with
58,9% in lactating sheep, the difference is significant (P <

«005).  Season and treatment appear to have little effect on
fertilisation,

When lactation and seasonal anoestrus are concurrent the
combined effects of faulty tubal transport and lowered fertil-
isation accompanied by the higher degree of embryo mortelity
known to occur during lactation are responsible for the poor
conception rates obtained,

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