1 9 . Of
the o va r e covered a t laparo t omy,1 1 . 5%
were a bnorma l .Of
the abnormal ova ,72%
wer e involut ed(
i . e . had crater indentati ons in th e vi tel lus)
,1 2%
had fragm ent e dcyto plasm a n d
1 6%
had a bnormally thi c k zonae pel lucida e .20.
I t is s ugges ted that involution i s n o t an abnormality wh ich wi l l prevent an ovum from being fertilised and developing normally and that i t is a nat ural cons equenc e o f the lack of fertilisation o f an o vum .2 1 .
The incid e n c e o f abnorma l ova d e c r eas ed from th e early to late breedi ng s eason .22 .
Th e inc i d e n c e o f abnormal unferti lis e d o va inc reas ed wi th increas ing i n t ervals from ons e t o f o e s t rus up to3-4
days . Mos t o f the abnormal ova recovered0-3
days af t er th e ons e t o f oes tr us had a bnormali t i es whi c h might be expe c t ed in ageing unferti l i s e d ova , bu t the o va recover ed3-4
days after the ons e t of oestrus had a bnormally thick zonae pelluc i d a e , an a bn ormali t y which did no t r epres ent a deg enera t i v e change expe c t ed i n unfertilised o va at this time.23 .
The r e was a marked in creas e in the incid enc e o f a bnorma l ova as t h e cul ture period l engthened . Th e inc i d enc e o f87
involuted o va d e c r eased markedly over the firs t
24
h o urs o f cultur e , but was opposed by a marked increase in the inc i d en c e o f fragment e d o va .2 4 . Wi thin c l eavage s tag es o f c ultured ova th e r e was us ually an increas e in the i n c i d en c e o f a bnormal o va as the c ul t ur e period l engthen e d .
D IMENS IONS OF OVA
2 5 . For ova at all c l eavage s tages , the average t o tal diame t e r , t h e average zonal cavi ty diamet er and t h e average zona pelluc i da thickness were found t o be 1 75 , 1 46 and 1 4 . 6 microns r e s pe c t i v e l y .
2 6 . Th e t o t a l volume o f ova cyt oplasm d e c r eas ed from t h e 2 - c e ll to the 1 6- c e ll s tage and th e m ean blas tomere vo l ume was approximat ely halved with each suc c essi ve c l eavag e .
S URVIVAL O F TRANS FERRED OVA
2 7 . I n the 1 966 br e eding and 1 966- 67 early an o e s trous s eas ons the d onor and r e cipient o f t rans ferred ova w e r e where pos s i bl e the same ewe . All ew es were mat e d t o th e entir e ram an d t h e o v a r e covered a t laparot omy were e i t h er t rans f erred bac k into same ewe immed i a t e ly after re covery
(
Con t r o l tran s f e r)
, or after c ultur e in vi tro . In the 1 966- 67 lat e anoes trous and 1 967breeding s easons th e donors and r e c i pi en t s were di f ferent ewes , t h e donors being mat e d t o ent i r e rams and the r e c i pients t o ' t eas ers • .
28 . O f 7 c ontrol t rans f e r experiments conduc t e d , 71 % w e r e s uc c ess ful . A total of 1 0 ova were trans ferred, 60% o f th ese being present as viable embryos a t s laught er of th e r e c i pi ent ew es .
29.
The r es ults from thes e cont r o l trans fers w e r e pr es ented t o indi cat e : the e f f e c t o f th e number o f r e ci pi en t c or pora lut ea ; t h e s ta t e o f the recipi en t g enital tract a t trans fer ; the numb er and c leavag e s tages of t h et rans ferred o va ; the s tage o f devel opmen t o f the t rans ferred o va and r e c i pi ent geni tal tracts at t rans fer ; and the
period the o va were h e ld in vi tro before trans fer, on the s u c c ess of the trans fer experimen ts .
30 .
O f22
t ran s f e r experiments involving the trans fer o f c u l t ured ova , only one was s u c cessful .A
t otal o f48
o va were t rans ferr e d ,2
of th e s e being present at s la ugh ter as viable embryos .31 . Pos s i bl e caus ed s ugges t ed for this l ow s u c c ess fo l l owing the trans fer of c ul t ured ova were : inc or r e c t r ela tionship b e tw e en the s tage of d e velopment o f the t rans ferred ova and r e c i pi en t geni tal t ra c t a t t rans fer ; fai lur e o f s o me r e c i pients t o ovulate prior to t rans fer ; t e chni q u e s us ed i n th e t rans f e r an d c ul t ur e o f ova .