Multiplication of five breeds of "exotic" sheep in New Zealand using the technique of embryo transplantation : a thesis presented in partial fulfilment for the requirements of the degree of Master of Philosophy in animal science at Massey University
Sheep of five* breeds imported into New Zealand and held at a
quarantine farm were increased in number through the use of embryo
transplantation (ET) procedures. For this, donor ewes after
superovulation treatment were inseminated with fresh semen of rams of
their own breed and flushed to recover embryos 5 or 6 day after onset
of oestrus. The embryos after classification and processing through
ten washes of flushing media were transported to a secondary quarantine
farm and transferred into synchronised recipient Coopworth and Romney
ewes. Some of the surrogate ewes received intravaginal progesterone
supplementation (CIDR) for 14 days after transfer. Details of lamb
production were recorded. This thesis reports the results of some
factors that can affect the success of a commercial ET programme.
Among the donor ewes 87-89% of the animals were in oestrus after
synchronisation and gonadotrophin treatment. The ewes not in heat
often had low or absent superovulatory responses. Superovulation was
induced with either FSH-P or Folltropin given as 7 or 8 intramuscular
injections at 12 h interval begining 72 h before withdrawal of the
progesterone treatment (CIDR). The gonadotrophin dose levels were
modified according to the breed and also as the programme progressed.
Most of the data were examined within breed.
The superovulatory response to either the type of gonadotrophin
preparation or the dose levels did not differ significantly.
The variation in recovery rate of embryos was not affected by the
type of gonadotrophin used, whether the animals treated were flushed on
one or two occasions, whether flushing was done 5 or 6 days after
oestrus, or according to the ovulatory response (classed as 1-8, 9-16
and >16 corpora lrttea counted).
Overall 85% of the ova were fertilised and had developed into
embryos. There were no significant differences in fertility between
inseminations done in the morning or the afternoon, or when flushed
once or twice, or when AI was followed by natural mating, or relative
to the ovulatory response. Moreover there was no significant
difference within the six breeds in the fertility rate.
The quality of the embryos, classified as "good" or "poor" on the
basis of their appearance and stage of development consistent with the
day of flushing (developmental age), was .significantly affected in
several of the breeds by the type of gonadotrophin, the dose levels,
the ovulatory response and the age of the embryos when recovered.
The pregnancy rate after the transfer of two embryos was 59%, 72%,
60%, 53%, 53%, 46% for recipients carrying DT,FT,FINN,GOT,OXD,WHM
embryos, respectively. The comparable ·values for embryo survival were
46%, 57%, 54%, 42%, 40%, 34%, respectively. In general among the
factors studied involving breed of recipient, degree of synchronisation
between donor and recipient, ovulation rate in the recipient, interval
from flushing to transplantation and progesterone supplementation it
was found that only the latter factor in the DT, FT and OXD breeds of
embryos was significant.The results from this multiplication programme after considering
409 treatments with gonadotrophin gave an average of 6.0 corpora lutea,
3.9 eggs recovered, 3.4 eggs fertilised and 1.5 lambs born per
treatment. It is concluded that the low recovery rate and poor
survival rate of the embryos are important factors to be overcome if a
significant increase in the number of lambs born is to be expected from
embryo transplantation. Work to overcome these problems is necessary,
but attempts should also be made to increase the OR through
modification of the gonadotrophin treatments. Support for this idea is
suggested because in some animals with a high OR satisfactory numbers
of eggs were fertilised and an increase of good quality embryos was
recorded.* Texel (from two sources, Danish (DT) and Finnish (FT) and considered
as separate breeds), Finnish Landrace (Finn), Gotland Pelt (Got), Oxford
Down (OXD), White Headed Marsh (WHM) breeds.