Dairy Sheep Symposium - the Department of Animal Sciences ...

Improved AI technique
Artificial insemination (AI) is a powerful tool in animal breeding programs, providing a means
to obtain rapid genetic progress. AI is widely used in dairy sheep and either fresh or frozen
semen can be used to inseminate ewes. In the past, the results obtained using frozen semen were
unsatisfactory, especially when the semen was deposited outside the uterus, but through the use
of improved diluents, pregnancy rates with frozen semen seem to approximate to those achieved
with fresh semen. AI fecundity rate in sheep is lower than in cattle and conception rates of 55-
60% are common in most sheep breeds. Recently several scientific advances have begun to put
AI within reach of the sheep producer.
The main value of laparoscopy for AI in ewes is that it provides a method for depositing semen
directly into the uterus. By doing so it reduces failure of fertilization, which previously occurred
after the conventional insemination of frozen/thawed semen in those ewes involved in ‘sire reference’
breeding schemes. Another aspect that will improve using laparoscopic techniques is embryo recovery
and transfer in MOET breeding programs. Indeed, the laparoscopic techniques that were developed
in the 1980’s are still regarded as a major advance towards a more welfare friendly approach for
implementing genetic improvement programs.
One of the mayor problems in artificial insemination is the semen transcervical application.
Due to the tightly interlocking nature of the cervix, the access to the uterus via its natural entry
point is extremely difficult in the ewe. This is the reason for ignoring it as a uterine entry point and
resorting to laparoscopy for direct intrauterine insemination in order to ensure fertilization with
frozen/thawed semen or embryo recovering (Robinson et al., 1999). In this regard, observations
that there is large between-ewe variation in the occurrence and strength of the cervical response is
particularly interesting; it may explain why conception, following cervical insemination, occurs
with apparent ease in some ewes but not others. The challenge in this point is to know which factors
are controlling this cervix behavior.
Sorted Semen for Production of Lambs of Pre-determined Sex
Research on flow cytometry of sperm for the purpose of predetermining gender of offspring
has led to a validated method to separate X from Y chromosome-bearing spermatozoa for use
with in vitro fertilization and embryo transfer, intratubal insemination or intracytoplasmic sperm
injection (Johnson, 1995). Recent experiments have demonstrated that normal lambs can be
obtained in vivo following laparoscopic deposition of 100,000 sex sorted spermatozoa in the tip
of each two horns of the uterus (Robinson et al., 1999). One of the limiting factors is the capacity
of sorting spermatozoa using this technique but the rapid increase already achieved in the speed
of sorting sperm suggests that the use of sexed semen in sheep will probably become a commercial
reality in the near future.
Cloning
Cloning technology has advanced very rapidly offering exciting opportunities for the improvement
of efficiency and sustainability of livestock production (Robl, 1999). The main uses
of cloning in animal breeding would be acceleration of genetic progress and rare animal conservation.
Genetic progress is dependent on the exploitation of genetic variation and cloning would
only have a limited use within breeding programs. Then the main advantage of cloning would be
based on the rapid dissemination of genetic progress from elite herds towards the commercial
farmer (Wooliams, 1997). Furthermore, cloning techniques will provide new methods for genetic
conservation of indigenous breeds that are in an endangered situation under the threat of imported
breeds that are being reared in intensive farming systems.