New Advances in Cryopreservation of Pig Embryos
Livestock Update, January 2002
Tina Gibson and C. M Wood, Virginia Tech
Exploiting the genetic potential of valuable lines of pigs is an on-going goal of swine breeders. Nucleus herds are an important part of the effort, but are expensive to establish and maintain, particularly when inbreeding is considered. Currently, a large amount of money is spent on transporting pigs all over the world to establish nucleus herds. Transportation can be fatal, however, decreasing the number of live animals upon arrival. Disease is also a risk when transporting pigs as new diseases may be introduced to the herd (Dobrinsky, 2001). Artificial insemination (AI) has been widely accepted in the swine industry, and is one tool used to introduce new germplasm into nucleus herds. High risks of disease transmission are common with AI, however, because of the possibility of diseases that can be transmitted through semen. Expense is also a factor, as it can be costly to sustain multiple breeding lines. Embryo transfer (ET) could reduce expense as storage, transportation, and live animal care would be very limited (Dobrinsky, 1997).
Although the swine industry has begun to use ET as a means to improve genetics, available techniques have posed several problems including threat of disease, high cost, and survivability of the embryos. Due to the high sensitivity of pig embryos to hypothermic environments, typical methods of cryopreservation have proven to be unsuccessful because the pig embryos cannot survive the low temperatures. Conventional preservation methods may damage the cytoskeleton of the embryo, but through research cytoskeleton stabilizers have been developed to produce viable embryos (Dobrinsky, 1997). During the process, embryos are frozen during the early development phase, and then warmed so they can be surgically transferred into recipient sows. In two trials, pregnancy rates of about 60% were achieved through this method as well as improved litter sizes (Dobrinsky et al., 2000). The first trial was conducted with four gilts, resulting in three litters totaling 19 live pigs. In a second trial, six of seven gilts farrowed a total of 42 live offspring. These pigs have grown to maturity and reproduced (Dobrinsky, 2001).
Further research is needed to take full advantage of using cryopreservation for ET, including higher pregnancy rates and improved reproductive management (Dobrinsky, 2001). For producers and the swine industry, this new technology may prove to be very important. The largest factor that will affect the swine industry is expense. Overall, superior genetics and decreased disease may out weigh expense. By conducting further research on cryopreservation and ET, the industry will be able to take full advantage of this technique.
Dobrinsky, J.R. 2001. Embryo preservation and transfer technology for swine production. J. Anim. Sci. 79(Suppl. 2):31. (Abstr.).
Dobrinsky, J.R., V. Pursel, C. Long, and L. Johnson. 2000. Birth of piglets after transfer of embryos cryopreserved by cytoskeletal stablization and vitrification. Biol. Repro. 62:564-570.
Dobrinsky, J.R. 1997. Cryopreservation of pig embryos. J. Repro. and Fertility 52:301-312.