The first equine clones were born in 2003, and now advertisements for cloning can be found in equine magazines, and the AQHA has considered registering cloned foals. There are more than 40 live cloned horses. What have we learned and what concerns do we have?
Foal Health Cloned foals do not seem to suffer the same abnormalities seen in cloned calves and lambs, in which “large offspring syndrome” results in oversized animals and organ system problems.
Our laboratory at Texas A&M has reported on the health of the 14 live foals we have produced. About half of the cloned foals had some issues at birth; the major problems were weakness and maladjustment, contracted tendons in the front legs, and enlarged umbilical remnant, some of which required surgical removal. Two of the foals died, one from pneumonia and one from complications after anesthesia. The remaining foals resolved their problems within a few weeks. Aside from one foal that had bladder stones in its first year, to our knowledge all cloned horses are currently healthy.
What is causing problems with cloned foals at birth? Most likely differences in gene expression (how the genes are being used) in the cloned foals. During cloning, the DNA of a skin cell from the donor animal is placed in a host egg (oocyte). The oocyte has to change all the “on/off” instructions attached to this DNA so the DNA can start to express the appropriate genes to make an embryo.
Sometimes these changes are not exactly correct. The problems we have seen at birth seem related to incorrect placental function, which is controlled by a complicated genetic system. There may