Maternal influence on pre- and postnatal growth of foals born after embryo transfer.

In the present study the growth and development of three pairs of matching gender foals from birth to maturity were compared. One Polish Pony embryo of each pair was transferred from a donor mare (mass 387-400 kg) to a much larger heavy type recipient mare (mass 561-780 kg). The other embryo of each pair underwent normal gestation (control). The transferred and control horses were examined at 9 and 13 years of age, and X-ray pictures were taken of their front legs to measure the length of the bones. On the basis of the results of this study, it is concluded that the processes of growth and development in transferred foals born to heavy type recipient mares can be divided into three phases. During the first fetal stage, body weight gain and growth are faster in transferred foals than in control foals. In the second phase, which comprises the suckling period, the transferred foals put on weight faster than control foals, but the growth rate is slower than during the first phase. In the third phase, after weaning, both body weight gain and growth rate are comparable to those of control foals.