Longitudinal Study of Growth and Osteoarticular Status in Foals Born to Between-Breed Embryo Transfers

• Embryo transfer into larger or smaller breeds is used to achieve phenotypic changes in equids.
• Genetic considerations apart, mares are determinant in foals growth.
• Tendencies are shown regarding the maternal impact on osteochondrosis predisposition of foals.
• The maternal impact extends beyond weaning time, at least until 1½ years of age.

The role of antenatal events on growth and predisposition to osteochondrosis (OC) was investigated in foals born to between-breed embryo transfers. Pony (P), saddlebred (S), and draft (D) horses were used. Control P-P (n = 21) and S-S (n = 28) pregnancies were obtained by artificial insemination. Enhanced and restricted pregnancies were obtained by transferring P or S embryos into D mares (P-D, n = 6 and S-D, n = 8) and S embryos into P mares (S-P, n = 6), respectively. Control and experimental foals were raised by their dams and recipient mothers, respectively, and weaned at age 6 months. Body measurements were recorded from birth to age 18 months. Osteochondrosis status was evaluated shortly after weaning and at age 18 months. Fetal growth was enhanced in P-D foals with overgrowth of most body segments until age 18 months. Fetal growth was restricted in S-P foals compared with S-D foals. Body weight, shoulder, and hip width of S-P foals grew slower before weaning but subsequently caught up after weaning. Other segments did not catch up, resulting in reduced body weight and withers' height in S-P compared with S-D foals at age 18 months. The relative risk of developing OC was increased in restricted S-P foals compared with S-S and S-D foals shortly after weaning where all S-P foals were OC positive. Only two S-P foals were still OC positive at age 18 months. These data confirm the impact of the intrauterine environment on growth, skeletal health, and possibly athletic capacities of horses.