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.