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

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 ¼ 21) and S-S (n ¼ 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 ¼ 6 and S-D, n ¼ 8) and S embryos into P mares
(S-P, n ¼ 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.