In utero programming of the postnatal growth and insulin sensitivity after between-breeds transfers in the horse

Genetics are responsible for determining the growth and size of different breeds of horses. Cross-breed embryo transfers were performed using Pony (P), Saddlebred (S) and Draft (D) horses to study growth and insulin-sensitivity in offspring. Control pregnancies (S-in Sand P-in-P) were obtained by Al. "Lush" pregnancies were obtained by transferring S (S in-D) and P embryos (P-in-D) into D mares. Restricted pregnancies were obtained by transferring S embryos into P mares (S-in-P). At 3 days, 4.5 months and one year, foals underwent an intravenous glucose tolerance test (IVGTT). At 6 and 18 months, insulin sensitivity was determined using a euglycemic hyperinsulinemic clamp. Birthweight was increased in P-in-D and S-in-D vs P-in-P and S-in-S controls (+57.2%,p=0.0007 and +8.9%,p=0.0597, respectively), and restricted in S-in-P vs S-in-S (-31.2%, p=0.0008). P-in O foals remained heavier than P-in-P until 18 months (+38.5%,p=0.0317), whereas S-in-D foals became similar to S-in-S between 6 and 18 months. S-in-P foals caught up with S-in-S foals after 9 months. Insulin response to glucose was increased in S-in-D and P-in-D foals at 3 days (p=0.0393 and p=0.0539), indicating insulin resistance. Results are pending for 4,5 months. Clamps at 6 months demonstrated the development of insulin resistance in P in-P vs S-in-S foals (p=0.0378). P-in-D remained insulin resistant and did not differ from P in-P. S-in-P and S-in-D foals were not different from S-in-S but insulin resistance was increased in S-in-D vs S-in-P foals (p=0.0293). IVGTT at one year and clamps at 18 months of age confirmed the increased insulin resistance of P-in-P vs S-in-S foals (p=0.0487), without effects of embryo transfer. Genetic programming of fetal and post-natal growth can be modified through embryo transfer in a larger or a smaller breed in the equine species and that glucose homeostasis is also affected post-natally. More data on plasma insulin concentrations will be available at the meeting.