Pop quiz: When does an equine fetus undergo the most profound growth and development?
You're right! It was a trick question.
Fetal foals gain about 1 lb (0.45 kg) a day during the last 90 days of gestation. Sure, that's impressive, but consider for a moment that in a split second, a single sperm fertilizes a single egg to produce a single cell with a complete set of DNA. That one cell immediately begins dividing, forming a multi-celled embryo with a functional circulatory system, rudimentary organ systems, and placenta before even leaving the oviduct and entering the uterus.
The rapidly growing embryo then takes on the entire uterus, migrating and altering the uterine environment to ensure its viability. Finally, at around day 16 after fertilization, the embryo implants into the lining of the mare's uterus where it will remain until time of parturition.
According to a recent review on the topic*, Dr. Tom Stout of the Department of Equine Sciences at Utrecht University, in the Netherlands, “embryo-maternal dialog during the first month is essential not only to conceptus survival but also has more profound and long-lasting implications,” citing epigenetic influence over the development of the fetus.
The embryo's meanderings combined with the delicate nature of the mare's uterus, propensity for infection and fluid retention, as well as myriad other causes, contribute to a high rate of early embryonic death.
Every breeding season, veterinarians pull out all the stops to get and keep mares in foal, yet sometimes lament the conditions they must work with; at times they are referring to body condition and nutritional well-being. By feeding broodmares appropriately in the months prior to breeding, the likelihood of pregnancy increases.
“Prior to breeding broodmares should have a body condition score of 5 or 6, tops, using the nine-point Henneke body condition score,” advised Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research (KER).
In addition to improved conception, pregnancy, and foaling rates, mares with an appropriate BCS also produce high-quality colostrum.
“This is especially true when mares are offered omega-3 fatty acid supplements prior to pregnancy and throughout gestation and lactation,” advised Crandell.
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