Researchers have been studying how mare nutrition during conception and pregnancy affect foal development in utero and after birth. | Photo: iStock

A mare’s body condition can affect pregnancy outcome and set her foal up for success or failure later in life.

The apple doesn’t fall far from the tree. A chip off the old block. Logistically, these endearing idioms about parent-child similarities make sense because progeny receive their genetic blueprint from each parent, half maternal and half paternal. But a variety of other factors also dictate characteristics of offspring—including maternal diet during ­gestation—and horses are no exception. 

A pair of trailblazers from the University of Cambridge, in England, conducted one of the first studies looking at how maternal environment can affect foal development in 1938. They found that newborn Shire-Shetland Pony cross foals were proportional in weight to their dams and almost the same weight as purebred foals of the maternal breed. That is, crossbred foals with Shire mothers were similar in weight to full Shire foals, and crossbred foals with Shetland mothers were similar in weight to full Shetland foals. The authors summarized their findings as an illustration of the interplay between nutrition and genetic factors, both of which are involved in fetal ­development.

During pregnancy the mare’s daily nutrient requirements increase to allow her to maintain body condition while supporting the growing fetus. During gestation she might gain 12-15% of her initial body weight, mostly attributable to fetal and placental tissues. The amount of energy, or calories, she needs above maintenance (when she’s not pregnant) levels typically doesn’t rise until the fifth month of gestation, after which the majority of fetal development occurs. After foaling, a broodmare must produce enough nutritious milk for the foal, while maintaining her own energy requirements for metabolism, digestion, activity, thermal regulation, and waste production