History-making racemares Rachel Alexandra and Zenyatta, both of whom were named Horse of the Year during their careers, were both confirmed to be carrying their first foals this week.

2009 Horse of the Year and champion 3-year-old filly Rachel Alexandra was bred to Curlin the morning of Feb. 21. She was confirmed to be in foal on Monday morning and her due date is Feb. 1, 2010. The gestation period for a horse is 11 months, but first-time mothers tend to foal late father than early.

Curlin, who, like Rachel Alexandra, is owned by Jess Jackson, was Horse of the Year in 2007-08. Racing’s all-time leading moneywinner counts the Breeders’ Cup Classic and Dubai World Cup among his victories. The son of Smart Strike’s first foals are yearlings this year, meaning they’ll hit the track in 2012.

2010 Horse of the Year Zenyatta, who was also named Eclipse champion older female from 2008-10, was bred to Bernardini the morning of Feb. 23. She was confirmed to be in foal on Thursday morning and is also due the first week of February 2012.

Bernardini was the champion 3-year-old of 2006, when he won the Withers, Preakness, Jim Dandy, Travers and Jockey Club Gold Cup. He enjoyed great success as a freshman sire in 2010, producing Grade 1 winner AZ Warrior and Group 1 winner Biondetti; two of his other graded winners Stay Thirsty and To Honor And Serve, are on the Kentucky Derby trail.

What’s next? Both Rachel Alexandra and Zenyatta were scanned and confirmed in foal 14-15 days after breeding, which is the earliest a pregnancy can be confirmed. The mares will be scanned again at the 26-28 day mark, and again at the 46-50 day mark. If there are no problems present with the embryo — which officially becomes a fetus at 50 days — at that point, then the mare is well on her way into pregnancy and the chances are good for a normal gestation and delivery.