You just ultrasounded two mares ages 4 and 5 years for a 14-…

You just ultrasounded two mares ages 4 and 5 years for a 14-day pregnancy examination.  Neither of the mares were determined to be pregnant. The owner reports that both mares were hand bred on their previous 2 cycles to the same 18-year-old stallion. The stallion has not bred any other mares this year. Which of the following would be most appropriate?