Is it permissible to slaughter a calf instead of two sheep for the Aqiqah of a male newborn, or one sheep for a female?

The Sunnah of 'Aqiqah is fulfilled for both male and female by sacrificing one calf, provided it is two years old or more. A calf that has reached two years of age is sufficient for the newborn, regardless of gender, and anything less than two years is not acceptable. The Sunnah of 'Aqiqah is also fulfilled by sacrificing one sheep for both male and female, though it is preferable to sacrifice two sheep for a male.