What species has the longest gestation period?

The species with the longest gestation period among the given options is indeed the horse. Horses typically have a gestation period of around 11 months, which can range from 320 to 380 days. This extended gestation period allows for the development of the foal, ensuring it is adequately sized and mature enough to survive once born.

In contrast, dogs and cats generally have much shorter gestation periods, usually averaging around 58 to 68 days for dogs and 64 to 67 days for cats. Cows also have a shorter gestation period of approximately nine months, more similar to that of humans rather than horses.

The longer gestation in horses is linked to their need for stronger physical development upon birth, which is essential for their survival and ability to keep up with the herd shortly after delivery.