The length of the oestrus cycle in goats can vary depending on the breed and individual animal. However, on average, the oestrus cycle of a goat lasts between 18 to 21 days. During this cycle, a goat is receptive to mating and may exhibit certain behaviors such as vocalization, restlessness, and a decrease in appetite. It's important to note that the oestrus cycle can also be influenced by various factors such as seasonality, nutrition, and age.