Centaurs have a two-sex reproductive model and comparable to Earth’s placental mammals. They experience puberty at about 15 Earth years in age; resulting in maturation of the gonads and production of gametes, their first seasonal antler growth, and in child-bearing centaurs, the start of the estrus cycle. The estrus cycle is extremely infrequent in centaurs by default, occuring once a year or less. Going into estrus causes the release of 6 eggs (3 in each uterine horn) for possible fertilization, swelling of the silk gland tissue, a change in pheromone production, and the growth of longer feathers on the lower back in preparation for larval passengers. A lack of fertilization causes the eggs to be released and the long back feathers to shed.
Pregnancy occurs if the eggs are fertilized by sperm, and the young develop until they are about 6 centimeters before they're released from the uterus. Gummy, pink, and rather undeveloped, the larvae crawl up onto the parent's back and latch onto a thread from the spinnerets. The silk is fatty and nutritious, comparable to mammalian milk, and the larvae feed on it and cling to the long feathers of the parent's back for 6 months until they're about 50 cm long. They then spin a silk dome over themselves on the parent's back and metamorphose underneath into the imago form, which physically resembles an adult centaur but smaller.
Having pregnancies, especially repeatedly, increases the rate of the estrus cycle. Matriarchs of a clan may go into estrus up to 4 times a year. Sex for reproduction is usually limited to the matriarch and her entourage, and enforced through social means. Although sex and relationships are a social norm between unrelated workers of a clan, uncondoned pregnancy is seen as a threat to the matriarchial power structure and can result in expulsion or culling of the resultant infants.
Usual methods of birth control are avoiding sex during a reproductive period and barrier methods, such as condoms for either sex. Because the vagina and phallus are both so short and wide, condoms usually have leg straps! Homosexual activity just involves flipping one partner around. Sex toys are similarly universal, having one dent and one bump. Centaurs also enjoy oral, rostral, and manual sex.
