Alpacas are unusual in their mating behaviours in a couple of ways.
Firstly, mating in alpacas is an unusually extended affair, with an average mating time of 30 minutes.
Males are ‘dribble ejaculators’, which means the semen dribbles out of the penis slowly and continuously, hence the need for an extended copulation.
Image from https://bas-uk.com/alpacapedia/alpaca-care/breeding/
Secondly, during mating, the penis passes through the cervix to deposit the semen in the uterus. This is unusual as most mammals deposit sperm in the vagina.
The males have a cartilaginous sickle-shaped penis tip that pushes through the cervix.
Alpaca Reproductive System. Vag = vagina, Cx = cervix, Ut = uterus, Ova and Ovi = ovaries
Image from Brennan et al., 2021
Alpaca Penis. Image from Brennan et al., 2021
Females alpacas, like many other hoofed animals, have a bicorne uterus, meaning the uterus is split into two uterine horns: a left and a right.
In alpacas, over 95 % of pregnancies happen in the left uterine horn.
References and Further Reading
Bravo PW, Moscoso J, Ordonez C, Alarcon V: Transport of spermatozoa and ova in female alpaca. Animal Reproduction Science. 1996, 43: 173-179.