» Blood Supply to Pelvic Wall and Viscera

The ovarian artery is similar to that of other animals in that it is tortuous and has branches to the uterine tube and to the tip of the horn of the uterus. The uterine branch of the ovarian vein is not as prominent in camelids as in some other animals, such as the sheep.

Despite llamas and alpacas being Artiodactyla, the blood supply to rest of their pelvic viscera and perineum has some interesting differences from that of other Artiodactyla. The internal iliac artery is of intermediate length in the llama, with a relatively caudal termination, similar to ruminants and pigs, but despite this, the distribution and origination of the intrapelvic vessels in the llama is more similar to that of the carnivore than to that of ruminants or other Artiodactyla.

The cranial gluteal artery is a branch of the internal iliac artery caudal to the body of the ilium and exits the pelvis through the greater sciatic foramen. The obturator artery and the iliolumbar artery arise via a common trunk about 1 cm caudal to the cranial gluteal artery. The internal iliac artery then terminates at the level of the third sacral vertebra as the caudal gluteal and internal pudendal arteries.

The vaginal or prostatic artery is a branch of the internal pudendal artery right after the internal iliac artery divides into internal pudendal and caudal gluteal branches. This pattern is like the carnivores and the mare and is in contrast to the usual artiodactyl pattern of a long internal iliac artery that gives rise to the vaginal or prostatic artery before it terminates as the caudal gluteal and internal pudendal arteries. The caudal gluteal artery exits the pelvis through its own foramen, cranial to the lesser ischiatic foramen.

The urethral artery is a branch of the internal pudendal artery, cranial to its termination. The middle rectal artery is usually absent in the llama, and the cranial rectal artery (from the caudal mesenteric artery) is prominent and serves the area usually supplied by the middle rectal artery.

The artery of the penis or clitoris, and the ventral perineal arteries, are the terminal branches of the internal pudendal artery. The ventral perineal artery is the source of arteries supplying several perineal structures, including the ischiocavernosus muscle and bulb of the penis in the male and vestibular bulb in the female, before supplying the caudal rectal artery in both genders. The ventral perineal artery ends in the ventral perineal region; it continues as the dorsal labial artery in the female. The blood supply to the penis (or clitoris) follows the branching pattern of the carnivore, with the artery of the penis dividing into the deep artery of the penis, the artery of the bulb of the penis, and the dorsal artery of the penis.

In the llama there is no branch to the uterus or ductus deferens arising from the umbilical artery. In the female, the main blood supply to the uterus is via a uterine artery originating from the vaginal artery, and in the male the artery of the ductus deferens is a branch of the prostatic artery. This follows the carnivore pattern rather than that of the horse or ruminant.

The blood supply to the uterus is asymmetrical, with the right uterine artery being larger than the left in 90% to 95% of animals in one study. Also in the llamas and alpacas in this study, there was a large crossover vein from the left horn of the uterus to the right uterine vein, and a parallel branch of the right uterine artery to the left horn of the uterus, so that much of the left horn is supplied by vessels from the right side. (In the other 5%-10% of animals, the asymmetry was present but was reversed in direction.) There was also an additional venous anastomosis connecting the right and left sides ventral to the cervix, as is seen in other domestic species. The authors of this study noted that this vascular pattern in camelids is interesting in light of the observation that the left uterine horn causes luteolysis in the right or the left ovary, while the right uterine horn causes luteolysis in the right ovary only; however, the study did not identify a place where blood from the left horn could drain to the right ovarian vein, and thus participate in a countercurrent mechanism with right-side ovarian arterial blood.