Final answer:
Carnivorous mammals are the primary host in the life cycle of Sarcocystis spp. They complete the sexual reproduction phase of the parasite, influencing the spread of infection to intermediate hosts.
Step-by-step explanation:
The primary host of Sarcocystis spp. in its life cycle is carnivorous mammals. Sarcocystis is a genus of parasites, and like many others, it has a complex life cycle involving different hosts. Carnivorous mammals serve as the definitive hosts where sexual reproduction of the parasite takes place, resulting in the release of infectious oocysts in the feces of the host. These oocysts can contaminate the environment and be ingested by intermediate hosts, such as birds or rodents, which then become infected. Inside these intermediate hosts, the parasite forms cysts in muscle tissues. When a carnivorous mammal then preys on these infected intermediate hosts, it ingests the cysts, and the lifecycle repeats.