As I discuss in this question, one of the early movements that was important in the development of Vaishnavism was the ancient Pancharatra movement, whose sacred texts consisted of detailed procedures to worship the sage Narayana, an ancient incarnation of Vishnu who was the son of Yama god of death and twin brother of the sage Nara. Since the Pancharatra texts originated from Narayana himself, they are followed by pretty much all mainstream Vaishnava Sampradayas, whether Sri Vaishnavas, Gaudiya Vaishnavas, etc. Among the most oldest Pancharatra texts are the Satvata Samhita, Paushkara, Samhita, and Jayakhya Samhita. But there is a Pancharatra text even older than these, and it is found within the Shanti Parva of the Mahabharata! It's called the Narayaniya, and it's an 18-chapter religious dialogue between Yudishthira and Bhishma on the importance of worshipping Narayana/Vishnu, similar to the Bhagavad Gita, an 18-chapter religious discourse between Krishna and Arjuna found in the Bhishma Parva of the Mahabharata.
In any case, one of the topics discussed in the Narayaniya is the issue of animal sacrifice, which the text has a negative view of. For instance, in this chapter of the Narayaniya, the ancient king Uparichara Vasu is praised for conducting an Ashwamedha Yagna (horse-ritual) without sacrificing animals:
In that great sacrifice, O monarch, all the requisite articles were collected. No animals were slain in it. The king had ordained it so. He was full of compassion. Of pure and liberal mind, he had cast off all desires, and was well-conversant with all rites. The requisites of that sacrifice all consisted of the products of the wilderness. The ancient God of gods (viz., Hari), became highly gratified with the king on account of that sacrifice.
The next chapter of the Narayaniya makes the prohibition even clearer. It relates to a dispute between the sages and the gods over the statement in the Vedas that "Ajas" must be sacrificed in a Yagna (fire-ritual). The gods said Ajas are goats, while the sages said the Ajas were vegetable seeds, and Uparichara Vasu was cursed for incorrectly siding with the gods:
The gods, once on a time, addressing many foremost of Brahmanas, said unto them that sacrifices should be performed by offering up Ajas as victims. By the word Aja should be understood the goat and no other animal.' The Rishis said, The Vedic Sruti declares that in sacrifices the offerings should consist of (vegetable) seeds. Seeds are called Ajas. It behoveth you not to slay goats. Ye deities, that cannot be the religion of good and righteous people in which slaughter of animals is laid down. This, again, is the Krita age. How can animals be slaughtered in this epoch of righteousness?' ... Learning what the opinion was that was entertained by the deities, Vasu, moved by partiality for them, said that sacrifices should be performed with animals. At this answer, all the Rishis, endued with the splendour of the Sun, became very angry. Addressing Vasu who was seated on his car and who had (wrongly) taken up the side of the deities, they said unto him,--Since thou hast (wrongly) taken up the side of the deities, do thou fall down from heaven.
So from all this it's clear that animal sacrifice is prohibited according to Pancharatra principles, which means that it's prohibited by mainstream Vaishnvaism. But as I discuss in this question, not all Vishnu-worshippers follow the Pancharatra texts. There is a small sect of Hinduism called the Vaikhanasas who worship Vishnu according to a different set of texts. The Vaikhanasa texts place less emphasis on the philosophical concerns of mainstream Vaishnavism, and more emphasis on ritualism and idol worship.
So my question is, what do the Vaikhanasa texts say about animal sacrifice? Do they forbid it like Pancharatra texts do? I know that Vaikhanasa texts say you don't have to perform Yagnas as long as you worship Vishnu in his idol form, but do they say that you can perform animal sacrifice in Yagnas if you want?