Which animals are unable to synthesize all of the required amino acids?

Swine, unlike ruminants such as beef cattle and sheep, as well as poultry, have specific limitations in their ability to synthesize certain amino acids. While all animals require amino acids for protein synthesis, swine are particularly notable for their need for some amino acids to be supplied directly through their diet. They require a balanced intake of essential amino acids, which they cannot synthesize in sufficient quantities on their own.

In contrast, ruminants, such as beef cattle and sheep, can utilize microbial fermentation in the rumen to synthesize some essential amino acids and are generally more efficient in managing protein byproducts. Poultry also have a well-studied requirement for amino acids but can typically synthesize more than swine can. Therefore, swine stand out in this context for their specific dietary needs regarding amino acid intake.