Protein deficiency, which may result from suboptimal feed intake or a deficiency of one or more of the essential amino acids, causes reduced gains, poor feed conversion, and fatter carcasses in growing and finishing pigs. In lactating sows, milk production is reduced, excess weight loss occurs, and sows may fail to exhibit postweaning estrus or have delayed return to estrus. For optimal use of protein, all essential amino acids must be liberated during digestion at rates commensurate with needs. Therefore, protein supplements should not be handfed at infrequent intervals but should be mixed with the grain or be available at all times with grain on a free-choice basis.
Certain long-chain polyunsaturated fatty acids are essential for swine. Linoleic acid is essential in the diet and is used to produce longer-chain fatty acids that are probably also essential. .