Yeast supplements include live yeast, yeast cell wall (YCW), purified outer layer of cell wall components such as mannooligosaccharide (MOS) and β-glucans, purified inner layer of cell wall, and yeast extract products. It is generally accepted that yeast products can improve pig gut health via improved gut integrity and maintenance of a healthy microbiome, leading to increased nutrition absorption, and thus improved overall pig performance.
Live yeast refers to yeast cells that are still alive and active. It is often used to improve digestion and promote gut health for ruminant animals.
After autolysis (using the yeast’s own enzymes) or hydrolysis (using added exogenous enzymes), the yeast extract and cell walls are separated using centrifugation before being dried. Usually, the yeast extract via autolysis contains higher levels of yeast nucleotides. However, the yeast extract via hydrolysis is more applicable due to a low salt concentration.
The composition of autolyzed yeast (AY)
The composition of autolyzed yeast (AY) has been summarized as 3.5-3.9% nucleic acids, 11-22% of β-glucan, 3-12% MOS, and 30-41% crude protein. Adding 0.2-0.5% AY to pig diets could improve the performance and immune function of weaned and finished pigs.
The composition of hydrolysed yeast (HY)
The composition of hydrolysed yeast (HY) includes 3.5% nucleic acids, 22.43-23% β-glucan, 15-15.6% MOS, and 40-53.2% crude protein. The effective inclusion rates of HY in diets for the weaned, grower, and finisher periods are 0.1-0.2%, 0.05-1.0%, and 0.1%, respectively.
The yeast cell wall fraction is mainly composed of polysaccharides, making up 15 to 30% of the dry weight of the whole cell. The inner layer of the cell wall mainly contains β-D-glucans which is used as the organic mycotoxin binder. Supplemental levels of the mycotoxin binder are recommended around 0.1 to 0.2%
The outer layer of the yeast cell wall is made of MOS and β-glucans. Adding purified β-glucan to early weaned piglets dets showed protective effects against E Coli infection by reducing bacterial excretion and diarrhoea. The recommended dosage of β-glucan is 100-200 ppm or 100 -200 g/MT feed. The purified MOS can attach the bacterial surface, and then protect the colonization of bacteria in the intestinal tract. Supplementation of MOS in the range of 500 to 1000 ppm or 500 g to 1 kg /MT feed.
In addition, approximately 1-20% of total nitrogen in yeast are derived from nucleic acids. Nucleotides are significantly required by cell replication process, particularly intestinal epithelial and lymphoid cells. Nucleotides are also important in immune system maintenance and prevent oxidative stress. The purified Nucleotide inosine monophosphate (IMP) is commercially available and recommended supplemental levels are ranged 500 ppm to 1000 ppm or 500 to 1000 g/Kg feed.