RESEARCH ▶▶▶


Yeast as a direct-fed microbial for neonatal calves


A review of yeast as a direct-fed microbial and the effects that it may have on calf performance.


BY SARAH J DAVIES, STELLENBOSCH UNIVERSITY, ORIGINAL SOURCE AFMA MATRIX MARCH – JUNE 2020 VOL 29 NO 1


I


Various strains of Saccharomy- ces cerevisiae (SC) are well ac- cepted as DFMs in the livestock industry.


n most dairy production systems, the greatest proportion of morbidity and mortality occurs among pre-weaned calves. In North America alone, the most recent records of calf morbidity and mortality rates were 34.9 and 6.4%, re-


spectively. More than half of the recorded mortalities were due to enteric infections, which are mainly caused by patho- genic organisms. Enteric infections are detrimental to calf growth and health, and thus have a marked effect on lifelong production and profitability. Neonatal calves may be predis- posed to infection due to poor immuno-competence and the prevalence of opportunistic bacteria in the hindgut during the first few weeks of life. To prevent the risk of infection, produc- ers have commonly administered antibiotics sub-therapeuti- cally to milk replacers and calf starters. However, this practice may not be feasible in the future since antibiotics have been


found to create resistant strains of bacteria, many of which are zoonotic and may pose a threat to human health. As a result, there is a movement towards reducing the prophylactic use of antibiotics in South African livestock production. The impor- tance of the gastrointestinal (GI) microflora in the develop- ment of the immune system has started to receive more atten- tion. As a result, there is a need to find alternative feed additives that can improve calf growth and health by modify- ing the resident GI microflora. Direct-fed microbials (DFMs), also referred to as probiotics, may meet this need.


Direct-fed microbials A DFM consists of live, naturally occurring micro-organisms that are beneficial to the host when administered in ade- quate doses. This may include prokaryotic or eukaryotic or- ganisms such as bacteria and yeast. A good DFM should be non-toxic and non-pathogenic, able to tolerate gastric acid, inhibit pathogen growth and enhance the defence mecha- nisms of the immune system. Yeasts may be ideal for this pur- pose because they have the ability to withstand the condi- tions of the digestive tract (such as a low pH), are resistant to antibiotics, and are significantly larger than bacteria (imply- ing that they can potentially inhibit pathogenic bacteria by stearic hindrance). Various feed additives containing yeast have been frequently used in livestock production. Two differ- ent types of supplements are commonly used: an active dry yeast (ADY), and a yeast culture (YC). An ADY is produced by drying a yeast biomass to preserve the cells and their


18 ▶ ALL ABOUT FEED | Volume 28, No. 3, 2020


PHOTO: SHUTTERSTOCK


PHOTO: TON KASTERMANS FOTOGRAFIE


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