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Baker, Lauren M.

Animal and Veterinary Sciences

2021

M.S.

Dietary yeast supplements are a popular feed additive in ruminant diets as its inclusion can favorably alter the rumen microbiota and fermentation, and subsequently improve animal health and production. Yeast are a rich source of amino acids, peptides, organic acids, carbohydrates, lipids, vitamins, and minerals. Inclusion of nutrient-rich yeast and yeast extracts in the diet promote the growth of select groups of rumen microbiota, subsequently improving digestibility, volatile fatty acids, and pH profile. However, the large variability within yeast types and composition has created inconsistent results on these parameters, and further investigation into yeast product variability is crucial for understanding its use in ruminant diets.The aim of this thesis was to evaluate six novel yeast extract treatments, different by origin and processing, and their influence on the abundance and diversity of rumen bacteria, protozoa numbers, digestibility, pH, and methane production. The study utilized a 6 x 6 Latin square design using dual-flow continuous culture fermenters (n = 6), including six 10-d periods consisting of 7-d of adaptation followed by 3-d of sample collection. Dietary yeast extract treatments were included at 4% on a dry matter (DM) basis of the total diet, where treatments and basal diets were combined and added to the fermenters twice daily in equal proportions (109 g DM total per fermenter/d). Treatments included 1) a Brewer's yeast extract with crude protein (CP) > 60% and a high degree of protein hydrolysis (BrE), 2) a blend of Brewer's yeast extract and Baker's peptone with CP > 65% and a mixture of high and low levels of protein hydrolysis and nucleotides (BrEPN), 3) a blend of Baker's yeast extract with CP > 50% and a mixture of high and medium levels of protein hydrolysis and nucleotides (BENH), 4) a blend of Baker's yeast peptone and yeast extract with CP > 65% and a mixture of high and low levels of protein hydrolysis and nucleotides (BEPN), 5) a blend of Baker's yeast peptone, Brewer's yeast autolysate, and Baker's yeast extract with CP > 50% and medium protein hydrolysis (BEPBrA), and 6) a blend of Baker's yeast extracts with CP > 60% and a mixture of medium and low levels of protein hydrolysis and nucleotides (BENL). Fermenter pH was recorded every minute using indwelling pH sensors, methane concentration was determined in triplicate twice daily at the time of feeding via a real-time gas analyzer system, and protozoa and bacteria samples were enumerated via microscopic and flow cytometry analysis, respectively. Bacterial DNA was extracted from harvested bacterial pellets for high-throughput sequencing of the 16S rRNA gene to determine bacterial abundance and diversity. Effluent samples were dried to determine DM disappearance and apparent digestibilities. Fermenter pH, methane, apparent digestibilities, and protozoa and bacteria enumerations were statistically analyzed via the PROC MIXED procedure of SAS. Fermenter pH, protozoa and bacteria counts, methane concentration, apparent digestibility, and bacterial abundance and diversity were not different across treatments. Yeast extract treatments provided at an inclusion rate of 4% on a DM basis, resulted in no differences on rumen microbiota and fermentation across treatments. Further examination of these yeast extract treatments in a dose-response study to determine efficacy as well as an in vivo study to determine their impact on animal health and production parameters could provide greater insight into the differences of yeast extract origin and processing in the rumen.