Effect of sun dry brewer spent yeast on chemical composition, in vitro digestibility, and ruminal degradation kinetics of wheat straw
Authors: Terefe Geberemariyam , Walelgne Mulugeta , Fekadu Dereje , Kitaw Getu , Dejene Mesfin , Kehaliu Aeimro , Mekonnen Bethlehem , Habteyesus Yohannse 
Published: June 2023

Abstract
Background
Dry brewer spent yeast (DBSY) has high crude protein (CP) (43.2%) and metabolizable energy (14.3 MJ/kg) contents and it is an alternative animal feed for the improvement of the productive and reproductive performance of the animals. This study was conducted to evaluate the effect of DBSY on the chemical composition, in vitro digestibility, and in situ degradability of wheat straw (WS).

Methods
Liquid brewer spent yeast (BSY) and water was mixed at a ratio of 1:5, respectively. The mixed debris soaked for 7 h in a 200-L plastic bucket. The water accumulated above the biomass was removed by tilting the container after the BSY was soaked in water. After three days of sun drying, DBSY was collected and removed with a scraper. The DBSY and wheat straw (WS) mixed uniformly. Different ratios of DBSY: WS (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50, respectively, on a DM basis) were prepared. Based on these ratios, the experiment was subjected to a completely randomized design with six treatments comprising DBSY0, DBSY10, DBSY20, DBSY30, DBSY40, and DBSY50. Rumen liquor was collected from the three cannulated Boran-Friesian steers (42 months old and weighed 480 kg). The steers were fed natural pasture hay ad libitum supplemented with 2 kg concentrate per day/head. The sample was incubated in a test tube at 39 °C for 48 h with 10 ml of rumen fluid and 50 ml of buffer solution. The enzymatic digestion with acid pepsin solution was continued for another 48 h. Blank and standard samples were also incubated with buffered rumen fluid for correction and precision check-up of in vitro organic matter digestibility. Digestible organic matter in the dry matter (DOMD) was determined after drying and ashing the residues. The sample (3 g and 2 mm sieve size) with nylon bags (6.5 X 14 cm and 50 μm pore size) was entered sequentially and manually pressed deep into the liquid phase of the ventral sac of the rumen and incubated in the rumens (6, 12, 24, 48, 72, and 96 h) of three fistulated Boran × Holstein–Friesian steers. After removing the bags from the rumen, it was washed in running water for 20 min. The bags with residues were dried at 55 °C for 72 h in an air-forced oven, hot weighed, and finally, the residues recovered for further CP and neutral detergent fibre (NDF) analysis.

Results
The highest ash, metabolizable energy, estimated digestible CP, DOMD, CP, Ca, P, Cu, Zn contents and the better DM, NDF, and CP ruminal degradability, and the lowest (P < 0.01) crude fibre, acid detergent fibre, NDF, K & Fe contents were observed in DBSY50 than the other DBSY inclusion level. In DBSY50, the potential degradability (PD) and effective degradability (ED) for DM of WS were improved by 52.22% and 56.17%, respectively. In DBSY50, PD and ED (NDF) in WS were increased by 60.34% and 65%, respectively. Similarly, in DBSY50, PD and ED (CP) of WS also improved by 54.20% and 63%, respectively.

Conclusion
The inclusion of DBSY can improve the limited utilization of wheat straw, but this study should be verified with a feeding experiment to identify and recommend the most promising, economical and biological inclusion level of DBSY.