August 09, 2018

Interpretive Summary: Effects of active dry yeast on ruminal pH characteristics and energy partitioning of finishing steers under thermoneutral or heat-stressed environment.

Interpretive Summary: Effects of active dry yeast on ruminal pH characteristics and energy partitioning of finishing steers under thermoneutral or heat-stressed environment.

beef cowsBy Surely Wallace

In an article published in July 2018 in the Journal of Animal Science, researchers studied how active dry yeast (ADY) supplementation affects the metabolism and rumen pH of feedlot steers under heat-stressed conditions.

Feedlot cattle fare poorly under increased heat characteristic of summer and extreme weather phenomena. Heat negatively impacts animal welfare and causes production losses from increased energy needs, per the National Academy of Sciences (2016). Therefore, creative and economically sound ways to deal with heat stress in feedlot finishing steers is needed. The authors chose to study ADY because previous studies in dairy cattle were promising.

In this study, eight 14-month-old British crossbred steers were housed in separate metabolic stalls. Each steer was given one of two diets: a control (CON) diet, or a control diet with ADY. The daily dose of ADY was 6 x 1010 CFU. After a feeding adjustment period, the steers were subjected to temperature conditions and data collected over 48 hours in a calorimetry chamber. Thermoneutral (TN) environment was 18±0.55°C with 20% relative humidity. The heat-stressed (HS) environment was 35±0.55°C with 42% relative humidity.

Results indicated ADY steers had better digestible energy (DE) and metabolizable energy (ME) compared to CON diet steers. The dry matter intake (DMI) of HS steers (6.43 kg/day) was significantly less compared to TN steers (7.10 kg/day). Dry matter digestibility (DMD) was reported to be significantly greater in ADY steers than CON steers. There was no significant difference in rumen pH with diet type at the end of 48-hour data collection period, although the authors report a trend towards increased rumen pH in TN steers fed ADY (5.81) versus CON diets (5.57). However, the rumen pH of TN steers (6.70) was significantly greater than HS steers (6.16). Nitrogen retention was not affected by temperature or diet type in this study.

Overall, the authors suggest potential for benefit of feeding steers a diet supplemented with ADY under TN but not HS conditions. With TN ADY steers, feed efficiency improved (DMD, DE, and ME) without negative impacts on DMI. A larger study on feedlot finishing steers under heat stress conditions is warranted, and the authors suggest that future studies should focus on feeding ADY at differing energy densities.

To view the full article, “Effects of active dry yeast on ruminal pH characteristics and energy partitioning of finishing steers under thermoneutral or heat-stressed environment,” visit the  Journal of Animal Science.