April 01, 2019

Interpretive Summary: Effects of active dried yeast in the diets of feedlot steers

Interpretive Summary: Evaluation of active dried yeast in the diets of feedlot steers. I. Effects on feeding performance traits, the composition of growth and carcass characteristics

By Dr. Thomas Powell

Due primarily to concerns over antibiotic resistance, growers ceased the practice of including subtherapeutic levels of antibiotics in food animal diets. One of the feed additives proposed to replace antibiotics for the purpose of improving growth performance in cattle is active dried yeast (ADY), specifically Saccharomyces cerevisiae. ADY is known to improve milk yield in dairy cattle. A study published by Texas A&M University in the Journal of Animal Science examined the effects of ADY in the diets of feedlot steers on feeding performance, growth composition, and carcass characteristics.

In the study 120 steers (3/4 Bos taurus × Bos indicus) were fed one of four diets for 164 d on a grower ration phase for 70 d transitioning over 14 d to an 80 d finisher ration phase. The four treatment diets were: a control diet during and after the grower phase (CC), control during and ADY after the grower phase (CY), ADY during and control after the grower phase (YC), and ADY during and after the grower phase (YY). For the ADY treatments, diets were supplemented with ~1.5 g/d (3 × 1010 CFU/d) of S. cerevisiae. Growth rate and feeding performance were monitored throughout the trial. Biometric growth measurements and ultrasound were taken at the beginning, midpoint, and end of the feeding period. Carcass characteristics and composition were measured postmortem.

The only difference observed between the treatments in all the live animal measurements taken was increased rate of rib girth circumference growth. The CY and YY groups grew the fastest, the YC group grew the slowest and the CC group was intermediate. At the end of the trial, the YY group had the largest rib girth circumference, significantly greater than the CC and YC groups (172.1 cm vs 161.9 and 154.2 cm, respectively). Additionally, there was a tendency for the YY group to accrue subcutaneous fat faster than the YC group. Other biometric measurements, feedlot performance, eating behavior, and ultrasound measurements were not different between treatments. 

At the end of the trial, percent body weight (BW) shrink was calculated after an 18 h fast and 12 h restriction from water. The YY group had a lower percentage BW shrink than the CC group. Although water consumption was not measured in this study, the BW shrink data indicates that there may be a tendency for ADY treated animals to drink more water. Carcass quality and composition were not different between treatments.

After observing the trends in the data along with prior analyses, the authors posit that most effects of ADY on growth and composition are likely too small to have been detected using this study’s sample size and that future studies on this additive should be designed to detect differences of 5% or less from the control.

To view the full article, visit the Journal of Animal Science