A meta-analysis of yeast products for beef cattle under stress conditions: Performance, health and physiological parameters

Yeast products (live yeast, yeast cell wall, yeast culture) have been added to the diet of beef cattle under conditions that characterize stress, such as receiving period, high-concentrate finishing diet, periods of elevated ambient temperature, with variable responses in animal performance, health and physiological parameters. Therefore, we conducted a meta-analysis to examine the yeast product's effects on performance parameters, health, and physiological responses of beef cattle. Studies that met the selection criteria included 27 articles. Twenty-seven studies with up to 119 treatments means were included in the data set. The magnitude of the effect (effect size) was assessed using weighted mean differences (WMD) for continuous results, between the yeast products addition and control treatments. The binary results (health parameters) were examined using risk ratio (RR). Heterogeneity was explored by meta-regression and subgroup analysis. The addition of yeast products increased (P < 0.04) animal performance with increase in dry matter intake (DMI; WMD = 0.083 kg/d), average daily gain (ADG; WMD = 0.036 kg/d), final body weight (WMD = 3.75 kg), and feed efficiency (WMD = 2.08 g/kg). In the current study, most of the responses had low heterogeneity (I2 < 25%), which means low inconsistency in the effect size estimates and independent response from the possible sources of heterogeneity included. Yeast products increased (P < 0.02) the digestibility of dry matter (WMD = 11.84 g/kg), organic matter, (WMD = 15.88 g/kg), crude protein (WMD = 26.99 g/kg), neutral detergent fiber (WMD = 36.84 g/kg) and, increased the average ruminal pH (WMD = 0.088), enabling a reduction in the risk ratio of severely abscessed occurrence (RR = 0.41). In blood parameters, yeast products decreased glucose (P < 0.01; WMD = -5.47 mg/dL) and increased (P < 0.04) urea (WMD = 1.59 mg/dL) and non-esterified fatty acid (WMD = 0.006 mM) concentrations. The acute-phases protein concentrations (Amyloid A, WMD = 3.79 mu g/mL and lipopolysaccharide-binding protein WMD = 11.01 mu g/mL) were also increased (P = 0.01) when the yeast product was fed. On the other hand, the risk ratio of occurrence of morbidity and mortality were similar (P >= 0.49; RR = 0.94 and 0.77 respectively). This meta-analysis indicated that yeast products increased animal performance, and the benefits can be attributed to better rumen health and increases in nutrient digestibility. (AU)