Retail Color and Aerobic Bacterial Count of Strip Steaks from Beef Cattle Fed Endophyte-Infected Tall Fescue Seeds

The objective of this study was to determine the effects of endophyte-infected tall fescue seeds on lean color and microbial growth of beef strip steaks during simulated retail display. Seeds of KY32 (E- or control) and KY31 (E+ or treatment; approximately 20 µg of ergovaline per kg of BW) were randomly assigned to twelve Angus steers (n = 6), blocked by initial BW. Steers were fed individually by using Calan® gates during a 70-d trial in the summer of 2015 followed by a 149-d withdrawal period and a 64-d trial in the winter of 2016. Steers were slaughtered after a 66-d finishing period at approximately 500 kg of BW. Strip loins were collected at 72 h post mortem and aged for 14 d. Loins were cut into 2.54-cm steaks, placed on black Styrofoam® trays, overwrapped with PVC film (O₂ permeability of 1.21 mL/cm²/d and water vapor permeability of 0.022 g/cm²/d; LINPAC Packaging-Filmco Inc., Aurora, OH), and placed under simulated retail display conditions for 7 d (2 to 4ºC, 900-lux fluorescent light intensity, and 80% relative humidity). Objective color and reflectance attenuance were recorded by a reflectance spectrophotometer. Total aerobic plate count was determined by using 3M™ Petrifilm™ Aerobic Count Plates (3M™, St. Paul, MN). Statistical analysis was performed by the GLIMMIX procedure of SAS 9.4 (SAS Institute Inc., Cary, NC) with treatment and retail day serving as fixed effects, and BW and slaughter day serving as random block effects. Steaks from treated steers had greater oxymyoglobin (1.04%) and less deoxymyoglobin (0.70%) proportions (P = 0.012 and 0.024, respectively). However, treatment did not influence other lean color attributes and total bacterial count (P ≥ 0.095). As expected, lightness (L*), redness (a*), and oxymyoglobin percentage decreased from 45.39, 32.60, and 67.40% on d 0 to 39.37, 21.74, and 48.40% on d 7 of retail display (P ≤ 0.004) regardless of treatment. Metmyoglobin and deoxymyoglobin increased (P ≤ 0.009) from 31.87 and 0.67% on d 0 to 38.96 and 14.03% on d 7 of retail display, respectively. Retail display also increased aerobic bacteria by 0.5 log CFU/g (P ≤ 0.020) for both treatment and control steaks. Feeding endophyte-infected tall fescue seeds followed by a long period of withdrawal had minimal effect on beef color and total bacterial count.