Inclusion of antibiotic alternatives in feedlot cattle diets: Impact on health status, cattle performance and meat quality

Although antibiotics are effective at diminishing the incidence of both bovine respiratory disease and digestive disorders and can promote growth in feedlot cattle, public scrutiny and concerns about antibiotic resistance are driving the cattle industry away from their use in production. Natural antibiotic alternatives derived from plants, bacteria and yeasts are increasing in popularity for use in cattle feeding operations. In this thesis, the effect of a yeast cell wall product on performance and health status of receiving steers was examined and the effect of supplementing an essential oils blend on finishing cattle performance, liver abscess incidence, carcass characteristics and meat quality was investigated. Yeast cell wall (YCW) products are the concentrated outer portion of the yeast that contains mannoproteins and β-glucan layers. These cell wall components adhere to bacteria and prevent their colonization in the gastrointestinal tract, helping to clear pathogens, increase the efficiency of the natural flora of the gastrointestinal tract, and enhance the immune system. This minimizes the amount of energy required to mount an immune response, and yields additional energy for growth purposes, thus increasing performance. Essential oils (EO) are secondary plant metabolites used by the plant for defensive purposes. Essential oils give a plant its characteristic fragrance and have antimicrobial, anti-inflammatory and antioxidant effects that can alter ruminal metabolism. Essential oils restrict bacterial growth by disturbing the cell membrane and inhibiting RNA and DNA synthesis of pathogens. In the first trial, a two-part experiment was conducted to determine the effects of Select TC™ (Select TC™; Alltech Inc., Nicholasville, KY) on the health status and performance of steers during the first two months of the feedlot period. Select TC™ is a proprietary blend of specialized mannan rich fractions and glucan rich fractions of yeast. Eighty crossbred steers were acquired from commercial sale barns in Mississippi and Georgia, and transported to Purdue University (West Lafayette, IN). Steers were allotted to 2 treatments: no feed additive (control, CON) or 13 g/d of Select TC™ (TC). In Exp. 1, 64 steers (246.5 ± 4.7 kg initial BW) were utilized to determine the effect of YCW supplementation on performance. In Exp. 2, 16 steers (247.1 ± 5.4 kg initial BW) were similarly allotted to two treatments (CON and TC), individually penned, and subjected to a lipopolysaccharide (LPS) endotoxin challenge. Morbidity data was collected from all 80 steers for the duration of the trial. Supplementation of Select TC™ did not alter performance or morbidity rates. After administration of LPS, rectal temperature and fat catabolism (P ≤ 0.04) were favorably decreased in steers supplemented with Select TC™, though there were no treatment effects on serum blood urea nitrogen, glucose, insulin or cortisol concentrations (P ≥ 0.31). Interleukin-6 concentrations decreased (P \u3c 0.0001) and interferon-γ concentrations increased (P = 0.07) after LPS administration in Select TC™ compared to CON steers indicating that Select TC™ steers had a stronger pro-inflammatory response. The effect of EO on performance, carcass characteristics, and incidence of liver abscesses were studied in a second trial. Seventy-two crossbred steers (358 ± 7.6 kg initial BW) were fed a 93% concentrate diet supplemented with no feed additives (control), 90 mg/steer tylosin (Tylan®; Elanco Animal Health, Indianapolis, IN) or 1 g/steer essential oils (CRINA®; DSM Nutritional Products; Parsippany, NJ). Performance traits (P ≥ 0.54) and carcass characteristics (P ≥ 0.19) were not affected by treatment. There were no differences in liver abscess prevalence (P = 0.88), though steers fed essential oils tended (P = 0.10) to have more moderately severe liver abscesses than steers fed tylosin or no feed additives. Lipid oxidation, pH, cook loss and tenderness were not affected by treatment (P ≥ 0.32), but purge loss was lower (P = 0.02) in steers supplemented with essential oils than in steers supplemented with tylosin or no feed additives. Overall, natural feed additives have potential for altering the health status, performance, carcass characteristics and meat quality of feedlot cattle. Select TC™ improves health and metabolic status of immune challenged cattle, but this may not result in quantifiable improvements in performance. Inclusion of an EO blend or tylosin in the diet of finishing steers did not affect growth performance or carcass characteristics, and little difference was observed in liver abscess data or meat quality attributes. Additional research is warranted to determine optimal conditions and inclusion levels to maximize the benefits of the product prior to widespread use rather than antibiotics