Evaluation of yeast, nonsteroidal anti-inflammatory, and metaphylaxis products in feedlot cattle: Mitigation of bovine respiratory disease and feedlot performance

Bovine respiratory disease (BRD) is the leading cause of morbidity and mortality in United States feedlots. Economic consequences associated with BRD include treatment costs, potential performance reduction, and increased labor requirements. Feedlot BRD is historically difficult to study as it is a disease of multi-factorial nature with low predictability. Therefore, improved means of BRD prevention and treatment as well as improved methods of studying BRD in newly received feedlot cattle continue to be important factors in reducing this economic burden and improving beef cattle health. The objective of the first study was to evaluate the feeding of a combination Saccharomyces cerevisiae live yeast and S. cerevisiae yeast cell wall supplement compared to a negative control in beef heifers administered a BRD challenge. Thirty-two heifers were challenged intra-nasally with 1 × 108 plaque forming units (PFU) of Bovine Herpesvirus-1 (BHV-1) followed by of 3.0 × 107 colony forming units (CFU) of Mannheimia haemolytica 72 h later. Blood was collected for 72 h following the M. haemolytica challenge. Heifers fed yeast had similar vaginal temperature to control heifers and serum concentrations of cortisol, leukocyte, haptoglobin, and NEFA were unaffected by the inclusion of dietary yeast (P ≥ 0.13). However, concentrations of serum glucose were greater (P = 0.01) in cattle fed yeast when while serum concentrations of urea N were decreased (P = 0.03) when cattle were fed yeast. While feeding the combination live yeast and yeast cell wall supplement did not affect the response of the immune variables measured to a BRD challenge, some aspects of the metabolic response to a live BRD challenge were improved when yeast was included in the diet. The objective of the second study was to evaluate the effects of inclusion of the same combination live yeast and yeast cell wall product in the diet of feedlot heifers on growth performance, carcass characteristics, and health during the feeding period. A generalized randomized complete block design with 2 time blocks, 2 treatments, and 8 pen replications per treatment (70 heifers/pen) was used in heifers fed for 166 d. Live growth performance measured by final BW, ADG, DMI, and G:F were not affected by the dietary inclusion of yeast (P ≥ 0.40). Similarly, carcass characteristics including HCW, dressing percentage, and distribution of quality and yield grades were unaffected by the dietary inclusion of yeast (P ≥ 0.28). Morbidity and mortality were also unaffected by treatment (P ≥ 0.14). Inclusion of the live yeast and yeast cell wall product did not affect the feedlot performance or overall health of heifers experiencing low morbidity and mortality during the feeding period. The third study was conducted to evaluate the effects of altered timing of administration of transdermal flunixin meglumine (FM) on the immune and metabolic response of beef heifers administered a BRD challenge. All heifers were challenged intra-nasally with 1 × 108 PFU of BHV-1 followed by 1.18 × 106 CFU of M. haemolytica 72 h later. Four treatments were used where transdermal FM was applied at the time of arrival, at the time of BHV-1 challenge, at the time of M. haemolytica challenge, or not at all (8 heifers/treatment). Vaginal temperature was similar when transdermal FM was applied at arrival or not at all, but reduced when transdermal FM was applied at the time of BHV-1 or M. haemolytica challenge (P = 0.04). Immune and metabolic variables measured including leukocyte counts, pro-inflammatory cytokines, NEFA, urea N, and haptoglobin were unaffected by administration of transdermal FM for 72 h following the BRD challenge (P ≥ 0.16). However, neutrophil oxidative burst capacity and L-selectin expression decreased following administration of transdermal FM (P ≤ 0.09). Application of transdermal FM was therefore effective for the reduction of pyrexia when applied during the BHV-1 or M. haemolytica challenge without affecting the immune or metabolic response to the BRD challenge, with the exception of a slight reduction in neutrophil functionality that could result in reduced neutrophil associated inflammation in cattle receiving transdermal FM. The fourth study was conducted to evaluate a multi-site field experimental design used to study relative efficacies of metaphylaxis products in feedlot cattle at high-risk for the development of BRD. Four locations enrolled 5,222 steers, bulls, and heifers in 3 treatments: gamithromycin (Zactran, 6 mg/kg BW), tildipirosin (Zuprevo, 4 mg/kg BW), or tulathromycin (Draxxin, 2.5 mg/kg BW) administered on-arrival. Treatments were mixed within pens and data were analyzed as a nested design such pen was nested within feedlot location. No treatment × feedlot interactions were detected for any variable analyzed (P ≥ 0.11). Morbidity from BRD was reduced in cattle receiving tulathromycin compared to tildipirosin, and tildipirosin compared to gamithromycin. Mortality was reduced in tulathromycin and similar between tildipirosin and gamithromycin. Similarly, HCW was heaviest when cattle received tulathromycin and similar between tildipirosin and gamithromycin. Advantages of the study design included the spread of labor and infrastructure strain associated with BRD outbreaks in large groups of cattle over multiple feeding locations and over time, theoretically equal exposure of animals in all treatments to pathogen exposure or any other random variation associated with pen, and the increased probability of consistent blinding of feedlot personnel to treatment. Disadvantages included the difficulty of measuring treatment feed intakes, limitation to studying means of prevention that are applied directly to the animal, and difficulty in enforcing different post-metaphylaxis intervals for each treatment. These data support the continued need for BRD research in the feedlot setting. While the inclusion of S. cerevisiae in the diet may affect some aspects of the metabolic response when cattle are immunologically challenged, these data do not support improvement to feedlot performance when cattle are at low-risk of BRD development. Furthermore, these data provide some evidence that application of transdermal FM during a BRD event could be an effective means of pyrexia reduction without affecting the immunological and metabolic responses to a BRD challenge, and with minimal reduction in leukocyte functionality. Finally, a multi-site field model where animals within treatment are mixed in a pen could provide a viable alternative to the randomized complete block design for the field study of BRD where large numbers of cattle at high-risk for BRD development are enrolled at one time and where infrastructure or labor limitations exist.