The use of antibiotics in food animals selects for bacteria resistant to antibiotics used in humans, and these might spread via the food to humans and cause human infection, hence the banning of growth-promoters. The actual danger seems small, and there might be disadvantages to human and to animal health. The low dosages used for growth promotion are an unquantified hazard. Although some antibiotics are used both in animals and humans, most of the resistance problem in humans has arisen from human use. Resistance can be selected in food animals, and resistant bacteria can contaminate animal-derived food, but adequate cooking destroys them. How often they colonize the human gut, and transfer resistance genes is not known. In zoonotic salmonellosis, resistance may arise in animals or humans, but human cross-infection is common. The case of campylobacter infection is less clear. The normal human faecal flora can contain resistant enterococci, but indistinguishable strains in animals and man are uncommon, possibly because most animal enterococci do not establish themselves in the human intestine. There is no correlation between the carriage of resistant enterococci of possible animal origin and human infection with resistant strains. Commensal Escherichia coli also exhibits host-animal preferences. Anti-Gram-positive growth promoters would be expected to have little effect on most Gram-negative organisms. Even if resistant pathogens do reach man, the clinical consequences of resistance may be small. The application of the 'precautionary principle' is a non-scientific approach that assumes that risk assessments will be carried out.

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Does the use of antibiotics in food animals pose a risk to human health? A critical review of published data

Morbidity and mortality from bovine respiratory disease (BRD) and associated losses in performance and carcass merit continue to plague the beef cattle industry. Several viral/bacterial agents are responsible for BRD, and interactions occur among the agents. Viral agents often predispose animals to bacterial infections, and Mannheimia haemolytica is the most frequently isolated organism in cattle with BRD. Laboratory tests are available to characterize organisms causing BRD using easily obtained nasal swab samples. Testing for persistent infection with bovine viral diarrhea virus can be done by a 2-stage technique using PCR and immunohistochemistry. Preconditioning programs that include preweaning viral vaccination programs along with castration could have a significant influence on decreasing BRD in the cattle feeding industry. Metaphylactic antibiotic programs continue to be effective; however, antibiotic resistance is a public concern, and additional management options (e.g., direct-fed microbials or other compounds with antimicrobial properties) deserve attention. Diets with an increased energy concentration achieved by decreasing the dietary roughage concentration may slightly increase the rate of BRD morbidity; however, these diets also increase ADG, DMI, and G:F compared with lower-energy, greater-roughage diets. The extent to which performance and BRD morbidity are affected by dietary protein concentration needs further study, but low and high protein concentrations should probably be avoided. Several trace minerals (e.g., Cu, Se, and Zn) affect immune function, but the effects of supplementation on performance and immune function in model challenge systems and in field studies are equivocal. Adding vitamin E to receiving diets at pharmacological levels (e.g., >1,000 IU x animal(-1) x day(-1)) seems beneficial for decreasing BRD morbidity, but it has little effect on performance. Given the limited ability to consistently modify immune function and BRD morbidity through dietary manipulations, we recommend that the diets for newly received cattle be formulated to adjust nutrient concentrations for low feed intake and to provide optimal performance during the receiving period.

Board-invited review: recent advances in management of highly stressed, newly received feedlot cattle.

Mannheimia haemolytica is the principal bacterium isolated from respiratory disease in feedlot cattle and is a significant component of enzootic pneumonia in all neonatal calves. A commensal of the nasopharynx, M. haemolytica is an opportunist, gaining access to the lungs when host defenses are compromised by stress or infection with respiratory viruses or mycoplasma. Although several serotypes act as commensals, A1 and A6 are the most frequent isolates from pneumonic lungs. Potential virulence factors include adhesin, capsular polysaccharide, fimbriae, iron-regulated outer membrane proteins, leukotoxin (Lkt), lipopolysaccharide (LPS), lipoproteins, neuraminidase, sialoglycoprotease and transferrin-binding proteins. Of these, Lkt is pivotal in induction of pneumonia. Lkt-mediated infiltration and destruction of neutrophils and other leukocytes impairs bacterial clearance and contributes to development of fibrinous pneumonia. LPS may act synergistically with Lkt, enhancing its effects and contributing endotoxic activity. Antibiotics are employed extensively in the feedlot industry, both prophylactically and therapeutically, but their efficacy varies because of inconsistencies in diagnosis and treatment regimes and development of antibiotic resistance. Vaccines have been used for many decades, even though traditional bacterins failed to demonstrate protection and their use often enhanced disease in vaccinated animals. Modern vaccines use culture supernatants containing Lkt and other soluble antigens, or bacterial extracts, alone or combined with bacterins. These vaccines have 50-70% efficacy in prevention of M. haemolytica pneumonia. Effective control of M. haemolytica pneumonia is likely to require a combination of more definitive diagnosis, efficacious vaccines, therapeutic intervention and improved management practices.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1466252307001375

Mannheimia haemolytica and bovine respiratory disease.

Mycoplasma bovis is an important and emerging cause of respiratory disease and arthritis in feedlot cattle and young dairy and veal calves, and has a variety of other disease manifestations in cattle. M. bovis is certainly capable of causing acute respiratory disease in cattle, yet the attributable fraction has been difficult to estimate. In contrast, M. bovis is more accepted as a cause of chronic bronchopneumonia with caseous and perhaps coagulative necrosis, characterized by persistent infection that seems poorly responsive to many antibiotics. An understanding of the disease has been recently advanced by comparisons of natural and experimentally induced disease, development of molecular diagnostic tools, and understanding some aspects of virulence, yet uncertainties regarding protective immunity, the importance of genotypic diversity, mechanisms of virulence, and the role of co-pathogens have restricted our understanding of pathogenesis and our ability to effectively control the disease. This review critically considers the relationship between M. bovis infection and the various manifestations of the bovine respiratory disease complex, and addresses the pathogenesis, clinical and pathologic sequelae, laboratory diagnosis and control of disease resulting from M. bovis infection in the bovine respiratory tract.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/B67DDCFE24AC1173A1EFCEE8EEAC0254/S1466252307001351a.pdf/div-class-title-span-class-italic-mycoplasma-bovis-span-pneumonia-in-cattle-div.pdf

Mycoplasma bovis pneumonia in cattle.

Vaccines and antibiotics are still relied upon as the standard methods of bovine respiratory disease (BRD) prevention, control, and therapy. Success in building disease resistance begins with genetic selection and continues with colostrum management and reducing pathogen exposure. Purchasing single-source cattle with a history of pre- and post-weaning procedures will minimize pathogen exposure and enhance immunity. Using cattle-handling techniques and facilities that promote low stress will allow host immune defenses to remain effective against bacterial and viral colonization. Lastly, controlling BRD must be managed through a comprehensive herd health immunization and management program that effectively addresses disease challenges common to the operation.

Control methods for bovine respiratory disease for feedlot cattle

Objectives To evaluate effects of tilmicosin when used in fever-based and metaphylactic treatment programs to attenuate acute undifferentiated bovine respiratory disease (BRD) in cattle that recently arrived at feedlots, and to evaluate the effects of tilmicosin for the treatment of BRD. Design Randomized-block controlled study. Animals 1,639 calves from livestock auctions. Procedures Cattle were assigned to 3 groups. Cattle in the nonmedicated (control) group were not given antibiotics during processing. Cattle in the fever-based treatment group were given tilmicosin (10 mg/kg [4.5 mg/lb] of body weight, s.c.) during processing when their rectal temperature was > or = 40 C (104 F). All cattle in the metaphylactic treatment group were given tilmicosin (10 mg/kg, s.c.) during processing. Calves with BRD were treated with tilmicosin (10 mg/kg, s.c.). Results Morbidity rates in the metaphylactic (30.4%) and fever-based (44.7%) treatment groups were less than that for the nonmedicated group (54.8%). Mortality rate for the metaphylactic group during the first 28 days (1.1%) and during the entire study (1.7%) was less than that for the nonmedicated group (3.3 and 4.6%, respectively). Differences were not observed in therapeutic response rates among calves with BRD that were treated. Clinical implications Fever-based and metaphylactic treatment programs that used tilmicosin decreased the prevalence of BRD and improved growth of calves. Metaphylactic treatment decreased the number of fatalities caused by BRD in high-risk calves. Fever-based treatment was less effective than metaphylactic treatment for decreasing the prevalence of BRD in newly arrived cattle.

Effects of tilmicosin on acute undifferentiated respiratory tract disease in newly arrived feedlot cattle.

Feedlot cattle ( = 128; BW = 549 ± 60 kg) were used to evaluate the effects of ractopamine hydrochloride (RAC) on growth performance, physiological response to handling, and mobility during shipment for slaughter in a study utilizing a split-plot design with a 2 × 2 factorial arrangement of treatments: 1) diet (CON [no β-adrenergic agonist] vs. RAC [400 mg·animal·d ractopamine hydrochloride for 28 d]) and 2) handling intensity (HI; low-stress handling [LSH; cattle moved at a walking pace with no electric prod use] vs. high-stress handling [HSH; cattle moved at a minimum of a trot and an electric prod applied while in the alley for posthandling restraint and during loading for shipment to the abattoir]). Cattle fed RAC tended to have greater ADG and G:F ( = 0.06), and had greater HCW and LM area ( = 0.04). The HI treatments were applied on the day after the 28-d growth performance period. Blood samples were collected before HI treatment (baseline), after HI treatments (POSTHAND), after transport to the abattoir (POSTTRANS), and during exsanguination at slaughter. A diet × HI interaction ( = 0.01) was observed in the change in cortisol from baseline to POSTTRANS, and there tended ( ≤ 0.07) to be diet × HI interactions for the change in epinephrine from baseline to POSTHAND and for the change in creatine kinase (CK) from baseline to POSTTRANS. Feeding RAC and HSH both increased the change from baseline to POSTHAND in norepinephrine and pH ( ≤ 0.05). The HSH cattle also had greater changes from baseline to POSTHAND in blood HCO, base excess, partial pressure of CO, lactate, cortisol, and glucose ( ≤ 0.01). Ractopamine and HSH both produced greater increases in CK concentrations from baseline to slaughter ( < 0.01). Mobility was not affected by RAC at the feedlot or following an average 6-h lairage ( ≥ 0.43). This study confirms RAC improves growth performance and suggests metabolic acidosis, a precursor to fatigued cattle syndrome, develops in cattle allowed to trot without the use of a lead rider regardless of RAC administration. Cattle fed RAC displayed altered hormonal responses to handling and transport stress, and the overall proportion of cattle with compromised mobility appears to increase later in the marketing channel. These findings warrant additional research aimed at better understanding the physiological response to stress and protect the welfare of cattle during shipment for slaughter.

Effects of ractopamine hydrochloride on growth performance, carcass characteristics, and physiological response to different handling techniques.

The objectives of this study were to: (1) evaluate the effect of metaphylactic tilmicosin on the health and performance of high-risk northern calves, and (2) determine the efficacy of tilmicosin for treatment of bovine respiratory disease (BRD) following its use in an arrival metaphylaxis programme. 400 crossbred steer calves weighing an average of 273 kg each were purchased at livestock auctions in South Dakota and Montana, and shipped to a commercial research feedlot in northern Colorado. At processing, calves were randomly assigned to one of two treatment groups: (1) non-medicated controls or (2) metaphylaxis with tilmicosin. Cattle assigned to the metaphylaxis group were administered tilmicosin once at label dose. Control cattle received no antibiotic at processing. Metaphylactic use of tilmicosin at processing reduced BRD morbidity compared to controls (25.5 vs, 56.5%, P<0.01). Average number of days to first pull were greater in the metaphylaxis group (13.9 vs. 9.6 d, P<0.01). BRD mortality and chronic rates did not differ between treatments. When calculated on a "deads out" basis, calves receiving tilmicosin at processing gained more weight during the first 28 d (1.66 vs. 1.41 kg/d, P<0.01), and 102 d on feed (DOF) (1.75 vs. 1.67 kg/d, P<0.01) compared with control calves. At harvest (191 DOF), daily gain tended to be greater (1.55 vs. 1.52 kg/d, P=0.10) for calves in the metaphylactic tilmicosin treatment group. There were no differences in feed intake or feed conversion between groups. Hot carcass weight tended to be greater for calves in the metaphylactic treatment group (359.8 vs. 353.5 kg, P=0.06). Other carcass traits did not differ. When tilmicosin was used as first treatment for calves with BRD, response rates were identical for both treatment groups (86%). No differences were observed between treatment failure (6.5 vs. 4.6%, P=0.68), first relapse (7.5 vs. 9.4%, P=0.71), second relapse (4.4 vs. 2.7%, P=0.72) or new episode (11.9 vs. 10.8%, P=0.85) rates for calves in the metaphylaxis and control groups, respectively. In this study, metaphylactic treatment with tilmicosin at processing decreased morbidity, and increased days to first treatment for those calves that subsequently required BRD therapy. Efficacy of tilmicosin as the first line therapy for BRD following its use in an on-arrival metaphylaxis programme was not compromised based on the results of this study.

Efficacy of metaphylactic tilmicosin for controlling bovine respiratory disease in high-risk northern feeder calves

The effects of handling intensity on the physiological response and carcass characteristics of feedlot cattle fed ractopamine hydrochloride were evaluated at the time of transport to slaughter. Eighty steers (BW = 668 ± 36 kg) representing 10 lots of similar breed, frame size, and degree of finish were blocked by lot, stratified by weight, and randomly assigned to 1 of 2 handling intensities (HI) over a 1,600 m dirt alley course: 1) low-stress handling (LSH) or 2) high-stress handling (HSH). For the LSH treatment, 4 penmates were kept at a walk with the use of a lead rider. For the HSH treatment, 4 penmates were kept at a minimum of a trot and received 2 applications of an electric prod (approximately 1 s per impulse) at 2 separate instances: first in the alley before post-handling sampling, and again during loading for transportation to the abattoir. Behavioral observations and physical indicators of stress were recorded a minimum of 1 h before handling (baseline), immediately after handling (POSTHAND), and while in lairage after a 200 km transport to the abattoir. Vital parameters were recorded at baseline and POSTHAND. Venous blood samples were collected via jugular venipuncture at baseline and POSTHAND, and mixed arterial and venous blood samples were collected during exsanguination at slaughter. Muscle tremors tended to be more prevalent in HSH cattle at POSTHAND ( = 0.10). The HSH cattle tended to have greater POSTHAND heart rate ( = 0.08); however, there was no effect of HI on POSTHAND respiration rate or rectal temperature ( 0.34). The HSH cattle had greater lactate, epinephrine, norepinephrine, cortisol, and glucose concentrations at POSTHAND ( ≤ 0.02). Additionally, HSH cattle had lower POSTHAND blood pH, bicarbonate, base excess, and partial pressure carbon dioxide ( < 0.0001). Bicarbonate concentrations were greater in HSH cattle at slaughter ( = 0.05); however, there were no differences between HI treatments for the remaining blood variables ( 0.11). Concentrations of stress hormones and CK were significantly greater at slaughter relative to baseline and POSTHAND for both LSH and HSH cattle ( < 0.001). These findings suggest cattle trotted without a lead rider develop metabolic acidosis, and illustrate the importance of low-stress handling at the time of transport for slaughter. Further research is warranted to develop strategies to mitigate stress at the time of transport and ensure the welfare of beef cattle presented to abattoirs.

Effect of handling intensity at the time of transport for slaughter on physiological response and carcass characteristics in beef cattle fed ractopamine hydrochloride.

Four-hundred steer and bull calves at high risk of contracting bovine respiratory disease (BRD) were included in a 28-day study to evaluate various tilmicosin metaphylaxis programmes for the control of BRD in feeder cattle. The trial animals, which averaged 473 lb at purchase, came from multiple auction markets in the southeast USA over a 3 day period and were transported to a collection facility in West Point, Mississippi for treatment assignment. Following treatment assignment calves were randomly loaded onto trucks and transported to a research facility in Canyon, Texas. Calves were blocked by day of purchase and randomly assigned to one of four treatments in a randomized complete block design: (1) non-medicated controls, (2) metaphylactic treatment with tilmicosin at the time of treatment assignment (pre-shipment treatment), (3) metaphylactic treatment with tilmicosin at the time of processing at the research facility (post-shipment treatment), or (4) metaphylactic treatment with tilmicosin at the time of treatment assignment (pre-shipment) and 72 hours later (post-shipment) at the research facility (combination treatment). Tilmicosin was administered at 4.5 mg per lb (10 mg/kg) BW (7.1 ml) based on the average purchase weight. Data were analysed by analysis of variance using the General Linear Model procedure of SAS. The model included treatment, replication, and treatment x replication as sources of variation. The BRD morbidity rate was reduced in all tilmicosin metaphylaxis treatment groups as compared with controls (54, 29, 15, and 15% for treatments 1 through 4, respectively). Furthermore, BRD morbidity was reduced in the post-shipment and combination treatment groups compared to the pre-shipment treatment group. All calves experiencing clinical BRD during the trial were treated with tilmicosin at 4.5 mg per lb (10 mg per kg) BW, by subcutaneous (SC) injection. There was no difference between treatment groups in the treatment success rate for animals treated for BRD with tilmicosin. Bovine respiratory disease mortality was higher in the combination treatment group compared to the pre-shipment and post-shipment treatment groups (2, 0, 0, and 4% for treatments 1 through 4, respectively). There was no difference in average daily gain (ADG), dry matter intake, or feed/gain among any of the treatment groups during the 28-day study. Results from this study confirm that metaphylactic use of tilmicosin is an effective tool to control BRD in feeder cattle. Tilmicosin administered at the time of arrival processing (post-shipment) was superior to pre-shipment treatment. Combination treatment (both pre- and post-shipment) with tilmicosin did not further decrease BRD morbidity when compared to post-shipment treatment alone.

Gary Vogel

Papers

Effects of tilmicosin on acute undifferentiated respiratory tract disease in newly arrived feedlot cattle.

Effects of ractopamine hydrochloride on growth performance, carcass characteristics, and physiological response to different handling techniques.

Efficacy of metaphylactic tilmicosin for controlling bovine respiratory disease in high-risk northern feeder calves

Effect of handling intensity at the time of transport for slaughter on physiological response and carcass characteristics in beef cattle fed ractopamine hydrochloride.

Effect of timing of tilmicosin metaphylaxis on control of bovine respiratory disease and performance in feeder cattle