Alternatives to conventional antibiotics for the prevention and treatment of commonly occurring diseases in feedlot cattle.

Antibiotic-resistant bacteria are a problem in human medicine. The development of antibiotic resistance in bacteria in feedlot cattle could have negative effects on their health and welfare and there is a theoretical possibility of transmission of antibiotic-resistant bacteria from food animals to humans. Alternatives to conventional antibiotics in feedlot health management could reduce the selective pressure for the development of antibiotic resistance. This review assesses the evidence supporting potential alternatives to conventional antibiotics in the prevention and treatment of diseases in feedlot cattle, including nitric oxide, plant extracts, supplemental yeast or yeast products, bacterial probiotics, organic acids, bacteriophages and non-specific immunostimulants. Further research is warranted with lactate utilising bacteria, the organic acid malate, bacteriophages and the non-specific immunostimulants ß-1,3 glucan and those based on pox viruses. However, none of the alternatives to conventional antibiotics investigated in this review have sufficient supporting evidence to date to justify their use with feedlot cattle. Frequently, statistically weak results and studies without negative controls are cited as support for similar studies. The health and welfare of feedlot cattle are dependent on the use of products that have robust supporting data to ensure efficacy and to avoid adverse outcomes.

Detection of Ureaplasma diversum in the upper airways of Australian feedlot cattle.

Bovine respiratory disease (BRD) exerts a major impact on the beef cattle industry nationally and worldwide, with a range of aetiological factors impacting its pathogenesis. Previous research has focussed on an increasing number of bacteria and viruses that have been shown to play a role in eliciting disease. Recently, additional agents have been emerging as potential contributors to BRD, including the opportunistic pathogen Ureaplasma diversum. To determine if U. diversum was present in Australian feedlot cattle and if that presence was linked to BRD, nasal swabs were collected from a cohort of 34 hospital pen animals and compared to 216 apparently healthy animals sampled contemporaneously at feedlot induction and again after 14 days on feed at an Australian feedlot. All samples were subjected to a de novo polymerase chain reaction (PCR) assay targeting U. diversum in combination with other BRD agents. U. diversum was detected at a low prevalence in cattle at induction (Day 0: 6.9%, Day 14: 9.7%), but in a significantly greater proportion of cattle sampled from the hospital pen (58.8%). When considering the presence of other BRD-associated agents, co-detection of U. diversum and Mycoplasma bovis was most common in hospital pen animals receiving treatment for BRD. These findings suggest that U. diversum may be an opportunistic pathogen involved in the aetiology of BRD in Australian feedlot cattle, in combination with other agents, with further studies are warranted to identify if a causal relationship exists.

Evaluation of practices used to reduce the incidence of bovine respiratory disease in Australian feedlots (to November 2021).

Bovine respiratory disease (BRD) has been identified as the most significant infectious disease of feedlot cattle in eastern Australia.1 Bovine respiratory disease causes economic loss due to medication costs, mortalities, excessive feed inputs associated with increased time on feed, reduced sale prices and associated labour costs. Bovine respiratory disease is a complex multifactorial condition with multiple animal, environmental and management risk factors predisposing cattle to illness. A range of microorganisms are implicated in BRD with at least four viral and five bacterial species commonly involved individually or in combination. The viruses most commonly associated with BRD in Australia are bovine herpesvirus 1 (BHV1), bovine viral diarrhoea virus (BVDV or bovine pestivirus), bovine parainfluenza 3 virus (PI3) and bovine respiratory syncytial virus (BRSV). More recently, bovine coronavirus has been identified as a potential viral contributor to BRD in Australia.2 A number of bacterial species have also been recognised as important to the BRD complex; these include Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Trueperella pyogenes and Mycoplasma bovis. Although one or more of the pathogens listed above can be isolated from clinical cases of BRD, there is no evidence that infection alone causes serious illness. This indicates that, in addition to specific infectious agents, other factors are crucial for the development of BRD under field conditions. These can be categorised as environmental, animal and management risk factors. These risk factors are likely to exert their effects through multiple pathways including reductions in systemic and possibly local immunity. For example, stressors such as weaning, handling at saleyards, transport, dehydration, weather conditions, dietary changes, comingling and pen competition might reduce the effectiveness of the immune system. Reduced immunocompetence can allow opportunistic infection of the lower airways with potential pathogens leading to the development of BRD. The objective of this paper is to critically review the evidence for management practices aimed at reducing the incidence of BRD in Australian feedlot cattle. Predisposing factors (Table 1) largely beyond the control of most feedlots, such as weather and exposure to respiratory viruses, are discussed separately, but these factors can generate indirect prevention responses that are discussed under the preventative practices categories. The current practices are classified as either animal preparation practices (Table 2) or feedlot management practices (Table 3).

Efficiency-corrected PCR quantification for identification of prevalence and load of respiratory disease-causing agents in feedlot cattle.

Bovine respiratory disease (BRD) is the most prevalent disease in feedlot cattle worldwide with Bovine alphaherpesvirus 1 (BoAHV1), Histophilus somni, Mannheimia haemolytica, Mycoplasma bovis, Pasteurella multocida and Trueperella pyogenes accepted to be common etiological agents associated with BRD. Although these agents are common in the upper and lower airways in clinical BRD cases, some also exist as normal flora suggesting their presence in the upper airways alone is not necessarily informative with respect to disease status or risk. To determine the relationship between presence, load and disease status, we investigated the relationship between load in the upper airways at induction and active BRD cases in feedlot cattle using efficiency-corrected PCR quantification. By this approach, we were able to accurately determine the prevalence and load of the key BRD agents in the upper respiratory tract showing that cattle in the hospital pen had a higher prevalence, and load, of these agents both singly and in combination compared to cattle sampled at feedlot induction. A combination of agents was the most accurate indicator of BRD risk with cattle with four or more agents detected in the upper airway more likely to be undergoing treatment for BRD than non-BRD ailments. In addition, M. bovis was rarely detected at feedlot induction but was identified at high prevalence in cattle in the hospital pen. These findings present a potential new technological approach for the investigation, analysis and identification of BRD-associated viral and bacterial agents for Australian feedlot systems as well as for BRD disease management and treatment.

Ruminal pH and its relationship with dry matter intake, growth rate, and feed conversion ratio in commercial Australian feedlot cattle fed for 148 days.

OBJECTIVES: Measurement of ruminal pH throughout a 148-day feeding period in cattle fed commercial diets and to relate this to feed intake, growth rate and feed conversion ratio. Factors contributing to variation in rumen pH, including meal frequency, duration and weight, and, total daily intake, were also evaluated. METHODS: Forty-eight cattle were randomly allocated to two pens and 12 randomly selected from each pen had rumen pH monitoring boli inserted. Ruminal pH was measured every 10 min and feed intake was measured continually. The cattle were fed a commercial feedlot diet for 148 days and weighed into and out of the feedlot to measure growth rate and to calculate feed conversion ratio. Cattle from both pens were registered to collect individual feed intake data using the GrowSafe® feed management system. RESULTS: Mean ruminal pH decreased with days on feed. Mean daily dry matter intake was the major contributor to greater average daily gain and lower ruminal pH. Lower mean ruminal pH was associated with greater average daily gain and lower feed conversion ratio, where it remained above the threshold of 5.6. There was no association between ruminal pH and average daily gain or feed conversion ratio for mean ruminal pH below 5.6. CONCLUSIONS: Ruminal acidosis can occur at any time during the feeding period, and the risk could be greater as days on feed increase. Feedlot production outcomes are not improved by ruminal pH depression below the threshold of 5.6.

Serological status of cattle to bovine viral diarrhoea virus and bovine herpesvirus 1 at entry to and exit from Australian feedlot backgrounding facilities.

A total of 6195 cattle were enrolled in this observational study. Serum antibody concentrations to bovine herpesvirus 1 (BHV1) and bovine viral diarrhoea virus (BVDV) were measured at entry to and exit from backgrounding facilities to assess their statuses on arrival and the extent of seroconversion to these viruses during backgrounding. The backgrounding facilities were contiguous with five feedlots in: Queensland (two sites), New South Wales, South Australia and Western Australia. Cattle were held in the backgrounding facilities for a minimum of 29 days and a median of 34 days. On backgrounding facility entry, 32.7% of the study population was seronegative to BVDV, but 85.7% was seronegative to BHV1. After commingling in the backgrounding facilities, of the cattle that were seronegative on backgrounding facility entry, 33.9% and 30.3% showed a serological increase to BVDV and BHV1, respectively. At backgrounding facility exit, when cattle were placed in their feedlots, 19.6% and 59.1% were seronegative to BVDV and BHV1, respectively, and 0.26% were persistently infected with BVDV. There was a strong association between seroincrease to BVDV and seroincrease to BHV1 (P = 0.005) at animal level in cohorts known to contain an animal persistently infected with BVDV.

Health and production effects of killed vaccines against Mannheimia haemolytica, bovine viral diarrhoea virus and bovine herpesvirus 1, in locally backgrounded feedlot cattle.

OBJECTIVES: This study evaluates the effects of respiratory vaccines on health and growth rates in cattle placed in local backgrounding facilities then feedlots. METHODS: A total of 7011 cattle entering backgrounding facilities contiguous with six feedlots in Australia were allocated to eight respiratory vaccine categories, including an untreated control category. The vaccines, against Mannheimia haemolytica, bovine viral diarrhoea virus and bovine herpesvirus 1, were administered in various combinations at backgrounding facility entry and subsequent feedlot entry. Cattle were held in the backgrounding facilities for a minimum of 28 days. RESULTS: During their feedlot phase, 3.7% of study animals were detected with bovine respiratory disease (BRD). BRD sub hazard was lowest in cattle vaccinated with Bovilis MH + infectious bovine rhinotracheitis® (sub hazards ratio: 0.47; 95% confidence interval: 0.27-0.83; P = 0.010), and point estimates for other vaccine combinations did not differ (P > 0.10) from controls. Six of the respiratory vaccine combinations decreased growth rate during backgrounding relative to untreated controls (P ≤ 0.003). Overall, the feedlot growth rate was not significantly affected by the vaccine category (overall Wald P = 0.191). CONCLUSIONS: Use of these respiratory vaccines in cattle held for at least 28 days in backgrounding facilities contiguous with their feedlots before feedlot entry reduces growth rate during the backgrounding period and does not result in large beneficial effects on either BRD risk or average daily live weight gain during the feedlot phase.

Antimicrobial use and stewardship practices on Australian beef feedlots.

OBJECTIVE: Improving antimicrobial stewardship in the livestock sector requires an understanding of the motivations for antimicrobial use and the quantities consumed. However,detailed information on antimicrobial use in livestock sectors is lacking. This cross-sectional study aimed to better understand antimicrobial use in the beef feedlot sector in Australia. DESIGN: A self-administered questionnaire asking about antimicrobial use and reasons for use was designed and mailed to beef feedlot operators in Australia. Respondents were asked to report the percentage of animals treated, purpose of use, and disease conditions targeted for 26antimicrobial agents. RESULTS: In total, 83 of 517 (16.1%) beef feedlot operators completed the survey. Monensin (61.0%of respondents) and virginiamycin (19.5%of respondents) were the most commonly reported in-feed antimicrobials. In-feed antimicrobial agents were most frequently used by respondents for treatment of gastrointestinal diseases (52.8%). Antimicrobials were used for growth promotion by 42.1% of respondents, with most (85.7%) reporting the use of ionophores(a group of compounds not used in human medicine). Short-acting penicillin(69.1%), short-acting oxytetracycline, and tulathromycin (both 57.3%) werethe most common injectable antimicrobial agents used. Injectable antimicrobials were most frequently used to treat respiratory (72.3%) and musculoskeletal (67.5%) conditions. CONCLUSION: Overall,the use of antimicrobials was appropriate for the purpose indicated, and there was a strong preference for drugs of low-importance in human medicine. The data described here stand to be a strong influence on the implementation of an antimicrobial stewardship program in the sector.

Health and production of feedlot cattle following supplementation with urea-molasses in starter pens.

OBJECTIVE: To determine the effect of providing a urea-molasses supplement to cattle during feedlot introduction on average daily gain, carcase weight and bovine respiratory disease (BRD) morbidity and mortality. METHODS: Commercial mixed sex, mixed breed cattle (387.4 ± 0.2 kg) were systematically allocated to receive 2.1 L/animal of urea-molasses during feedlot introduction (n = 2307) or remain untreated (n = 2336). Cattle remained in the feedlot for an average of 40 days until reaching slaughter weight. Body weight data was collected prior to feedlot induction and all cases of BRD morbidity and mortality were determined during feeding. Hot standard carcase weight and P8 fat thickness were determined at slaughter. RESULTS: Average daily gain (1.94 ± 0.06 vs 1.93 ± 0.06, P = 0.650), BRD incidence (6.46% vs 5.53%, P = 0.183) and BRD mortality (0.17% vs 0.21%, P = 0.752) did not differ between supplemented and unsupplemented cattle. The BRD incidence was higher (P = 0.017) when cattle without permanent incisors were supplemented with urea-molasses (7.26%) compared with unsupplemented cattle (5.26%), and was also higher in steers compared with heifers (12.7% vs 7.8%, P < 0.001) and higher in cattle purchased from saleyards compared with cattle purchased off paddocks (12.4% vs 5.7%, P < 0.001). CONCLUSIONS: Health and production were not significantly improved following supplementation of cattle with urea-molasses during feedlot introduction. BRD incidence was, however, significantly related to cattle sex and source. Further research is required to understand the relationship between feeding high non-protein nitrogen sources and BRD morbidity in young cattle.