Single‐dose Pasteurella multocida and Histophilus somni autogenous vaccines administered at induction significantly improved feedlot cattle performance and profitability in Australia

Abstract

Background

Bovine respiratory disease (BRD) is the most economically important disease affecting feedlot cattle. While viral pathogens are initiating agents, bacterial coinfections exacerbate disease severity. Vaccines for Pasteurella multocida and Histophilus somni are not commercially available in Australia.

Methods

This trial evaluated the efficacy of a single‐dose autogenous vaccine targeting P. multocida and H. somni, administered intramuscularly at induction, on carcase characteristics, feed conversion efficiency and health performance in feedlot cattle.

Results

Vaccinated cattle showed a 6.20% lower prevalence of subclinical BRD than controls (16.50% vs. 22.70%), corresponding to a 27.31% lower likelihood of subclinical BRD with vaccination. Vaccinated cattle exhibited improved performance, with a 2.86% increase in average daily gain, a 0.50% increase in hot standard carcase weight, a 0.81% increase in loin eye muscle area and a 2.68% increase in dry matter intake compared with controls. Vaccinated cattle showed lower odds of lung consolidation compared with controls (odds ratio [OR] = 0.73), indicating a 27.00% reduction in the likelihood of consolidation. Similarly, vaccinated cattle showed a 35.50% reduction in pleurisy scores relative to controls (OR = 0.65). Despite slightly higher feedlot costs, vaccinated cattle achieved a higher total end value and higher gross profit margins with a cost–benefit ratio of 6.95.

Conclusions

Given the overall reduced BRD incidence during the study period, the observed results may be influenced by pathogen prevalence, vaccine dosage, timing, route of administration and environmental factors. While the single‐dose vaccine improved subclinical disease outcomes and growth performance, further studies, including a two‐dose vaccine trial, are required to assess the full potential of the anamnestic immune response.

Abbreviations

ADG

average daily weight gain

BRD

bovine respiratory disease

CLMMs

cumulative link mixed models

DMI

dry matter intake

DOF

days on feed

EMA

loin eye muscle area

EMM

estimated marginal mean

GLMMs

generalised linear mixed models

HSCW

hot standard carcase weight

LMMs

linear mixed‐effects models

MSA

meat standards Australia

OR

odds ratio

REML

restricted maximum likelihood

BRD is the single most economically important disease of feedlot cattle, derived from its effects in reduced growth performance, increased morbidity and mortality and high treatment costs. ¹ , ² The multifactorial nature of BRD, arising from interactions among environmental stressors, host susceptibility and a diverse array of pathogens, indicates the complexity of managing this disease. ³ , ⁴ Viral agents such as bovine herpesvirus‐1, bovine respiratory syncytial virus, bovine viral diarrhoea virus, parainfluenza virus‐3 and the Mollicute Mycoplasma bovis (M. bovis) are frequently detected and presumed to be primary initiators of BRD. However, empirical evidence supporting this assumption remains limited. Infection by these agents then predisposes cattle to the development of pneumonia caused by secondary opportunistic bacterial pathogens such as Mannheimia haemolytica (M. haemolytica), Pasteurella multocida (P. multocida) and Histophilus somni (H. somni). ⁵ , ⁶ , ⁷ These bacterial pathogens exacerbate pulmonary inflammation, resulting in pneumonia, lung consolidation and pleurisy—pathological conditions that impair respiratory function, systemic health and nutrient metabolism, culminating in significant reductions in growth efficiency and mortality. ⁶ Moreover, in studies conducted in the United States, some of these bacterial pathogens exhibit high frequencies of antimicrobial resistance, particularly against commonly used antibiotics such as tulathromycin and oxytetracycline, ⁶ , ⁸ further complicating treatment strategies and highlighting the need for preventative measures such as targeted vaccination approaches.

Despite advancements in diagnostic and therapeutic interventions, subclinical BRD remains a critical yet under‐recognised challenge. Chronic, subclinical infections associated with BRD pathogens such as P. multocida and H. somni can significantly impact cattle growth and metabolism by triggering proinflammatory immune responses, redirecting metabolic energy from anabolic to catabolic pathways. ⁷ , ⁹ These subclinical manifestations, which often escape detection and intervention, indicate the need for preventative strategies that go beyond treating overt clinical signs to address the broader spectrum of BRD‐related production inefficiencies.

Commercially available vaccines are often administered to feedlot cattle to prevent or reduce infection caused by BRD pathogens such as M. haemolytica and some viral agents. ⁷ , ¹⁰ , ¹¹ , ¹² However, a critical gap exists in the availability of effective vaccines for P. multocida and H. somni. Moreover, in areas where commercially available vaccines exist for P. multocida and H. somni, their efficacy remains uncertain. ¹³ , ¹⁴ There are no registered commercially available vaccines targeting P. multocida and H. somni in Australia.

Autogenous vaccines, derived from pathogenic isolates unique to a given herd or production system, can potentially improve the management of respiratory diseases. By incorporating P. multocida and H. somni strains isolated directly from the feedlot environment, autogenous vaccines enable a high degree of immunological specificity. ¹³ Additionally, as the prevalence profiles of BRD pathogens vary throughout the production cycle, with some increasing specifically at feedlot entry, ¹⁴ , ¹⁵ , ¹⁶ administering autogenous vaccines at induction is often undertaken because it represents the first practical opportunity for intervention within feedlot management. Although protective antibody concentrations typically require at least 2 weeks to develop and thus may not immediately prevent early infections, induction vaccination contributes to disease mitigation, particularly in cattle with prior exposure capable of mounting an anamnestic response. ¹⁷ Moreover, given that cattle encounter significant stressors and novel pathogens during feedlot entry ⁶ , ¹⁵ , ¹⁶ and that BRD incidence peaks within the first 2 months of feedlot entry, ¹⁸ , ¹⁹ induction vaccination can support broader strategies to enhance targeted disease mitigation and resilience during the early phases of feedlot acclimatisation. Hence, the current study aimed to evaluate the efficacy of single‐dose autogenous vaccines targeting both P. multocida and H. somni, administered at induction in a commercial feedlot setting. By comparing vaccinated and unvaccinated cohorts, the study examined the potential benefits of using autogenous vaccines against P. multocida and H. somni and its impact on growth performance, feed efficiency and health outcomes.

Materials and methods

Study design

This study evaluated vaccine efficacy based on primary outcomes, including hot standard carcase weight (HSCW), and secondary outcomes, such as carcase characteristics, feed conversion and health performance. For statistical power calculations, the primary unit of interest used was a block of cattle, each consisting of two pens of cattle, with approximately 120 cattle per pen, and the analysis was conducted at the pen level. The within‐block standard deviation of pen‐mean HSCW was estimated as 5.7 kg using data from 161 historical closeouts from the study feedlot over the preceding 18 months. For each block, HSCW means were calculated for two pens, and the within‐block standard deviation was determined. Based on this estimate, a study with 12 blocks (24 pens in total) was calculated to have 80% power to detect a significant difference at P < 0.05 using a two‐sided paired t‐test if the pen‐mean HSCW differed between vaccinated and control pens by 5.25 kg. Differences between pens within blocks were minimised by closely matching pens in location, management, induction date, or any other relevant factors. A total of 2880 cattle were included, with 12 pens each assigned to the Treatment (n = 1440) and Control (n = 1440) groups (Table 1). Data were collected at the pen and individual animal levels, with pens as the experimental unit. All cattle were sourced directly from vendors and were not backgrounded before feedlot entry. No other BRD‐related vaccines were administered to the cattle before induction.

Table 1.

Summary of performance indicator variables by treatment groups

	Minimum		Maximum
Description	(vaccine)	(control)	(vaccine)	(control)
Average daily gain (ADG, kg/day)	0.71	0.71	2.59	2.60
Dentition	0	0	6	6
Dressing percentage (%)	38.8	41.0	65.0	66.3
Dry matter intake	5.94	5.81	15.0	14.8
Eye muscle area (cm2)	61	63	99	99
Hot carcase weight	252.5	248.5	480.0	502.5
Induction weight	293	289	558	566
Live weight	459	451	881	917
Marbling (AUS score)	0	0	6	6
Marbling (MSA score)	200	190	760	770
Meat colour (score)	1.5 (1C)	1.5 (1C)	4	4
MSA index	56.26	55.82	68.85	68.44
P8 fat depth (mm)	4	7	40	35
Weight gain (kg)	116	118	372	379

The experimental groups received 2 mL of either the IVP1 (a vaccine formulation consisting of adjuvant, H. somni antigen and P. multocida antigen, referred to as vaccine) or IVP2 (adjuvant only, referred to as control) between June 22, 2023, and January 18, 2024. Both treatments were administered intramuscularly in the neck during induction. Cattle selection followed strict inclusion and exclusion criteria to ensure consistency and suitability. Eligible cattle were healthy Angus and Angus crossbreeds under 2 years of age, single‐sex, with body weights ranging from 300 to 600 kg at induction. Health and suitability assessments, including body condition, demeanour and rectal temperature, were conducted before the enrolment of cattle into the trial. Cattle failing to meet these criteria were excluded, while postinclusion withdrawal was limited to mortality. Upon arrival, cattle were tagged with unique identifiers and were immediately provided with ad libitum water and allocated starter rations. To reduce bias, randomisation was used to balance the allocation of cattle, and blinding protocols were implemented for all investigators involved, from treatment administration to data analysis. The blinding code was disclosed only after the statistical analysis was completed.

Pen management and feeding conditions

Pens were cleaned before cattle entry. Subsequently, the pens were cleaned at 50 to 60‐day intervals using an excavator and dump truck. Cattle were housed in pens with a capacity of 120 animals each, occupying 1500 m², with access to ad libitum water and 500 m² (~4.2 m² per cattle) of shade. Feedlot grain was processed using steam flaking with a 3 MW fire tube boiler and R&R roller mills. Water troughs were cleaned once per week. Dry matter testing of feed was conducted daily, while nutritional analysis was performed quarterly. Pen hygiene was maintained through weekly water trough cleaning and daily removal of wet feed from bunks. Cattle were monitored daily for health events by trained personnel, with hospital pens after a 5‐day rotation system to manage treatments and recovery. Animals requiring extended care were transferred to convalescent or chronic pens as necessary.

The diet was mixed immediately before delivery to the feed bunk, with its composition varying from entry to exit of the feedlot. It included combinations of almond hulls, steam‐flaked barley, barley silage, barley straw, bread, cottonseed, molasses, supplements, vegetable oil and steam‐flaked wheat. The target flake weight percentage for barley was maintained at 38–39 kg/hL and for wheat at 42–44 kg/hL, with target moisture contents of 23.5% and 22.5%, respectively. The diet was provided ad libitum throughout the feeding period and consisted of two rations: a starter ration and a finisher ration. Cattle were transitioned from the starter to the finisher ration by adjusting the diet in 20% increments every second day, with the finisher ration fed exclusively from day 12 onwards. The diet was delivered twice daily at approximately 8:45 am and 12:30 pm.

Vaccine production and formulation

H. somni and P. multocida isolates were obtained from lung tissue samples collected from euthanased feedlot cattle diagnosed with BRD at the study site. These were subjected to whole genome sequence analysis as described by Alhamami et al. ²⁰ , ²¹ to identify representative strains of the dominant multi‐locus sequence types (P. multocida ST79 and ST394) or phylogenetic groups (H. somni) for incorporation into the vaccine. A killed bacterial vaccine was then produced through four key stages: inoculum preparation, antigen production, vaccine formulation and blending and packaging. Genome‐sequenced clinical isolates were retrieved from −80°C storage, inoculated into sterilised Tryptone Soya Broth (TSB) and incubated at 35°C in a shaker for 12–166 h. The inoculum was then transferred to a 10 L bioreactor under controlled conditions (35°C, pH 7.0 ± 0.5, 100 RPM agitation and 1.0 L/min aeration), with bacterial growth monitored until it reached the set end‐point. The antigen was inactivated using formaldehyde, transferred to sterile antigen bags and mixed at room temperature for at least 24 h. Vaccine formulation involved calculating the required antigen concentration (0.5–1.5 × 10⁹ CFU/mL), adjusting pH to 6.5 and adding Adjuvant #1, followed by 2 h of mixing, before adding Adjuvant #2 and blending for 30 min. The final vaccine was aseptically dispensed into sterile bags or bottles, labelled and stored at 4°C until release for on‐farm safety testing.

Sampling, measurements and observations

Pen riders monitored health events daily, and treatments were administered according to standard feedlot practices. Detailed records of diagnoses, treatments and pulling events data were maintained for each cattle. Causes of morbidity and mortality, such as BRD, were categorised and analysed to determine treatment impacts. Morbidity, defined as the proportion of cattle requiring medical interventions, and mortality, consisting of all recorded deaths, were monitored throughout the trial. Health events, including identifying cases of BRD, were recorded and treated according to standard feedlot practices. Sick cattle were pulled and treated and then transferred to hospital pens until they were transferred back to their home pen or culled. Any adverse events, including any harmful or unintended effects on animals, humans, or the environment, were recorded.

Slaughter dates ranged from November 22, 2023, to July 4, 2024. Cattle designated for slaughter were drafted approximately 1 week before exit and held in exit pens (1–12) until shipment. To maintain consistency, replicates consisting of treatment and control groups were matched and drafted on the same day. After drafting, cattle were provided their full feed allocation the day before shipment and had access to feed until approximately 7:00 am on the day of departure. Transportation to Teys Australia abattoirs in Naracoorte, SA, or Wagga Wagga, NSW, was conducted using B‐Double combination trucks, accommodating approximately 50 cattle per load (48–55 cattle, depending on weight). If cattle from an entire pair (one control pen and one treated pen) could not be shipped on the same day, an equal number of animals were selected from each pen within the pair until both pens were emptied.

Cattle body weights were recorded at induction and before slaughter, with exit weights estimated at the abattoir using industry‐accepted formulae. Carcase data, including HSCW, fat depth (P8 and Rib), loin eye muscle area (EMA), Meat Standards Australia (MSA) marbling score and MSA index, were collected and analysed to evaluate treatment effects. Data collection occurred at both the pen and individual animal levels. All abattoir‐related information, including lairage details and identification maintenance, was systematically recorded in the MSA database, with animal identification from the abattoir kill file matched to the feedlot exit file.

For each animal, lung health was assessed postmortem in the feedlot or in the abattoir using a standardised scoring system. Consolidation and pleurisy scores were recorded on ordinal scales using macroscopic examination and palpation of lungs on the offal table, with each lobe scored individually based on the percentage of consolidation. The anatomical distribution of lung lobes was considered, with reference percentages assigned to each lobe. ¹⁴ Pleurisy was scored from zero to three based on severity, with Score zero indicating no pleurisy, Score one representing pleuritic tags between lung lobes with or without small surface tags, Score two involving significant pleuritic tags and minor lung adhesion to the thoracic wall requiring trimming and Score three indicating severe adhesion of the lung to the thoracic wall or, in rare cases, to adjacent structures within the thoracic cavity. ²² Lung status was classified as abnormal if the pleurisy score was greater than one and an average consolidation score of each lobe greater than five; otherwise, it was categorised as normal. For cattle that died in the feedlot, postmortem examinations were conducted to assess respiratory and systemic abnormalities, including lung consolidation, pleural fluid and abscesses. Vaccine efficacy was assessed based on primary outcomes, including HSCW, average daily weight gain (ADG) and secondary measures, such as carcase characteristics, feed conversion ratio and health performance. The study design was aligned with internationally recognised guidelines, including the OECD “Recommendations on the Governance of Clinical Trials” (2013) and the FDA's “Good Clinical Practice, Guidance for Industry” (VICH GL9, 2001).

Cost–benefit analysis

This study evaluated the cost–benefit impact of single‐dose autogenous vaccines targeting P. multocida and H. somni in feedlot cattle by comparing production, health and economic performance between vaccinated and nonvaccinated groups. The proportion of cattle requiring first and second BRD treatments, dosage per kg of body weight, medication cost per ml and associated labour expenses were recorded for both groups. Veterinary expenditures, including induction costs, transport and feedlot handling fees, were incorporated into the total health expenditure. Production costs, including feed, veterinary and transport expenses, were calculated both per cattle and per lot. Final sale weights, carcase weights and dressing percentages were documented at slaughter, and total end values were determined based on prevailing market prices. Gross profit margins were calculated as the difference between total production costs and total revenue from cattle sales. The benefit–cost ratio of vaccination was determined by comparing the additional vaccination cost to the difference in profit per cattle between vaccinated and nonvaccinated cattle.

Statistical analysis

Statistical analyses were conducted to evaluate the effects of treatment on carcase traits, production outcomes, lung health and morbidity and mortality rates. BRD morbidity was classified as either clinical or subclinical. Clinical BRD morbidity was defined as cattle diagnosed as BRD‐positive by a trained pen rider based on clinical signs, including behavioural indicators such as depression and reduced feed intake, as well as increased respiratory rate and nasal discharge, and subsequently pulled for treatment at least once. Subclinical BRD morbidity was determined based on lung pathology, where cattle with an average lung consolidation score greater than five or a pleurisy score greater than one were classified as subclinical cases.

The effects of vaccination on cattle performance and meat quality outcomes were assessed using generalised linear mixed models (GLMMs) fitted with the glmer function in R. ⁶ For binary outcomes, a binomial transformation was used. Continuous variables were analysed using linear mixed‐effects models (LMMs), ²³ while proportion and ratio data were analysed using GLMMs with a binomial distribution. Count variables were analysed using GLMMs with a negative binomial regression. Ordinal outcomes, such as lung score data, were analysed using cumulative link mixed models (CLMMs) with a logit link, incorporating Block as a random effect. ²⁴ Multinomial logistic regression models were used to assess morbidity and exit status.

Models were fitted with treatment (Control vs. Vaccine) as a fixed effect and were evaluated with additional covariates, such as induction weight and days on feed, and block fitted as a random effect. The lung consolidation score model specifically included consolidation site and treatment as fixed effects. The association between lung pathology and key production outcomes, including HSCW, ADG and carcase quality traits, was evaluated using linear mixed‐effects models. Fixed effects included induction weight, pleural score and consolidation score, while Block was included as a random factor. Model assumptions were validated through residual diagnostics, and parameter estimation was conducted using restricted maximum likelihood (REML) methods. Statistical analyses were performed in R (version 4.4.0) using packages such as lme4, ⁶ ordinal ²⁵ and emmeans. ⁶

Results

A total of 2880 cattle were inducted into the trial. During the trial period, 20 cattle died, with 13 deaths attributed to BRD and seven to other causes. Six cattle were classified as rejects, including three identified as treatment failure rejects, and HSCW data were available for only one. Additionally, one animal could not be tracked and was excluded from the analysis. The remaining cattle (2853) from 24 pens that were categorised under 12 blocks were slaughtered. A summary of major performance indicator variables is presented (Table 1).

Carcase traits and performance outcomes in vaccinated and control cattle

A one‐unit increase in pleural score was associated with a 1.3% reduction in ADG (P = 0.04) and a 1.4% decrease in total weight gain (P = 0.04), while consolidation score had no significant effect on total weight gain (P = 0.22) and ADG (P = 0.37). Similarly, HSCW decreased by 0.6% per unit increase in a pleural score (P = 0.01), whereas the consolidation score remained unaffected. Dressing percentage and meat quality traits (MSA index, MSA marbling, AUS marbling) were unaffected by either lung pathology measure.

Analysis of cattle performance and meat quality outcomes showed improvements in the vaccinated group compared with the control group (Table 2). Total weight gain was 2.7% higher in vaccinated cattle than in controls (P = 0.000), associated with a 2.9% greater ADG (P = 0.000). HSCW was only 0.5% greater in vaccinated cattle (P = 0.043) and EMA was 0.8% (P = 0.007) greater than control cattle. There was no significant effect of vaccination on meat quality traits, including meat colour, marbling and MSA index.

Table 2.

Summary of treatment effects on carcase and performance traits

Description	Control	Vaccine (% change) a	SE	P value
Average daily gain (ADG, kg/day)	1.502	1.545 (2.9)	0.045	0.000
Dressing percentage (%)	54.60	54.40 (−0.4)	0.003	0.001
Eye muscle area (cm2)	79.486	80.131 (0.8)	0.382	0.007
Hot standard carcase weight (HSCW, kg)	358.705	360.511 (0.5)	3.446	0.043
Marbling (MSA score)	435.579	432.476 (−0.7)	6.775	0.470
Meat colour (score)	2.735	2.761 (1)	0.064	0.224
MSA index	62.513	62.450 (−0.1)	0.274	0.407
P8 fat depth (mm)	16.143	16.463 (2)	0.745	0.118
Weight gain (kg)	231.772	238.097 (2.7)	5.178	0.000

^a Percentage change in performance indicators of the vaccine group relative to the control group.

Effect of vaccination on feed intake and conversion efficiency

In the control group, out of a total of 221,791 cattle days, 218,217 (98.4%) were recorded in home pens, while the remaining 3,574 (1.6%) were in hospital pens. Similarly, in the vaccinated group, out of a total of 221,436 cattle days, 218,148 (98.5%) were in home pens, with the remaining 3,288 (1.5%) in hospital pens. Cattle in the vaccine group showed higher feed intake than the control group, particularly in home pens. A dry matter intake (DMI) of 11.5 kg/cattle/day was observed in the vaccine group, compared with 11.2 kg/cattle/day in the control group (P = 009). In hospital pens, DMI was marginally higher in the vaccine group (10.1 kg/cattle/day, P = 0.458) compared with the control group (10.0 kg/cattle/day), though this difference was not statistically significant (Figure 1, Table 3).

Figure 1.

Trends in dry matter intake of cattle in home pen across days on feed by treatment groups.

Table 3.

Feed intake and conversion by treatment group

Description	Control	Vaccine (% change) a	SE	P value
Home pen: DMI (kg/day)	11.24	11.54 (2.7)	0.218	0.009
Home pen: FCR (feed: Gain)	7.641	7.704 (0.8)	0.175	0.621
Home pen: FCE (feed: Gain)	0.131	0.131 (0)	0.003	0.765
Hospital pen: DMI (kg/day)	10.04	10.13 (0.9)	0.128	0.458
Hospital pen: FCR (gain/feed)	6.862	6.819 (−0.6)	0.253	0.719
Hospital pen: FCE (gain/feed)	0.148	0.150 (1.4)	0.006	0.402

^a Percentage change in performance indicators of the vaccine group relative to the control group.

The vaccinated cattle ate 2.8% more (Table 3), which is associated with the 2.9% greater ADG (Table 2), so there was no significant difference in feed conversion traits (Table 3).

Effect of vaccination on cattle morbidity, mortality and treatment frequency

Before analysing the current trial data on cattle BRD morbidity, a five‐year dataset from the feedlot, covering both the period before and during the study, was collected and summarised. The analysis showed an average BRD morbidity of 0.56% (Figure 2).

Figure 2.

Trends in BRD morbidity over a 5‐year period (2019–2024).

The GLMM results herein showed no significant treatment effects on mortality between the Vaccine and Control groups, with identical percentages. Similarly, no significant differences were observed for BRD‐related mortality or mortality from other causes. No difference was observed in clinical BRD probability between the vaccine (estimated marginal mean [EMM] = 0.073) and Control (EMM = 0.068) groups (P = 0.586). In contrast, subclinical BRD was significantly lower in vaccinated cattle, with an EMM of 0.087 compared with 0.140 in the control group, resulting in an odds ratio (OR) of 0.59 (95% confidence interval [CI]: 0.47–0.73; P = 0.000). This indicates that vaccinated cattle had a 41% lower likelihood of developing subclinical BRD compared with the control group. The cumulative prevalence of subclinical BRD aligned with these findings, showing a lower prevalence in vaccinated cattle (16.5%) compared with controls (22.7%) (Table 4).

Table 4.

Effect of vaccination on clinical and subclinical bovine respiratory disease (BRD) morbidity in feedlot cattle

Description	Control EMM (prevalence %)	Vaccine EMM (prevalence %)	Odds ratio (OR)	OR (95% CI)	P value
Clinical BRD morbidity	0.068 (8.5)	0.073 (9.0)	1.077	(0.826, 1.402)	0.586
Subclinical BRD morbidity	0.140 (22.7)	0.087 (16.5)	0.586	(0.473, 0.725)	0.000

EMM, estimated marginal mean.

No significant differences were observed between treatment groups on pull instances, including BRD‐related cattle‐pulling events. Percentages of cattle receiving one or more, two or more, or three or more treatments were also similar between groups. Similarly, BRD‐related treatment percentages showed no significant differences between groups (Table 5).

Table 5.

Treatment effect on cattle mortality and morbidity

Description	Control	Vaccine	SE	P value
One or more treatments (%)	9.56	9.99	0.12	0.687
Two or more treatments (%)	9.10	9.78	0.12	0.513
Three or more treatments (%)	2.98	3.30	0.20	0.604
BRD one or more treatments (%)	6.89	7.45	0.14	0.528
BRD two or more treatments (%)	1.06	1.41	0.32	0.351
Mortality (%)	0.68	0.67	0.45	0.969
BRD mortality (%)	0.31	0.47	0.57	0.470
Other mortality (%)	0.34	0.14	0.84	0.272

For morbidity, treatment effects for the “Healthy” outcome were not significant. Similarly, for the “Others” morbidity category, treatment effects were not significant. Similarly, for exit status, treatment effects for both “Reject” and “Slaughtered” outcomes were not significant.

Vaccination improved lung health outcomes

Vaccination showed a significant protective effect on lung consolidation scores, although the magnitude of this effect varied among specific lung sites. The odds of lung consolidation were significantly lower in the vaccinated group compared with the control group, with an OR of 0.730 (95% CI: 0.62–0.86; P = 0.001), indicating a 27% reduction in the odds of consolidation in vaccinated cattle (Table 6, Figure 3).

Table 6.

Odds ratio (OR) of treatment effects on lung health outcomes

Description	Analysis category	OR	Confidence interval (95% CI)	P value
Lung status	Normal lung status	1.704	(1.375, 2.111)	0.000
Pleurisy score	Lung pleurisy	0.645	(0.643, 0.647)	0.000
Consolidation score	Overall	0.730	(0.623, 0.856)	0.001
Consolidation site	Apical left caudal	0.981	(0.733, 1.314)	0.899
Consolidation site	Apical left cranial	1.105	(0.823, 1.482)	0.508
Consolidation site	Apical right caudal	1.236	(0.922, 1.657)	0.157
Consolidation site	Apical right cranial	1.663	(1.271, 2.175)	0.001
Consolidation site	Diaphragm left caudal	0.973	(0.719, 1.317)	0.86
Consolidation site	Diaphragm right caudal	0.996	(0.736, 1.347)	0.977
Consolidation site	Right middle	1.139	(0.854, 1.519)	0.375

Figure 3.

Heat map of lung consolidation scores by site and treatment group.

For lung status, assessed using a binary GLMM, the effects of vaccination varied by site. At the Apical Left Caudal and Apical Left Cranial sites, no significant differences were observed between vaccinated and control groups. Similarly, the Diaphragm Left Caudal, Diaphragm Right Caudal and Right Middle sites showed no significant differences. However, significant effects were noted at the Apical Right Cranial site, where vaccinated individuals had significantly increased odds of lung consolidation, with an OR of 1.66 (95% CI: 1.27–2.18; P = 0.001).

The odds of having a higher pleurisy score in the Vaccine group were 35.5% lower than in the Control group (OR = 0.65, 95% CI: 0.64–0.65, P = 0.000). Similarly, the overall odds of having a normal lung status in the Vaccine group were 1.7 times higher than in the Control group (OR = 1.7, 95% CI: 1.38–2.1, P < 0.000) (Table 6, Figure 4).

Figure 4.

Pleurisy score distribution by treatment group.

Economic impact of vaccination on feedlot cattle

Total feedlot costs were slightly higher in the vaccinated group ($1,012,325.11 vs. $999,521.80); however, the cost per kg of weight gain was lower ($2.99 vs. $3.02). Vaccinated cattle had a higher total end value ($7,047,327 vs. $6,969,143), which led to a higher gross profit margin per cattle ($1578.01 vs. $1543.26).

Vaccination reduced BRD‐related treatment costs, offsetting health expenditures and increasing slaughter value. The estimated additional value per vaccinated animal was $44.43, reflecting higher liveweight at sale compared with controls. Vaccinated cattle also showed a reduction in feedlot health‐related costs of $54.45 per head, primarily due to numerically lower treatment costs. When these cost savings and additional sale value were aggregated and compared with the vaccination expenditure, the overall estimated benefit–cost ratio was 6.95.

Discussion

This study evaluated the efficacy of a single‐dose autogenous vaccine against P. multocida and H. somni, administered intramuscularly to feedlot cattle at induction, by assessing its impact on carcase traits, health and overall feedlot cattle performance. Vaccination improved some of the assessed traits, including ADG, HSCW, EMA and DMI, indicating the effect of the vaccine on growth and feed efficiency. The vaccinated group showed an increase of 0.043 kg ADG compared to the control group. Moreover, vaccinated cattle showed a 6.20% lower cumulative prevalence of subclinical BRD compared with controls (16.50% vs. 22.70%), representing a 27.31% lower likelihood of subclinical BRD associated with vaccination relative to the control group. In the home pens, the vaccinated group showed a higher DMI (11.5 kg/cattle/day) compared with the control group (11.2 kg/cattle/day). Furthermore, the vaccine showed site‐specific effects on lung consolidation, with significant improvements observed in areas such as the apical right caudal region. The vaccine also significantly reduced pleurisy severity, improving pleural health by 35.5% and decreasing the odds of abnormal lung status by 41.2%. By mitigating disease severity and reducing inflammation and stress, the vaccine allowed for better nutrient utilisation, promoting muscle accretion and overall growth. However, given the low overall BRD prevalence and limited data on the impact of P. multocida and H. somni infection in feedlot cattle, ²⁶ the observed effects may not fully represent the true efficacy of the vaccine as the efficacy of BRD vaccines in feedlot cattle is multifaceted, influenced by vaccination timing, type (killed vs. modified‐live), route of administration, dosage and disease dynamics. ²⁶ , ²⁷ , ²⁸ , ²⁹

Consistent with previous study, ³⁰ the current findings was associated with a lower likelihood of subclinical BRD and no effect on clinical BRD cases, which is suggesting that factors beyond vaccination, such as management practices and environmental conditions, may influence disease occurrence. ³¹ Alternatively, it is possible that some cattle showing BRD symptoms in the pens were not identified, leading to an underestimation of clinical cases. The observed significant improvement in key growth parameters, including ADG, HSCW, EMA and lung health in the vaccinated group compared with the Control group, suggests that the single‐dose autogenous vaccine effectively reduced the subclinical impacts of respiratory pathogens, enabling cattle to allocate more metabolic energy toward growth rather than immune responses. It has been shown that chronic subclinical infections can significantly impact cattle growth and metabolism by triggering proinflammatory immune responses. ⁸ , ³² These responses redirect energy from anabolic to catabolic pathways, reducing nutrient utilisation efficiency for growth. ⁸ , ³² Proinflammatory cytokines such as IL‐1, IL‐6 and TNF‐α override normal metabolic control, inducing insulin resistance and protein catabolism in muscle while promoting hepatic acute phase protein synthesis. ⁸ This immune activation decreases feed intake, average daily gain and feed efficiency in livestock, ultimately affecting carcase weight and quality. ³³

Despite these improvements, no significant differences were observed in P8 fat depth, MSA index, marbling score, dentition and meat colour, which aligns with the understanding that these traits are less responsive to health interventions compared with growth performance traits. ³⁴ , ³⁵ Moreover, dressing percentage showed a statistically significant decrease in the vaccinated group. However, as no measurements of carcase composition or gut fill were collected, the basis for this difference remains unclear and may reflect random variation rather than a direct effect of vaccination. The available evidence on the BRD vaccine efficacy is mixed. For instance, vaccination has also been associated with improved growth traits, such as increased ADG, feed efficiency and longissimus muscle area, ³⁷ , ³⁸ as well as reduced initial disease treatment rates. ³⁸ However, other studies observed no significant differences in treatment rates or weight gains between vaccinated and nonvaccinated groups. ³⁹ Comparisons between single‐dose and double‐dose regimens further highlight variability, with some findings showing that single‐dose protocols can be as effective as double‐doses in reducing morbidity. ³⁶ , ⁴⁰ Furthermore, as BRD is a multiaetiological condition, the specific contribution of each BRD aetiology to the overall impact on carcase traits remains unknown. Therefore, the observed effects might not fully represent the direct influence of vaccination on carcase characteristics.

The effects of vaccination against BRD on DMI and growth performance in feedlot cattle vary depending on pathogen type, vaccine formulation and management practices. While some studies reported temporary decreases in DMI and weight gain after vaccination, particularly with modified‐live vaccines, ⁴¹ , ⁴² others found no significant differences in DMI or growth between vaccinated and nonvaccinated groups. ³⁹ , ⁴³ , ⁴⁴ Moreover, modified‐live vaccines have been linked to more favourable feeding behaviours compared with killed vaccines or no vaccination. ¹² In the current study, vaccination increased DMI in home pens, likely reflecting improved respiratory health and reduced subclinical disease stress. However, FCE and FCR were not significantly different between vaccinated and control groups, suggesting that higher feed intake did not directly translate to improved feed efficiency. These findings indicate that feed conversion traits, influenced by factors such as diet composition and environmental conditions ⁴⁵ may overshadow the effects of vaccination under certain circumstances.

In the current study, no significant differences in mortality were observed between the vaccinated and control groups, aligning with previous studies that have reported mixed effects of vaccination in feedlot cattle. Some double‐dose‐based studies have found no significant benefits of vaccination on BRD incidence or performance traits, ¹¹ , ³⁵ , ³⁷ , ⁴⁶ while others have reported improvements in ADG, carcase traits and reductions in BRD morbidity. ²⁷ , ³⁷ , ⁴⁷ , ⁴⁸ , ⁴⁹ Some studies have reported reduced BRD morbidity and increased antibody titres after single‐dose or double‐dose vaccination against M. haemolytica and H. somni at feedlot entry. ³⁶ Similarly, a single‐dose subcutaneous administration of a M. haemolytica bacterin‐toxoid vaccine showed reduced BRD morbidity, ⁵⁰ though this approach showed no significant effect on overall mortality. Similarly, a two‐dose regimen of a H. somni bacterin, administered intramuscularly at feedlot entry with a booster given 2 weeks later, significantly reduced early morbidity but had no significant effect on overall mortality. ¹⁰ The low prevalence of BRD in the current study may have limited the ability to detect vaccine efficacy in preventing clinical disease. Nevertheless, the lower cumulative prevalence of subclinical BRD in vaccinated cattle compared with the control group, in this study, suggests improved immune protection and reduced lung pathology. ⁵¹ Subclinical BRD, which likely predominated, can impair growth and metabolism by redirecting metabolic energy from growth to immune defence due to proinflammatory responses. ⁵² While the vaccine may reduce subclinical disease effects, it does not appear to prevent clinical BRD or associated mortality in individual cattle. Given that BRD is frequently initiated by viral infections, ² with secondary bacterial infections such as P. multocida and H. somni, ⁵³ evaluating the overall effect of these pathogens and the efficacy of associated vaccines on BRD remains complex.

The vaccine demonstrated protective effects on respiratory health, as shown by reduced subclinical BRD morbidity. Vaccination was associated with a 27% reduction in the odds of lung consolidation (OR = 0.73) and a 35.5% reduction in pleurisy severity scores (OR = 0.65). However, the effects on lung consolidation varied by anatomical site, with no consistent reductions observed across all lung regions and increased odds of consolidation recorded in the apical right cranial lobe. This variability may reflect the complex interplay between pathogen distribution, local immune responses and the anatomical predisposition of cranioventral lung lobes to infection. ⁵⁴ , ⁵⁵

Vaccinated cattle generated higher total end values and gross profit margins due to reduced health costs ($54.45/cattle) and increased liveweight value ($44.43/cattle), resulting in an additional net profit of $34.75 per cattle slaughtered. Similarly, a previous study showed economic advantages associated with adding P. multocida bacterin‐toxoid in vaccination protocols, reporting benefits of up to $20.86 CAD per cattle compared with vaccines without P. multocida. ⁵⁶ These findings collectively indicate that vaccination against key respiratory pathogens not only improves animal health and welfare but also delivers significant financial benefits.

Differences in vaccine efficacy in feedlot cattle may be influenced by factors such as vaccination timing, route of administration, pathogen types, dosage, cattle stress levels and season. ²⁶ , ⁴⁶ , ⁵⁷ The timing of vaccination remains a topic of debate, with evidence suggesting that vaccinating at feedlot arrival, a common practice ⁵⁷ , ⁵⁸ may not always be optimal. ⁵⁹ Studies indicate that vaccination 15 days before weaning and 15 days before feedlot entry can reduce BRD incidence compared with vaccination at weaning or upon arrival. ⁶⁰ , ⁶¹ However, vaccinating calves at 67 and 190 days of age showed similar immune responses to vaccination at 167 and 190 days. ⁶² Moreover, limited evidence supports vaccination efficacy against respiratory diseases under feedlot conditions, ³⁹ though a rapid onset of protection against infectious bovine rhinotracheitis was observed with modified‐live vaccines administered 72–96 h before the challenge. ⁶³ Reports on the route of vaccine administration also showed mixed results. Subcutaneous vaccination was found to be as effective as intramuscular vaccination in reducing BRD morbidity, ³⁶ while intramuscular protocols demonstrated lower pneumonia incidence compared with intranasal and control groups. ²⁷ Intranasal vaccination combined with parenteral vaccines reduced BRD mortality but had no impact on morbidity or performance. ²⁸ , ⁶⁴ Some studies found no significant differences in performance outcomes between administration routes. ²⁹ Overall, limited data support the efficacy of vaccines against respiratory diseases under feedlot conditions, as treatment rates and weight gains often remain unaffected by vaccination. ³⁹ The efficacy of vaccines, however, may depend on the specific pathogen targeted, given the multifactorial aetiology of BRD. P. multocida is frequently isolated in BRD cases, with prevalence rates up to 54.8%. ⁶⁵ However, its role as a primary pathogen is debated, as it is also a commensal in the upper respiratory tract. ⁶⁶ Similarly, H. somni has been positively associated with BRD, with higher bacterial counts indicating disease presence, ⁶⁷ and varying prevalence rates of H. somni in BRD cases, ranging from 39% in Brazil ⁶⁸ to higher levels in some European shipments. ⁶⁹ H. somni and P. multocida infections in cattle exhibit seasonality, with H. somni showing higher occurrences in late autumn and early winter. ⁷⁰ Similarly, P. multocida were detected at high frequencies during colder months in young calves, although this seasonal pattern was not observed in older feedlot cattle. ⁷¹ Hence, the observed results of the current study might be affected by vaccination timing and route of administration.

This current study revealed several inherent challenges in evaluating the efficacy of dual autogenous vaccines against P. multocida and H. somni under feedlot settings. The absence of serological data limits the ability to assess the immune response of the animals, leaving a gap in understanding the impact of the vaccine. Moreover, BRD is a multifactorial condition characterised by complex interactions among pathogens, host factors and management practices. ⁷² Coinfections, which often go undetected, can subtly influence animal performance without obvious clinical signs, ⁷³ , ⁷⁴ potentially confounding the findings of the study. Additionally, the exclusion of cattle with compromised health status, low body condition, or poor temperament before enrolment may limit the applicability of these findings to commercial feedlot settings, where such selection is uncommon and the physiological demands of mounting an immune response under greater stress may be more noticeable. In seasons where the prevalence of the target pathogens is low, the assessed traits may not capture the true effect of the vaccine on cattle, further complicating the evaluation. Furthermore, the relative contribution of P. multocida and H. somni to the overall burden of BRD remains unclear, as BRD is frequently reported as a collective condition without pathogen‐specific attribution.

Conclusion

This study showed that a single‐dose autogenous vaccine targeting P. multocida and H. somni improved key performance traits, including ADG, HSCW, DMI and EMA, and provided site‐specific respiratory health benefits, such as reduced subclinical BRD, reduced pleurisy severity and lung abnormalities. However, the absence of significant effects on mortality and other carcase traits indicates the complexities of addressing the multifactorial aetiology of BRD. The persistent detection of BRD pathogens in vaccinated cattle and the lack of H. somni isolation indicate the need for improved pathogen‐specific surveillance and optimised vaccination strategies. Vaccinated cattle resulted in higher financial returns compared with the control group, indicating the economic benefits of using the vaccine in feedlot cattle. While the vaccine shows promise in mitigating subclinical disease impacts, further study is required to refine its efficacy and better address the challenges of BRD prevention in feedlot systems.

Ethics statement

The study adhered to the Animal Welfare Regulations of Australia and South Australia, with ethical approval granted by the University of Adelaide Animal Ethics Committee (Approval No. S‐2022‐TBA).

Conflicts of interest and sources of funding

The authors declare no conflicts of interest or sources of funding for the work presented here.

Werid, GM. , Batterham, T. , O'Meara, L. , Petrovski, K. , Pitchford, WS. and Trott, DJ. , Single‐dose Pasteurella multocida and Histophilus somni autogenous vaccines administered at induction significantly improved feedlot cattle performance and profitability in Australia. Aust Vet J. 2026;104:37–49. 10.1111/avj.70012

Data availability statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.