Abstract
PICO question
 In auction market calves at high risk of developing bovine respiratory disease (BRD), does delayed (14–30 days) vaccination with a modified live vaccine (MLV) for viral respiratory pathogens versus administration of MLV on arrival (within 24 hours of arrival) to the stocker operation, result in less calves with BRD morbidity diagnosed based on visual signs and rectal temperature >40°C, or less calves with BRD mortality?
 
 Clinical bottom line
 Category of research question
 Treatment
 The number and type of study designs reviewed
 Four papers were critically reviewed. All were randomised complete block designs
 Strength of evidence
 Moderate
 Outcomes reported
 In stocker calves, delaying administration of a MLV for respiratory viruses may result in numerically lower initial BRD morbidity rates, while giving at arrival may result in numerically lower BRD retreatments. One study shows statistically lower cases of BRD morbidity after the third antimicrobial treatment in cattle vaccinated on arrival with both a clostridial and MLV for respiratory viruses compared to cattle vaccinated on arrival with clostridial vaccine and delayed MLV for respiratory viruses. No conclusion about mortality can be drawn due to inconsistent numerical conclusions between studies
 Conclusion
 Due to conflicting evidence and a general lack of statistically significant differences in morbidity and mortality outcomes, a definite answer regarding the impact of delayed MLV respiratory vaccination in stocker calves cannot be made
 
 How to apply this evidence in practice
 The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient’s circumstances and owners’ values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources.
 Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.
 
Highlights
Vaccine: Pentavalent modified live vaccine (MLV) containing infectious bovine rhinotracheitis virus (IBRV), bovine viral diarrhoea virus (BVDV) type I and II, bovine respiratory syncytial virus (BRSV), parainfluenza-3 virus (Pl3); (BoviShield GOLD® 5, subcutaneously; Pfizer Animal Health)
First bovine respiratory disease (BRD) treatment %
This study indicated that fenceline contact between vaccinated and non-vaccinated calves was possible
Summary
Due to conflicting evidence and a general lack of statistically significant differences in morbidity and mortality outcomes, a definite answer regarding the impact of delayed MLV respiratory vaccination in stocker calves cannot be made. Clinical scenario Stocker cattle are young and lightweight calves (often somewhere in the range of 204–250 kg) purchased to utilise pasture for frame-growth before moving to a feedlot for the finishing phase of their production life. Since this is often a situation where recently weaned calves are commingled, bovine respiratory disease (BRD) is a concern. The evidence There is no statistical evidence that delayed MLV administration for viral respiratory pathogens reduces BRD morbidity or mortality in stocker calves. While there is some evidence of numerical reductions in BRD morbidity, there is disagreement in the numerical differences in retreatment and mortality rates between arrival and delayed vaccinated calves between studies
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