Study links subclinical BRD with slower growth in dairy heifers: full analysis

A retrospective study published in Frontiers in Veterinary Science suggests that subclinical bovine respiratory disease detected at weaning is associated with both lower growth performance and distinct nasal and fecal microbiota profiles in dairy replacement heifers. In the study population of Holstein-Friesian and Jersey heifers, animals classified as healthy were heavier and posted greater average daily gain than heifers with subclinical BRD, pointing to a measurable performance penalty even when respiratory disease is not obvious at the pen side. (holoruminant.eu)

That finding fits with a broader shift in calf-health research. BRD has long been recognized as one of the most important diseases in young cattle, but recent work has focused on the role of the respiratory microbiome and on the limits of relying only on visible clinical signs. A 2023 meta-analysis found that calves with BRD tended to have lower respiratory microbiome Shannon diversity than controls, while also noting that study methods and sampling location can strongly shape results. Earlier work in preweaned dairy calves with and without ultrasonographic lung lesions found little difference in overall nasopharyngeal diversity by pneumonia status alone, but did identify differences in specific taxa such as Pasteurella, underscoring how subtle and context-dependent these microbial signals can be. (frontiersin.org)

The new study appears to build on that same idea: subclinical disease may not always produce dramatic microbiome disruption, but it can still be associated with changes in community structure, especially among less abundant organisms that may be biologically important. That is notable because low-abundance taxa are often overlooked in field discussions, yet they may influence resilience, inflammation, or colonization resistance in ways that affect whether a calf stays healthy through stressful transition periods. The study also connects those microbial findings with growth outcomes, which is where the work becomes especially relevant for replacement-heifer management. (holoruminant.eu)

There is some supporting industry context from Teagasc-linked materials tied to this research stream. In a 2025 Teagasc update on respiratory disease in dairy-beef calves, the organization said calves with lung lesions in Grange research had reduced live-weight gain of 0.12 kg/day, reinforcing the production cost of respiratory disease even when the main conversation is often centered on treatment or mortality. Teagasc has also highlighted BRD as one of the most common and costly diseases in bovine production, with concern not just for welfare but for antimicrobial use and long-term productivity. (teagasc.ie)

Direct outside commentary on this specific paper was limited in the sources available, but the surrounding literature points in a similar direction. Sabine Scully’s recent work on calf fecal microbiota and health status has likewise shown that disease states in young dairy heifers can be associated with reduced microbial diversity or shifts in specific bacterial groups, even when broad management factors such as colostrum source do not explain the effect. Taken together, that body of work suggests the microbiome may be more useful as a marker of calf health trajectories than as a stand-alone diagnostic shortcut. That’s an inference from the available studies, rather than a direct claim from a single paper. (frontiersin.org)

Why it matters: For veterinarians, herd-health consultants, and calf managers, the practical message is that subclinical BRD deserves attention because missed cases may still reduce growth in future replacements. If a calf looks broadly well but carries lung lesions or mild respiratory changes, the cost may show up later in average daily gain, age at breeding targets, or overall rearing efficiency. The study also adds weight to using thoracic ultrasound and standardized respiratory scoring as complementary tools, rather than waiting for overt clinical disease before intervening at the group level. (pubmed.ncbi.nlm.nih.gov)

It also matters because microbiome findings may eventually help refine risk stratification, but they are not ready to replace field diagnostics. The 2023 BRD microbiome meta-analysis emphasized that health status, sampling location, and dataset differences all influence results, which means veterinarians should be careful about overinterpreting any one microbial signature. For now, the stronger near-term value is in pairing microbiome research with practical surveillance, ventilation and housing improvements, vaccination planning, and early-life management that reduces respiratory challenge. (frontiersin.org)

What to watch: The next step is whether prospective studies can show that nasal or fecal microbiota patterns predict which calves will go on to develop subclinical lung disease, and whether those signals hold up across farms, breeds, and management systems well enough to inform routine herd-health decision-making. (frontiersin.org)