Planning ahead for a smoother housing season

Eoin stands at the shed door with the gate half open, watching the last of the calves amble in off the autumn grass. The straw is fresh, the vaccination record is up to date, weaning happened gradually weeks ago. By every checklist he’s read, he’s done the right things. And yet he hesitates, because he knows from past years that none of that guarantees a quiet winter. The coughing, when it starts, usually starts after the gate closes — once calves are standing in a shed, breathing the same air, for hours at a time. What happens inside that building matters just as much as what happened before the calves walked in.

Air you can’t see is the first problem

Most of the obvious groundwork — tight calving dates, creep feeding, gradual weaning — happens outdoors, in daylight, where problems are visible. Ventilation problems are not. A Swiss study that monitored ammonia and climate conditions in calf fattening housing over 14 weeks found that even in working commercial sheds, ammonia concentrations at animal level averaged between 5.9 and 9.4 parts per million across four-hour measurement windows. That is not an extreme figure — it is what ordinary, functioning calf housing produces when air isn’t moving fast enough to clear it. The researchers used six fixed sensors positioned where calves actually stand, plus four mobile sensors physically attached to the calves’ heads, alongside separate loggers tracking temperature, humidity and carbon dioxide. The point of using sensors on the calves themselves was to check whether fixed wall- or pen-mounted monitors were telling the same story as what an individual animal was actually breathing — and the comparison showed measurable differences between the two, meaning a single sensor in a shed corner can understate what a calf standing in a corner, under a doorway, or near still air is really exposed to.

Ammonia irritates the respiratory lining before any bacteria or virus gets involved, making it easier for pathogens to take hold afterwards. That is the practical takeaway: ventilation isn’t about avoiding draughts, it’s about exchanging stale, ammonia-laden air for fresh air continuously, without creating a cold stream directly onto the calves. A shed can look clean and still be building up exactly the kind of air that primes a calf for pneumonia.

The shed itself behaves like a hidden member of the herd health plan — get its air moving properly and much of the groundwork laid before housing is protected; get it wrong and that groundwork is undone within days.

One jab isn’t the same as two

A lot of attention goes to the timing of vaccination relative to weaning, but less is said about what finishing the course actually achieves biologically. A small, early-stage study tracking metabolic changes in calves after an intranasal RSV and Pi3 vaccine found that plasma levels of twelve metabolites shifted measurably after vaccination compared with unvaccinated calves, including compounds linked to bile acid and immune signalling pathways. This was laboratory research on a limited number of Holstein Friesian calves, not a farm trial, so it shouldn’t be read as proof of how much protection any individual animal gets. What it does show is that the body’s systemic response to a mucosal vaccine takes time to develop and is biologically real, not just a formality on a label. Stopping after one dose, or giving the second dose too close to the housing date, risks moving calves into higher-ammonia, higher-density air before that response has had the chance to build.

Grass in the rumen, silage in the bunk

Housing day is also a diet change day, and it is often treated as an afterthought once the vaccination and weaning boxes are ticked. Calves coming off grass have rumens adapted to a wet, high-moisture, lower-density feed; switching abruptly to silage and concentrate changes fermentation patterns and can dent appetite for several days at exactly the point when the immune system is under the most pressure from new air, new neighbours and a new routine. Overlapping grass and housed feed for several days, rather than switching on the day the gate closes, and checking that trace mineral provision matches the new diet rather than the grazing one, reduces the number of separate stresses landing on a calf at once. None of this replaces vaccination or weaning management — it sits alongside it, inside the shed, where the other work can be undone if ignored.

The calf you bought is not the calf you bred

A closed suckler herd like Eoin’s faces a narrower set of risks than a yard mixing in bought-in or multiple-source cattle. A Spanish study screening bacteria involved in bovine respiratory disease in dairy heifers, sampling 855 animals in 2017, found that the prevalence of five key respiratory bacteria — including Mannheimia haemolytica and Mycoplasma bovis — varied with season, geographic region, farm size and antibiotic use. That variation matters most for anyone bringing in cattle from outside: animals from different farms, regions and management systems are statistically more likely to be carrying different bacterial profiles than animals born and raised together. For mixed-source groups, a longer isolation period before mixing with the home herd, and separate airspace rather than just a separate pen, does more to limit spread than any single treatment once calves are already coughing.

Bedding, drainage and the space between calves

Ventilation and stocking density are connected in a way that is easy to underestimate. The same ammonia readings recorded in Swiss calf housing accumulate faster where bedding stays wet and where calves are packed close enough that airflow between them stalls. Deep, dry bedding that is topped rather than left to compact, floors that drain rather than pool, and groups kept small enough that each calf has genuine airspace around it all work in the same direction as a well-set ventilation system — reducing the ammonia and moisture load the lungs have to cope with every hour of every day indoors.

Back at the shed door

Eoin finishes counting calves through the gate and looks up at the ridge vent before he does anything else. The vaccination dates are logged, the diet change is staged over several days, and the bought-in replacement heifers are in their own airspace for now. None of that shows up as a single line on a calendar the way weaning or a vaccine date does — but it’s the part of the plan that decides whether the next ten weeks are quiet or loud.

Sources

• Assessment of Ammonia Concentrations and Climatic Conditions in Calf Housing Using Stationary and Mobile Sensors (2024)
• Identification of systemic immune response markers through metabolomic profiling of plasma from calves given an intra-nasally delivered respiratory vaccine (2015)
• Prevalence of bacteria involved in bovine respiratory disease in dairy heifers in Spain: influence of environmental factors (2025)