How to Detect Sick Feedlot Calves Earlier: What Actually Works in Large Herds

By Dr Duncan Houston

Detecting sick calves in a feedlot is one of the hardest jobs in cattle production. The problem is not just the number of animals. It is that most sick calves do not look obviously sick until they are already well into disease.

By the time a calf is clearly depressed, off feed, or showing respiratory signs, you are often dealing with a more advanced case with lower recovery rates.

This is where newer monitoring systems are changing the approach. They do not replace people, but they help identify calves earlier, before the disease becomes obvious.

Quick Answer

Early detection of sick feedlot calves, especially those with respiratory disease, is critical for improving survival and performance. Technology like sensor-based ear tags can detect changes in temperature and behaviour before visible signs appear, allowing earlier treatment. The real benefit comes from acting on alerts quickly, not just collecting data.

Why is early detection so important?

Bovine respiratory disease is the most significant health issue in feedlots.

The challenge is that early disease is subtle.

What typically happens:

• Calf develops early infection

• Behaviour and temperature change slightly

• No obvious visual signs yet

• Disease progresses before detection

What this leads to:

• Delayed treatment

• Lower response to antibiotics

• Higher mortality

• Reduced weight gain

Clinical insight

In practice, the calves that are easiest to treat are the ones you almost miss.

Why do people miss sick calves?

Even experienced pen riders miss early cases.

Common reasons:

• Large numbers of animals

• Subtle early signs

• Time pressure during checks

• Variability between calves

What matters most

Human observation is good at spotting obvious disease.
It is less reliable for catching early disease.

How do monitoring systems detect illness earlier?

New systems use continuous data instead of snapshot observation.

What they track:

• Skin temperature changes

• Movement patterns

• Behavioural shifts

What changes first:

• Reduced activity

• Slight temperature elevation

• Altered movement patterns

These changes often occur before visible clinical signs.

Clinical insight

The value is not just the data.
It is identifying patterns you cannot see during a single yard check.

What does this look like in practice?

Typical system setup:

• Ear tags with sensors

• Data collection through receivers

• Alerts sent to staff devices

What happens on the ground:

• Calves flagged for abnormal patterns

• Staff inspect those specific animals

• Earlier treatment decisions

Decision checkpoint

Technology only works if flagged calves are checked promptly.
Delayed response removes most of the benefit.

How serious is delayed detection?

Low risk

• Mild early disease

• Good response to treatment

Action: Early treatment, high recovery

Moderate risk

• Clear clinical signs

• Reduced appetite

Action: Treatment still effective but slower recovery

High risk

• Advanced disease

• Severe respiratory signs

Action: Lower treatment success, higher loss risk

Critical

• Recumbent or severely compromised

• Poor response to treatment

Action: Emergency care, poor prognosis

What else could affect detection accuracy?

Technology is not perfect and must be used properly.

Common challenges:

• Incorrect baseline settings

• Environmental effects on temperature readings

• Missed alerts

• Poor staff follow-up

Clinical insight

The system does not replace judgement.
It supports better decisions when used correctly.

When should you act on an alert?

• Any calf flagged for abnormal behaviour or temperature

• Multiple alerts in the same group

• Increased alerts after stress events such as transport or weather change

Decision checkpoint

If you are seeing repeated alerts, investigate immediately. Do not wait for visual confirmation.

What should you do right now?

Step 1

Ensure alerts are being monitored consistently

Step 2

Inspect flagged calves as soon as possible

Step 3

Check for early clinical signs

Step 4

Treat promptly if disease is suspected

Step 5

Track patterns across groups

Time-based guidance

• Alerts should be acted on the same day

• Delays reduce treatment success

What are the real benefits?

• Earlier treatment of disease

• Reduced mortality

• Improved weight gain and performance

• More efficient use of labour

• Better overall herd monitoring

What matters most

The benefit comes from earlier decisions, not just better data.

Common mistakes when using detection systems

• Ignoring or delaying response to alerts

• Relying entirely on technology without inspection

• Poor setup or calibration

• Not training staff properly

• Failing to review data trends over time

How do you get the most out of these systems?

• Set clear response protocols

• Train staff on how to interpret alerts

• Review performance regularly

• Adjust thresholds based on conditions

• Combine data with clinical judgement

Clinical insight

The best results come from combining technology with experienced observation, not replacing one with the other.

FAQ

Do detection systems replace pen riders?
No. They support earlier detection but still require human assessment.

How early can disease be detected?
Often before visible signs appear, based on behaviour and temperature changes.

Are these systems worth the cost?
They can be, especially in large operations where early detection reduces losses.

What is the biggest benefit?
Earlier treatment, which improves recovery and performance.

What is the biggest risk?
Not acting on alerts quickly enough.

Final Thoughts

Detecting sick calves earlier is one of the most valuable improvements you can make in a feedlot system.

The goal is not to replace people. It is to give them better information sooner, so they can act before disease becomes advanced.

When early detection is combined with fast, confident decision-making, outcomes improve across the board, from survival to growth to overall herd performance.

If you are considering implementing monitoring systems or want to improve how you respond to early disease signals, ASK A VET™ can help guide setup, refine protocols, and support better decision-making across your operation.