Your detection delay is the number of days between a problem starting on the farm and someone knowing about it. You can work out yours in about ten minutes. Find the last three problems that cost the farm money, write the date each one started and the date somebody knew, and average the three differences. On average, a problem has been running for half the time between two checks when it is found. A farm that checks every 30 days finds a problem after 15 days. At an assumed CAD 80 a day (replace it with yours), that is CAD 1,200 for one problem. The decision is how often to check each thing.
Why is the delay at least half the interval?
A farm that checks something every 30 days, with a problem equally likely to start on any day, finds the average problem 15 days after it began. The figure holds for a water trough as much as for a bulk fuel tank.
Looking harder at the check does not shorten that wait. A problem that only the check would catch waits, from the day it starts, for the next check.
Half the interval is also the best case, because it assumes someone spots the problem the first time they look. A manager on a 7-day check averages three and a half days, provided the check catches it. The interval changes when someone decides to change it, which makes it a planning decision.
The same arithmetic applies when the check is a laboratory test and the interval runs in years. Soil sampled every four years shows a change in fertility that is, on average, two years old. The guide to which fields have a current soil test lists, in an afternoon, the fields already past that interval.
How often do the published guides say to check?
Guides for livestock and crops give an interval for some checks and none for others. Half of each published interval is the average age of a problem when someone finds it.
| What is being checked | Published interval | Average age of a problem when found |
|---|---|---|
| Lactating dairy cows, welfare inspection | At least once a day | Half a day |
| Field corn, pest scouting before pollination | Every 7 days | 3 to 4 days |
| Dairy herd, monthly milk recording | 22 to 37 days between tests | 11 to 19 days |
| Extensive beef cattle in northern Australia, muster (the round-up of the herd) | About twice a year | Roughly 3 months |
| Dairy cattle in general, welfare inspection | No number set | Depends on the interval the farm sets |
The World Organisation for Animal Health sets animal welfare standards for its member countries. Its code says lactating cows should be inspected at least once a day. For dairy cattle in general it asks for inspection at intervals appropriate to the production system and the risks to the health and welfare of the cattle. That leaves each farm to set its own number.
The international guidelines for milk recording take a test every four weeks as the reference and allow 22 to 37 days between tests. At the long end, Meat and Livestock Australia, the research and marketing body of the Australian red meat industry, says northern cattle properties are mustered typically twice each year. Bringing the herd in twice a year does not mean each animal is looked over twice, so for a single animal the gap can be longer.
How many days of warning does a crop check leave you?
A crop guide ties the interval to the days of warning before damage, which the livestock standards above do not. In Ontario, the provincial agriculture ministry (OMAFRA) tells soybean farmers to scout every 7 to 10 days until aphids are found, then every 3 to 4 days as they approach the threshold. The soybean aphid is a small insect that feeds on the plant’s sap.
The threshold is 250 aphids per plant, increasing on 80 percent of the plants, between growth stages R1 and R5 (flowering to the start of seed fill). OMAFRA says that count gives roughly 7 to 10 days of lead time before aphids reach the economic injury level, the point where the cost of control equals the yield lost.
Set that lead time beside the interval, using the two OMAFRA figures. If the aphids pass the threshold just after a check, a 10-day interval finds them 10 days later, and the whole lead time has gone. A 4-day interval finds them within 4 days and leaves at least 3 of the 7 days. That is why the guidance shortens the interval as the count approaches the threshold.
The University of Wisconsin’s corn scouting manual reasons the same way: field visits must be scheduled such that increases in pest populations are detected as soon as economic thresholds are reached. The economic threshold is the pest count at which treating pays for itself. The manual sets weekly visits until pollination and about ten days between visits after it, because by then there is little danger of pests passing the threshold between visits.
These figures are for one pest in one province. Your crop, your pest and your threshold differ, and only the way of reasoning carries over. The same test works for any check on the farm. Find how many days pass between a problem starting to cost money and the point where acting no longer saves it, and keep the interval shorter than that.
Is seeing the herd every day the same as knowing?
No, and a German study measured the gap. Veterinarians assessed lameness on dairy farms in three regions of Germany and compared what they found with the farmers’ own estimates. On average, farmers were aware of only 45.3, 24.0 and 30.0 percent of their lame cows, in the north, east and south.
Those farmers walk past their cows every day and the problem is visible, yet in the east they knew of only about one lame cow in four. The veterinarians examined the cows and counted; the farmers estimated. The study counted lame cows, not days, so it cannot say how long each cow went unnoticed. It does show that a daily look can miss most of the problem, which is why half the interval is the shortest average delay a farm can have.
What do you write first, and how long does it take?
Working out the delay takes no new system. The date somebody knew usually sits in a message or a service record, and an invoice or a log entry gets you close to the date the problem began.
Fuel and machinery are two places where you can set a check on a fixed interval with records you already keep. Fuel bought against the hour meter compares, machine by machine, the fuel bought with the hours run. A gap has ordinary causes to rule out before anyone suspects theft, such as a faulty meter or a wrong delivery. The manufacturer’s service interval compares that interval with the hour meter, to see how many hours each machine is overdue.
The detection delay turns a general worry into a decision with a name on it. “We should keep a closer eye on things” cannot be assigned to anyone or checked next month. “The person who fills the water troughs moves from a four-day to a two-day check, and we measure the delay again in a month” can be. Shortening an interval starts with a decision about who checks and how often. For the other routines that keep a farm running, start from the farm management guide.