The Resistance of a Cow

Episode Summary

Executive Summary: Radiolab investigates “stray voltage,” a mystery in which dairy cows stop drinking water and instead drink urine. The story traces farmer reports in Denmark and the U.S., competing explanations from skeptics and experts, and the physics of electricity in modern dairy barns. It ends with a mixed verdict: some cases may be real, but many alleged cases likely reflect nutrition, barn design, and herd-management changes rather than electricity.

Main Topics: The Danish cow mystery (Priority: 5/5): A Danish journalist, Klara Grunel, investigates a farm where cows refuse water and drink each other’s urine, leading to suspicion that something is wrong on the farm. Stray voltage as a farm-wide explanation (Priority: 5/5): Farmers and some consultants argue that electricity leaking into barns and water systems can shock cows, alter behavior, and cause production losses. Electricity’s rise and power-line backlash (Priority: 4/5): The episode places stray voltage in the larger history of electrification, power plants, and the spread of high-voltage lines through rural America, including farmer protests. Scientific testing of cow sensitivity (Priority: 5/5): Researchers in Wisconsin and elsewhere test how much voltage triggers cow reactions, using controlled experiments and the concept of cow resistance. Resistance, barn design, and changing dairy systems (Priority: 5/5): A major dispute centers on whether modern free-stall barns and wet slurry environments make cows far more conductive than older studies suggested. Alternative explanations for symptoms (Priority: 4/5): Veterinarians and dairy scientists argue that poor diet, mineral deficiency, overcrowding, social behavior, and management changes can explain urine drinking and reduced water intake. Lingering uncertainty and practical fixes (Priority: 4/5): The episode closes with ongoing disagreement over the true prevalence of stray voltage, but also notes that some farms did identify electrical issues and improved after repairs.

Key Arguments: Cows refusing water and drinking urine can appear where stray voltage is suspected, but the symptom pattern is not proof of electricity alone. Power-company and scientific skeptics argue that many alleged stray-voltage cases fall below thresholds known to change cow behavior. Researchers originally set cow resistance at 500 ohms based on older tie-stall barns, but critics argue modern free-stall, wet environments may lower resistance substantially. Veterinarians say urine drinking is often caused by mineral deficiency, especially potassium, not necessarily electricity. Changes in dairy farming—from tie stalls to large free-stall and milking-parlor systems—may have created new stressors that look like electrical problems. Some individual farms did have genuine electrical faults, and when those were corrected, cows returned to normal behavior. The controversy persists because farmers, utilities, and scientists are all using different assumptions about cow behavior, barn conditions, and acceptable electrical exposure.

Data Points: Cows on Gregus Christensen’s farm: about 200 - The Danish farmer’s barn held roughly 200 cows that were refusing normal water intake. Distance from farm to home: 4.5 kilometers - Klara Grunel says she lived very close to Gregus Christensen’s farm. Daily cow water intake: about 150 pounds of water per cow per day - Mentioned to show why hauling off-site water was impractical. Wisconsin stray-voltage task force created: 1986 - The state formed a formal task force to investigate farmer complaints. Wisconsin farm investigations since 1990: over 9,000 - Doug Reinemann notes the state has conducted thousands of stray-voltage investigations. Reported stray-voltage cases handled by electrician Larry Neubauer: close to 4,000 to 5,000 - His estimate of the number of cases he had worked on. First reports in New Zealand: early 1960s - Doug Reinemann traces the earliest known reports of farm electricity sensitivity to New Zealand. Cow resistance standard: 500 ohms - The long-standing benchmark used in stray-voltage policy and research. Idaho study sample: over 170 cows across 6 dairies - Richard Norell’s team tested modern free-stall cows to reassess resistance. Revised cow resistance estimate: 200 ohms - The Idaho study’s lower estimate, which critics say was never fully published or resolved. Voltage threshold analogy: 9-volt battery on the tongue - Used to illustrate the approximate level where cows might show behavioral changes. Current threshold: 2 milliamps at 500 ohms with 1 volt - Used in the physics explanation of how voltage and resistance translate into current. Potential current at 250 ohms: 4 milliamps with 1 volt - Illustrates how lower resistance could double current through a cow. Potential current at 200 ohms: higher than 4 milliamps with 1 volt - Used to argue modern cows could be more sensitive than older standards assume. Utility response to Jill Nelson: electrical changes made to the farm - After Larry Neubauer identified stray voltage, the power company corrected the system and symptoms reportedly improved.

Pivotal Quotes: "I was just like, this seems like something's very off." — Klara Grunel: Her reaction after reading the article about cows refusing to drink water. "Stray voltage is horrible. It will destroy you." — Unnamed farmer / interviewed farmer: Describing the perceived impact of electrical leakage on dairy herds and farm finances. "If you want to imagine what the cow experiences, put a 9-volt battery on your tongue." — Doug Reinemann: Explanation of the threshold used to describe how cows respond to small electrical stimuli.

Implications: The episode shows how hard it is to prove causation in agriculture: real electrical faults can exist, but symptoms may also come from nutrition and management. As power demand grows, the stray-voltage debate may resurface unless standards, farm design, and testing methods keep pace.