A calf develops diarrhea during her first weeks of life. The farm treats her, she recovers and within days the immediate crisis is over. As months pass, she grows into a replacement heifer and eventually enters the milking herd. By the time she calves for the first time, few people are thinking about the illness she experienced as a calf.
But new research suggests her body may not have forgotten. A study published in the Journal of Animal Science found the effects of neonatal diarrhea can persist for years, reducing milk production across multiple lactations and challenging the assumption that surviving calves fully recover.
The Disease Ends, But the Effects May Remain
Neonatal diarrhea is among the most common health challenges facing dairy calves. Producers and veterinarians understand its immediate impacts, including treatment costs, labor demands, reduced growth and mortality losses. What has been less clear is what happens to the calves that survive and eventually enter the milking herd.
To answer that question, researchers examined records from 1,907 Holstein cows on a commercial dairy farm in northern China. The dataset included 700 animals that experienced neonatal diarrhea and 1,207 healthy controls. The first signs of a lasting impact appeared long before the cows entered the parlor.
Calves that experienced diarrhea had lower weaning weights (97.5 versus 101 kg), and years later, the differences were still detectable. During first lactation, cows with a history of neonatal diarrhea measured a median withers height of 134 centimeters compared with 135 centimeters in healthy herdmates.
Although the differences were modest, they suggest an illness during a critical developmental period can alter growth long after clinical recovery. Some of the physical differences became less obvious as the animals aged. By later lactations, body condition scores and height measurements were increasingly similar between the two groups. If growth measurements were the only data available, it would be easy to conclude the animals had largely caught up.
The Production Gap Didn’t Disappear
The milk records, however, revealed the effects of neonatal diarrhea extended far beyond the calf barn. While researchers expected some lingering impacts, the persistence of the production losses across multiple lactations was striking.
First lactation: The first warning sign
The earliest indication appeared during first lactation. Cows that had experienced neonatal diarrhea produced a median 305-day milk yield of 10,831 kg, compared with 11,492 kg for healthy cows. Peak milk production was also lower, reaching 59 kg per day versus 60 kg per day. Altogether, affected cows produced approximately 661 kilograms less milk during their first lactation.
Second lactation: The gap persists
Researchers might have expected the production difference to narrow as animals matured. Instead, the gap remained. During second lactation, cows with a history of neonatal diarrhea produced a median 305-day milk yield of 10,669 kg, compared with 10,956 kg in healthy cows, a difference of approximately 287 kg. Peak milk yield also remained lower at 61 kg per day compared with 63 kg per day.
The effects were not limited to milk volume. During the early postpartum period, second-parity cows that had experienced neonatal diarrhea produced 24 kg of corrected milk per day compared with 27 kg in healthy animals. Researchers also reported lower milkfat percentages and lower fat-to-protein ratios, suggesting the disease influenced milk quality and production efficiency as well as total output.
Third lactation: The hidden cost becomes clear
The most dramatic differences emerged during third lactation. Cows that experienced neonatal diarrhea produced a median 305-day milk yield of 10,343 kg, while healthy cows produced 11,430 kg. The gap had grown to 1,087 kg of milk over a single lactation. Peak milk yield followed the same pattern, reaching 56 kg per day in affected cows compared with 61 kg per day in healthy herdmates.
Rather than fading over time, the losses appeared to accumulate, with the largest deficit emerging during third lactation.
A Different Way to Think About the Cost of Scours
Most discussions about calf diarrhea focus on treatment costs, labor demands and mortality. This study suggests those visible losses may represent only part of the economic impact.
For veterinarians, the findings reinforce the value of preventive measures such as colostrum management, sanitation, pathogen control and rapid intervention. While these programs are often justified by their ability to reduce illness and death, they may also help protect future milk production.
The study’s central message is simple: The cost of calf diarrhea is not always paid during calfhood. In this study, its effects were still measurable years later, reducing milk production in cows that should have been among the herd’s most productive animals.
