In people and many animals, how the body handles sugar (glucose) and the hormone insulin changes throughout the day thanks to something called circadian rhythms—our internal 24-hour clocks. Until now, scientists didn’t know if dairy cows had the same kind of daily rhythms when it comes to processing glucose, which is a key fuel source for producing milk.
To find out, researchers tested 12 lactating Holstein cows at different times of the day to see how well they cleared glucose from their blood and how their insulin levels responded. The cows were given glucose through an IV, and their blood was sampled over a two-hour period at 3 a.m., 9 a.m., 3 p.m., and 9 p.m. To make sure feeding habits didn’t affect the results, cows were fed evenly across the day.
The results? Both glucose and insulin responses showed clear daily patterns, peaking in the late morning and early afternoon. This means cows process glucose more efficiently at certain times of day—just like humans and other animals. Interestingly, another energy-related compound in the blood called NEFA (nonesterified fatty acids) did not show a daily pattern.
Why this matters: Understanding when cows are most sensitive to insulin could help farmers and veterinarians better manage feeding, health treatments, and care—especially for cows in early lactation, a time when they’re more prone to metabolic issues like insulin resistance, ketosis, or fatty liver.
Link to Full Research Article:
Read the full study in the Journal of Dairy Science
