The time of day when you collect a milk sample influences milk urea nitrogen concentrations. This can be a concern for herds that collect test-day milk samples at the morning milking one month and the afternoon milking the next month, explains Herb Bucholtz, extension dairy cattle nutrition specialist at MichiganStateUniversity. MUN values obtained from these samples can vary significantly, particularly for herds milked three times per day. “This needs to be considered,” Bucholtz says. “Otherwise, accurate and reliable MUN results will not be obtained to make informed decisions for diet formulation.” If possible, collect individual milk samples for MUN testing at the same time of day.