Short communication: Are group size and pasteurization of whole milk associated with diarrhea and growth of pre-weaned organic dairy calves?

The objective of our study was to assess effects of pasteurization of milk and group size on the prevalence of diarrhea and daily growth in organic pre-weaned calves. Our study was conducted in six organic dairy herds where 353 pre-weaned calves were randomly placed in groups of two or four calves from one week of age. Three herds used pasteurized milk in a first five-month period and un-pasteurized milk in a second five-month period and three herds used unpasteurized in the first and pasteurized in the second period. The number of colony forming units (CFU)/mL was measured from samples of pasteurized and un-pasteurized milk fed to the calves. Diarrhea was measured as fecal smear under and/or at the tail and hind legs and as liquid feces. Heart girth growth was estimated using inflexible measuring tape. Group size and pasteurization were not significantly associated with either diarrhea or daily growth. •Housing in pairs compared to groups of four did not affect calf diarrhea or growth.•Bacterial counts in pasteurized and un-pasteurized whole milk varied widely between farms.•Pasteurization of whole milk did not affect diarrhea or growth.