Feeding whole, raw, milk to calves from either the bulk tank or waste milk (cows under treatment) has been common practice for many years. However, it does come with risks for disease transmission which cannot easily be overcome unless the milk is treated to reduce the overall load of “bugs”. The types of diseases which can be transferred to a calf from the dam via raw milk include Johne’s, Salmonella, E coli, Cryptosporidium and Mycoplasma, among others. 
 
The best method of reducing the pathogen load of raw milk is through on-farm pasteurisation. While still an uncommon technology on New Zealand farms, we are likely to see growth in its adoption as farm size steadily increases. The most common type of pasteurisation unit is a batch pasteuriser which is designed to heat a small quantity of milk (up to a few 100 litres) for around 30 minutes. Most units take the milk to 63 degrees C. This level of pasteurisation does not sterilize the milk, but rather, reduces the pathogen load. At 63 degrees C for 30 minutes, the majority of bugs we are trying to keep out of our calves will be at negligible levels. 
 
A less costly method of “treating” milk is adding citric acid. This is not a chemical form of pasteurisation but rather a method of preserving milk by lowering its pH to around 4-4.5. Getting milk pH to this lower level can reduce the load of bacteria such as Salmonella or Mycoplasma. However, the effectiveness of this strategy is dependent on the eventual pH of milk after the citric acid has been added and become stable in the milk solution. Hence, if this method is being used, it is wise to measure the pH to assess how much risk of bacteria spread has been lowered. This method is not satisfactory for reducing Johnes disease risk. It should also be noted that treating colostrum with citric acid is not advisable as it ruins the immunoglobulins (IgG) in this precious commodity. 
 
Farmers should recall that feeding calves with milk powder is a good low risk alternative to disease control provided dilution instructions are followed accurately.