Background: A cow’s production life is defined as a series of lactations, which are generally about a year long. Once she calves, she begins producing milk (the start of the lactation), and will continued to be milked until about 60 days before she is due to have her next calf. Ideally, this calf-to-calf cycle takes about a year. Sixty days prior to calving, she is ‘dried off’, which means we stop harvesting milk and allow her to have a period of rest before the next calf. These ‘dry’ cows are usually housed in a separate area or facility on the farm and fed separate rations.
At dry off, cows will generally be vaccinated and, depending on the farm or the history of the individual cow, receive an infusion of antibiotic into each quarter, followed by an inert bismuth based teat sealant. Cows that have had a mastitis event in the previous lactation or have a subclinical infection at dry-off usually receive antibiotic and teat sealant in each quarter; cows that have no history of mastitis and no evidence of a subclinical infection received only teat sealant.
Drying off a cow is a two-step process. She is milked a final time, teat ends are cleaned with an alcohol swab, and the antibiotic is infused, teat ends are then cleaned again and the teat sealant infused. Despite every attempt to make sure this is done in as hygienic a manner is possible, the reality is that there is risk of teat, hand or syringe contamination with manure and bacteria. Every time we cross a teat end with a syringe, we risk introducing bacteria and creating an iatrogenic infection. For cows that receive both an antibiotic and a teat sealant, we have to cross the teat end twice and so we double the risk.