More than 50% of deaths in pre-weaned dairy heifers in the US is attributed to diarrhea (USDA 2010). When dairy producers and calf caretakers devote their efforts towards disease prevention, they can minimize their use of drugs to treat calf diseases. As concerns about antimicrobial resistance increase, it is especially important to re-examine drug use on dairies. This publication will focus on the use of drugs to treat dairy calfhood illnesses. Respiratory disease and diarrhea are the two most common illnesses that result in drug use in pre-weaned dairy calves. Respiratory disease is commonly caused by both viruses and bacteria and usually requires antibiotic treatment to address the bacterial component of the disease complex. Diarrhea in pre-weaned calves is more common than respiratory disease and is most commonly caused by viruses (Rota and Corona) and protozoa (such as Cryptosporidium) that are not killed by antibiotics. Occasionally, diarrhea can also be caused by bacteria such as E. coli K-99 and Salmonella, which require antibiotic treatment. Determining if a calf with diarrhea needs treatment with antibiotics can be challenging when relying only on loose feces as a clue. For example, calves infected with Salmonella or E. coli K-99 will typically have yellow or white loose feces; however, yellow loose feces is also caused by coronavirus infections. The purpose of this publication is to assist dairy producers and calf caretakers with treatment decisions for diarrhea in pre-weaned dairy calves.
Consequences of DiarrheaWhen a calf has diarrhea, there are several consequences:
- The calf loses fluids in the feces leading to dehydration.
- The calf loses strong cations such as sodium (Na+) that causes an imbalance of strong cations and strong anions (such as Cl-), creating metabolic acidosis (excess of acid in the body).
- The calf may develop electrolyte imbalances because of losses of electrolytes in the feces.
- The calf loses weight due to reduced appetite or not absorbing nutrients from the gut.
- There is the potential for overgrowth of gram-negative bacteria (like E. coli) in the small intestine.
- There is an increased chance for development of bacteremia (bacteria in the blood), particularly in calves with failure of passive transfer of immunity (those that may not have or did not receive enough quality colostrum) or calves with severe diarrhea.
Not all these consequences happen in every case of diarrhea. Some calves simply have fluid and electrolyte losses, while others may have more severe clinical signs (high fever, emaciation, etc.). In addition to the consequences of the primary infection, calves may also develop secondary infections because their immune systems were compromised during their initial illness. The actual cause of death of diarrheic calves is not always known but likely includes dehydration and bacteremia or septicemia.