There are some changes coming in our industry's ability to use antibiotics.
Since the Animal Medicinal Drug Use Clarification Act (AMDUCA) went into effect in 1996, a food-animal producer has been able to use antibiotics for extralabel uses provided it is under the direction of a licensed veterinarian within a valid veterinary-client-patient relationship (VCPR) and the requirements of the regulations have been met. Prior to AMDUCA, extralabel use was technically illegal but was allowed under regulatory discretion by the Food and Drug Administration's Center for Veterinary Medicine (CVM).
There are, however, a group of antibiotics for which CVM prohibits extralabel use. This includes the nitrofurans, chloramphenicol, nitroimidazoles, sulfonamides in lactating dairy cattle, glycopeptides and fluoroquinolones. There are also other drugs in this group, which emphasizes the need to have a veterinarian involved in your drug choices.
One of the most recognizable drug groups for beef producers in this list would be the fluoroquinolones. You'll recognize the trade names Baytril® (enrofloxacin) and A-180® (danofloxacin). Baytril is approved for treatment of respiratory disease in cattle and for treatment and control of respiratory disease in swine. A-180 is approved for treatment of respiratory disease in cattle. Any use of these drugs other than as described on the label is illegal.
Cephalosporins may be added. On July 3, CVM published in the Federal Register a proposed rule to include cephalosporins on this list of antibiotics with prohibited extralabel use. Beef producers will recognize ceftiofur (Naxcel®, Excenel® and Excede®) as the cephalosporin labeled for use in beef and dairy cattle.
The comment period on this proposed rule ends Nov. 30. A question-and-answer document with a link to the original proposed order of prohibition may be accessed at www.fda.gov/cvm/CVM_Updates/CVMupdateCepha_QA.htm.
Read these documents and you'll find that the CVM concerns leading to the proposed rule include cephalosporin resistance in Salmonella isolates from humans and animals. A key concern is the spread of extended-spectrum beta-lactamase (ESBL) genes that impede the ability of advanced cephalosporins to treat diseases such as invasive salmonellosis in humans.
These ESBLs are a type of enzyme produced by bacteria that inactivate the molecular structure of cephalosporins, including advanced cephalosporins developed to counteract other beta-lactamases. Specific genes responsible for the presence of these enzymes have been identified.
It would take several issues of BEEF to just scratch the surface of all the data and issues leading to this proposed rule, as well as debating the underlying agendas that may be involved. My goal is to alert you to an impending potential change in our ability to treat systemic disease related to E. coli and Salmonella in cattle.
Scours in calves is still most appropriately addressed through fluid administration and correction of blood acid/base imbalance. But when the gut wall is compromised and bacteria enter the blood, a cephalosporin has been a valuable tool when extralabel requirements have been met.
Management is paramount. Each animal-production segment will face unique challenges as our ability to address E. coli and Salmonella infections continues to erode. Use of some older approved products with significant resistance may actually aid the infection by suppressing competing bacteria.
For calf scours, it's important that diagnostic tests be performed early to identify the pathogen and, if it's bacterial, determine the antibiotic susceptibility profile. In situations where milk replacer is used, talk to your veterinarian before using products that contain tetracyclines or neomycin as there's a good chance E. coli or Salmonella may already be resistant to these drugs and all we'll be doing is eliminating competition for the pathogens.
I've found I must special order milk replacers without these antibiotics included. The same concerns apply to routine use of scour boluses; you'd better know what you're treating.
In beef cattle, it's been demonstrated that paying careful attention to cattle density during calving will aid in reducing scours occurrence. Strategically moving cattle and attention to the calving environment should also be part of your plan. Make sure you're addressing the occurrence of coccidiosis and viral pathogens as these infections damage the gut wall, making it easier for bacteria to invade the blood stream.
This is one more example of where we have the opportunity to plan for a change; those who do will experience the least negative effects. I'd get started.
-- Mike Apley, DVM, Kansas State University