– Dr. Michelle Arnold, UK Veterinary Diagnostic Laboratory
Most KY-born calves leave the farm and enter marketing channels, usually through auction markets, into stocker and backgrounding operations. Not surprisingly, late fall and winter are difficult seasons to keep feeder calves alive in KY due to major health challenges. Weather is just one of many risk factors that play a role in Bovine Respiratory Disease (BRD) or “Shipping Fever” development. Most auction market calves are sold as “high risk calves”, meaning they are lightweight (≤ 500#), young (estimated 6-8 months), unweaned (or abruptly weaned on the trailer on the way to the yards), unknown health history, never or poorly vaccinated and most are trace mineral (copper and selenium) deficient. At the auction barn, they are mixed or “commingled” with similar weight calves from multiple farms then sold, allowing respiratory “bugs” to spread prior to delivery to the stocker/backgrounder facility or feedlot. After arrival and a brief rest period, these calves are usually processed through the chute and receive multiple vaccines, deworming, are implanted and the bulls are castrated. These calves will typically break with respiratory disease within the first 2 weeks after arrival and require at least one antibiotic treatment. It is estimated that 60-70% of calves marketed through sale barns are considered at high risk for disease.
Over the last few years, the bacterium Histophilus somni (formerly known as Haemophilus somnus) has emerged as the major bacterial pathogen responsible for the rapid development of disease and death in feeder operations. While Mannheimia haemolytica, often referred to as “Pasteurella”, has traditionally been the most important bacterial species in “shipping fever” bronchopneumonia, Histophilus somni (HS) can cause similar disease symptoms but is proving very difficult to treat and control with traditional methods. Unlike typical BRD outbreaks that peak at 14 days after arrival to the stocker or backgrounding facility, “histophilosis” cases start at 3-4 weeks on feed. “Somnus” is normal flora in the upper respiratory tract and survives on mucosal surfaces in “biofilms”, a jelly-like matrix that serves as protection from antibiotics and the host immune system. Viruses and stress can trigger bacteria to leave the biofilm and enter the lungs. From there it can travel via the bloodstream to joints, other organs (especially the heart), and to the brain. The disease can happen anytime in any season, but most clinical cases occur between October and January. Previously, disease due to “Somnus” was found primarily in Northwestern and Midwestern states in the USA and Canada but cases are now being diagnosed throughout the US, including Kentucky. Most comprehensive studies have been conducted in Canada where histophilosis accounts for an estimated 40% of the death loss in feedlots.
The Histophilus somni Disease Complex (HSDC) is a term used to describe the disease when “Somnus” reaches the lungs and extends systemically to the brain, heart and joints. Components of the HSDC include:
- Rapidly Fatal Pneumonia: Some animals with “Somnus” pneumonia are simply found dead due to lung damage called “severe fibrinous pleuritis”. This is a common finding in western Canadian feedlots and is seen 30-90 days after arrival. The lungs are usually the only organ affected and are found covered in a thick sheet of fibrin, a tough protein substance composed of long fibrous threads, while the lungs themselves are collapsed underneath.
- Bronchopneumonia: Some calves with “Somnus” develop typical signs of BRD including depression, off feed, cough, excessive nasal discharge and difficult or rapid breathing. Respiratory signs with fever of 104°F or above confirms the diagnosis of BRD but detection of the bacteria and/or viruses involved must be done at a diagnostic laboratory. Treatment is often very difficult and unrewarding in the field when “Somnus” is involved because it can hide within neutrophils and macrophages that normally destroy bacteria. In the laboratory, the “Somnus” bacterium is usually susceptible to many antibiotics.
- Heart Muscle damage: “Somnus” can cause a “necrotizing myocarditis” when it localizes in the muscles of the left ventricle of the heart. Death can be rapid with no previous signs (similar to a heart attack) or chronic heart failure leads to “poor doers”.
- Thrombotic meningoencephalitis-myelitis or “TME”: This is a disease of older calves and yearlings that affects the brain. During an outbreak, individual cases occur sporadically in separate pens in a feed yard. Signs include depression, fever, blindness, down and death; this can look like signs seen with polioencephalomalacia or “brainers”. Treatment with antibiotics is most often ineffective.
- Other Manifestations: Arthritis with joint swelling, laryngitis and middle ear infections with drainage from the ear canals may also be seen, similar to Mycoplasma bovis infections.
Diagnosis of Histophilus somni disease in a live calf is challenging because it is present in the upper airways of both healthy and diseased calves so swabs taken from deep in the nose will not necessarily tell the story of what is causing disease in the lungs and elsewhere. “Somnus” is difficult to grow in the laboratory, especially if the calf was treated with antibiotics, so the PCR assay is strongly recommended in addition to culture for detection. Mixed lung infections with other disease- causing bacteria such as Mannheimia haemolytica and Pasteurella multocida can easily overgrow Histophilus somni on a culture plate so the identification may be missed when relying on traditional bacterial culture methods alone. Culture is still necessary to identify which antibiotics should be effective. Unfortunately, the transfer of genetic elements that causes multi-drug antimicrobial resistance to develop in Mannheimia haemolytica is also now found to be operating in Histophilus somni.
As a buyer, what can you do when it seems like the odds are stacked against good health? First and foremost, remember that respiratory disease is no longer concentrated within the first two weeks on feed but outbreaks may develop throughout the first month or more. “Metaphylaxis”, the practice of mass-medicating all individual calves in a group with a long-acting antibiotic on arrival, is highly effective for reducing early BRD morbidity and mortality in high-risk calves by up to 50%. After one antibiotic is used up front for metaphylaxis, treatment protocols typically consist of a 2nd antibiotic for first pulls, a 3rd antibiotic for the next treatment and possibly a 4th antibiotic for a final treatment before calling the calf a “chronic” and treatment is stopped. Research has shown that at each retreatment, the BRD bacteria become more resistant to multiple antibiotics and response rates decline. To make these antibiotics effectively last throughout the first month on feed, it is important to understand and observe the antibiotic’s “post-treatment interval” or PTI. This interval is the time when an effective antibiotic is already in the calf and the treated animals are not eligible for retreatment until the end of the interval. All the upper tier antibiotics, including Draxxin®, Excede®, Baytril®, Zactran®, Zuprevo®, Micotil®, Advocin® and Nuflor®, easily have a 5 to 7-day PTI. During the PTI, the antibiotic suppresses and delays disease onset while the calves are acclimating to their new environment. Instead of focusing on BRD detection and pulling new cases during the PTI, the focus is shifted to adapting the cattle to their new environment, feed, social structure, and daily activity. Conversely, by shortening the treatment interval and becoming overly aggressive with retreatments, the antibiotics are essentially used up by the time Histophilus somni shows up.
Prevention of histophilosis is difficult. This is not a disease complex managed through a needle. There are older “Somnus” vaccines available but they are not considered effective under field conditions except they may help lessen the severity of the brain form of disease. Biosecurity and biocontainment practices must be followed. Stress plays a major role in disease through immunosuppression so excellent nutrition and management are critical. Control should begin with minimizing well-recognized factors predisposing to BRD:
- Make your arrival pens comfortable. In an article by Chad Engle from the US Meat Animal Research Center about transitioning calves to the feed yard, he wrote, “I like to think of our feed yards as five-star hotels. Once these calves step into our “hotel”, they should be greeted by knowledgeable handlers, fresh feed, clean waterers and clean pens. We never put new calves into pens that do not have fresh hay and ration in the feed bunks. It is our job in the feed yard to show those calves that the feed yard is the best place on earth for them to be.” Keep the feeding area clean and free of standing liquid manure. Good sanitation, especially regularly cleaning and sanitizing waterers, feed bunks and working chutes is imperative not only at arrival but throughout the backgrounding period.
- Give them some bunk space! Transitioning to confinement and learning to eat from a bunk means smaller calves don’t get as much access to feed. Extra bunk space is often overlooked but incredibly important. In some studies, simply providing plenty of space for all calves to eat without having to fight for a position at the bunk has proved as effective as treatment with antibiotics for prevention of disease. Furthermore, don’t make calves clean the bunk before you offer additional feed. Moldy, musty, hot, wet, manure- or urine-contaminated feed is not going to be eaten and should be promptly removed. Water contaminated with manure will not be consumed, either. Calves that don’t eat and drink will get sick, guaranteed.
- Don’t push calves on feed too fast. These calves are transitioning from a diet of predominately grass or forage to a new diet of grain offered in a bunk and hay. Too much grain too quickly results in subacute acidosis which throws them off feed. Once again, calves that don’t eat will get sick, guaranteed.
- Get trace minerals in them. Cattle with extremely low blood concentrations of the trace elements selenium and copper have difficulty fighting any disease challenge. An injectable trace mineral supplement (such as Multimin 90®) is a short-term solution to boost the copper and selenium levels during the initial arrival period. However, it is very important to quickly get calves consuming an energy and protein dense diet with vitamins and minerals added to meet their high nutritional needs.
- PI test calves as soon as possible. A BVD-PI calf is born with the BVD virus and sheds virus everywhere it goes for its entire life. Identification and removal of PI calves is critical to stop the spread of BVD virus to other calves and avoid a BRD wreck. The BVD virus attacks the immune system where it destroys the production of disease-fighting white blood cells causing severe immunosuppression. Secondly, the virus works cooperatively with other respiratory viruses to make them more aggressive and deadly. This combination attack results in substantial respiratory disease and death loss in the stocker/backgrounder industry.
- Do not pen new arrivals next to calves that were purchased last week! That load purchased last week is likely rapidly spreading bacteria and viruses from calf to calf and these bugs can easily transfer across the fence into the noses of new arrivals. Try to load your farm with calves as quickly as possible rather than buy a load every week for 4 weeks and combine them in same area. This is a sure-fire recipe for disaster.
- Keep feed bunks and watering troughs clean. Feed bunks and watering troughs are known areas for disease transmission. Keep sick cattle, especially chronic pneumonia calves that haven’t responded to treatment, away from healthy calves and manage their feed and water separately. Do not allow nose-to-nose contact between sick pens and healthy pens. Calves with swollen joints should be placed in pens with deep bedding, plenty of room and easy access to feed and water.
- Consider delaying or minimizing vaccination for respiratory disease and delaying castration of bulls until through the transition period. Vaccination is probably the most misunderstood practice utilized in feeder calf management. Antibodies need to be in place before exposure to disease-causing organisms, similar to car insurance must be purchased before a car wreck to be of any use. Many producers have unrealistic expectations that full protection from respiratory disease is in place once a vaccine is given on arrival. Mounting an immune response (making antibodies) is not “free” but takes energy and protein resources at a time when calves have limited feed intake. If you have concerns that newly purchased calves are at high risk to get sick, it has been proven that delaying vaccination with a modified live (MLV) 5-way respiratory virus vaccine for 1-2 or even 3 weeks can be done without affecting the morbidity and mortality rate. In other words, waiting until they are stronger will not result in more sickness and death than you would have had anyway. As a matter of fact, it may help keep them eating and drinking better without the vaccine-induced fever. Same with castration; delaying until through the transition along with using pain medication at the time of castration (such as Banamine Pour-On®) will lessen the negative immune system effects.
- Buy preconditioned calves when possible. Buying preconditioned calves that have been weaned for at least 45 days and vaccinated for respiratory diseases prior to weaning (especially BVD) and dewormed will help decrease, but does not eliminate, the potential for sickness and death loss.
In summary, incoming high-risk feeder calves require extra vigilance to avoid excessive sickness and death loss. Excellent nutrition and management are critical to reducing the stress in new arrivals. Due to Histophilus somni emerging as a primary pathogen in BRD, there is a need to preserve antibiotic efficacy throughout a longer arrival period of 30 days instead of 14. By observing a 5-7 day post-treatment interval after administration of an antibiotic, less resistance will develop and this allows the immune system to do its job most effectively. Consult your veterinarian for treatment protocols best suited for your operation.