Aonghus Lane MVB MRCVS PgCert. Applied Poultry Science Cert. DHH, Resident student at the European College of Poultry Veterinary Science (ECPVS) St David’s Poultry Team
Lameness in broilers is generally the result of infectious agents, such as bacteria and viruses, or developmental issues, such as rickets, tibial dyschondroplasia, or angular limb deformities. With growing pressure on commercial broilers to achieve low FCRs and high average daily gains, the pressure on the birds’ bodies to maintain homeostasis (harmony of the bodies different systems) can be immense.
While enterococcus lameness is not a new development in commercial broilers, it appears to have increased in prevalence in recent years. The most well-known form of enterococcus infection in broilers is Enterococcus caecorum, which induces a very typical clinical sign of bilateral leg paralysis, where the bird appears to “dog sit”. It is the authors experience that while enterococcus caecorum is still prevalent, other types of enterococci are now more regularly implicated in lameness. Co-infections with E. coli are also common as is the presence of reovirus, with the question arising which has come first enterococcus or E. coli / reovirus.
The question is how the bacteria gets from its normal habitat in the intestinal tract to joints, bones and internal organs of the body?
Enterococci are normal commensals (inhabitants) and/or transient residents of the intestinal tract of birds (Kense & Landman, 2011). When probiotic formulations of enterococcus are fed, they reduce the numbers of pathogenic E. coli and clostridial bacteria (Cao et al, 2013), pathogen associated systemic infections and gut health related problems. This supports the evidence for a positive role for enterococcus in poultry gut health.
If we look at the digestive tract of the chicken its main role is in the digestion and absorption of nutrients, and to achieve this function there is a vast network of blood vessels which facilitate the uptake of nutrients for transport around the body (Awad et al, 2017) but it also acts as a delivery system for immune cells and nutrients for protection and nourishment of the cells which form the digestive tract. This intimate relationship between the digestive tract and its blood supply is a likely route of enterococcus spread around the body. During periods of stress or digestive upset, the cells lining the digestive tract can lose their integrity leading to breakdown of the tight junctions which link each individual cell together, or if the insult is great enough it can lead to cell death. This in turn will lead to a breakdown of the primary defence barrier of the intestinal tract and translocation of bacteria into the vascular network (Awad et al, 2017). This sets in motion a cascade of events which leads to a bacteraemia (bacteria in the blood), settling of bacteria throughout the body in capillary networks (tiny blood vessels with sluggish blood flow) and seeding of various sites with bacteria. If the bird’s immune system is compromised or if the infective load of bacteria is too great it can lead to the establishment of an infectious process which can present as lameness.
So, how do we avoid this “gut leakage” and lameness development?
• Avoid compromising chicks
Stress in our birds can lead to a reduced effectiveness of the tight junction which bind the cells lining the gut (Awad et al, 2017). Issues such as overheating, or chilling of chicks can lead to stress which can at this very early-stage lead to gut leakage. Inappropriate feed and water intakes in the early brooding stage can also lead to increased stress in the newly hatched chick.
• Establish a healthy gut flora
The gut flora or microbiome is the population of microorganism which inhabit the intestinal tract and are responsible for its healthy functioning. The use of pre and probiotics, competitive exclusion products and organic acids can help speed up the development of a healthy gut flora or its reestablishment after a challenge.
• Coccidiosis control
Coccidiosis leads to damage of the cells lining the intestinal tract, resulting in malabsorption of nutrients, which in turn can lead to a change in the gut flora as a result of excess nutrients remaining in the tract. This can lead to overgrowth of inappropriate bacteria. All of which effects the integrity of the gut leading to leakage of bacteria into the blood, and establishment of a bacteraemia and thus infection. Effective coccidiosis disinfection at intercrop to reduce challenge is critical as is maintenance of good environmental conditions in the poultry shed.
• Control of immunosuppressive viruses
Infectious Bursal Disease Virus, or Gumboro Disease as it is more commonly known, is a major cause of immunosuppression in young chickens. Effective control can be achieved with a strategic vaccination programme, provided vaccine handling and administration is carried out to the recommended standard.
• Clean water
The importance of clean water is a critical piece in the care of all types of poultry. Commercial broilers can drink anything from 1.8-2 times as much water in comparison to feed, so one could argue water is twice as important. Poor water quality can lead to ingestion of bacteria which can upset the microbiome. The composition of water is also important as excess levels of minerals, chemical elements and heavy metals can also lead to gut flora disruption and digestive upset. A robust water sanitation and monitoring system is a must.
• Cleaning and disinfection
The use of effective disinfectants at intercrop to reduce bacterial and viral loads of the house and its equipment is critical. Strict adherence to dilution rates and application procedure as per the manufacturers guidelines is vital. Whole house fumigation allows areas which are difficult to reach with disinfectants to be targeted after initial disinfection. Monitoring of the cleaning and disinfection procedure should be undertaken to assess its effectiveness.
While translocation of enterococcus from the intestinal tract is believed to be one route in the development of enterococcal lameness, infection via the respiratory tract is also suspected. With focus on reduction of footpad dermatitis through the maintenance of dry litter and environmental conditions, this can lead to dustier environmental conditions containing high levels of enterococcus which are inevitably inhaled by the birds (Jung & Rautenschlein, 2014).
Original written for Poultry Business magazine