The poultry industry with its modern production lines places great demands on the birds' musculoskeletal system in terms of growth rates for broilers and egg production for laying hens. Any insufficiencies in the birds' nutrition or management will often lead to musculoskeletal diseases, which are normally characterised and diagnosed by lameness. Lameness and gait abnormalities in different poultry species are considered diseases of high significance not only as a result of its welfare implications on birds, but also due to the financial losses to the poultry industry as a result of birds downgrade and increasing birds’ market age.

Efficacy of PoultryStar® for Reducing Lameness in Broilers

Causes of lameness in various poultry species

The incidence of lameness has recently started to increase in poultry for many reasons. For instance, the main cause of lameness in broilers in the 1980s was tibial dyschondroplasia (TD); in the 1990s, the emergence of infectious bursal disease (IBD) with its immunosuppressive nature caused high incidence of bones and joints bacterial infection. A few years later, the removal of meat and bone meal from poultry diets and increasing levels of pollution led to calcium and/ or phosphorus deficiencies. In addition, after the EU ban on antibiotic growth promoters (AGPs) in 2006 (EC council regulation No 1831/2003), incidences of lameness and gait problems have increased.

Many risk factors could be associated with the occurrence of lameness in birds and the condition is usually multifactorial. These factors include birds’ genotype, sex, age, growth rate, body weight and the length of dark periods in the lighting system used. For instance, younger, lighter female birds of slower growth tend to have a lower incidence of lameness than older, heavier male birds, particularly if these birds are subjected to shorter dark periods. Several causes can result in lameness in poultry including viral infections of soft tissues, bacterial infections of skeletal and soft tissues, and skeletal deformities.

Bacterial chondronecrosis with osteomyelitis

The most common cause of lameness in commercial broilers is bacterial chondronecrosis with osteomyelitis (BCO). The term BCO encompasses necrotic degeneration and microbial infection, primarily within the proximal heads of the femur and tibia.

Femoral head necrosis/BCO is caused by bacteria that reach the joints via the blood vessels that penetrate the bones to nourish the bones and the cartilages. The translocated bacteria adhere directly to the cartilage matrix preferably in the growth plates of growing bones, where they are harbored in microfractures.

Figure 1. Stages of proximal femoral head degeneration leading progressively to bacterial chondronecrosis with osteomyelitis (BCO):
1 Normal proximal femoral head; 2 Femoral head separation (FHS: epiphyseolysis); 3-5 Progressive necrosis, ulceration, erosion and fracturing of the growth plate (femoral head transitional degeneration, FHT);
6-8 Perforation, fracturing and necrosis/osteomyelitis of the femoral head (femoral head necrosis FHN).(Courtesy R.F. Wideman)

As the bird's immune system cannot access these microfractures, the bacteria grow rapidly and begin destroying bone minerals (Figure 1). This occurs primarily in the hip joints, proximal femur or proximal tibia. The damage caused by the festering of BCO bacteria leads, first to subclinical lesions and ultimately, if unchecked, to lameness. Certain bacteria like E.coli and Staphylococcus aureus have a special tropism for cartilages and once in circulation, they are very likely to anchor into the cartilage matrix. They can be transmitted from breeder parents, contaminated egg shells or hatchery sources, or enter via the respiratory system or gastrointestinal tract.

How could probiotics have an impact on the incidence of lameness?

Enteric bacteria can translocate from the intestine and migrate into the systemic circulation. Once these bacteria enter the circulation, they can reach the capillaries that irrigate the bones. Probiotics might interfere with the development of osteomyelitis by attenuating intestinal populations of pathogenic bacteria, by improving gut health and gastrointestinal tract mucosal barrier, by reducing bacterial leakage (translocation) across the gut wall and by priming the immune system to better eliminate translocated bacteria. Intestinal protection by means of probiotic supplementation could lead to fewer bacteria reaching the articular surface, thereby reducing the incidence of BCO and subsequently lameness.

Evaluating PoultryStar as a Prophylactic Treatment for Lameness by Using a Wire Flooring Model to Induce Lameness in Broilers

In order to study the development of lameness, a wire flooring model for inducing lameness in broilers was developed by a group of researchers under the direction of Professor Wideman at the Department of Poultry Science, University of Arkansas, USA.

As the incidence of lameness is low in research flocks, the phenomenon has been difficult to study so far, which has hampered efforts to develop measures that may help producers. Growing broilers on wire flooring provides an excellent experimental model for reproducibly triggering significant levels of clinical lameness attributable to osteochondrosis and osteomyelitis of the proximal femur and tibia to enable statistically sound studies. Leg disorders and lameness are commonplace when birds are reared in cages with wire flooring due to high stocking densities and lack of exercise.

The results of a study to evaluate the effect of PoultryStar on lameness were published in the April issue of 'Poultry Science', (R.F. Wideman, 2012. A wire-flooring model for inducing lameness in broilers: Evaluation of probiotics as a prophylactic treatment. Poultry Sci., 91:870-883).

In this study, a series of four independent experiments were carried out to evaluate the efficacy of the host-specific multi-species probiotic PoultryStar as a prophylactic feed additive for preventing the onset of lameness in broilers by using the wire flooring model for inducing lameness in broilers.

PoultryStar is a well-defined, host-specific multi-species synbiotic product that promotes a beneficial gut microflora through the combined action of carefully selected probiotic microorganisms and prebiotic fructo-oligosaccharides. It is designed to improve gut health and increase chicks' resistance to pathogenic infections.

Trial design

Broiler chicks from three different commercial hatcheries were placed at more than 60 birds per pen at one day of age (approximately 690 square centimetres per chick). All chicks received standard hatchery vaccinations for Marek's disease, tenosynovitis and infectious bursal disease virus.

At 14 days of age, the population was reduced to between 50 and 55 of the largest, healthiest chicks per pen (approximately 900 square centimetres per chick).

The day 14 culling protocol was instituted because necropsies of runts during the first 10 days revealed macroscopic evidence of systemic bacterial infection including osteomyelitis.

Feed and water were provided ad libitum. The control diet was a commercial 23 per cent crude protein, corn- and soybean meal-based chick starter (crumbles) formulated to meet or exceed minimum National Research Council (1994) standards for all ingredients.

Birds were randomly allocated to different experimental groups reared either on wood shavings litter flooring (control) or wire flooring and were fed the control feed alone or control feed mixed with PoultryStar at a dosage of 0.5kg per ton during the whole period or used litter.

Lame birds were removed as soon as the onset of lameness was noticed, and were euthanised via carbon dioxide gas inhalation and necropsied. All survivors at day 56 were considered to be clinically healthy. Survivors were euthanised via carbon dioxide gas inhalation and necropsied to assess sub-clinical lesion incidences in the proximal heads of the femora and tibiae. Euthanised birds were necropsied within 30 min post-mortem.

The SigmaStat® ANOVA package (Jandel Scientific, 1994) was used to compare body weight among experimental groups, treatments and genders. For comparisons of lesion incidences, the individual bird was used as the experimental unit, and the SigmaStat Z-test procedure was used to compare proportions.

Results and discussion

Table 1 illustrates a summary of the results of the four independent experiments. Comparing between the Wire-Control groups, the addition of PoultryStar to the control diet significantly reduced the incidences of lameness in all experiments.

Conclusion

The results of these studies demonstrate that the multi-species probiotic PoultryStar consistently reduced the incidence of clinical lameness in broilers raised on wire flooring in four statistically significant experiments.

The most common cause of lameness, bacterial chondronecrosis with osteomyelitis (BCO), may be reduced by administering PoultryStar prophylactically from the first day of rearing.

PoultryStar was shown to reduce the development of clinical lameness by interfering with bacterial translocation into sub-clinically damaged voids or clefts in the proximal femoral and tibial epiphyseal plates. These experiments indicate that bacterial translocation from the gastrointestinal tract is likely to be a significant route contributing to haematogenous infection.

The multi-species probiotic PoultryStar administered prophylactically from the first day of rearing can provide a plausible alternative to antibiotics for reducing the incidence of BCO.

October 2012