Leg Health

Lameness and poor locomotion in broiler chickens can not only affect production performance, but has welfare implications as well. Poor gait scores can negatively affect welfare audits and results in sub-optimal performance. Flocks with good leg health grow to their genetic potential, have better feed conversion rates and result in fewer processing downgrades.

Lameness and poor locomotion in broilers is caused by either non-infectious conditions (ie. bone deformities) and infectious causes (ie. bacteria and viruses) and inadequate nutrition, or a combination of each. Genetic selection has, for the most part, greatly reduced the incidence of non-infectious causes of leg problems. But good barn and bird management can play a large role in the prevention of infectious causes.

Aviagen Group Inc. held a “Science to the Field” seminar on the topic of leg health in mid-April preceding the London Poultry Show in London, Ont. Several renowned speakers were featured and gave their insights from the field and research on leg health, what common problems are seen in the field and how improvements have been made through genetics and how management is key for preventing leg problems caused by infectious agents.

Genetic Improvement
There is growing societal concern that rapid growth rate results in poor leg health, and thus affects the welfare of broilers.

In the past 50 years, the growth rate of broilers has increased 300 per cent due to intense genetic selection.

Dr. Derek Emmerson, vice-president of research and innovation with Aviagen, says that in the past, the focus on genetic improvement was solely on growth, however, leg strength and skeletal structure and integrity became a focus for the company starting in the 1970s. Since the company has such large pedigree population, it allows geneticists to have a large genetic pool to work with and allows for a high selection intensity.

Intense selection led to a great reduction in metabolic diseases such as ascites, and Tibial Dyschondroplasia, a leg deformity. The breeding company employs various systems to identify birds with poor leg health, including the use of x-rays and ultrasounds and assessing gait scores to remove birds with potential problems from the breeding stock.

Anne Marie Neeteson, vice president of welfare and compliance at Aviagen, says that in Canada, the company is fortunate to have access to processing data collected by the Canadian Food Inspection Agency (CFIA), which helps it to determine the incidence of leg problems occurring in the field, which in turn helps it develop selection programs.

Both Emmerson and Neeteson noted that genetic progress does not happen overnight — it takes four years to see improvement and select traits from grandparent stock to see the results at the processor level. “It’s a challenging task, but not impossible,” says Neeteson. A large part of the challenge, says Emmerson, is that selecting traits to improve leg health, metabolic health, liveability, etc. is that the selection does not account for environmental influences.

“Genetics is not everything,” says Neeteson. “A large influencer is being a good farmer.”

Common Leg Problems
Dr. Nick Dorko, Global Head of Veterinary Technical Services for Aviagen, reviewed the common leg problems in broilers.

Rickets, TD

Both Rickets and Tibial Dychondroplasia (TD) result from an abnormality in the formation of bone and the growth plate. Rickets is a disease of young, growing animals while TD is most often seen in broilers greater than 20 days of age. The abnormalities are often associated with dietary insufficiencies of calcium (Ca), phosphorus (P), or vitamin D3, or an imbalance in the Ca:P ratio.

As noted by Emmerson, Aviagen has been selecting against TD and Dorko agrees, saying that he doesn’t see this as having a genetic component anymore, but rather the cause is usually related to feed and/or a gut issue. 

Problems due to infectious agents

Bacterial and viral challenges in the flock due to poor barn hygiene, stress, density, poor feeder and water spacing, poor litter quality, improper ventilation and poor water quality can result in leg problems such as Bacterial Chondronecrosis with Osteomyelitis (BCO), Synovitis, “Kinky Back” (Vertebral Osteoarthritis), and “Green Leg”. 

Bacteria, particularly Staphylococcus aureus, can travel to bone and cause infection if given the opportunity (via scratches, the feet, vaccination). This bacteria is ubiquitous in environments where poultry are hatched, reared, and processed, says Dorko. Reoviruses can cause arthritis and have been implicated as a cause of malabsorption syndrome, which can be an indirect cause of leg problems.

Resolving the cause of leg problems is often difficult because the causes are often multifactorial, he says. He feels that in addition to good barn management and decreasing environmental stress on the birds, the prevention of respiratory, enteric (gut) and immunosuppressive diseases is essential for preventing leg problems.

Prevention and Control

Nutrition

Dr. Mark DeBeer, global head of nutrition for Aviagen, noted that feed formulation problems, although uncommon, can contribute to leg problems. However, factors that can affect malabsorption of nutrients (such as disease and infectious agents) are the primary issue.

He says “some of the things we do that we think increase bone strength really don’t.” It was previously believed that Ca and P were key for promoting bone development and growth rate, however it is now becoming clear that Vitamin D3 is the main driver. “Getting all three of these nutrients at the right ratios and levels in the feed is key for success,” he says.
It’s known that Vitamin D3 can increase muscle growth by increasing breast yield, although how this occurs is not yet known, and it is currently being researched, he says.

Dr. Nick Dorko says that dietary insufficiencies of Vitamin D, Ca and P is usually caused by improper levels in the feed, or a problem with feed handling — feed that is old or has been stored during hot weather can result in the destruction of vitamin D or other fat soluble vitamins. Moulds and fungus can also destroy nutrients, he says. One thing all farms should do, says Darko, is to retain a feed sample from each delivery until the end of the flock so that it can be tested if problems should arise. “It sounds simple, but many people don’t do this.”

Malabsorption of Ca, P or Vitamin  D can be caused by a damaged intestine or decreased liver function, and from a depressed feed intake (either not enough feed is available, or weak birds have resulted from poor brooding management). Indirect causes include diarrhea and digestive issues (resulting from enteric viruses, coccidiosis, poor quality feed), mycotoxins (these can cause liver damage), the wrong form of Vitamin D in the feed (ie. D2 instead of D3).

Both DeBeer and Dorko noted that the improper use of phytase can also be a contributing factor. The function of phytase can be affected by improper application and mixing, matrix values and degradation. 

Lighting

It was once believed that near-continuous light (23 hours per day) was necessary to achieve the growth potential in broilers. However, recent research by Karen Schwean-Lardner and Hank Classen, both with the Department of Animal and Poultry Science at the University of Saskatchewan, has dispelled this myth and has shown that a reduction in the hours of light per day will still promote growth while keeping the health and welfare of the birds in mind. 

Schwean-Lardner and Classen examined the growth and welfare performance of broilers raised under four different lighting programs: 14L:10D, 17L:7D, 20L:4D, and 23L:1D, beginning at seven days of age. All of the birds were raised using 23 hours of light for the first seven days.

Performance data showed that providing more hours of darkness compared to near-continuous light slowed early growth, but resulted in market growth rates as good or better than near-continuous lighting. Of the four lighting regimes, birds raised using the 20L:4D had the best growth performance at market age and similar to the other programs using longer dark periods, resulting in improved health and welfare.

Compared to near-continuous light, providing a longer dark period resulted in improvements in economically important traits, such as: improved feed conversion, improved growth rates, and a reduction in mortality, particularly mortality resulting from metabolic and skeletal issues.

This research is now part of an Aviagen technical document for producers “Lighting for Broilers”, which is available on Aviagen’s website.

Brooding Management
Dr. Stew Ritchie of Canadian Poultry Consultants Ltd. in Abbotsford, B.C., concluded the day with a discussion of the Platinum Brooding® program, which he developed with his business partner Dr. Bill Cox to help poultry producers give their flocks the best early start, thereby preventing issues that can affect performance, including leg problems.

As noted by other presenters, failures during the brooding period can have significant consequences on bird health and performance. The program provides hands-on training for producers on brooding practices and disease prevention, and has been so successful that Aviagen has now partnered with it to provide the program across Canada in the coming year, as well as offering the course for U.S. producers with the University of Georgia.

Ritchie says that optimal brooding establishes steady state eating patterns early, which improves performance parameters, which significantly benefits animal welfare and food safety as well.