*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Kamuela, Hawaii. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected]
BROILER lameness is one of the top economic and animal welfare issues facing the modern broiler industry.
Despite improvements in nutrition, health and genetics over the past decades, too many flocks end up with birds that are partially or completely immobile, according to Dr. R. Mitchell, vice president of technical services for Perdue Farms Inc.
Mitchell presented his perspective on broiler lameness in the U.S. during the Australian Poultry Nutrition Symposium in February.
Mitchell said the incidence of birds with leg problems has been estimated to be between 2% and 6%. A recent large study in the U.K. found that more than 27% of birds, on average, had poor walking ability, and 3.3% were considered clinically lame. It is hard to infer the same level of leg problems for the U.S. broiler industry, however, due to the many differences in management, genetics and environmental issues between the regions.
Mitchell's presentation looked at the current status of both infectious and non-infectious leg problems in the U.S. and explored how integrators have changed their perspective from leg problems being a production-related issue to a welfare issue.
Rickets is the classic nutrition-related leg problem. Most cases of field rickets are due to some error in feed manufacturing. Clinical rickets is not common in the U.S. due to improvements in nutrition and feed manufacturing.
The incidence of subclinical rickets is difficult to assess but still periodically appears with little or no specific cause. Subclinical rickets has been linked to other conditions such as femoral head necrosis, osteomyelitis, bone fractures and other lameness-related problems.
In Mitchell's experience, subclinical rickets is often associated with "soft bones," which are normally observed around two to three weeks of age and are detected on routine health surveys. These cases do seem to respond to water-soluble vitamins, and Mitchell has hypothesized that it is related to fat-soluble vitamin absorption. Some poultry companies that are using coccidiosis vaccines routinely use water-soluble vitamin D as a preventive for rickets and soft bones.
Phillips et al. has suggested that the phosphorus requirement from 0 to 10 days of age in current commercial strains of birds may be much higher than the National Research Council bulletin recommends or the industry is currently using.
Tibial dyscondroplasia (TD) is a lesion characterized by a mass of avascular cartilage in the metaphysis of the proximal end of the tibiotarsus and tarsalmetatarsis. TD has long been associated with fast-growing broilers. The condition was once considered the major cause of lameness in broilers.
Genetic selection, with the use of a lixiscope, has greatly reduced the incidence of TD. TD is frequently associated with other deformities such as valgus-varus and rotated tibia.
Valgus-varus deformities (VVDs) — tibia rotated out or in, twisted legs or spraddle legs — are an angular deformity of the long bones. Primary breeders have selected against VVDs through various methods; however, VVD is still common in many U.S. broiler flocks.
Varus may be observed early (less than two weeks of age), usually due to the displacement of the gastrocnemius tendon. Varus observed at this age may be related to incubation or early chick handling.
Valgus is a more common condition and occurs later in the growout cycle, normally starting at around five to six weeks of age. The valgus condition worsens with age. Bone mineralization has been found to be low in severe VVD limbs.
Rotated tibia is frequently included with the VVD condition but has a different pathology. Rotated tibia is sometimes seen in conjunction with other leg problems such as TD and bacterial chondronecrosis, which points to some common link such as nutrition, malabsorption or genetics.
Mitchell noted that VVD, including rotated tibia, is the most common form of non-infectious lameness in broilers based on his experience and is exacerbated by heavy weights. Mitchell suggested that visiting the thigh and/or drum deboning line of a large bird processing plant is a good way to gauge how much VVD is present.
Bacterial chondronecrosis (BOC), frequently referred to as femoral head necrosis, is probably the most common cause of lameness in the U.S. broiler industry today, according to Mitchell.
BOC is thought to be initiated by a micro-trauma to poorly mineralized columns of cartilage cells in the proximal growth plates of the leg bones. The condition normally starts to develop clinical signs after five weeks of age and becomes worse as the birds add more weight.
The incidence of BOC has increased with the increase in average bird size in the U.S. broiler industry. A major portion of the U.S. broiler industry produces birds for deboning plants that approach or exceed 4.0 kg liveweight. Most of these flocks are grown as straight-run birds, so many of the males will exceed 4.5 kg (9.9 lb.).
Dr. Wideman of the University of Arkansas, using the wire floor model, has developed theories on the role of stress and immunosuppression in the development of BOC. It is thought that bacteria translocate from the gastrointestinal tract or respiratory system and settle into the areas of the growth plate with poor blood flow. This model has suggested new research into preventive strategies for BOC.
Kinky back (spondylolisthesis) emerged as a disease of importance in the U.S. in 2008. Affected birds become completely lame and are unable to access feed and water. This condition is associated with an abscess in the free thoracic vertebrae (T4). Enterococcus cecorum is normally isolated from the abscess, although species of staphylococcus are frequently present. The only treatment is culling.
Mitchell said, in his experience, kinky back frequently repeats on the same farms and in the same houses. The industry has combated this problem by increasing layout time, using between-flock cleanout or composting litter and disinfection. The kinky back seen in flocks today is not the same as the classical genetic condition that carries the same common name.
Tenosynovitis, viral arthritis caused by reovirus infection, has been relatively rare in broiler flocks over the past 15 years, and broilers are not frequently vaccinated for the common strains of reovirus. Recently, a novel strain of reovirus emerged in the U.S. broiler industry, and available strains of vaccine are not providing protection, according to Mitchell.
Mitchell noted that until this past year, he personally has had very little experience with reovirus in broiler flocks. One Perdue Farms operation reported severe leg problems, including soft bones and legs that were completely stuck out to the side. In the worst-affected broiler flocks, up to 40% of the birds had to be culled. The affected flocks were traced back to specific breeder flocks in one area.
Affected breeder flocks shed the virus for six to eight weeks, normally around peak production, and no clinical symptoms are present in the hens.
Other integrators in the same area experienced a similar problem a few months earlier.
Economic losses in the affected broiler flocks are large as a result of increased mortality and plant condemnations. Some integrators have started moving chicks from breeder flocks identified as reovirus positive into small bird programs to limit the losses.
One reason for the lack of large-scale studies of lameness is the difficulty in measuring lameness. The five-point scale (0-5) gait score has been widely used and reported in studies in the European Union. In this system, a score above three is considered lame.
The National Chicken Council welfare guidelines (2010) have a simpler three-point scale (0-2) and account for the observation that even perfectly normal broilers may appear ungainly. These methods may work well for a research program when looking at individual birds, but in Mitchell's opinion, in large-scale broiler production, these are not very good methods to assess the flock's overall leg health.
A recent publication from Spain (Marchewka et al., 2013) demonstrated that transect walks through the broiler house hold good potential as a routine monitoring tool.
Mitchell stated that his company routinely uses a similar method to assess lameness incidence in production houses. In this method, the number of birds affected by different categories of lameness are counted while walking a specific designated route through each house. Mitchell feels that this method is more accurate and practical than doing gait scores on a small sample set of birds.
Many broiler integrators have changed their perspectives on lameness over the last 10 years from being concerned about how many birds are being lost to leg problems (economic loss) to the impact on overall bird welfare and product quality.
Mitchell said his company has been on the forefront of animal welfare in the U.S. and was the first broiler company to receive Humanely Raised Process Verified Program approval from the U.S. Department of Agriculture.
Mitchell went on to note that Perdue has learned a lot from the acquisition of a smaller company that specializes in the production of organic and antibiotic-free chickens. This company complies with some of the most rigid welfare practices in North America.
These practices include growers keeping detailed records of birds culled for leg abnormalities and performing leg assessments at key times during the flock. Daily culling of lame birds using proper euthanasia techniques is not only encouraged; it is required as a part of the grower contract, and growers that do not comply risk losing their contract.
Most, if not all, integrators encourage euthanizing lame and unthrifty birds. It is in their best interest since these birds will typically end up being condemned in the processing plant.
The act of culling lame birds, however, can be tedious and difficult. The average age of poultry growers continues to rise, and the physical demands of culling older birds can be taxing. Also, since lameness frequently develops in the last weeks prior to marketing, many growers may see culling as reducing their profits.
This reluctance to cull is not limited to the U.S. In a large-scale assessment of lameness in U.K. broiler flocks, Knowles et al. noted that more than 3% of the birds classified as lame, according to the U.K. gait assessment method, were allowed to persist in the flock despite strict protocols for culling birds that rate at a gait score above three.
Lighting (photoperiod, intensity and wavelength) is one of the most important yet poorly understood aspects of poultry husbandry, according to Mitchell. Many top growers closely guard their lighting program, even locking the control box to protect their "secret."
Recent work by Dr. Clawsen's group at the University of Saskatchewan has demonstrated the effect of reduced photoperiod on performance and leg abnormalities. Reduced light periods of 14 and 17 hours were found to significantly improve gait scores and infectious related issues versus 20 and 23 hours.
The most basic light program for many growers is 23 hours of light to one hour of dark. Many poor-performing farms actually perform better on this type of program. However, Mitchell said his company had recently implemented programs with longer dark periods and believes benefits were seen in both welfare and performance. Many growers are implementing the dark period at night so sunlight doesn't illuminate the house through the ventilation system.
Light intensity has been shown to have lesser effects on welfare than photoperiod. However, the U.S. industry, as a whole, believes that there are benefits of lower light intensity (one to five lux) after brooding. Much of the U.S. industry has adopted enclosed housing in order to improve environmental control. Increases in infectious process in the processing plant and the resulting downgrades have driven growers to reduce light intensity, according to Mitchell.
He further stated that while he has little evidence that reducing light intensity affects leg health, it does make it difficult for growers to interact with and assess their flocks. Mitchell said his company welfare program requires light intensity in the broiler house to be bright enough to read a newspaper. This provides enough light to observe the flock.
Work from North Carolina State University showed that incubation temperature and chick transport stress negatively affected the incidence of leg abnormalities such as twisted legs and crooked toes.
Chicks are frequently in holding rooms for several hours prior to placement. Producers should routinely monitor rectal temperature during holding and transport to determine if overheating is occurring. The importance of proper chick transport is still an overlooked area, according to Mitchell.
As previously noted, translocation of bacteria from the gastrointestinal tract or respiratory system is thought to be a major contributor to BOC. Wightman found that a probiotic regime significantly reduced the incidence of BOC in the wire-floor model.
Many integrators in the U.S. still routinely use antibiotic growth promoters. A few companies, including Perdue, have removed all growth-promoting antibiotics from their broiler feeds and treat flocks only when they become ill. Preventive therapies, such as probiotics, yeast cell wall and other "natural" products, are now frequently used in feeds, but there is general confusion about their actual effects.
Broilers have been developed to consume feed and grow fast. Lameness is frequently cited as having a direct link to fast growth. While it is true that many slow-growing breeds have fewer leg problems, Mitchell noted that many faster-growing flocks have few lameness issues, and many slower-growing flocks have more lameness issues.
Many restrictive-feeding techniques have been tried, and early restriction has shown some success in reducing lameness issues. Feeding a low-nutrient density diet also may reduce overall leg problems, but the result is a loss in key economic drivers like feed conversion and yield.
A group from the Welfare Quality project (www.welfarequality.net) has published a feeding regime to eliminate lameness in broilers by feeding a rotating cycle of high-protein/low-energy and high-energy/low-protein diets.
Mitchell remarked that while he has not tried this approach in the field, other approaches have shown little or no evidence of improvement in lameness unless the restriction is so severe that it dramatically reduces bird performance. Mitchell said he feels that controlling photoperiod is much more practical and effective in reducing leg problems than quantitative or qualitative feed restriction.
The Bottom Line
Lameness continues to be a major productive loss to broiler producers and compromises the welfare of the birds.
Improvements in nutrition, health, management and genetics have reduced the incidence of many types of leg problems. A comprehensive approach that includes all of these areas is essential to reducing lameness in broilers. A comprehensive approach must include the poultry grower because removing broilers before they become a welfare problem is critical.
The annual meeting of the Australian Poultry Science Symposium is organized by the Poultry Research Foundation of the University of Sydney and the Australian Branch of the World's Poultry Science Assn.
Fifty-two technical papers were presented, highlighted by eight invited speakers from exceptional international organizations, including The Ohio State University, The Hebrew University of Jerusalem in Israel, John Black Consulting in Australia, Schothorst in the Netherlands, the Universiteit of Leuven in Belgium, USDA's Agricultural Research Service, Purdue University and Perdue Farms Inc.
This year marked the 25th anniversary of the symposium. In recognition of this milestone, a special welcome session was held. I attended the meeting this year and was surprised and humbled when I heard Dr. D. Balnave mention my name while presenting a history of the Australian Poultry Science Symposia at the welcome session.
"The international status achieved by the (symposium) was shown by the comments of the respected journalist William A. Dudley-Cash writing in the U.S. magazine Feedstuffs in April 2001," Balnave said. "He stated, 'One of the most outstanding poultry science symposiums is sponsored by the Poultry Research Foundation of the University of Sydney and the Australian Branch of the World's Poultry Science Assn.'" Indeed, it is one of the best.
Proceedings of the symposium may be found at http://sydney.edu.au/vetscience/apss/proceed.shtml.
Marchewka, J., T. Watanage, V. Ferrante and I. Estevez. 2013. Poul. Sci. 92:2588-2599.
National Chicken Council. 2010. Accessed at: www.nationalchickencouncil.org/wp-content/uploads/2012/01/NCC-Animal-Welfare-Guidelines-2010-Revision-BROILERS.pdf.
Wideman, R. Jr., K. Hamal, J. Stark, J. Blankenship, H. Lester and K. Mitchell. 2012. Poul. Sci. 91:870-883.