Etiology and control of leg problems in broilers

Leg problems occur to a varying extent depending on various bird-related factors. For modern meat-type birds, such as broiler chickens, the problems can become very complex as the birds gain weight faster than they can build their bone structure to support that weight.

Both sexes can have leg problems, but male chicks encounter more problems than female, as indicated by the higher gait score, i.e., reduced ability to walk on a surface due to pain, biomechanical problems or both. At the age of 4 weeks the chickens could still run well but by 7 weeks they ran poorly. The speed at which the chicks deteriorated between weeks 4-6 was greater than that between weeks 6-7.

Effects of incubation conditions

Eggs stored for too long (10 days or more) before being set in the incubator can lead to an increase in the number of crippled and weak chicks. Eggs incubated with insufficient moisture are also more prone to hatching chicks with lameness or other leg problems. Raising the temperature of the eggs by just 1°C, from 37.5°C to 38.5°C, on embryonic days 4-7, can also influence the growth of the long bone in the chick leg.

Temperatures greater than 37°C should therefore be avoided to ensure optimal bone development at hatching. It should be noted that any leg disorders in young poultry may be genetic. This means that if lame birds are treated and used in breeding programmes, it is likely that their offspring will have issues, too.

Housing management

Floor surfaces should be covered with litter materials, such as pine shavings, chopped straw or peanut hulls, to give the birds a good footing and traction. Materials like corn cobs or sawdust should not be used as they become packed down and mouldy when wet. Birds on wet litter tend to develop tender footpads, swollen hocks and breast blisters with dermatitis.

Housing should not be mounted on slippery surfaces or the birds will have straddled or splayed legs. Once they get to this point, the problem is almost impossible to correct. Crowding at feeders and water troughs should also be avoided as this tends to put the birds’ legs under undue stress and cause a variety of hock disorders.

High temperature is often associated with an increased incidence of leg disorders, particularly at a high stocking density. The lighting system used in poultry houses also affects bird leg health and well-being. With intermittent lighting, the proportion of chicks with leg problems will be smaller.

Nutritional factors

Studies have shown that excess protein content in feed, especially animal protein, leads to impaired purine metabolism in the body. This results in the conversion of purines into large amounts of uric acid and urates which are then deposited in internal organs and joints. This leads to swelling and deformation of the toes and leg joints, resulting in lameness. Therefore, managing dietary energy and protein intake during broiler growth is crucial to meet growth needs and prevent leg disease.

Calcium and phosphorus play a vital role in healthy bone growth. A deficiency of these elements can lead to chondroplasia or osteoporosis, thereby causing a variety of leg disorders in chickens. The optimal ratio of calcium to phosphorus in broiler chicken starter and grower diets is about 2:1. The utilisation of calcium from different sources in the diet is relatively high in broilers, while phosphorus is usually present in the form of phytate phosphorus, resulting in a low utilisation rate. Therefore, non-phytate phosphorus sources are usually considered for inclusion in diets. This will increase plasma phosphorus concentrations and also increase tibial ash and phosphorus content in the tibia.

Vitamins are also necessary to prevent leg disorders. A deficiency of vitamin B6 can affect the structural integrity of collagen in the bone matrix and alter fracture strength. Vitamin D deficiency in the diet can reduce the absorption of calcium and phosphorus and lead to chondroplasia and rickets. Vitamin E has strong antioxidant properties, which helps maintain normal muscle structure and peripheral blood vessel function. Thus, a deficiency in vitamin E can lead to muscle dystrophy, resulting in impaired mobility and an increased incidence of leg deformities, particularly lateral or medial deviation of the distal tibia or proximal talus.

Strict control of mycotoxins in poultry feed is a key measure in reducing leg problems in chickens. Mycotoxins cause skeletal disorders, such as rickets, due to their toxic effects on the liver and kidneys, thereby preventing the conversion of vitamin D3 and its absorption. Feed storage at the right temperature and humidity, control of insects in feed and chemical treatment using formic acids, are all effective means of controlling mycotoxins, preventing leg disorders and other health-related issues in hens.

Effects of viral diseases

Mycoplasma synoviae is an important pathogen in the poultry industry leading to synovitis, as well as diseases of the respiratory tract. Similarly, retroviruses, including avian leucosis viruses, make a significant contribution to leg problems through the infiltration of myelocytes in the leg bones and periosteum of the ribs.

Staphylococcus aureus is another pathogenic strain causing leg problems, such as bone and joint infections, which compromise bird welfare and cause economic losses due to downtime, reduced productivity and carcass contamination in the slaughterhouse.

The following biosecurity programme is recommended for the control of viral infections:

• Limitation and control of access to poultry flocks
• Pressure washers, brushes, hoses, water and disinfectant
• Cleaning and disinfection of crates, containers, laying cages and feeding equipment, before and after use
• Cleanliness of farm and surroundings
• Keeping wild birds, dogs, cats, rodents or other livestock away from poultry buildings and feed stores
• Supply of only clean, fresh drinking (potable) water to birds
• Proper disposal of damaged eggs, dead birds, litter and manure
• Particular focus on hatcheries and proper egg handling

Parasites and leg problems

Studies have shown that infection with Eimeria spp., an intracellular protozoan parasite, causes disruption of the intestinal environment and an imbalance in homeostasis. This can lead to the multiplication of pathogens and result in coccidiosis which increases susceptibility to leg disease in chickens. Vaccination, good management practices and treatment with anti-coccidial drugs are key measures to control parasite infection.

Scaly leg mites in chickens can also cause leg disorders, such as lameness. Scaly leg mites bore under the scales of the chicken’s legs. The scales enlarge, get rough and become infected. If not treated early, the bird can go lame. To treat this the bird’s legs should be soaked in an oil or cream to suffocate the mites. Treatment should be repeated every 3-4 days for 2 weeks. The old scales will then fall off over time and be replaced with new scales.