Technical Bulletin

To: All Clients

Subject: Bone disease in broiler chickens in Europe

Dr Barry Thorp from the Roslin Institute gave a presentation to a European veterinary meeting on the above subject. I thought that my notes on the presentation might be of interest.

Bone pathology is related to production stresses. Changes in the pattern of stress can result in changes in the pathology. The two main problems affecting broiler bones are Femoral Head Necrosis and Osteoporosis. The former causes gait abnormalities and culling while the latter causes difficulties in processing due to bone breakages. Tibial dyschondroplasia is less common than it once was. When it does occur it is generally related to hyopcalcaemic rickets.

Femoral Head Necrosis (the epiphyses of other long bones are often also affected) occurs when bacteria attach to the walls of metaphyseal vessels. This leads to thrombosis (blockage of vessels) and widespread chondro-necrosis. Staphylococcus sp. are most commonly involved. Abnormal cartilage growth resulting in longer blood vessels in the cartilage (e.g. hypophosphataemic rickets) increases the risk.

Studies of bone mineralisation in broilers has been carried out at Roslin. Bone ash should be over 30% with an approximate ratio of 2:1 Ca:P. Low total ash has been identified as a problem in Northern Ireland broilers and inadequate phosphorus in Dutch broilers (believed to be the result of anti-pollution controls on phosphorus sources).

Other factors contributing to problems are:
Cost of mineral raw materials
Variable quality
Exclusion of traditional products
Inadequate knowledge of the true requirement.

Much of the information even in recent NRC documents is actually based on research from the 60's and 70's during which the birds and their management were substantially different. The implications of measures designed to modify growth rate (lighting and feed management) for mineral nutrition have not been established. Much of the phosphate in plant-derived raw materials is bound and of variable availability. It can be released by the action of phyatases which can be present in digestive juices (very low levels, probably absent in chickens), produced by microbes in the gut (very variable), present in the raw material or supplemented artificially (both types are destroyed by temperatures of 70-80 C which are now commonly used in feed processing). Casein phoshopeptides may become the ideal phosphorus source as they dramatically improve calcium and phosphorus utilisation and are not Vitamin D dependent. They are currently being studied for use in human nutrition and for the replacement of dental fluoride treatments but it is hoped that they can be produced at a price which would allow their inclusion in animal feeds in a few years time.

 

If you have any queries arising from this please do not hesitate to contact one of us.

Paul McMullin