KEEPING broilers free from some of the most common issues that cause processing rejects is not only a way to demonstrably improve on-farm welfare, it will also enhance the profitability of a farm.

According to Brendan Graaf, a broiler specialist at Cobb Europe, reducing downgrades should be seen as a priority, whether you are a contract grower or internal farm manager.

See also: Sainsbury’s to lower broiler stocking densities

“The UK already sets a high bar in terms of bird welfare, but we always want to build on it.”

At the recent virtual Northern Broiler Conference, Mr Graaf offered farmers tips for managing some of the most common causes of downgrades – Scratching, bruising and cellulitis, pododermatitis and breast myopathies.

Scratching, Bruising and Cellulitis

Scratching, bruising and cellulitis (SBC) is the most common cause of downgrades, and are often very closely linked closely together – cellulitis requires a scratch to allow bacteria to enter, for example.

A key way to reduce the risk of SBC is to ensure birds have enough feeders and drinkers, reducing competition.

Mr Graaf recommends between 45-65 birds per 33cm feeder pan and at least 12 birds per nipple in high-flow systems or ten birds/nipple in low-flow setups.

chicks drinking from a lubing system

Daily checks should ensure that feed and drink reach every part of the shed, as unnoticed breakdowns can create competition.

And feed programmes that restrict the natural appetite of birds should be avoided – feeders should never run empty.

When lights are switched off and on can be key risk points for SBC, as birds naturally want to consume more food just before it goes dark and again when the lights come on.

Across the shed, lighting should be even and ideally dimmed on and off to prevent competition.

Dark periods should last no more than 6 hours, Mr Graaf says; otherwise birds may wake up too hungry and compete for feed.

When walking birds or during catching it is also important to move calmly and do everything you can to reduce flightiness.

Pododermatitis and hock burns

Pododermatitis is a significant indicator of bird welfare, and as such, processors and retailers take its reduction very seriously.

The condition is caused by ammonia, which is formed by uric acid from bird faeces interacting with moisture in the litter.

Once there, it irritates any contact areas the birds have with it, such as foot pads, hocks, and the breasts in severe cases.

It affects younger birds more because they have more tender skin, so paying attention to litter dryness, particularly for the first 18 days, is vital.

The material used for litter should be of good quality and highly absorbent, Mr Graaf says.

Drinker lines need to be well maintained, with the correct flow rates to minimise spillage.

Drip cups have a positive effect in reducing the amount of water getting into litter, as well.

Dry litter is maintained by appropriate ventilation, and minimum vent levels should be based on the moisture that birds add to the house.

broiler chickens
©Tim Scrivener

Work has suggested that, for every litre of water taken in by birds, up to one litre is released back into the house and potentially back into the litter.

“Ventilation needs to be able to remove that daily. Making sure that enough moisture is removed will keep litter dry and reduce the risk of pododermatitis.”

House humidity should be kept between 50%-60% at all times – certainly below 65%, and if it is above 70%, wet litter will result.

On cold, misty and rainy days, there is generally still more moisture in the air inside a house than there is outside.

“Generally, growers will want to step back on their ventilation on days like this because they are afraid of bringing cold moist air into the house.

“But on cold rainy days minimum ventilation rates often need to be increased to make sure that enough moisture is removed from the house.”

Breast myopathies

The two primary myopathies that cause downgrades in the UK are white striping and woody breast.

“The exact mechanisms are not fully understood, but we have come a long way and understand some of the underlying mechanisms that cause it.

“Brooding is absolutely essential in reducing the incidence of white striping and wooden breast,” Mr Graaf explains.

In particular:

  • Early feed and water intake – can help to stimulate satellite cell (muscle stem cell) activity to increase the number of muscle fibres in the breast.
  • Avoid stress – that can inhibit satellite cell activity.
  • First-week growth should ideally be 4.8 times the day-old weight.
  • Steady growth – after the first seven days, growth should be close to the breed-specific growth curve for the rest of the cycle, with growth that is too rapid increasing the risk of woody breast.

“We want to get the first seven days right – good foundations, then steady growth through the rest of the cycle.”

A general observation is that hotter temperatures are thought to increase the risk of breast myopathies.

If it’s too hot, there is the potential for more oxidative stress and hypoxia in breast muscle.

Birds that are too hot will pant – itself a general stressor – tend to move less, and sitting down can increase pressure on breasts and reduce blood flow.

Long periods of darkness have also been linked with myopathies, as birds’ internal temperature increases when lights are off.

“Our recommendation emphasises temperature management, particularly after 21 days when stocking densities become higher.

“Follow breed guidelines and monitor bird behaviour to keep them happy and comfortable throughout the cycle.”

For a recording of the 2022 virtual Northern Broiler Conference contact Carole Arnold, email:

For more technical insight from Cobb Europe, see the recently launched ‘Cobb Acadamy’, an online education platform that invites individuals to enrol in courses on various poultry-related topics taught by industry experts throughout the year. 

More information can be found on Cobb’s website.