Wet litter linked to high acidity

There is something wholesome about fresh wood shavings – the faint smell of pine, the appearance of new fallen snow. It represents the last act of broiler house cleaning before the new crop of day-old chicks arrives.

But within three weeks, this scene will have changed dramatically. For over half of UK broiler farmers, the litter will have “turned” and, despite the best efforts of heating, raking, topping up, ventilating and even rotavating, the shed has wet litter.

Ten years ago vets at the University of Liverpool asked over 600 randomly selected broiler farmers about wet litter. Three-quarters had seen it during the previous year and over half reported it in at least one shed during their last flock. A more recent study suggests little has changed since then.

Wet litter is important because it is associated with hock burn, pododermatitis and poor performance. But what is wet litter? Is it one condition? Are all broiler farmers talking about the same thing? How good are they at recognising it?

To answer these questions researchers at the University of Liverpool have been conducting fresh research, with some surprising results.

“We chose a representative sample of farmers from five major UK companies and asked them to send us samples for laboratory analysis if they thought they had wet litter,” explained veterinary researcher Phil Hepworth. “We didn’t define what it was or what we wanted. We just asked them to make the decision.”

Research has revealed a marked difference in p~H levels between dry (left) and wet (right) litter. Wet litter is typically more acidic.

Back in the laboratory, Dr Hepworth compared the moisture content and pH (acidity and alkalinity) of wet litter samples with normal samples requested from farmers at the same stage of the production cycle.

The moisture content of each was then plotted against its pH and tested to see if they fell into distinct clusters (see chart).

To the researchers’ surprise, the wet litter samples were almost all acidic, typically with a pH of less than six and moisture content of over 45%.

“This is the first time low pH has been associated with wet litter,” said Dr Hepworth. “Previously alkaline pH, associated with ammonia, has been perceived as the major litter problem and current litter treatments often aim to acidify the pH. But adding acidifier to litter that is already acid would be counter productive.”

These new findings also beg the question “Is it low pH or high moisture that causes the skin damage of pododermatitis and hock burn?” If it is low pH, then buffering poultry litter with bicarbonate may alleviate the problem.

“Both acids and alkalis can act as skin irritants and it is important to know what you are dealing with,” said Dr Hepworth. “Fortunately, measuring litter pH is relatively easy and disposable pH paper indicators, with a range of five to nine, can be obtained via the web. Use of these indicators may also assist as early warnings of wet litter.”

The response rate in this study was 93%. “The farmers were very co-operative,” commented Dr Hepworth. “I think it indicates their interest in wet litter and their frustrations in not being able to control it.”

Liverpool University findings

The Liverpool group is now analysing the data from the most recent studies to identify factors associated with wet litter.

“We know that the problem is seasonal with the highest incidence in winter,” says group leader Prof Kenton Morgan.” We also have identified breed, coccidiosis, feed equipment failures and thinning as factors that increase the risk of wet litter on the farm.

“Our aim now is to use more detailed information, collected from individual sheds, to identify risk factors for wet litter which are specific to that shed. All this depends on the accuracy with which farmers can identify wet litter and we now have this information too.”

By comparing farmer reporting of wet litter with the results of data clustering, the probability that a farmer will correctly identify wet litter if they have the problem is 88%. If asked if the litter is “normal”, the probability that this will be reported correctly is 85%.

“These values appear reassuring, but they also show that in about 13% of cases ‘false positives’ or ‘false negatives’ are reported. Measuring pH may improve this and add a simple tool to assist in the management of this complex problem.”