Course: Tackling common poultry diseases | Last Updates: 7th October 2015
With the advent and growth of free-range egg production, two formerly rare complaints are becoming increasingly problematic, particularly in spring.
Impaction of the gizzard, intestine or crop is usually caused by the ingestion of too much long grass, which cannot be processed and forms a plug, resulting in low productivity and higher mortality.
Often the producer reports dull and lethargic birds which are just not thriving. It is an icreasing problem because there are more birds which are ranging outdoors. The problem has recently been picked up in routine disease surveillance by the Veterinary Laboratories Agency.
What is impaction?
An impaction is simply the filling of an organ with something that should not be there – usually, in the case of free-range hens, long grass or string. Crop impaction is more frequently seen in broilers, which gorge themselves on food without drinking enough. This leads to a blocked and pendulous crop, which can swell so much it suffocates the bird.
However, it can also occur on free-range sites, where there are not enough feeders or drinkers for the birds, meaning timid hens are hungry for grass when the popholes open.
Lighting and the layout of feeders and drinkers is also important. Look at the stocking densities around the shed – if there are dark spots the birds tend to congregate around the lighter areas, putting pressure on feeding and drinking.
Gizzard impaction occurs when the gizzard becomes blocked with grass or other matter, which can also pass into the upper part of the intestine.
What causes it?
The primary reason for gizzard or crop impaction is long grass, but foreign matter such as bailer twine, plastic, string, or even woodchip shavings and straw bedding can also be to blame. Impaction is often a problem for new producers with virgin ranges and discarded building materials.
There is also a seasonal component, as when the grass is long in springtime you are more likely to see impacted gizzards. Young birds coming into lay, which have high nutritional demands and are turned out onto a spring flush of grass, are therefore most at risk.
The grass and other fibrous material has filled the gizzard and worked through to the duodenum.
To reduce the threat of impaction, producers should always keep grass short. Although grazing with sheep can be one option to avoid wasting the grass, it can also pose disease risks to the birds, so is not usually advisable.
Instead, producers should top the grass regularly with a flail mower, ideally during dry periods so that it wilts quickly. Any grass which has already become too long should be removed after cutting.
Birds just aren't equipped to eat long blades of grass – if you have long and damp cuttings you should remove them.
Poor muscle contraction in the crop or intestine, which can lead to impaction, can also be the result of worm damage to the gut, Marek's Disease, or vitamin deficiencies. It is, therefore, important to worm birds regularly, feed a multi-vitamin to young birds on arrival to the farm, and to vaccinate against Marek's Disease.
What else can I do?
Poultry gizzards are designed to grind up food in a mixture of grit, but too often producers do not supply sufficient grit for the birds.
There is an assumption that when they are ranging they will pick up stones, but the birds do need to have access to plenty of grit so that timid birds can also make use of it.
They should then be relatively well equipped to grind up smaller amounts of grass. However, producers should not rely on oyster shell or limestone grit, which are designed to improve egg shell quality – instead, they should use granite or flint-based grit which will not be easily broken down.
Also look at whether the birds received enough grit during rearing as a lot of rearers don't bother. As birds tend to eat discarded feathers during moulting, grit is important from the first couple of weeks onwards.
The difficulty can be in providing grit without destroying automatic feeder tracks. Try using tube feeders or feed pans and ensure young birds are given grit upon arrival to the laying unit.
|Crop full of grass and other fibrous material. Loss of breast muscle can also be seen (bottom right).||Grossly distended gizzard and stomach. The stomach has been cut so that the grass it contains can be seen.|
How is impaction diagnosed?
Crop impaction can be identified by an abnormally large or pendulous crop, which is firm to the touch. Sometimes this is simply due to overeating on the hen's behalf, so should be carefully monitored to see if it disappears. Producers need to handle their birds a bit more regularly, so they can pick up on problems that bit earlier.
However, diagnosis of an impacted gizzard is virtually impossible without carrying out a post mortem as it is very difficult to spot in a live bird. The bird would be noticeably dull and miserable and in severe cases they will become dehydrated and emaciated.
This is because the plug of grass blocks the passage of water and essential nutrients through the intestine. Formerly well-fleshed birds may become lethargic and lose weight – so producers should weigh their birds regularly to identify any unevenness in the flock.
Productivity is likely to dip, and mortality may rise – so producers can easily confuse the condition with other diseases or perhaps a worm burden. But upon a post-mortem a blocked gizzard and upper intestine will be clearly identifiable, and action taken to prevent further cases in the flock.
How is it treated?
There is no treatment for gizzard impaction – mild cases may be remedied by supplying grit and keeping grass ranges short. But if the birds are severely impacted they will die. Typically, only a small percentage of the flock will be affected, but this will clearly still have an impact on production and profitability.
Impacted crops can sometimes be treated if they are identified early enough. In some cases the bird can be held upside down and the contents of the crop carefully massaged back up through the oesophagus. This can be particularly effective in the case of sour crop, where the contents remain relatively liquid but have become acidic. However, it does carry the risk of suffocation or aspirated pneumonia if the bird is not allowed sufficient time to breathe.
Surgically cutting the crop open and removing the contents is another option, although not particularly practical in a commercial environment.
If the hens are helped to survive, they are probably never going to use their feed efficiently again, so productivity will remain affected. Taking steps to prevent cases of impaction in the first place is therefore the most valuable and cost-effective course of action.
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