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Author: C. Bennett - Animal Industry Branch, Manitoba Agriculture and Food
Before broiler chickens are shipped to the processing plant, feed is withdrawn
on-farm to assist in emptying the birds' digestive tracts and reduce the chances
that the carcasses will be contaminated during processing. A carcass can be contaminated
while hanging on the processing line if food leaks out of the crop through the
mouth; feces are excreted from the vent; or material in the digestive tract is
released by nicking, cutting or tearing the intestine during processing. Any of
these contaminants may contain bacteria that will adhere to the carcass. Proper
feed withdrawal produces an empty gut that can be processed efficiently without
contaminating the body cavity or surface of the carcass.
Two windows of opportunity exist to successfully process chickens. Between these
windows, is a "wall" where potential for contamination is high and line
speeds may need to be reduced significantly. The first window occurs at eight
to 12 hours after a bird stops eating. At this time, the gut is almost completely
empty but still strong and unlikely to break during processing. Any individual
bird that is without feed or "off-feed" for 15 to 16 hours poses a potential
problem at the plant. The intestine will be weakened by the extended hours off-feed
and filled with gas and released intestinal lining. The probability of carcass
contamination increases dramatically during this period. The second window normally
starts at 18 hours off-feed. By this time, the bird has flushed out the released
intestinal lining and has started to produce new villi. A bird processed in this
second window of opportunity will have a weaker intestine than a bird processed
in the first window, but the intestine will contain very little material that
could contaminate the carcass if the intestine is damaged during processing.
The events observed in broiler chickens during feed withdrawal are part of a natural
cycle that occurs every night in chickens in the wild. In nature, chickens eat
during the day and rest at night. Their intestines empty and the intestinal lining
begins to slough. The sloughing occurs because birds do not maintain the flow
of blood to an intestinal lining that is not absorbing food.
Examination of Digestive Tracts of Birds at Different Stages of Feed Withdrawal
A bird's digestive tract will undergo a fairly typical pattern of change as time
off-feed progresses. By knowing the signs of how the digestive tract changes,
it is possible to examine viscera on the processing line and estimate how long
individual birds have been off-feed. Careful observation also provides signs of
improper feed and water withdrawal. Some of the signs to watch for are outlined
below.
Zero Hours of Feed Withdrawal
Feed and digesta are found in the crop, stomach (proventriculus), gizzard and
intestine. Because it is full of digesta, the intestine is round and tubular and
will remain round as long as it is prepared to accept new feed (up to about four
hours after the last meal). Some isolated areas of the intestine will not contain
digesta due to the peristaltic muscle movements which move feed through the intestine
in "waves." The gut wall is very elastic and curls back on itself when
cut open lengthwise. As long as feed is passing through the gut, the ceca dump
their contents on a regular basis and will be relatively small compared to later
stages of feed withdrawal.
Two Hours of Feed Withdrawal
As long as the birds have had two or three drinks of water, most of the feed in
the crop has been solubilized and passed into the stomach and gizzard. The crop
is almost completely empty and the duodenum (loop of intestine immediately after
the gizzard) is starting to empty.
Four Hours of Feed Withdrawal
The crop is empty but the gizzard contains some feed. The gizzard is a "hang
down" organ and generally passes out feed only as new feed enters. Since
the bird has stopped eating, no new feed is entering the gizzard to push out the
remaining feed. The gizzard empties only if the bird drinks excess water or after
a long feed withdrawal time. The gall bladder is small but will start to increase
in size as feed is no longer passing through the upper half of the intestine.
The liver will start to shunt bile to the gall bladder to be stored instead of
passing it on to the intestine. Liver colour has not yet changed. For the most
part, the intestine still has a rounded, tubular appearance.
Six Hours of Feed Withdrawal
Ideally, the gizzard contains firm, dry material which is comprised mostly of
feed. The last feed to enter the gizzard has been squeezed hard by the gizzard
muscle, helping to "wring out" most of the moisture in the feed. If
the bird drank excess water after emptying the crop, the gizzard will contain
watery fluid and the last feed in the gizzard will be in the intestine. Due to
reduced peristaltic muscle movement, this material may remain in the intestine
for ten hours until the gut lining breaks down and creates sufficient liquid in
the gut to help flush out the remaining feed. Until then, this material is often
trapped in the last third of the intestine. It is desirable to keep the last feed
in the gizzard.
The top half of the intestine starts to flatten due to the absence of digesta.
The size of the duodenum is at a minimum at this time. Afterwards, it will get
larger in both length and diameter due to gas production. The duodenum lies in
the portion of the body which will be cut by the body cavity opener and vent cutter
as the carcass hangs on the processing line in the plant. A small duodenum is
less likely to be cut during this process.
The intestines have their maximum breaking strength and will maintain this resistance
to breakage for the next six hours. After 12 hours off-feed, intestine breaking
strength declines dramatically. The gall bladder is still small but starting to
increase in size as the liver begins to shunt bile to it.
Eight Hours of Feed Withdrawal
(Start of First Window)
The duodenal loop is enlarged due to the gas production that occurs as the
gut lining breaks down and bacteria numbers increase. The rest of the intestinal
lining is intact and very little of it will release when lightly scraped with
scissors. Cutting open the intestine at mid-gut (at Meckel's diverticulum or
the yolk stalk remnant) will reveal villi in good condition. If a finger is
placed under the intestine and scissors are used to scrape the exposed villi
on that section of intestine, a rough surface similar to a cat's tongue can
be felt. The intestine is almost completely empty of feed and most of the intestine
is flat. Small amounts of gas are present in the intestine.
 
The liver has now been depleted of glycogen for several hours and is darker
and smaller than at zero hours of withdrawal.
Twelve Hours of Feed Withdrawal
(End of First Window)
Most of the intestine (beyond the duodenum) is flattened. Flattened intestines
are less likely to be nicked, cut or torn when the body cavity opener and vent
cutter cut into the carcass as it hangs on the processing line. The villi are
not as easy to feel when performing the "cat's tongue" scratch test
and the intestine does not readily curl back on itself when cut lengthwise.
From this point on, a steady decline in intestinal breaking strength occurs.
Thirteen Hours of Feed Withdrawal
Enough broken down intestinal lining has accumulated in the duodenum to trigger
the gall bladder to release bile. Reverse peristalsis, the backward movement
of material which regularly occurs in chicken digestive tracts, carries the
bile from the intestine into the gizzard. Some of this bile may then run back
into the crop during processing. Green bile staining of the gizzard is a good
indicator that a bird has been off feed for 13 hours or longer. Some gall bladders
now start to appear smaller as they dump their bile contents.
 
Coagulated protein may appear in the gizzard. This protein is from broken down
gutting lining that has been carried into the gizzard by reverse peristalsis.
The protein coagulates when it reacts with the acid in the gizzard, much the
same way cottage cheese forms when the protein in milk reacts with an acid.
Fifteen to Seventeen Hours of Feed Withdrawal
The intestine is almost entirely rounded as it fills with gas and gas may bubble
out if the intestine is nicked. The entire gut lining is broken down and sloughed
lining is found in much of the intestine. Almost nothing is felt when performing
the "cat's tongue" scratch test to detect villi. Due to dehydration,
the crop tends to stick to the carcass and is difficult to pull out; crops and
sometimes stomachs will break as the viscera are removed from the carcass. The
gizzards are becoming more difficult to peel.
 
Eighteen Hours of Feed Withdrawal
(Start of Second Window)
The broken down intestinal lining has passed out of the bird and the intestinal
villi are starting to rebuild. The villi can be detected with the "cat's
tongue" scratch test and little material scrapes off when scissors are
run over the exposed intestinal lining. The intestine is now flattened again
and little gas production is visible. The intestine has lost about one-third
of its breaking strength during the past six hours and the crops are still difficult
to remove due to dehydration. Contamination is lower than "between the
windows" because the intestines are now empty and relatively dry instead
of being filled with gas and sloughed intestinal lining. If the bird does not
receive feed in the next several hours, the intestine will start to slough again.
A Guide to Judging Time of Withdrawal
After First Window Has Passed
Signs Feed Withdrawal Has Extended Beyond
First Window (13+ Hours)
- Crops and stomachs break more easily during processing.
- Gizzards and sometimes crops are stained green with bile.
- Some gizzards are completely empty.
- Gizzards are tougher to peel.
- More gizzards contain feathers, litter or feces.
- Denatured protein ("cottage cheese") is found in some gizzards.
- Some gall bladders (those that have not dumped their contents) are greatly
enlarged.
- Bile, urates or orange casts (sloughed lining) are seen in the truck
crates or floor.
Signs Feed Withdrawal Has Reached Second
Window
- Smaller, shorter duodenum.
- Flattened intestine.
- Little sloughing or gas in intestine.
- Can feel villi during "cat's tongue" scratch test.
- Some or all of signs of extended withdrawal listed above.
Do Not Be Fooled by False Signs
- Reverse peristalsis can bring previously sloughed material back into
the duodenum. If the villi are rejuvenated,
- the sloughed material in the duodenum is old.
- Feed found in the crop could be due to water run back from the gizzard.
Suspect this problem if the gizzard is empty.
- Excess water consumption can flush bile out of the gizzard. Bile staining
may not be observed in every bird after13 hours of withdrawal. Watch for
excess fluid.
Summary
Proper feed withdrawal will reduce carcass contamination. By understanding how
the digestive tract reacts to time off-feed, you can better judge how to withdraw
feed from your birds. The goal should be to process as many birds as possible
after they have passed most of their feed, but before the intestinal lining
has started to slough. Flocks handled in this manner will process more easily,
with less contamination, and increased edible meat delivered to the plant.
Acknowledgements
The information on this web page and in the factsheet is based on the Chicken
Feed Withdrawal Workshop held on April 25, 2001 at the University of Manitoba.
The workshop was conducted by Dr. Stan Savage, retired Poultry Extension Specialist
at the University of Georgia, and the workshop would not have been possible
without his expertise. The workshop was organized by Manitoba Agriculture and
Food and the Animal Science Department at the University of Manitoba.
Reference
Stan Savage. 1998. Feed Withdrawal: A practical look at its effect on intestine
emptying, contamination and yield. Pfizer Inc.
C. Bennett
Animal Industry Branch, Manitoba Agriculture and Food
August, 2002
Author: C. Bennett - Animal Industry Branch, Manitoba Agriculture and Food
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Who saw this article? New!
 DISCUSSIONS ON THIS ISSUE.
 
| 02/16/2005 |
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I appreciate your acticle, and I now have a better understanding on feed withdrawal. Please I don't know if the organization can send me detailed information from a magazine containing any issue that has to do with poultry. Chris Ogbeta - P.O. Box 1809 Benin City - Edo State - Nigeria. | Answer Checked by Engormix.com  |
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