Agriculture

A Picture Guide of Chicken Feed Withdrawal

The information on this web page was excerpted from the factsheet, "Chicken Feed Withdrawal." A complete copy of the factsheet can be downloaded here (PDF 431KB).

A thorough description of chicken feed withdrawal can be read in the factsheet, "Feed Withdrawal: A practical look at its effect on intestine emptying, contamination and yield," which is posted on the Manitoba Agriculture and Food website.


Before broiler chickens are shipped to the processing plant, feed is withdrawn on-farm to assist in emptying the birds' digestive tracts and reduce the chances that the carcasses will be contaminated during processing.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.

Zero Hours of Feed Withdrawal - Feed in intestine

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.

Two hours of feed withdrawal - Crop opened to reveal small amount of soft feed remaining

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.

Four hours of feed withdrawal - Intestines are still rounded

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.     

Ideal gizzard (firm, dry feed) Six hours of feed withdrawal - Empty gizzard with fluid inside

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.       

Eight hours of feed withdrawal - Lining readily scrapes off of exposed duodenum Six hours of feed withdrawal - Intestine is empty, but villi are intact. Very little lining will scrape off Six hours of feed withdrawal - Some gas may be observed 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.

Twelve hours after feed withdrawal - Flattened intestine

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.     

Thirteen hours of feed withdrawal - green gizzard contents Thirteen hours of feed withdrawal - bile in a cut open crop

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.

15-17 hours after feed withdrawal - Gas bubbling out of nicked intestine 15-17 hours of feed withdrawal - Lining readily scrapes off of most of intestine 15-17 hours of feed withdrawal - Orange-tinged, sloughed intestinal lining

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.

18 hours of feed withdrawal - Rebuilt intestinal lining

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 after 13 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.

Carlyle Bennett
Animal Industry Branch, Manitoba Agriculture and Food
August, 2002