Feed Withdrawal: Effects on Contamination and Carcass Yield
Removal of feed and water from market-aged broilers and turkeys before catch and live haul is a standard management practice that has been used by the poultry industry for many years. The primary reason for holding birds off feed before processing is to allows time for the birds' digestive tracts to become empty before they enter the processing plant. With proper feed withdrawal, there is a reduction in carcass contamination, carcass reprocessing (washing and trimming) and carcass condemnations during processing. Thus, length of feed withdrawal has a significant effect on product safety, quality and yield.
In general, feed withdrawal refers to the total length of time that birds are held without feed before processing. This means that feed withdrawal not only includes the length of time that the birds are held in the house without feed (before catch), but it also include the length of time the birds are in- transit and the length of time the birds are held in the live hold area at the processing plant. Recommended feed withdrawal times have historically been as short as 4 hours to as long as 14 hours, with the most common recommendations being between 8 and 12 hours of feed withdrawal. An 8 to 12 hour feed withdrawal program allows enough time for digestive tract clearance, but the time without feed is not so great that carcass yield loss due to fasting is too high. In practice, most processing plants attempt to process broilers after a 10 to 13 hour feed withdrawal period; however, there is wide variation in commercial feed withdrawal programs because of difficulties in scheduling flocks, catching, transportation and processing.
When a company designs their feed withdrawal program, they are basically deciding what they want in the birds' digestive tracts when the birds enter the processing plant. In order for the feed withdrawal program to work as designed, birds must have normal feed consumption and normal feed passage during the last week before withdrawal. When birds do not have normal eating patterns, there is greater variability in the content and condition of their digestive tracts, and this can be detrimental for the processing plant in terms of contamination. According to research, there are over 20 different factors that have been identified as having both an independent, as well as a combined effect on feed withdrawal. Table 1 list only a few of the factors affecting feed withdrawal. Because of the numerous factors affecting feed withdrawal, it is easy to see why it is so difficult to control the condition and contents of the broiler's intestinal tract.
Table 1. Some of the factors affecting broiler feed withdrawal
Time in house, in-transit, and in holding shed.
Condition of Gastrointestinal Tract
Once birds arrive at the processing plant, there is very little that can be done to alter their condition. If the birds are scheduled to be processed too soon after they arrive at the plant (feed withdrawal time less than 6 to 7 hours), they will still have feed in their digestive tracts when they enter the processing plant. Carcasses from these birds are more likely to be contaminated because the large, rounded intestines are easily cut, or torn during evisceration, and the force of evisceration may push material out onto the carcass. Too short of feed withdrawal can not be corrected simply by holding the birds longer in coops at the plant because these birds will not have normal feed passage (slower). On the other hand, if the length of feed withdrawal time is too long (greater than 13 to 14 hours), the intestines begin to weaken (Figure 1) and the gall bladder enlargers making both of these items more susceptible to breakage.
Figure 1. Intestinal strength of broilers held off feed for various lengths of time
To study the relationship between feed withdrawal and digestive tract contents, we evaluated the intestinal tracts of 50 to 125 broilers from each of 3 different commercial plants in the U.S. The contents of the crop and gizzard were noted upon dissection, and gizzard bile was reported on a percentage basis. Intestinal shape was scored as: 1) round and containing digesta (partially digested food and feces); 2) flat and void of digesta; or 3) round and containing intestinal gas. Table 2 shows the results of this study.
Birds off feed for 0 to 3 hours were actively passing feed (round, full intestines), and the gizzards from these birds had no evidence of bile. Birds off feed for 9 and 12 hours gave similar results when their intestinal tracts were evaluated. These birds had water in their crops, or their crops were empty, and their gizzards contained mostly litter. Bile was found in approximately 30% of the gizzards off feed for 9 and 12 hours. However, the intestines of these birds were flat and thus, optimal for evisceration. The intestines of birds off feed for 14 hours or longer were rounded due to production of intestinal gas, and data from another study indicate that this is the period of time when intestinal strength begins to decline (Figure 1). Reduced intestinal strength with excessive feed withdrawal has recently become extremely important to the industry because of the current inspection regulation. With the regulation, the industry trend has been to hold birds off feed for over 12 hours because of the difficulties and fear associated with meeting the zero tolerance for carcass fecal material and acceptable carcass E. coli levels. Moreover, companies frequently forget that increasing feed withdrawal beyond the recommended times solely to reduce contamination may have dramatic negative implications on other issues.
Live Shrink and Carcass Yield
In addition to affecting the contents of the birds' digestive tract, length of feed withdrawal has a dramatic impact on carcass yield. When birds are held without feed, they begin to lose weight. This weight loss is called live shrink. During the first 5 to 6 hours of feed withdrawal, the majority of the bird's weight lost (80 to 85%) will be due to evacuation of the digestive tract. After this initial withdrawal time, weight loss will be between 0.25 and 0.35% of the bird's body weight per hour of feed withdrawal depending upon the birds age, gender, grow-out house temperature, eating patterns before feed withdrawal, and preslaughter holding conditions (cooping time and holding temperature). Figure 2 shows the live shrink for commercial broilers at three different ages.
Figure 2. Live Shrink for broilers at 42, 44, or 48 days of age after various feed withdrawal times
Live shrink was greater in male broilers than for female broilers. With live shrink, a broiler held off feed for an extra 3 hours before processing (e.g., 15 hours instead of 12 hours), will weigh approximately 14 grams less than a broiler processed 3 hours earlier. This is a combination of 3 hours of less feed for growth and live shrink. In an operation that processes 125,000 birds a day, for 5 days a week, an extra 3 hours of feed withdrawal could equate to reducing the live weight processed each week by 1,750 kg. This does not mean that broilers given no feed withdrawal will have the highest carcass yields. In fact, birds full of feed that weigh the same as birds held off feed have lower carcass yields because their initial weight includes the digestive tract contents. Figure 3 shows data for live weight, dry carcass weight, and chilled carcass weight for 45 day old male broilers.
Figure 3. Effect of length of feed withdrawal on live shrink and dry carcass yield
Results showed that carcass yield was highest for broilers on a 6 hour feed withdrawal schedule. A 6 hour feed withdrawal program would be impractical for industry; however, data demonstrate that the highest yields will be obtained by companies who strike a balance between live shrink and carcass contamination.
Additional Factors to Consider
1. Keep good records of your actual feed withdrawal time. You may not be operating on the schedule that you think you are operating.
2. Monitor your flock for proper house temperature, litter moisture, and eating patterns. Are the birds moving about in the house? Are the birds gorging?
3. Try to avoid disturbing the flock immediately after feed withdrawal. This slows the evacuation of the digestive tract.
4. Keep the birds on litter as long as possible to facilitate digestive tract emptying.
5. During hot weather, keep the birds as cool as possible in the house and in the holding area. During cold weather, these two areas (house and holding area) may have extremes in temperature, and this will affect evacuation.
6. Do not allow birds to run out of feed before the scheduled time; however, if the feeders are empty at the time feed is to be removed, leaving them down until the catch crew arrives will minimize litter consumption.
by Julie K. Northcutt - The University of Georgia
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