prevalence of
gastrointestinal lacerations
at slaughter and effect of feed withdrawal
W.E.M. Morrow
[1], P.R. Davies
[2],
J. Eisemann
[1], M.T. See
[1]
, and K. Zering
[3]
Summary
To
help producers decide whether they should withdraw feed prior to slaughter, we
designed a study that examined the effect of feed withdrawal on the prevalence
of gastrointestinal lacerations at slaughter. We assigned treatments to a
finishing floor of 1133 National Pig Development barrows that were sent to
slaughter in 3 groups. Each marketing
group (feed withdrawn once, first group; twice, second group; or three times,
third group) had an equal number of pigs that had feed withdrawn for 0
(control) 12, or 24 hours. Withdrawal of feed before slaughter decreased the
weight of the gastrointestinal tract. The least-squares means weights (+
se) of the gastrointestinal tracts of pigs with no feed withdrawal (7.7kg +0.06)
were greater (P = 0.0001) than the pigs with 12 hr feed withdrawal (6.6kg +0.06)
and they were greater (P = 0.07) than the pigs with 24 hr feed withdrawal
(6.4kg +0.06). The proportion of gastrointestinal tract lacerations
ranged by day from 8.3% to 23.9%, but the differences were not significant (P =
0.32). Neither marketing group (feed withdrawn once, twice, or three times) nor
the hours feed was withdrawn (0, 12, or 24) affected lacerations.
Introduction
To
decrease the proportion of PSE pork, Eikelenboom et al. (1991) recommends
producers withdraw feed from hogs 12-24 hours prior to slaughter (1). Because
producers in the USA are penalized for selling hogs outside a narrow weight
range, most who have all-in/all-out facilities will send their hogs to
slaughter over 3-4 weeks. In most cases, they withdraw feed from the last load
but earlier loads are usually on full feed until they are shipped. Withdrawing
feed from hogs before slaughter decreases the weight (2, 3) and presumably
solid contents of the gastrointestinal tracts. Consequently, because they are
lighter, slaughter workers are less likely to lacerate them during evisceration
resulting in decreased carcass contamination (3). This study investigated the
effect of 0, 12, or 24 hours feed withdrawal before slaughter on the weight of
the gastrointestinal tract and the number and location of lacerations to the
tract.
Materials and methods
Subjects:
In March 1998, 1133 National Pig Development (NPD) barrows from a nursery site
were weighed, individually identified and assigned, blocked by weight, to 36
pens. The barn had 40 pens—the other 4 pens held the cull pigs and the extreme
lightest and heaviest pigs that were excluded from the study. Each pen of 29-32
pigs had pigs of similar minimum and maximum weight with similar variation
between pens. Maximum variation within a pen, rather than minimum, allowed us
to progressively select the heaviest third of pigs for slaughter from each pen
and simulate the slaughter close-out of a barn of pigs where on about three
occasions the heaviest third in the barn are taken to slaughter.
Treatments:
Treatments included feed withdrawal of 0, 12, and 24 hours and marketing group
(1, 2, and 3) selected on weight and having feed withdrawn once, twice, or
three times prior to shipment. Feeders to the pens on 12 or 24 hour withdrawal
treatment and containing hogs scheduled for slaughter were shut off and any
feed in the feeding troughs was returned to the pens’ feeders. The experimental design was a 3 by 3
factorial.
Shipments: For the first and second marketing groups, the 10 heaviest pigs in each
pen were visually identified and shipped (feed withdrawn once or twice). The
third marketing group consisted of all pigs remaining in all the test pens.
Pigs were individually tattooed with a unique 4 digit identifying number coded
to describe the day and treatment. In lairage, pigs had free access to water but
not feed.
Gastrointestinal
tracts (GIT): Standard evisceration
procedure at the plant was as follows: the head was removed, the brisket cut
open, the abdominal cavity opened, the anus (bung) dropped, then the
gastrointestinal tract and thoracic cavity contents (pluck) were cut from the
carcass and placed on a tray. On the tray, the esophagus was cut from the
stomach and the pluck removed and placed on a hook for further processing.
Immediately after the abdomens were opened we tagged the gastrointestinal
tracts with temporary paper numbered tags which we correlated to the carcass
tattoos. The gastrointestinal tracts were then removed from the viscera trays,
placed in plastic bags and taken off-line for us to examine. Each tract was
examined in detail, section by section, and noted which sections (stomach,
small intestine, cecum, and colon) were lacerated.
Statistical
Analyses: All data were analyzed in
SAS. Categorical data were examined initially in the PROC FREQ and then GENMOD
procedure.
Results
Pigs
were loaded and left the farm between 2-5 am, traveled for 1hr 15 min (range: 48
min to 1 hr 45 min) and held in lairage for 3hr 50 min (range: 1 hr 58 min to 4
hr 47 min). Overall, 15.7% of the 773 gastrointestinal tracts examined were
lacerated in one or more sections (Figure 1.).
Figure 1. Percentage of lacerations
overall and by sections
Withdrawal of feed before slaughter decreased the
weight of the gastrointestinal tract. The least-squares means weights (+
se) of the gastrointestinal tracts of pigs with no feed withdrawal (7.7kg +0.06)
were greater (P = 0.0001) than the pigs with 12 hr feed withdrawal (6.6kg +0.06)
and they were greater (P = 0.07) than the pigs with 24 hr feed withdrawal
(6.4kg +0.06). The proportion of gastrointestinal tract lacerations
ranged by day from 8.3% to 23.9%, but the differences were not significant (P =
0.32). Neither marketing group (feed withdrawn once, twice, or three times) nor
the hours feed was withdrawn (0, 12, or 24) affected lacerations. Also,
gastrointestinal tract weight increased (P = 0.0001) as carcass weight increased.
Discussion
The proportion of
lacerations in this study (15.5%) was higher than previously reported
(4-5%)(3). The difference may be due in our study to the high processing speed
for evisceration (18 pigs per minute) and/or a more detailed examination of the
gastrointestinal tracts in this study which may have decreased under-reporting.
As expected, the weight of the gastrointestinal tracts decreased with
increasing duration of feed withdrawal.
From the perspective of bacterial
contamination, an important finding is the low prevalence of cecal lacerations
and lack of association of cecal lacerations to treatment or carcass weight.
This is important because most contamination occurs after singing (5) and the
ceca is the second highest site for recovery of Salmonella (71%) after the
palatine tonsils (93.5%) (6). In addition, the cecum usually has a very fluid
content, which could readily spill and potentially grossly contaminate the
carcass. The association of lacerations to particular sections of the
gastrointestinal tract may arise because of the effect of feed withdrawal
(stomach and colon) and carcass weight (small intestine), on the rhythm of the
evisceration process.
Implications
Based on these data the
incidence of gastrointestinal lacerations at slaughter is not affected by
withdrawing feed from hogs prior to slaughter.
References
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W. Sybesma, (1991). Effects of feed withdrawal before
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K. B., D. S. Bailey, J. R. Bollinger, M. P. Fournier, D. W. Hartman, E. W.
Mills, C.
A. B. Meyers, and P. Pitcher. (1996). Effect of feed withdrawal prior
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M.F., M. A. Carr, D. B. Bawcom, C. B. Ramsey, and L. D. Thompson. 1997.
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G.E.C., 1990. Working towards quality. Aspects of quality control and hygiene
in the
meat industry. Thesis, Utrecht University, the Netherlands.
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R.L., A. Pospischil, and R. Rose. 1989. Distribution of persistent Salmonella
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