Introduction
In addition to the effects of feed withdrawal on carcass quality
the possibility that it will also increase the proportion of pigs
with gastric ulcers must be considered. The mechanisms by which
gastric ulcers develop are not understood, however, if acid is
a major factor and the pH of proximal stomach contents declines
as time post-feeding progresses, then it is possible that feed
withdrawal will initiate damage to healthy mucosa or accentuate
damage where it exists already. The impact of feed withdrawal
would likely be magnified if repeated several times. The result
could be decreased growth rate due to severe lesions or death.
For the pork industry to remain competitive in domestic and international
markets it must continue to focus on the needs of the customer.
Withdrawing feed from hogs before they are slaughtered has the
following potential benefits: decreased weight and contents of
the gastrointestinal tract resulting in fewer lacerations and
consequently decreased risk of carcass contamination, less feed
wastage, increased yield, fewer carcasses with PSE, and decreased
cost of manure treatment at the abattoir. The potential disadvantages
include a possible reduction in live weight, possible reduction
in tenderness and juiciness (Ellis 1996), a possible increase
in the proportion of pigs excreting Salmonella spp. and
consequently an increased risk of carcass contamination, and the
possibility of an increased prevalence of gastric ulcers. To
effectively implement feed withdrawal as a standard production
practice these benefits and disadvantages should be evaluated as a system.
Objectives
To determine the effect of withdrawing feed from pigs at 0, 12, or 24 hours before they are shipped to slaughter and the effect of sorting by weight and withdrawing feed once, twice, or three times in a carcass-merit situation on:
Procedures
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 and the other 4 pens were used to hold 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. By design, however, this procedure confounds the
effects of repeated feed withdrawal with pig weight because the
lighter weight (presumably slower growing) pigs are exclude from
the first marketing group. Pigs were presumed homozygous stress
negative because they came from lines that had been DNA tested
and found negative for the HAL 1843 gene. In June, the 6 pens
that had the fewest pigs (attrition from death and culling) were
deleted from the study because they exceeded our needs.
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. Treatments were allocated at random, blocked
on pen prevalence of Salmonella spp. as determined from
the fecal sampling in May and June. Feeders to the pens containing
hogs for slaughter were shut off and any feed in the feeding troughs
was returned to the pens' feeders.
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 closed out the barn and consisted of all pigs remaining
in all the test pens. In the second marketing group, an accident
at the packing plant resulted in the loss of all data on all the
pigs (60) for that day (Table 1). Pigs were individually tattooed
with a unique 4 digit identifying number coded to describe the
day and treatment. Time in transport and lairage were recorded
by the person accompanying the pigs. In lairage, pigs had free
access to water but not feed.
| Feed withheld, hours | Feed withheld, hours | Feed withheld, hours | ||||||||
| June 22 | ||||||||||
| Marketing | June 23 | |||||||||
| Group 1 | June 24 | |||||||||
| June 25 | ||||||||||
| June 26 | ||||||||||
| June 29 | ||||||||||
| Marketing | June 30 | |||||||||
| Group 2 | July 1 | |||||||||
| July 2 | ||||||||||
| July 6 | ||||||||||
| July 8 | ||||||||||
| Marketing | July 9 | |||||||||
| Group 3 | July 10 | |||||||||
| July 13 | ||||||||||
| July 14 | ||||||||||
| Total | 907 | |||||||||
| aData from all July 2 pigs were lost because of an industrial accident in the plant. | ||||||||||
Statistical Analyses: All data were analyzed in
SAS. Categorical data were examined initially in the PROC FREQ
and then GENMOD procedure. The following tests were adopted:
where cell frequency was less than 5 for one or more cells, Fisher's
Exact test; where data were ordinal, Mantel-Haenzel Chi-Squared;
otherwise, Pearson's Chi-Squared. Continuous dependent variables
were analyzed in PROC GLM using a variety of models.
Results
Pigs were loaded and left the farm between 2-5am, traveled for
1hr 15 min (range: 1 hr 45 min to 48 min) and held in lairage
for 3hr 50 min (range: 4 hr 47 min to 1 hr 58 min).
We evaluated a total of 752 stomachs for damage. The esophageal
region of the stomach was scored, and signs of chronic damage
to stomach tissue and constriction of the esophagus were noted.
The scoring system ranged from 1 (normal, healthy tissue) to
7 (ulcerated completely). No stomach was given a score of 1.
Almost every stomach evaluated showed bile staining. The percentage
of pigs with each ulcer score across all treatments is shown in
Figure 1. Scores of 3-4 reflect tissue that was roughened, often
with elongated projections and breaks in the tissue. Scores of
5 and above indicate presence of increasingly severe ulcerations.
Because stomach damage was highest in pigs in the third marketing
group (3 times treatment) with no relation to time of feed withdrawal,
carcass weight was considered as a variable that might explain
the greater prevalence of damage in the 3 times treatments. There
was an interaction (P <.01) between the effect of length of
feed withdrawal and marketing group for carcass weight such that
carcasses were lighter as length of feed withdrawal increased
and they were also lighter as the number of times that feed was
withdrawn increased. The lightest carcasses were from the pigs
that had feed withdrawn for 24 hours and were in the third marketing
group (Figure 3).
Discussion
These data show that withdrawal of feed prior to slaughter, for up to 24 hours, did not lead to an increase in stomach damage when compared to the appropriate control group. The relation of severity of damage, chronic damage, and esophageal constrictions to carcass weight suggests that the impact of chronic ulcers on growth of pigs may be greater than is widely appreciated. However, the cause(s) of chronic stomach damage in this population of pigs is(are) not known.
We found a high prevalence of severe ulcers that probably were
established before we started the feed withdrawal treatment.
We suspect that these ulcers were primarily responsible for the
lighter carcass weight in the third marketing group. If so, then
gastric ulcers are contributing to a major decrease in growth
efficiency and meat quality. This hypothesis needs to be investigated
at other finishing sites and the underlying cause further explored.
