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Original research
Peer reviewed
Lincomycin-medicated feed for the control of porcine proliferative
enteropathy (ileitis) in swine
Nathan L. Winkelman, DVM; John P. Crane, BSc; Gregory D. Elfring,
MS; D. Dal Kratzer, PhD; David M. Meeuwse, BS;
Ken J. Dame, BS; Susan L. Buckham, MS; Connie J. Gebhart, PhD
Winkelman NL, Crane JP, Elfring GD, et al. Lincomycin-medicated
feed for the control of porcine proliferative enteropathy (ileitis)
in swine. J Swine Health Prod. 2002;10(3):107-111. Also available as a PDF.
NLW: Swine Services Unlimited Inc, 10 E 6th Street, Morris,
MN 56267; JPC, GDE, DDK, DMM, KJD, SLB: Pharmacia Animal Health,
Division of Pharmacia Corp, Kalamazoo, MI 49001; CJG: Veterinary
Pathobiology, University of Minnesota, St Paul, MN 55108. Corresponding
author: John P. Crane, Pharmacia Corp, 7000 Portage Rd, Kalamazoo,
MI 49001; Tel: 616-833-2646; E-mail: john.p.crane@pharmacia.com.
Summary
Objective: To evaluate the efficacy of lincomycin (Lincomix
20 Feed Medication; Pharmacia Animal Health, Kalamazoo, Michigan)
at 44 and 110 ppm administered in feed for control of porcine
proliferative enteropathy (PPE) in swine challenged with mucosal
homogenate.
Methods: A total of 312 commercial crossbred pigs at
two sites were randomly assigned to receive lincomycin in feed
at either 44 or 110 ppm, or no treatment. On 2 consecutive days,
each pig was inoculated orally with Lawsonia intracellularis
in the form of porcine intestinal mucosal homogenate. Animals
were observed until clinical signs of disease were seen, then
pigs assignedto treatment groups received lincomycin in the feed
daily for 21 days. Control animals received no treatment. Clinical
observations and performance were assessed throughout the study.
Necropsies were conducted at the end of the study or at death.
Results: The L intracellularis challenge produced
a high incidence of clinical disease. The incidence of diarrhea
and scores for abnormal clinical impression were lower and ADG
and feed conversion efficiency were better in groups treated with
either dose of lincomycin than in untreated controls. Mortality
was lower in the group treated with lincomycin at 110 ppm than
in the untreated controls.
Implications: Under the conditions of this study, lincomycin
administered in feed at 44 and 110 ppm for 21 consecutive days
was effective in controlling clinical signs of PPE, and at 110
ppm also reduced mortality associated with PPE.
Keywords : swine, porcine proliferative
enteropathy,Lawsonia intracellularis, lincomycin, feed
medication
Received: March 16, 2001
Accepted: December 10, 2001
Porcine proliferative enteropathy (PPE),
also known as ileitis, is an enteric disease of pigs worldwide.1-3
It is characterized by thickening of the mucosaof the small intestine
and occasionally the large intestine. Pathognomic lesions consist
of proliferative immature crypt cells in the intestinal epithelium,
with free-floating bacteria in the apical cytoplasm.The causative
agent is Lawsonia intracellularis,1-3 but development
of PPE requires the involvement of other enteric bacteria. This
was demonstrated by McOrist et al,4 who showed that
gnotobiotic pigs are resistant to challenge and infection by L
intracell-ularis unless pre-dosed with a minimal inoculum
of normal gastrointestinal microflora. A variety of Campylobacter
species have been isolated from proliferative lesions. However,
oral inoculation of these bacteria has never reproduced the disease,
suggesting that they are secondary agents which may contribute
to the disease.1,4-6
The use of polymerase chain reaction (PCR) and immunological
detection methods has shown that strains of L intracell-ularis
isolated from geographically distinct worldwide locations
are practically indistinguishable.2 Isolates from different
geographical locations also have similar fastidious growth characteristics.2,7
Pathogenicity of both US and European strains has been confirmed
in model studies.1,2,5
Porcine proliferative enteropathy occurs in a chronic form,
comprising both necrotic enteritis and porcine intestinal adenopathy
(PIA), and an acute hemorrhagic form known as porcine hemorrhagic
enteropathy. A subclinical form also exists.1,8,9
Chronic PPE, the most common form of the disease, occurs mainly
in growing pigs 6 to 20 weeks of age,1,3 and manifests
primarily as a transient reduction in the rate of weight gain.
Inappetence and diarrhea are also occasionally observed. Commonly,
clinical signs are not readily apparent.1,8,9 When
diarrhea occurs, it is generally moderate, with loose stools of
normal to gray-brown color and no visible blood. Morbidity is
usually 5 to 20% in affected herds.1,3
The acute form of the disease occurs more commonly in young
adults (4 to 12 months old) and is manifested by acute anemia,
hemorrhagic diarrhea, and sudden death. Up to 50% of affected
animals may die.1,3
In vivo hamster challenge models and in vitro testing of L
intracellularis in host cell tissue culture systems have been
used in an attempt to predict the efficacy of various antibiotics
in treatment of PPE.3,10 However, it is difficult to
correlate the results of these studies to field efficacy. Challenge
models have been developed in swine. A swine challenge model was
employed in a study to determine appropriate in-feed doses of
lincomycin for a prevention and control program.11
Daily treatment with lincomycin at either 44 ppm or 110 ppm was
initiated 4 days before challenge. Both doses were found to be
effective in reducing mortality and improving production parameters
compared to no medication. Although prevention-control, in-feed
programs are used in the field, treatment is more commonly initiated
when clinical signs are already present in the herd. This study
was designed to evaluate the efficacy of in-feed lincomycin in
controlling PPE (ie, reducing mortality, reducing incidence and
severity of clinical signs, and improving production parameters)
when treatment was not initiated until inoculated animals were
showing clinical signs of PPE.
Materials and methods
Study animals
A total of 312 commercial crossbred pigs were included in the
study. Pigs of known health status were purchased from local farms
that used segregated early weaning management. Healthy pigs weighing
between 6.8 and 13.6 kg were acceptable for inclusion. At the
time the pigs were purchased, the source farms had no history
of clinical disease due to L intracellularis, Brachyspira hyodysenteriae,
B pilosicoli, Salmonella serovar Choleraesuis, Actinobacillus
pleuropneumoniae, transmissible gastroenteritis virus, or
porcine reproductive and respiratory syndrome (PRRS) virus. The
source herds were screened for PPE by indirect fluorescent antibody
(IFA) assay (reciprocaltiter of 30 was considered positive) and
for PRRS virus by ELISA (HerdChek PRRS ELISA; IDEXX Laboratories,
Westbrook, Maine) (a sample:positive ratio >=0.4 was considered
positive).
Housing and feeding
The study was conducted at Sites A and B, two locations in
Minnesota remote from other swine facilities.
Site A. One hundred and eighty pigs were housed
in two adjacent modern nursery barns, each with two rows of eight
pens (3.0 m2) separated by an alley. Pens had perforated
plastic grating floors, and each pen provided one five-hole dry-feed
feeder and two nipple waterers. In each barn, pigs were housed
in 15 pens in groups of six. Solid plastic partitions between
pens prevented pig-to-pig contact and feed transfer. The buildings
were environmentally controlled using negative-pressure mechanical
ventilation with integrated heater and fan controllers. Barn and
ambient temperatures were measured continuously by computer.
Site B. One hundred and thirty two pigs were housed
in a single barn, which was a renovated, wooden pig nursery building
containing two rows of five and six pens (3.6 m2) separated
by an alley. Pens had vinyl-covered expanded metal floors, and
each pen provided one six-hole dry-feed feeder and two nipple
waterers. Solid vinyl planks fitted together prevented pig-to-pig
contact and feed transfer between pens. Pigs were housed in groups
of 12. Heat was provided by a thermostatically controlled gas-fueled
furnace. Ventilation consisted of an exhaust fan for exit air
and an inlet mixing tube which allowed outside air to be blended
with inside air and circulated over the pens. Environment monitors
automatically recorded the building temperature.
Treatment assignments
At each site, pigs were randomly allocated to pens and pens
to treatment by a computer-generated plan using PROC PLAN of the
SAS System.12 Pens of the same block were located as
close as possible to each other.
Site A. The experimental design was a randomized complete
block design. Pigs were grouped in blocks by weight before challenge.
A pen of six pigs was the experimental unit. Treatment groups
received one of two dosages of lincomycin (Lincomix 20 Feed Medication;
Pharmacia Animal Health, Kalamazoo, Michigan) administered in
feed. A complete block contained three pens: one for each treatment
group (44 and 110 ppm lincomycin), and one for the nonmedicated
control group. There were ten replicates of each treatment and
the control group.
Site B. The experimental design was a randomized incomplete
block design. Pigs were grouped in blocks by weight before challenge.
A pen of 12 pigs was the experimental unit. Treatment groups received
one of two dosages of lincomycin (Lincomix 20 Feed Medication;
Pharmacia Animal Health) administered in feed. A complete block
contained three pens: one for each treatment group (44 and 110
ppm lincomycin) and one for the nonmedicated control group. One
block was incomplete because there was one less pen for the 110
ppm group, ie, there were four replicates of the 44 ppm treatment
group and the nonmedicated control group, and three replicates
of the 110 ppm treatment group.
Inocula
The inoculum used in this study was pooled intestinal mucosal
homogenate derived from previously challenged pigs manifesting
gross pathology of PPE. To obtain the homogenate, mucosa was scraped
from small intestines affected with moderate to severe PIA and
(or) necrotic PPE lesions, and suspended at a 1:1 ratio in sucrose-phosphate-glutamate
(SPG) buffer, pH 7.0, which contained sucrose (0.218 mol per L),
monobasic potassium phosphate (KH2PO4; 0.0038
mol per L), dipotassium phosphate (K2HPO4;
0.0072 mol per L), and L-glutamic acid (0.0047 mol per L). The
source for all reagents was Sigma (St Louis, Missouri). The mucosal
suspension was homogenized in a blender. Homogenates were stored
at -70°C until used, and thawed and stored on ice on days
of use. Samples were submitted on ice to the Department of Veterinary
Pathobio-logy, University of Minnesota, for enumeration of L
intracellularis by immunoperoxidase staining, and to confirm
absence of the following potentially confounding enteric pathogens
(methods in parentheses): Brachyspira species (dark field
microscopy), Salmonella Choleraesuis (culture on sheep
blood agar, MacConkey agar, XLD agar, Brilliant Green agar), and
[beta]-hemolytic Escherichia coli (culture on sheep blood
agar, MacConkey agar). All pigs at both sites were inoculated
before assay results were available.
At each site, a total infective dose of 108 to 109
L intracellularis was estimated (on the basis of findings
in previous studies) and administered by gavage to each pig in
two equal divided doses of approximately 15 to 30 mL per dose,
24 hours apart.
Records and observations
The study was conducted according to both US13 and
European14 Good Clinical Practice guidelines. All personnel
who assessed and recorded clinical signs and who performed and
recorded performance measures were masked to treatment.
Evaluation of efficacy was based a test-control comparison
of percent mortality, percent of pigs with diarrhea, percent of
pigs with abnormal clinical impression scores, and growth performance
parameters, including average daily gain (ADG), feed intake, and
feed conversion efficiency (FCE). Mortality, diarrhea, and clinical
impression scores were recorded every day from inoculation (Day
0) until the day treatment began, then every other day until study
termination.
Diarrhea scores were assigned as follows: 1 = no diarrhea;
2 = semi-solid stool, no blood; 3 = watery stool, runs through
the floor slats, no blood; 4 = blood-tinged feces, loose or formed;
5 = profuse diarrhea with blood or very dark tarry feces.
Clinical impression scores were obtained from the sum of the
pig demeanor score and the abdominal appearance score, divided
by two. Pig demeanor scores were recorded as follows: 1 = normal;
2 = slightly to moderately depressed, listless, will stand; and
3 = severely depressed, recumbent, unwilling to stand. Abdominal
appearance scores were recorded as follows: 1 = normal; 2 = moderately
gaunt; 3 = severely gaunt.
Feed consumption and body weights were recorded weekly. Feed
was weighed daily and added manually to individual feeders. Uneaten
feed was weighed weekly to permit calculation of weekly pen feed
consumption. Pen feed consumption was correctedfor mortality by
calculating consumption by pig-day. One pig-day was each day one
pig was alive in the pen.
Necropsies were performed on all pigs by the investigator either
at death or at study termination (one day after the end of the
21-day treatment period). Gross pathological evaluation of the
intestines was made by the investigator. Ileal segments from all
pigs were submitted in buffered formalin to the Department of
Veterinary Pathobiology, University of Minnesota, for histopathological
testing using an immunoperoxidase staining technique incorporating
monoclonal antibody to
L intracellularis.
Treatment initiation
At Site A, treatment was to be initiated when >=10% of pigs
in each barn had cumulatively manifested either watery diarrhea
(score >=3) or abnormal clinical impressionscores (>=2).
At Site B, treatment was to be initiated when >=20% of the
pigs had cumulatively manifested either abnormal fecal scores
(>=2) or abnormal clinical impression scores (>=2), with
at least one pig per pen meeting these criteria. Until treatment
began, all animals were fed the same unmedicated diet. Medication
was added to this diet at 44 or 110 ppm for the two treatment
groups, and unmedicated feed continued to be supplied to the control
groups. Diets were manufactured in bulk and were color and letter
coded to maintain masking. Samples of each batch were analyzed
before the study to confirm the correct concentrations of lincomycin
and freedom from other antibiotics.
Statistical design and analysis
The experimental design for both studies was a randomized block
design with pen as the experimental unit. Pigs were blocked by
weight to reduce the impact of weight as a potential confounding
factor. Treatment efficacy was assessed by measures of pen mortality,
diarrhea, clinical impression, and performance variables as defined
below. Mortality was defined as the percentage of deaths in a
pen due to PPE. Diarrhea was defined as the percentage of pig
observations in a pen with a diarrhea score >=2 duringthe treatment
period. Abnormal clinical impression was defined as the percentage
of pig observations in a pen with either a pig demeanor score
or an abdominal appearance score >=2 during the treatment period.
Average daily feed intake (ADFI) was calculated by dividing
the total amount of feed consumed during the treatment period
by the number of pig-days. Average daily gain was calculated by
dividing total weight gain of the pen by the number of pig-days.
Feed conversion efficiency was calculated by dividing ADG by ADFI.
Animals that died of diseases other than PPE were excluded
from the analyses. To adjust feed consumption for excluded animals,
the pen average for individual daily consumption was subtracted
for each day the excluded pig was present in the pen.
Treatment differences in these variables were investigated
using a pooled analysis of variance for the two sites, weighted
on the number of pigs per pen. When necessary, variables based
on pen percentages were transformed using the Freeman-Tukey arcsin
to better satisfy model assumptions for the statistical analyses.
Mean values and the P values for the one-sided t
test ([alpha]=.05) of treatment comparisons represent the results
of the pooled analysis.
Results
The source herds were serologically negative for PRRS virus
and L intracellularis. Average pig weights at the beginning
of the study were 9.3 kg at Site A and 10.8 kg at Site B.
Brachyspira species, Salmonella Cholerae-suis,
and [beta]-hemolytic E coli were not identified in the
challenge homogenates. The challenge dose of L intracellularis
was 5.5x108 organisms per pig at Site A, and 1.8x109
organisms per pig at Site B.
Treatment was initiated at each site on Day 7 post challenge.
At Site A, 50% of pigs in one barn and 60% of pigs in the other
had cumulatively manifested grade 3 diarrhea by Day 7, with this
score observed in at least one pig in 100% of pens. The pre-treatment
occurrence of diarrhea was nearly equal in the nonmedicated control
group (30.4% of pig-days), the 44-ppm-lincomycin group (29.7%
of pig-days), and the 110-ppm-lincomycin group (28.9% of pig-days).
At Site B, 61% of pigs had cumulatively manifested grade 2 diarrhea
and 40% had manifested grade 3 diarrhea by Day 7, with at least
grade 2 diarrhea observed in at least one pig in 100% of pens.
Pre-treatment diarrhea occurred less frequently in the nonmedicated
control group (15.8% of pig-days) than in the 44-ppm-lincomycin
group (24.6% of pig-days) or the 110-ppm-lincomycin group (26.3%
of pig-days).
A total of 40 of the 312 pigs died or were humanely euthanized
during the 28-day study period. Eleven were diagnosed pre- and
(or) post-mortem with diseases other than PPE. Enteritis associated
with Salmonella serovars or E coli was diagnosed
in five pigs, pulmonary disease in two pigs, and miscellaneous
morbidities in four pigs. Data obtained from these 11 pigs were
excluded from the analysis.
Results for the primary clinical variables (mortality due to
PPE, diarrhea, and abnormal clinical impression) are presented
in Table 1. Mortality was lower for the group treated with 110
ppm lincomycin (P<.05) than for unmedicated controls.
Groups treated with either 44 or 110 ppm lincomycin had less occurrence
of diarrhea and abnormal clinical impression (P<.05)
compared to the nonmedicated controls (Table 1). Also, groups
treated with either 44 or 110 ppm lincomycin had better ADG and
FCE (P<.05) than the nonmedicated control group (Table
1).
Necropsy results confirmed infection with L intracellularis:
greater than 50% of pigs either manifested classical PPE intestinal
lesions or were positive for L intracellularis by tissue
immunohistochemistry.
Discussion
In addition to mortality, the disease parameters important
to the pig producer are principally performance related. The chronic
form of PPE primarily causes a depression in FCE and growth,1,3
resulting in increased time to market, increased feed costs, and
uneven pig weights. All of these factors increase the producer's
cost of raising pigs. In addition to such management practices
as improved sanitation and reduction of stress factors, the strategic
use of an in-feed antibiotic, such as lincomycin, to control the
disease and help maintain uniform pig performance through the
period of risk, is an important consideration.
The PPE challenge model used in this study utilizes conventional
market pigs. It consistently reproduces clinical signs and pathology
typical of field cases of PPE15 and has been shown
to be repeatable. Performance of the model in this study was consistent
with previous studies (N. Winkelman, DVM, unpublished
data, 2001).
On necropsy, diseases other than PPE were diagnosed in a small
minority of pigs (3.5%), principally enteritis due to either salmonellae
or E coli. This multi-etiology has been observed in field
cases of PPE.16,17 These pathogens were not identified
in the mucosal homogenates used as inocula, and it is, therefore,
most likely that the sources were the pigs themselves. Results
from these animals were excluded from the analysis. As lincomycin
is not active against members of the Enterobacteriaceae, it is
not likely that any such underlying pathogenic etiology in the
non-excluded pigs biased the results in favor of lincomycin. The
incidence and severity of disease occurring at both sites (40%
to 55% incidence of grade 3 diarrhea) prior to initiation of treatment
was probably greater than would normally occur in the field. Nevertheless,
lincomycin administered in feed at both 44 and 110 ppm was effective
in reducing clinical signs and ameliorating performance deficits
(ADG and FCE) due to PPE.
Results of this study and data from a previously published
report11 show that in-feed regimens of lincomycin (44
and 110 ppm) approved for the control and treatment of swine dysentery,
a disease that manifests clinical signs similar to those of PPE,
are also effective in the treatment of PPE.
Implications
- Under the conditions of this study, lincomycin administered
in feed at either 44 or 110 ppm for 21 consecutive days, beginning
after the onset of clinical signs, controlled diarrhea and clinical
signs associated with PPE in treated pigs compared to nonmedicat-ed
controls.
- Under the conditions of this study, lincomycin administered
in feed at either 44 or 110 ppm for 21 consecutive days, beginning
after the onset of clinical signs, improved ADG and FCE in treated
pigs compared to nonmedicated controls.
- Under the conditions of this study, lincomycin at 110 ppm
reduced mortality due to PPE in treated pigs compared to nonmedicated
controls.
References - refereed
1. McOrist S, Gebhart C. Porcine proliferative enteropathies.
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of Swine. 8th ed. Ames, Iowa: Iowa State University
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States isolates of Lawsonia intracellularis from porcine
proliferative enteropathy resemble European isolates. Swine
Health Prod. 1996;4:119-122.
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Vet Microbiol. 1998;62:59-72.
References - non refereed
10. Gebhart CJ, McOrist S. A hamster challenge model for evaluating
effectiveness of chlortetracycline in prevention/control of porcine
proliferative enteropathy. Proc AASP. 1995;93-99.
11. Winkelman N. Dose determination trial for lincomycin in
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Allen D. Leman Swine Conf Res Abstr. 1998:27.
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