Posted by Administrator on June 24 2009 08:28
Introduction and objective
Ileitis, also know as procine proliferative enteropathy is a widespread swine enteric disease caused by Lawsonia intracellularis (LI). The prevalence of ileitis has been established by several studies and the disease can cause significant financial losses. In 1996, Tylan Premix (tylosin phosphate) was approved for the prevention and control of ileitis. More recently Enterisol Ileitis vaccine was approved as an aid in the prevention and control of ileitis.
There is a well-characterized intestinal homogenate challenge model in which the efficacies of many products have been tested. However, there have been no scientific papers published describing the efficacy of the Enterisol Ileitis vaccine in this challenge model or studies comparing other products to the Enterisol Ileitis vaccine in a LI challenge model in a well controlled research trial. Many questions have been raised about the relative efficacy of Enterisol Ileitis vaccine and the most established pharmaceutical intervention, Tylan Premix. The objective of this study was to answer these questions by comparing the clinical efficacy of the two products in a well controlled and blinded research trial.
Materials and methods
Barrows and gilts were sourced from a farm with no clinical history of ileitis or LI infection. Prior to movement to the research facility, a diagnostic screen was conducted to document negative ileitis status, which consisted of sampling two pigs per litter for fecal polymerase chain reaction (PCR) for LI and LI serology via immunoperoxidase monolayer assay (IPMA). At weaning, pigs were transported from the source farm to the research facility and individually identified by ear tags. After a 15 day acclimation period, animals were individually weighed and ranked by weight within gender. Pigs that were the lightest in weight or in poor body condition were not included in the trial animal pool. At day 0 (5 weeks of age) one hundred twenty animals were assigned to treatment pens consisting of 4 animals per pen and 6 pens per each of 5 treatment groups. Pigs were assigned to replicates via gender and weight, with one block consisting of 1 gilt and 3 barrows per pen. The assignment of pigs to a treatment within the genderweight block was accomplished by using Microsoft Excel random numbers generator. In each treatment there was the mixed gender pen, 2 barrow pens, and 3 female pens. All pens for a designated treatment were housed in the same isolation room to prevent any transmission of LI between treatment groups.
Animals were housed in a research isolation building in identical rooms with thermostat regulated temperature control with identical ventilation. Incoming and exhausted air from each room was hepafiltered. Animal pens consisted of plastic tubs on stands with plastic slatted flooring and approximately 5ft2 of floor space per animal.
The treatment groups were as follows, with the challenged groups receiving the challenge at day 28 and all pigs being necropsied at time of removal from the trial or at the end of the trial (day 56).
Treatment Group 1: Strict control: Pigs not challenged and no Tylan or Enterisol Ileitis vaccine administered.
Treatment Group 2: Challenged control: Pigs were challenged at day 28 of trial (9 weeks of age) with LI gut homogenate and no Tylan or Enterisol Ileitis vaccine administered.
Treatment Group 3: Enterisol Ileitis vaccine administered at day 0 (5 weeks of age) and pigs were challenged at day 28 of trial (9 weeks of age) with LI gut homogenate.
Treatment Group 4: Tylan in feed at 100 gms per ton starting on day 25 and at 40 grams per ton starting on day 46 through the end of the trial (day 56). Pigs were challenged at day 28 of trial (9 weeks of age) with LI gut homogenate.
Treatment Group 5: Enterisol Ileitis vaccine administered at day 0 (5 weeks of age) with Tylan in feed at 100 gms per ton starting on day 25 and at 40 grams per ton starting on day 46 through the end of the trial (day 56). Pigs were challenged at day 28 of trial (9 weeks of age) with LI gut homogenate.
All pigs had ad libitum access to feed and water from arrival at the facility to the end of the trial. Diets were formulated to be identical across treatments except for the addition of Tylan premix to the feed of treatment groups 4 and 5 beginning on day 25 of the trial. Phase feeding of diets was used so that nutritional content of the diets matched the age and size of the pigs. When changing from one dietary phase to another, all treatment groups were switched on the same morning. All feed was bagged and color-coded by the manufacturer and handled so that study personnel were blinded to treatment codes until the study was completed.
Enterisol Ileitis (LI Avirulent Live Culture, Serial 296- 061, Expiration Date: 17 Feb 04) was administered as per label directions on day 0 to pens in treatment groups T3 and T5 so that the animals received full dose of vaccine as per its label. The frozen vaccine was provided by Nelson Laboratories, Sioux Falls, SD 57104 and stored at -80°C until used. A four-hour water supply, based on an average animal weight, was calculated. Sodium thiosulfate was used as per label recommendations to neutralize any effect of chlorine in the water. Each pen was supplied with a vaccine volume and dose based on four animals per pen and an average animal weight across the vaccinated treatment groups. The vaccine dose for each pen was offered via a pen-specific reservoir connected to the pen drinker as the only source of water for 4 hours. T3 and T5 treated pens consumed the entire vaccine volume within the fourhour time period immediately after offering the vaccine. The veterinarian performing the clinical scoring and necropsies during the course of the trial was blinded to the groups that received the vaccine.
On day 28, animals in treatment groups T2, T3, T4, and T5 were given a 50 mL intragastric challenge dose consisting of intestinal mucosal homogenate containing 6.8 x 108 LI organisms per ml. Animals in T1 were administered an intragastric placebo challenge consisting of physiological saline. Challenge material was supplied and prepared by Dr. Nathan Winkelman, Swine Services Unlimited Inc., Morris, MN. An aliquot of the challenge material was shipped to Dr. Connie Gebhart, University of Minnesota Diagnostic Laboratory, for characterization and titration of the material.
Challenge material was administered by Dr. Nathan Winkleman and Dr. Ryan Saltzman. To minimize any effects of aging of the prepared challenge material, the challenge material was administered by rotating through the treatment groups and challenging only half the pens and then challenging the other half of the pens in each of the treatment groups. In addition, the two administrators each challenged half the pens in each treatment group.
Pen feed disappearance was recorded weekly or when a diet change was made. Individual pig weights were recorded weekly. Clinical observations of each pig were recorded by a veterinarian blinded to the treatment groups twice a week from day 0 to day 28 and three times a week thereafter. Sera for IPMA evaluation for LI antibodies was collected on days 0, 14, 28, and weekly thereafter. Fecal PCRs for LI were performed weekly on each pig and at necropsy, samples of ileum, cecum, and spiral colon were submitted for evaluation via H & E staining and immunohistochemistry. At necropsy, the order of pens being necropsied was rotated to minimize time or sampling bias in lesion scoring. At gross necropsy, intestinal lesion length and severity were scored by Dr. Winkelman who was blinded to the treatment groups.
An independent statistician who was blinded to the treatment groups performed the statistical analyses on the live animal performance data. The growth parameters were analyzed using the Mixed model procedure of SAS. These data were analyzed as 2 × 2 factorial. Tylan premix and Enterisol Ileitis vaccine main effects are reported as well as the interaction.
Results
Two animals from the T2 (challenged control group) and a third animal from T4 group died or were removed from the trial prior to day 56. One of the pigs removed from the T2 group was found dead and lesions and laboratory diagnosis were consistent with ileitis as the cause of death. The other pigs were moribund at time of removal and lesions and laboratory diagnostics were not consistent with clinical ileitis.
Overall the lesions found at necropsy on day 56 (4 weeks after challenge) were mild when present and IHC testingwas positive in less than half of the challenged pigs. This was expected, as the peak incidence and severity of lesions in the challenge model used usually are seen 14-18 days post challenge. Historically, the lesions produced by this infectious model are resolving after 18 days post-challenge.
Of the 96 challenged pigs, ninety had positive LI PCRs and 93 had positive IPMA serology results post challenge. No strict control pigs had positive IHC results at day 56 and in each of the challenged groups, no more than 50% of the pigs were positive for LI via IHC on any of the 3 tissues.
There was no significant interaction between the Tylan and Enterisol interventions. Tylan premix improved average daily gain (P = 0.007) and feed efficiency (P = 0.0008) during the 8 weeks of the study. Enterisol LI vaccine improved feed efficiency (P = 0.007) during the 8 weeks of the study. Tylan premix improved average daily gain (P = 0.03) and feed efficiency (P = 0.02) during the period 4 weeks after the LI challenge while Enterisol LI vaccine did not improve average daily gain (P = 0.29) or feed efficiency (P = 0.25) during the period after the LI challenge.