Impact of in-feed antibiotic regimens on pig performance and expression of clinical and subclinical diseases

Introduction

Determine the impact of purge and continuous feed additive regimens in grow-finish for the control of ileitis and respiratory disease caused by P. multocida as expressed through improved performance parameters of improved feed intake, growth rate and feed conversion.

Materials and methods

During the grow-finish period starting at 45 days post-weaning (avg. wt.47lbs) dietary treatments were:

1. (CONTRL) Control – no feed additives to slaughter
2. (CTCDNPUL) Chlortetracycline (CTC)/Denagard® (400/35 g/t) for 2 weeks followed by control to slaughter
3. (CTCPUL) CTC (400 g/t) for 2 weeks followed by control to slaughter
4. (NOVRTS) CTC/Denagard® (400/35 g/t) for 2 weeks, CTC (400 g/t) for 2 weeks, Tylan®(20 g/t) for 2 weeks, CTC/Denagard® (400/35 g/t) for 2 weeks and Tylan® (10 g/t) to slaughter
5. (TYLPUL) Tylan® (40 g/t) for 2 weeks followed by control to slaughter
6. (TYSTEP) Tylan® (40 g/t) for 4 weeks, 20 g/t for 4 weeks and 10 g/t thereafter.

There were a total of 36 pens of pigs placed on-test at weaning with 52 pigs per 10’ × 18’ fully slatted pen in a randomized complete block experimental design with wean date/pen location within the barn used as the blocking factor. Each pen in the tunnel ventilated facility had a 4-hole wean-finish feeder and 2 wean-finish cup drinkers.

Pigs (PIC 337 × Camborough®) were weaned from 2 filtered farrowing sites that were PRRS and M. hyopneumoniae negative. At arrival, pigs were individually ear tagged, weighed and assigned to pens such that pig weight and variation in weight within pen across all pens weaned on the same date were similar.

Pigs were vaccinated at weaning and on day 30 post-wean for PCV (Schering-Plough/Intervet Circumvent®PCV). On day 30 postwean pigs were vaccinated with Newport Laboratories 12063 autogenous bacterin (Haemophilus parasuis, Strep suis, Actinobacillus suis, and Mycoplasma hyopnuemoniae) used by the production system. On day 36 post-wean pigs received oral vaccines for erysipelas, salmonella, and ileitis (Boehringer Ingelheim Vetmedica). 

At approximately 47 lb bodyweight, the pigs were individually weighed with the gilts removed to room 1 and barrows remaining in room 2 (36 pens/sex (room)) at the research site. A total of 4 pigs were randomly removed from pens at this time to minimize differences in pigs per pen within a block due to death loss during the double stock period. A total of 1800 pigs began the growfinish phase of the experiment (CONTL–301, CTDNPUL–297, CTCPUL-299, NOVRTS-301, TYLPUL-300 and TYSTEP-302 head). Diets during the grow-finish period contained 30% DDGS until just prior to slaughter when the DDGS level was reduced to 15%. SID lysine declined from 1.14% to 0.68% over the course of the trial. Diets were changed on each weigh date.

Pens were weighed every 2 weeks. All pigs were individually weighed prior to removal of the first pig from a room for sale to slaughter and all pigs remaining were individually weighed at each subsequent sale date. The method of sale to slaughter was to remove 5 pigs/pen at the first sale, 5 pigs per pen on the next week’s sale day, and the remaining pigs 2 weeks after the second sale. Sale of gilts began one week after sale of barrows.

In the event of lameness at death, joint fluid swabs were taken and submitted to the University of Minnesota Veterinary Diagnostic Laboratory (UMnVDL), St Paul, MN. From day 80 to day 117 post wean limbs from dead pigs in the facility (whether or not a pig was on- or off-test) were submitted to the UMnVDL for identification of M. hyosynoviae and M. hyorhinis lesions and possible culture of these organisms from joint lesions. Limbs from a total of 20 out of 26 pigs that died or were euthanized during this time period were submitted. At the conclusion of the trial 5 pigs/pen from 1 pen of pigs within each sex within each dietary treatment were sampled for serum and nasal swabs. Oral fluids were collected using the rope test procedure. Samples were sent to the Iowa State VDL for PCR for M hyorhinis and M hyosynoviae. 

Beginning on day 74 and continuing to day 130 post-wean pens were scored for lameness a total of 9 different times. In every pen, the person doing the scoring recorded the number of pigs observed to be stiff or unwilling to rise/walk and the number of pigs observed to be lame with lameness defined as the pig being extremely reluctant or unable to bear weight on one or more limbs.

The pen of pigs (36 barrow pens and 36 gilt pens) was the experimental unit for pig performance data. The randomized complete block ANOVA included block and diet in the model. Because of blocking, sex was not specifically examined in the general model as it was included in the block effect. Individual pig treatment data, removals and death loss were examined by Chi-Squared analysis. 

Results and discussion

Of the 1800 pigs that were individually weighed to begin the grow-finish phase of the experiment on day 45 post-weaning, 1726 pigs (95.9%) were delivered for slaughter. An additional 15 pigs (0.8%) were sold as light and/or cull pigs. The remaining 59 pigs (3.3%) were removed from pens because of individual pig welfare considerations or died during the experiment. There was no effect of experimental treatments on the number of pigs dead, pigs removed or morbidity as measured by the number of pigs given injectable treatments.

During the double-stock nursery phase prior to individually weighing pigs on test, the ADG was 0.785 lb/d with a 1.24 F/G. There was no difference (P = 0.175) between dietary treatments for pig weight at the time of individual pig weighing on day 45 post weaning (Table 1). On day 59, and every subsequent weigh period until sales, pigs fed the NOVRTS regimen were the heaviest (P < 0.05 all periods). Pigs fed the NOVRTS regimen were 6.3 pounds heavier when delivered to slaughter than pigs on all other dietary treatments (278.9 lb vs 273.6 lb, P = 0.013). There was no difference in variation in pig weight within the pen on day 45 or day 138 (just prior to first removal for sale).

The response to the dietary additions of CTC/Denagard® at 400/35g/t (day 45-59), CTC at 400 g/t (day 59-74), and Tylan® at 20 g/t (day 74-87) occurred during the first three 2-week periods when average daily gain for NOVRTS fed pigs was always the highest. Daily gain for all pigs fed diets containing growth promoting additives was higher than CONTRL for the day 45-59 period (P < 0.05). During the day 59-74 period, only the NOVRTS and TYSTEP diets contained additives, with pigs fed the NOVRTS treatment of 400 g/t CTC having a 0.10 lb/d higher daily gain than pigs fed diets containing 40 g/t Tylan® (P < 0.05). For the day 74 to 87 period, pigs fed diets containing 20 g/t Tylan® (NOVRTS and TYSTEP) had a higher daily gain than pigs fed all other diets (P < 0.05) which contained no growth promotant.

Because of the faster daily gain for the first 42 day period, even with no differences in the rate of gain between experimental treatments for day 87-102 , day 102-115, day 115-127 or day 127-138 periods (P > 0.1), pigs on the NOVRTS treatment grew faster (P = 0.027) than all other pigs for the day 45-138 period. For the period day 45 to 138 when the first sale began, there was no effect of experimental diets on the variation in daily gain within a pen (P = 0.549), similar to the lack of difference in variation for weight within the pen. This suggests that the response to the NOVRTS treatment was similar for all pigs in the pen. If the response had been dependent in part on the pigs initial weight (for example lightest pigs have a better daily gain response than heavier pigs in a pen), there should have been a difference in the variation in daily gain in a pen.

The improved daily gain for the NOVRTS fed pigs during the first 6 week period was due to improved feed intake for these pigs for the first four 2-week periods, which resulted in an improved feed intake from day 45 to 138 (P < 0.05) compared to all other treatments. Overall (day 45 to 159), pigs fed the NOVRTS diets had an improved feed intake compared to all other treatments except for pigs fed the CTDNPL diet (P < 0.05). The effects of the varying feed additive regimens on feed conversion efficiency were variable between periods, with a tendency for the TYSTEP to have the best feed conversion for the day 45 to 138 period (P = 0.071). However, there was no effect of feed additive regimen on overall feed conversion for the day 45 to 159 period ( P = 0.590). 

While there appears to be a sharp spike in the number of pigs identified as stiff and lame between day 74 and day 77 (Figure 1), may be due to the time of day that the observations were made. The day 74 observations were made in the afternoon as the pen of pigs was moved to the pen scale during weighing of the pens of pigs. The day 77, 81 and 84 observations were made early in the morning upon entering the barns when the pigs were just beginning to move about for the day. It could be that the number observed as stiff and lame would have been higher had the day 74 observation been taken at a similar time in the morning versus the afternoon observation.

While lesions suggestive of bacterial infection of the joint were noted in several instances on limbs submitted to the UMnVDL, only 1 pig was confirmed to have M hyorhinis in the joint sampled. At the conclusion of the experiment, 7/12 pooled nasal swab samples were positive for M. hyorhinis and 2/12 were positive for M. hyosynoviae. Oral fluid sampling appears to be a more sensitive indicator since 9/12 were positive for M. hyorhinis and 12/12 positive for M. hyosynoviae. Further investigation as to the significance of these PCR results needs to be evaluated.

Acknowledgements

Thank you to Dr Erin Strait at Iowa State University for the experimental PCR for the minor Mycoplasma spp. We would also like to thank the SVC Research staff for help in the animal phase of the trial and clients for supplying the pigs.