FIELD EVALUATION OF THE EFFICACY OF THE VACCINE RESPISURE IN THE CONTROL OF ENZOOTIC PNEUMONIA IN SWINE

AVALIAÇÃO DA EFICÁCIA DA VACINA RESPISURE NO CONTROLE DE PNEUMONIA ENZOÓTICA DE SUÍNOS EM CONDIÇÕES DE CAMPO

ABSTRACT

A study was conducted in Brazil from June to November 1999, to evaluate the efficacy of RespiSure (Pfizer Animal Health) in the control of enzootic pneumonia in a commercial swine herd. Twenty-four (24) pregnant sows were randomly allocated into two groups (T1 and T2) of 12 sows each based on expected parturition dates. Piglets from sows in T1 (131) received two IM injections of 2 mL saline solution, and piglets of T2 (133) received two doses (2 mL IM) of RespiSure on day 0 of study (between 6 to 12 days of age) and 20 days later. Piglets were weaned on day 20, and moved to grower/finisher unit on day 55 randomly assigned to 6 pens/treatment. Individual pig weights were taken on days 20, 55 and 144. Feed was weighed by pen from day 55 to 144. All pigs were slaughtered on day 145 (115 pigs in T1 and 118 in T2) and lung lesions were blindly scored during inspection at slaughter. Vaccination with RespiSure, resulted in a significant (P<0.05) lower lung lesion score (0.20% versus 2.5%), lower frequency of pigs with lung lesions (23.7% versus 57.4%), higher mean weight at slaughter (92.28 kg versus 83.96 kg), higher daily weight gain per pig (0.70 kg/day/pig versus 0.63 kg/day/pig) and better feed conversion ratio (2.527 versus 2.905) compared to control.

KEY WORDS:
Mycoplasma hyopneumoniae; vaccine; enzootic pneumonia; swine; efficacy.

RESUMO

Um estudo foi conduzido entre junho e novembro de 1999, em uma criação comercial de suínos no Brasil, para avaliar a eficácia da vacina RespiSure (Pfizer Saúde Animal) no controle da pneumonia enzoótica. Vinte e quatro porcas prenhes foram distribuídas randomicamente em dois lotes de 12 porcas para obtenção dos leitões utilizados nos grupos controle (T1) e vacinado (T2). Os leitões do grupo T1 (131) receberam duas injeções (2 mL IM) de salina estéril e os do T2 receberam duas doses (2 mL IM) de RespiSure no dia 0 do teste (6 a 12 dias de idade) e 20 dias depois. Os leitões foram desmamados no dia 20 e no dia 55 foram transferidos para a unidade de terminação (6 baias/tratamento). Nos dias 20, 55 e 144, os suínos foram pesados individualmente. A ração foi pesada diariamente do dia 55 ao dia 144. No dia 145 os suínos foram abatidos (115 suínos de T1 e 118 de T2) e as lesões de pneumonia nos pulmões foram avaliadas em forma de escores por uma pessoa que desconhecia os tratamentos. A vacinação com RespiSure, teve significativamente (P<0,05) menor média de escores de lesões (0,20% versus 2,5%), menor freqüência de suínos com lesões pulmonares (23,7% versus 57,4%), maior média de peso ao abate (92,28 kg versus 83,96 kg), maior ganho de peso médio diário (0,70 kg/dia/suíno versus 0,63 kg/dia/suíno) e melhor conversão alimentar (2,527 versus 2,905) comparado ao controle.

PALAVRAS-CHAVE:
Mycoplasma hyopneumoniae; vacina; pneumonia enzoótica; suínos; eficácia.

INTRODUCTION

Enzootic pneumonia has been reported from many countries and has long been recognized as one of the most common and economically important diseases occurring in swine (ROSS, 1999). Mycoplasma hyopneumoniae, the causative agent of enzootic pneumonia in swine, is a member of the genus Mycoplasma that belongs to the cell wall-deficient class Mollicutes (MANILOFF et al., 1992).

The clinical expression of the disease has been described as a non-productive cough that begins about 1 month after nursery pigs are placed into continuous flow finishing units. The cough persists in individual pigs for 4 to 6 weeks and then diminishes gradually (CLARK, 1999). Loss associated with the disease is the result of a complex interaction between the Mycoplasma and other infections, poor management, and poor environmental conditions (ROSS, 1999). The control and prevention of M. hyopneumoniae infections are based on the use of antibiotics, hygienic management and vaccination (POMMIER et al., 2000).

The purpose of the present study was to evaluate the efficacy of the vaccine RespiSure (Pfizer Animal Health) in the prevention of lung lesions and to determine if vaccination has an effect on daily weight gain and on feed conversion ratio in a commercial pig herd in Brazil.

MATERIALS AND METHODS

Experimental design and treatments

This experiment was a controlled and randomized clinical field study. A commercial farrow-to-finish farm was selected for its known history of enzootic pneumonia confirmed through serological assays.

Twenty-four (24) pregnant sows were randomly selected and allocated in two groups, T1 and T2 with 12 sows each based on expected parturition dates and similar distribution of parities. One hundred and thirty-one (131) piglets born from T1 sows received an IM injection of 2 mL sterile saline solution on day on test 0 (DOT 0), when they were between 6 and 12 days old and 20 days later they received a second injection. One hundred and thirtythree (133) piglets from T2 sows were vaccinated IM on those same days with a 2 mL dose of RespiSure. The piglets were weaned on DOT 20 and were moved to the grower/finisher unit on DOT 55.Piglets were allocated randomly by litter to six pens per treatment (two litters in each pen) in the grower/ finisher unit. The piglets were housed in similar conditions, received the same feed and were subjected to the same management. The animals did not receive any antibiotic treatment and were individually monitored during the entire experimental period of 5 months. All pigs were slaughtered by pen on day 145.

Local and adverse reactions were checked during a 30 minute period following each vaccination.

Lung Lesion Scores

At slaughter the lungs with Mycoplasma like lesions were scored based on the scoring system described by MADEC & KOBISCH (1982). The examiner was unaware of the treatment administered.

Body Weight

All pigs were weighed individually at weaning (DOT 20), on the day they were moved to grower/ finisher facilities (DOT 55), and on the day before slaughter (DOT 144) to calculate the weight gain during each growth phase.

Feed Conversion Ratio

The feed consumed per pig was calculated for each pen between DOT 55 and 144 in order to calculate the feed conversion ratio for that time period. Feed conversion ratio was calculated as the feed consumed per pen divided by the weight gain per pig.

Statistical Analysis

Lung Lesions: before statistical analysis the total lung lesion score (%) was transformed by taking the arcsine of the square root of the total score divided by 100. The transformed total lung lesion score was analyzed using a general linear mixed model analysis of variance. Back-transformed treatment least squares means were calculated. Pairwise comparisons between treatments were made using Fisher’s protected LSD.

Body weight: Pairwise comparisons between treatments were made for each data collection time point (DOT) using Fisher’s protected LSD. Average daily gains between treatments were compared using estimate statements.

Feed conversion ratios were analyzed using a general linear mixed model analysis of variance. Treatment least squares means were calculated. Pairwise comparisons between treatments were made using Fisher’s protected LSD.

All statistical analyzes were done using an a value of 5% (P≤ 0.05).

RESULT

The initial number of piglets included in the study was 131 in T1 group and 133 in T2 group and, at the end of study, 115 pigs remained in T1 and 118 in T2 (Table 1). Sixteen (16) pigs of T1 and 15 of T2 group died during the study period. There was no mortality related to respiratory disease.

Table 1
Number of pigs included in the study and mortality during the experiment.

Groups/ treatment	Sows	Number of pigs in the study
		Initial	Final	Mortality
Tlsaline	12	131	115	16 (12,2 %)
T2- RespiSure	12	133	118	15 (11,3 %)

No adverse reactions were observed in any of the RespiSure vaccinated or saline treated control pigs.

Lung Lesion Scores

The number of pigs presenting Mycoplasma hyopneumoniae like lesions at slaughter was significantly (P<0.05) lower in the vaccinated group. The frequency of pneumonia lesions was 57.4% in the T1 group compared to 23.7% in the T2 group (Table 2). The average pneumonia lesion score was 92% lower (P< 0.05) in the vaccinated group, that had a mean of 0.20% of the lungs area affected compared to 2.5% in T1 (Table 3).

Table 2
Frequency of pigs with Mycoplasma like lung lesions.

Group/ treatment	Pigs with s lung lesion	Pigs without lung lesions	Total
T1- saline	66 (57.4%)a	49 (42.6%)a	115
T2- RespiSure	28 (23.7%)b	90 (76.3%)b	118

• ^{a, b}
  =Between treatments, columns with different superscripts are significantly different (P<0.05).

Table 3
Severity of lung lesions back transformed least squares means (%).

Back transformed least square means (%)	T1- Saline solution	T2- RespiSure	% decrease
2.50a	0.20b	92

• ^{a, b}
  = Between treatments, lung lesions back transformed least squares means with different superscripts are significantly different (P<0.05).

Body Weights

The body weight least squares means per pig were significantly (P<0.05) higher in the vaccinated group on days 55 and 144 compared to the salinetreated control (Table 4). The final mean weights per pig was 83.96 kg in the T1 group compared to 92.28 kg in the RespiSure vaccinated pigs. The average daily weight gain (ADWG) per pig in T2 group (0.70 kg/day/pig) was also significantly (P<0.05) higher than the ADWG in the control group (0.63 kg/day/ pig) from day 20 to day 144 (Table 5) and during the grower/finisher phase that were respectively 0.81 kg/day/pig and 0.74 kg/day/pig.

Table 4
Least squares means of body weights per pig.

Group/ treatment	Least Squares Means of Body Weights per Pig (kg)
	DOT 20	DOT 55	DOT 144
T1- saline	5.43a	18.42a	83.96a
T2- RespiSure	6.06a	19.92b	92.28b

• ^{a, b}
  = Between treatments, at each day on test (DOT), means with different superscripts are significantly different (P<0.05).

Table 5
Average daily weight gain per pig (kg/pig/day) during each weighing period.

Group/ treatment	Mean Daily Weight Gain per Pig (kg/day)
	DOT 20 to DOT 55	DOT 20 to DOT 144	DOT 55 to DOT 144
T1- saline	0.37a	0.63a	0.74a
T2- RespiSure	0.40a	0.70b	0.81b

• ^{a, b}
  =Between treatments, means of each period with different superscripts are significantly different (P<0.05).

Feed Conversion Ratio

The feed conversion ratio was significantly (P< 0.05) better in the vaccinated pigs (Table 6). The feed conversion ratio was 2.527 in the vaccinated group and 2.905 in the control group during the grower/ finisher phase from day 55 to day 144.

Table 6
Feed conversion ratio during the grower/finisher phase (From day on test 55 to day on test 144 of study).

Feed Conversion Ratio	T1- Saline solution	T2- RespiSure
	2.905a	2.527b

• ^{a, b}
  =Feed conversion with different superscripts are significantly different (P<0.05).

DISCUSSION

The swine herd included in this study was exposed to a high M. hyopneumoniae challenge, as shown by the high pneumonia rate observed at slaughter in the non-vaccinated control group (57.4%). Despite this high challenge, a significantly reduced pneumonia rate of 23.7% was obtained by the vaccination. The decrease observed in the frequency of pigs with lung lesions was higher than described by POMMIER et al. (2000), that reported a reduction from 73.9 % in the control group to 53.2 % in the vaccinated group.

A significantly lower lung lesion score was obtained by vaccination compared to saline control. The total lung lesion score back transformed least squares means in vaccinated group was 0.20% and in the control group was 2.5% (P<0.05), a reduction of 92%. POMMIER et al. (2000) reported a reduction in the severity of lung lesions by about 50% in vaccinated pigs.

Economic loss attributable to enzootic pneumonia has long been associated with reduced rate of weight gain and feed efficiency (ROSS, 1999). POINTON et al. (1985) reported that the growth rate of pigs affected by enzootic pneumonia was reduced by 12.7% between 50 and 85 kg body weight. ROSS (1999) found that the growth rate of pigs exposed to infected dams was reduced by 15.9%, and feed conversion was decreased by 13.8%. In the present study the final mean weight per pig (92.28 kg) as well as average daily weight gain per pig (0.70 kg/ day) of the vaccinated pigs were significantly higher (P<0.05) than observed in the control group (83.96 kg, ADWG 0.63 kg/day). The observed lower lung lesion scores associated with the improvement of daily weight gain in the vaccinated group is in agreement with HILL et al. (1992) that reported an inverse relationship between growth indicators and volume of lung lesions at slaughter. These results differ from those described by POMMIER et al. (2000), that did not find significant differences among average daily weight gain per pig when compared to non vaccinated group. The feed conversion ratio in the present study was also significantly better (P<0.05) in vaccinated pigs (2.527) than that observed in the control group (2.905) during the grower/finisher phase from day 55 to day 144. In the particular conditions of a field clinical trial, management techniques or sanitary status of the herd can interfere with the effects of vaccination or treatment of respiratory diseases on the improvement of zootechnical parameters (POMMIER et al., 2000). Thus, to minimize the interference of management and therapy in the experiment, the swine herd chosen to conduct this study did not utilize metaphylactic antibiotic treatment during any production phase.

The mortality rates were similar in vaccinated (11.3%) and control group (12.2%) from the birth to slaughter, and the causes were not related to respiratory disease.

The present study has demonstrated the efficacy of vaccination with RespiSure in the control of enzootic pneumonia caused by M. hyopneumoniae, under high field challenge conditions, in Brazil. Vaccination with RespiSure reduced not only the frequency of lung lesions and the lung lesion scores, but also improved the mean of body weight, the average daily weight gain per pig and the feed conversion ratio.

ACKNOWLEDGEMENT

The authors would like to thank Ms. Vickie King (Pfizer Animal Health, NY, USA) for the statistical analysis.

REFERENCES

• CLARK, K.L. Mycoplasma hyopneumoniae: Serology/ Vaccinology. In: ANNUAL MEETING OF AMERICAN ASSOCIATION OF SWINE PRACTITIONERS, 29., 1998, St. Louis, Missouri. Proceedings. p.365-369.
• HILL, M.A.; SCHEIDT, A.B.; TECLAW, R.F.; CLARK, L.K.; KNOX, K.E.; JORDAN, M. Association between growth indicators and volume of lesions in lungs from pigs at slaughter. Am. J. Vet. Res, v.53, p.2221-2223, 1992.
• MADEC, F. & KOBISCH, M.: Bilan lésionel des porcs charcutiers à l’abattoir. Journées de la Rech. Porcine Fr., v. 14, p. 405412, 1982.
• MANILOFF, J.; MCELHANEY, R.N.; FINCH, L.R.; BASEMA, J.B. (Eds.) Mycoplasmas: molecular biology and pathogenesis., Washington, DC.: .American Society for Microbiology, 1992.
• POINTON, A.M.; BYRT, D.; HEAP, P. Effect of enzootic pneumonia of pigs on growth performance. Aust. Vet. J , v. 62, p.13-18, 1985.
• POMMIER, P.; KEITA, A.; PAGOT, E.; FLOCHLAY, A. Field efficacy of a Mycoplasma hyopneumoniae vaccine in the control of enzootic pneumonia in swine. Ver. Méd. Vét, Toulouse, v.151, n.8-9, p.835-840, 2000.
• ROSS, R.F. Mycoplasmal diseases. In: STRAW, B.; D’ALLAIRE, S.; MENGELING, W.L.; TAYLOR, D.J. (Eds.) Diseases of swine, 8 ed. Ames, Iowa: Iowa University Press, p.495509, 1999.

Publication Dates

• Publication in this collection
  20 Sept 2024
• Date of issue
  Jan-Mar 2002

History

• Received
  24 Aug 2001
• Accepted
  27 Nov 2001