lnwrnationa/ Journal o]" b'r,nl Microbb~h~.s,~.". 15 ( I °~2 ) 313 - 317 ~t~ Iq92 Elsevier Science Publishers B.V. All rights reserved 1111~8-16tl5/92/$115.1111
313
FOOD 1111495
Prevention of colonization by Salmonella enteritidis PT4 in broiler chickens N . M . Bolder, L.A.J.T. van Lith, F.F. Putirulan, W.F. J a c o b s - R e i t s m a
and R.W.A.W. Mulder Sl~'lderholt Centre for Poult~' Resear('h and h~formaticm Sertice,~, Agri( ultural Resear('h Delnirtmcnt (DLOL Beekl~'rgen, The Netherland.~
Field experiments in The Netherlands and in Scandinavian countries h~we shown that an undefined microflora originating from SPF adult poultry will reduce considerably the colonization of young chicks by Sahnonelia. A commercial product from this so-called Nurmi concept, Broilact ~. was studied for its effectiveness in preventing infection of broilers with Sabmmclha emeruMi,~ PT4 (S,e.). Two trials were carried out, in which the birds were exposed to S.c. via "seeder" birds placed among them, The trial perit~l was 21 days and each week one third of the chicks was killed and their caecal contents examined for salmonellas. The results of the first trial can be summarized as foUows, (I) After 2 weeks the number of "seeder' birds carrying the Sahmmella decreased sharply; 12) the proportion of infected chicks in the Broilact ~-treated group was lower than in the non-treated group; (3) Counts t~f S.c. in the non-treated group were higher than in the Broilact" group. Results of the second trial were comparable, although no salmonellas could be isolated after the second week. Key words: Samumella (,meritidi,~: Colonization, prevention of: Competitive exclusion; Chicks
Introduction Since 1988 Salmonella enteritidis has played an increasingly important role in foodborne disease. The problem started with laying hens and their eggs, but the incidence ,;f S. enteritidis in broilers has also increased. Good hygienic practices in broiler slaughterhouses have not yet resulted in a Salmonella-free end-product. To produce a product which is Salmonella-free, control measures also need to be taken at the growing stage. One of these measures is the application of competitive exclusion (CE), a concept in which the rapid build-up of a natural intestinal microflora is induced, and where attachment of undesirable microorganisms to the intestinal epithelia is inhibited. This technique, the so-called Nurmi concept, is based upon research by Nurmi and Rantala (1973) and has been further developed for mass application. Corresl~mdence to: N.M. Bolder, Spelderholt Centre for Poultry Research and lnformaUon Services, Agricultural Research Department (DLO), 7361 DA Beekbergen, The Netherlands.
314 The use of defined protective cultures in the U.K. and Canada has shown some success under laboratory, conditions, but results have lacked reproducibility. Such preparations have not been used under field conditions, in The Netherlands field experiments have shown that spray application of an undefined microflera from SPF adult poultry to day old broiler chicks reduces Salmonella colonization considerably (Goren et al., 1988). in the Scandinavian countries, and recently in the U.S.A., an undefined microflora is given via the drinking water. In Finland and Sweden a commercial product is used, and shows beneficial effects (Wierup, 1991). The present study was carried out to investigate the effectiveness of Broilact ~ in preventing broiler chicks from being colonized by S. enteritidis PT4.
Materials and Methods
in two trials, newly hatched Hypeco broiler-type chicks were obtained from the Spelderholt hatchery. The hatching eggs were not treated with any antibiotic but were disinfected with formaldehyde prior to brooding. The broiler-breeder flock was tested twice for Salmonella by taking 2 x 100 g samples of fresh caecal and faecal material mixed together. Immediately after hatching, the day-old chicks were placed in their final housing, and divided into 7 groups each of 30 chicks, kept on wood shavings in separate pens with their own feed and water supply. Prior to separation the chicks were dosed orally with 0.25 ml of Broilact ~. The following test groups were used: Group 1: control group without Broilact ~, no Sabnonella challenge. Groups 2 and 3: control groups without Broilact ~, but with Salmonella challenge. Groups 4-7: Broilact~-treated groups, with Salmonella challenge. To check the initial Salmonella status of the chicks, hatching debris such as egg shells, dead-in-shell chicks and fluff were collected and analysed. The birds were challenged 2 days after treatment with Broilaet ~ by adding 6 so-called 'seeder' chicks to each pen. At the day of hatch each 'seeder' chick was challenged orally with 5 x 107 CFU/chick of a nalidixic acid-resistant S. enteritidis PT4 strain in 0.5 mi of physiological saline. This strain was isolated from poultry and grown in brain heart infusion broth (Oxoid, CM 225) with 25 m g / I nalidixic acid. The 'seeder' chicks from the challenge control group were given 0.5 ml of physiological saline. Prior to placing the 'seeder' chicks in their pens, they were tested for Salmonella by swabbing individually. The broiler feed used contained no coccidiostat or growth promoter and had been pelleted. It was tested for Salmonella by taking 2 x 200 g samples. Each week, 10 broilers from each group, plus 2 'seeder' chicks were killed humanely. After weighing each bird, both caeca were removed. The surfaces of the caeca were disinfected with alcohol and the caeeal contents sampled aseptically and diluted in Buffered Peptone Water (BPW) (Oxoid, CM 509). Ten-fold dilutions were plated on Brilliant Green Agar (BGA) (Oxoid, CM 329) containing 50 ppm nalidixic acid and incubated at 37 °C for 48 h. Typical colonies were counted
315 and randomly checked to confirm the presence of the challenge organism. Where counts were below the detection level of 10-" C F U / g of caecal material, the primary dilution in BPW was enriched at 37 ° C for 24 h, followed by selective enrichment in Rappaport-Vassiliadis Broth (RV) (Oxoid, CM 66q~ at 4 3 ° C for 48 h. After 24 and 48 h, the RV Broth was streaked on B G A and incubated at 37 ° C for 48 h. Suspect colonies were investigated serologically.
Results and Discussion
T h e b r e e d e r flock producing the eggs for both trials was Samoneila-negative when the hatching eggs were collected. No salmonellas were found in the samples of hatching debris, nor in the feed samples or in wcmd shavings. T h e water supply also appeared to be SabnoncUa-free. Table ! gives percentages of S. enteritidis-positive chicks after 1, 2 and 3 weeks, T h e figures show a positive effect of the Broilact ~" treatment, although not all birds remained S.e.-negative. In the second trial no salmonellas were found at the third week of sampling, not even after enrichment. During both trials both the n u m b e r of S. enteritidis-positive chicks decreased, and the n u m b e r of S. emeritidis per g of caecal contents, in Table I! a division is made between birds with above and below 102/g. Broilact'' treatment resulted in a decrease in the n u m b e r of birds with high S. enteritidis counts at weeks 2 and 3. In both trials, some of the control birds a p p e a r e d to be Sabnonella-positive but only after enrichment (Tables ! and !!). It is not clear how these birds became infected. Prior to placing the 'seeder' birds in the cages they were individually sampled for salmonellas by swabbing fresh faecal material. All these 'seeder' birds app e a r e d to be S. enteritidis shedders on the day they were transferred. After 1 week, most of them continued to show high counts of S. enteritidis in their caeeal contents. In the first trial the counts varied between 2 × 104/g and 2 × 106/g, and in the second trial between 8 × 103/g and 6 x 10b/g. At 2 weeks of age, only 5 out
TABLE 1 S. enteritidis (S.e.) incidence in broiler chicks after treatment with Broilact ~ Group Trial I Control Control + S.c. Broilact~ Trial 2 Control Control + S.e. Broilact'~
Number of birds
c/; Positive week I
week 2
I0 20 40
I0 45 20
0 55 5
I0 20 40
I0 30 20
I0 5 2.5
week 3 I0 20 8 0 0 0
316 TABLE II Counts of S. enteritMis (S.c.) from broiler chicks after treatment with Broilaet " Group
Number of birds
week I > 102 ,,
< 102
week 2 > 10z
< i02
week 3 > i02
Control
I0
0
l
0
0
0
I
Control + S.c. Broilact " Trial 2
20 40
8 8
i 0
5 0
6 2
4 I
0 2
10
0 2 4
i 4 4
0 I 0
I 0 I
0 0 0
0 0
< i0 z
Trial I
Control C o n t r o l + S.c. Broilact R
20 40
0
" CFU/g of caecal content.
o f 12 broilers were S. enteritidis-positive in the first trial ( c o u n t s b e t w e e n 1 x 1 0 2 / g a n d 5 × 1 0 * / g ) whilst in the s e c o n d trial n o S. alteritidis-positive birds w e r e f o u n d at this stage (see T a b l e Ill). T h e lack o f ability o f this S. enteritidis strain to c o n t i n u o u s l y colonize the ' s e e d e r ' birds could hardly have b e e n anticipated, in o t h e r e x p e r i m e n t s this strain p r o v e d to be very virulent ( B o l d e r et al., 1991) a n d c o l o n i z e d chickens very well for at least 3 weeks. Selection o f a strain with nalidixic acid resistance might be the explanation. A f t e r i n c u b a t i o n for 24 h, the test strain p e r f o r m e d p o o r l y on B G A with o r w i t h o u t 50 p p m nalixidie acid, but after extension o f the i n c u b a t i o n time to 48 h, g r o w t h a p p e a r e d to be typical. Protais et al. (1990) f o u n d p o o r isolation rates for S. enteritidis with R V e n r i c h m e n t b r o t h in c o m p a r i s o n with T e t r a t h i o n a t e broth. T h e u n e x p e c t e d l y p o o r p e r f o r m a n c e o f the p r e s e n t test strain m i g h t be related to the isolation m e t h o d s used, so the isolation m e t h o d for S. alteritidis n e e d s to be r e c o n s i d e r e d . T a b l e IV
TABLE Iii Counts of S. enteritidis (S.e.) from 'seeder' birds Group Trial I Control Control + S.e. Broilact ~ Trial 2 Control Control + S.e. Broilact '~
Number of birds
week I > 102 ,,
< 10z
week 2 > 102
< 102
week 3 > 102
< 10z
2 4
0 3
0 0
0 I
I 0
0 I
0 0
8
7
0
4
0
0
1
2 4
0 4
0 0
0 0
0 0
0 0
0 0
8
8
0
0
0
0
0
~' CFU/g of caecal content.
317 TABLE IV Weight (g) of chicks after killing Group Trial I Control Control + S.c. Broilact " Trial 2 Control C'.)l,)rol + S.c. Broilao "
week I
week 2
week 3
n
g
n
g
n
g
It) 2ll 40
251.4 246.4 239.0
tO 2t) 4~)
512.7 50~.~ -'¢,";,i
It) 2ll 37
842.9 S84.~ 881,4
i(I 20 40
233.2 223.0 248.9
10 2(1 4t)
483,6 483.7 523.1)
9 14 3t~
696.7 67t1.2 705.8
gives t h e r e s u l t s for b i r d w e i g h i n g s i m m e d i a t e l y a l t e r killing. T h e m e a n w e i g h t o f t h e B r o i l a c t ~" g r o u p in trial l w a s l o w e r t h a n t h a t o f t h e c h a l l e n g e c o n t r o l g r o u p , w h e r e a s in t h e s e c o n d trial t h e B r o i l a c t " c h i c k s p e r f o r m e d b e t t e r t h a n e i t h e r o f t h e o t h e r g r o u p s . T h e m e a n w e i g h t at 3 w e e k s o f a g e d i f f e r e d b e t w e e n t h e two trials, b u t t h e c h i c k s in trial ! w e r e 3 d a y s o l d e r at the d a y o f s l a u g h t e r .
Conclusions C o m p e t i t i v e e x c l u s i o n o f S. emeritidis by t r e a t i n g d a y - o l d c h i c k s w i t h B r o i l a c t "' d e c r e a s e s t h e i n c i d e n c e o f S. enteritidis in g r o w i n g b r o i l e r s . A l s o t h e n u m b e r o f S. enteritMis-positive b i r d s d e c r e a s e d m o r e r a p i d l y t h a n in n o n - t r e a t e d b i r d s . T h e r e is n o o b v i o u s e x p l a n a t i o n for t h e p o o r c o l o n i z a t i o n by S. enteritMis in t h e 'seeder' birds. C o m p e t i t i v e e x c l u s i o n c a n b e o n e o f m a n y m e a n s o f r e d u c i n g ) h e Sabnonella p r o b l e m , b u t it s h o u l d b e a p p l i e d in c o m b i n a t i o n w i t h o t h e r m e a s u r e s , s u c h a s g o o d h y g i e n i c p r a c t i c e s in t h e e n t i r e p o u l t r y p r o d u c t i o n c h a i n .
References Bolder. N.M., van Lith, L.A.J.T, and Mulder, R.W.A,W. (IL)91) Production of Salmonella enteritidis contaminated eggs after artificial inoculation ol laying hens. Proceedings 10th Symposium on the Quality of Poultry Meat; Safety and marketing aspects, ed. R.W.A.W. Mulder and A.W. de Vries, D(~)r~verth, 12-17 May, The Netherlands, pp. 27-34, Goren, E., de Jong, W.A.. D~a)rnenbal, P., Bolder, N.M., Mulder, R.W.A.W. and Jansen, A. (1988) Reduction of salmonella infection of broilers by spray application of intestinal microflora: a longitudinal study. Vet. Q. 10, 24~}-255. Nurmi, E. and Rantahl, M. (1~)73) New aspects of Salmonelhl infection in broiler production. Nature 241,210-21 I. Protais, J., Lahcllec. C. and lk)scher, E. (1990) Techniques de detection des Salmonelles. L'Aviculteur, Dec., 31. Wierup, M., Wahlstrlim, It. and Engstr~im, B. ( It)g1) The experience of a ten years use of CE culture as a part of the Salmonella control program in Sweden. Proceedings of the International Symposium on cohmization control of human pathogens in poultry. D(~)rwerth, May 17, The Netherlands.
313
FOOD 1111495
Prevention of colonization by Salmonella enteritidis PT4 in broiler chickens N . M . Bolder, L.A.J.T. van Lith, F.F. Putirulan, W.F. J a c o b s - R e i t s m a
and R.W.A.W. Mulder Sl~'lderholt Centre for Poult~' Resear('h and h~formaticm Sertice,~, Agri( ultural Resear('h Delnirtmcnt (DLOL Beekl~'rgen, The Netherland.~
Field experiments in The Netherlands and in Scandinavian countries h~we shown that an undefined microflora originating from SPF adult poultry will reduce considerably the colonization of young chicks by Sahnonelia. A commercial product from this so-called Nurmi concept, Broilact ~. was studied for its effectiveness in preventing infection of broilers with Sabmmclha emeruMi,~ PT4 (S,e.). Two trials were carried out, in which the birds were exposed to S.c. via "seeder" birds placed among them, The trial perit~l was 21 days and each week one third of the chicks was killed and their caecal contents examined for salmonellas. The results of the first trial can be summarized as foUows, (I) After 2 weeks the number of "seeder' birds carrying the Sahmmella decreased sharply; 12) the proportion of infected chicks in the Broilact ~-treated group was lower than in the non-treated group; (3) Counts t~f S.c. in the non-treated group were higher than in the Broilact" group. Results of the second trial were comparable, although no salmonellas could be isolated after the second week. Key words: Samumella (,meritidi,~: Colonization, prevention of: Competitive exclusion; Chicks
Introduction Since 1988 Salmonella enteritidis has played an increasingly important role in foodborne disease. The problem started with laying hens and their eggs, but the incidence ,;f S. enteritidis in broilers has also increased. Good hygienic practices in broiler slaughterhouses have not yet resulted in a Salmonella-free end-product. To produce a product which is Salmonella-free, control measures also need to be taken at the growing stage. One of these measures is the application of competitive exclusion (CE), a concept in which the rapid build-up of a natural intestinal microflora is induced, and where attachment of undesirable microorganisms to the intestinal epithelia is inhibited. This technique, the so-called Nurmi concept, is based upon research by Nurmi and Rantala (1973) and has been further developed for mass application. Corresl~mdence to: N.M. Bolder, Spelderholt Centre for Poultry Research and lnformaUon Services, Agricultural Research Department (DLO), 7361 DA Beekbergen, The Netherlands.
314 The use of defined protective cultures in the U.K. and Canada has shown some success under laboratory, conditions, but results have lacked reproducibility. Such preparations have not been used under field conditions, in The Netherlands field experiments have shown that spray application of an undefined microflera from SPF adult poultry to day old broiler chicks reduces Salmonella colonization considerably (Goren et al., 1988). in the Scandinavian countries, and recently in the U.S.A., an undefined microflora is given via the drinking water. In Finland and Sweden a commercial product is used, and shows beneficial effects (Wierup, 1991). The present study was carried out to investigate the effectiveness of Broilact ~ in preventing broiler chicks from being colonized by S. enteritidis PT4.
Materials and Methods
in two trials, newly hatched Hypeco broiler-type chicks were obtained from the Spelderholt hatchery. The hatching eggs were not treated with any antibiotic but were disinfected with formaldehyde prior to brooding. The broiler-breeder flock was tested twice for Salmonella by taking 2 x 100 g samples of fresh caecal and faecal material mixed together. Immediately after hatching, the day-old chicks were placed in their final housing, and divided into 7 groups each of 30 chicks, kept on wood shavings in separate pens with their own feed and water supply. Prior to separation the chicks were dosed orally with 0.25 ml of Broilact ~. The following test groups were used: Group 1: control group without Broilact ~, no Sabnonella challenge. Groups 2 and 3: control groups without Broilact ~, but with Salmonella challenge. Groups 4-7: Broilact~-treated groups, with Salmonella challenge. To check the initial Salmonella status of the chicks, hatching debris such as egg shells, dead-in-shell chicks and fluff were collected and analysed. The birds were challenged 2 days after treatment with Broilaet ~ by adding 6 so-called 'seeder' chicks to each pen. At the day of hatch each 'seeder' chick was challenged orally with 5 x 107 CFU/chick of a nalidixic acid-resistant S. enteritidis PT4 strain in 0.5 mi of physiological saline. This strain was isolated from poultry and grown in brain heart infusion broth (Oxoid, CM 225) with 25 m g / I nalidixic acid. The 'seeder' chicks from the challenge control group were given 0.5 ml of physiological saline. Prior to placing the 'seeder' chicks in their pens, they were tested for Salmonella by swabbing individually. The broiler feed used contained no coccidiostat or growth promoter and had been pelleted. It was tested for Salmonella by taking 2 x 200 g samples. Each week, 10 broilers from each group, plus 2 'seeder' chicks were killed humanely. After weighing each bird, both caeca were removed. The surfaces of the caeca were disinfected with alcohol and the caeeal contents sampled aseptically and diluted in Buffered Peptone Water (BPW) (Oxoid, CM 509). Ten-fold dilutions were plated on Brilliant Green Agar (BGA) (Oxoid, CM 329) containing 50 ppm nalidixic acid and incubated at 37 °C for 48 h. Typical colonies were counted
315 and randomly checked to confirm the presence of the challenge organism. Where counts were below the detection level of 10-" C F U / g of caecal material, the primary dilution in BPW was enriched at 37 ° C for 24 h, followed by selective enrichment in Rappaport-Vassiliadis Broth (RV) (Oxoid, CM 66q~ at 4 3 ° C for 48 h. After 24 and 48 h, the RV Broth was streaked on B G A and incubated at 37 ° C for 48 h. Suspect colonies were investigated serologically.
Results and Discussion
T h e b r e e d e r flock producing the eggs for both trials was Samoneila-negative when the hatching eggs were collected. No salmonellas were found in the samples of hatching debris, nor in the feed samples or in wcmd shavings. T h e water supply also appeared to be SabnoncUa-free. Table ! gives percentages of S. enteritidis-positive chicks after 1, 2 and 3 weeks, T h e figures show a positive effect of the Broilact ~" treatment, although not all birds remained S.e.-negative. In the second trial no salmonellas were found at the third week of sampling, not even after enrichment. During both trials both the n u m b e r of S. enteritidis-positive chicks decreased, and the n u m b e r of S. emeritidis per g of caecal contents, in Table I! a division is made between birds with above and below 102/g. Broilact'' treatment resulted in a decrease in the n u m b e r of birds with high S. enteritidis counts at weeks 2 and 3. In both trials, some of the control birds a p p e a r e d to be Sabnonella-positive but only after enrichment (Tables ! and !!). It is not clear how these birds became infected. Prior to placing the 'seeder' birds in the cages they were individually sampled for salmonellas by swabbing fresh faecal material. All these 'seeder' birds app e a r e d to be S. enteritidis shedders on the day they were transferred. After 1 week, most of them continued to show high counts of S. enteritidis in their caeeal contents. In the first trial the counts varied between 2 × 104/g and 2 × 106/g, and in the second trial between 8 × 103/g and 6 x 10b/g. At 2 weeks of age, only 5 out
TABLE 1 S. enteritidis (S.e.) incidence in broiler chicks after treatment with Broilact ~ Group Trial I Control Control + S.c. Broilact~ Trial 2 Control Control + S.e. Broilact'~
Number of birds
c/; Positive week I
week 2
I0 20 40
I0 45 20
0 55 5
I0 20 40
I0 30 20
I0 5 2.5
week 3 I0 20 8 0 0 0
316 TABLE II Counts of S. enteritMis (S.c.) from broiler chicks after treatment with Broilaet " Group
Number of birds
week I > 102 ,,
< 102
week 2 > 10z
< i02
week 3 > i02
Control
I0
0
l
0
0
0
I
Control + S.c. Broilact " Trial 2
20 40
8 8
i 0
5 0
6 2
4 I
0 2
10
0 2 4
i 4 4
0 I 0
I 0 I
0 0 0
0 0
< i0 z
Trial I
Control C o n t r o l + S.c. Broilact R
20 40
0
" CFU/g of caecal content.
o f 12 broilers were S. enteritidis-positive in the first trial ( c o u n t s b e t w e e n 1 x 1 0 2 / g a n d 5 × 1 0 * / g ) whilst in the s e c o n d trial n o S. alteritidis-positive birds w e r e f o u n d at this stage (see T a b l e Ill). T h e lack o f ability o f this S. enteritidis strain to c o n t i n u o u s l y colonize the ' s e e d e r ' birds could hardly have b e e n anticipated, in o t h e r e x p e r i m e n t s this strain p r o v e d to be very virulent ( B o l d e r et al., 1991) a n d c o l o n i z e d chickens very well for at least 3 weeks. Selection o f a strain with nalidixic acid resistance might be the explanation. A f t e r i n c u b a t i o n for 24 h, the test strain p e r f o r m e d p o o r l y on B G A with o r w i t h o u t 50 p p m nalixidie acid, but after extension o f the i n c u b a t i o n time to 48 h, g r o w t h a p p e a r e d to be typical. Protais et al. (1990) f o u n d p o o r isolation rates for S. enteritidis with R V e n r i c h m e n t b r o t h in c o m p a r i s o n with T e t r a t h i o n a t e broth. T h e u n e x p e c t e d l y p o o r p e r f o r m a n c e o f the p r e s e n t test strain m i g h t be related to the isolation m e t h o d s used, so the isolation m e t h o d for S. alteritidis n e e d s to be r e c o n s i d e r e d . T a b l e IV
TABLE Iii Counts of S. enteritidis (S.e.) from 'seeder' birds Group Trial I Control Control + S.e. Broilact ~ Trial 2 Control Control + S.e. Broilact '~
Number of birds
week I > 102 ,,
< 10z
week 2 > 102
< 102
week 3 > 102
< 10z
2 4
0 3
0 0
0 I
I 0
0 I
0 0
8
7
0
4
0
0
1
2 4
0 4
0 0
0 0
0 0
0 0
0 0
8
8
0
0
0
0
0
~' CFU/g of caecal content.
317 TABLE IV Weight (g) of chicks after killing Group Trial I Control Control + S.c. Broilact " Trial 2 Control C'.)l,)rol + S.c. Broilao "
week I
week 2
week 3
n
g
n
g
n
g
It) 2ll 40
251.4 246.4 239.0
tO 2t) 4~)
512.7 50~.~ -'¢,";,i
It) 2ll 37
842.9 S84.~ 881,4
i(I 20 40
233.2 223.0 248.9
10 2(1 4t)
483,6 483.7 523.1)
9 14 3t~
696.7 67t1.2 705.8
gives t h e r e s u l t s for b i r d w e i g h i n g s i m m e d i a t e l y a l t e r killing. T h e m e a n w e i g h t o f t h e B r o i l a c t ~" g r o u p in trial l w a s l o w e r t h a n t h a t o f t h e c h a l l e n g e c o n t r o l g r o u p , w h e r e a s in t h e s e c o n d trial t h e B r o i l a c t " c h i c k s p e r f o r m e d b e t t e r t h a n e i t h e r o f t h e o t h e r g r o u p s . T h e m e a n w e i g h t at 3 w e e k s o f a g e d i f f e r e d b e t w e e n t h e two trials, b u t t h e c h i c k s in trial ! w e r e 3 d a y s o l d e r at the d a y o f s l a u g h t e r .
Conclusions C o m p e t i t i v e e x c l u s i o n o f S. emeritidis by t r e a t i n g d a y - o l d c h i c k s w i t h B r o i l a c t "' d e c r e a s e s t h e i n c i d e n c e o f S. enteritidis in g r o w i n g b r o i l e r s . A l s o t h e n u m b e r o f S. enteritMis-positive b i r d s d e c r e a s e d m o r e r a p i d l y t h a n in n o n - t r e a t e d b i r d s . T h e r e is n o o b v i o u s e x p l a n a t i o n for t h e p o o r c o l o n i z a t i o n by S. enteritMis in t h e 'seeder' birds. C o m p e t i t i v e e x c l u s i o n c a n b e o n e o f m a n y m e a n s o f r e d u c i n g ) h e Sabnonella p r o b l e m , b u t it s h o u l d b e a p p l i e d in c o m b i n a t i o n w i t h o t h e r m e a s u r e s , s u c h a s g o o d h y g i e n i c p r a c t i c e s in t h e e n t i r e p o u l t r y p r o d u c t i o n c h a i n .
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