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The Live-Weight Gain of Growing Pigs Experimentally Infected with Massive Doses of Hyostrongylus Rubidus (Nematoda) Larvae
Br. vet.]. (1970), u6, 579
THE LIVE-WEIGHT GAIN OF GROvVING PIGS EXPERIMENTALLY INFECTED WITH MASSIVE DOSES OF HYOSTRONGYLUS RUB/DUS (NEMATODA) LARVAE By
J.
B.
CAS TEL I NO,
* I. V.
HER B E R TAN D
I.
J.
LEA Nt
Department of Agricultural and Forest Zoology, University College of North Wales, Bangor
SUMMARY
Clinical symptoms of mild fever, listlessness, inappetite, diarrhoea, and reduced weight gains are described for the first time following pure infections of H. rubidus in minimal disease (M.D. ) growing pigs. Clinical symptoms are most marked 3-5 days and 20-28 days after infections with 200,000 or 500,000 infective larvae. Lower infestation rates have caused no debility to growing animals. The depressed growth rate is most marked 3-4 weeks after infection. INTRODUCTION
Numerous reports have suggested that Hyostrongylus rubidus, the red stomach worm of pigs, causes a number of clinical symptoms as varied as diarrhoea, constipation, inappetence, voracious appetite, anaemia, emaciation, loss in weight and death. The parasite has been found in animals showing the "thin sow syndrome". Lean, Castelino & Herbert (1969), in a study of hyostrongylosis in experimentally infected growing pigs, reported no clinical symptoms and no difference in weight gain between uninfected animals and their litter mates which were infected with larvae ranging in number from 20,000 to 150,000. In the present study the project was extended to cover higher infections, in order to see whether the above symptoms could be associated with pure infestations of H. rubidus and, if so, at what level of infection. MATERIALS AND METHODS
Two litters of conventionally reared Large White x Landrace M.D. (minimal disease) pigs were used. The animals were infected per os with infective larvae. Litter A, which was 56 days old, was divided into three groups of three animals each: Group I received 500,000 larvae each, Group 2 received 200,000 larvae each and Group 3 served as uninfected controls. The infection in two animals from each of Groups I and 2 was terminated with three treatments of anthelmintict given over three consecutive days, beginning 35 days after infection • Present address: Dept. of Zoology, University College, Nairobi, Kenya. t Present address: Dept. of Agriculture, Wye College, Nr. Ashford, Kent. t I dose of Thibenzole (Merck, Sharpe and Dohme) at 100 mg./Kg. liveweight followed by I dose of Atgard V (Shell Chemical Co. ) at 40 mg.JKg. liveweight, followed by a further dose of Thibenzole at the same dose rate as before. No signs of toxicity were seen.
580
BRITISH VETERINARY JOURNAL,
126, II
when the faecal egg counts were very low. These four animals were then reinfected one week after the last anthelmintic dose, each with 500,000 H. rubidus infective larvae. At the same time, two animals from Group 3 were infected for the first time with 500,000 H. rubidus larvae each. Litter B, 86 days old, consisted of five animals, divided into two groups of two, the fifth animal being used as the uninfected control. Groups I and 2 were infected with 500,000 and 20,000 larvae respectively. The infection in one of the animals in Group I was terminated on the tenth day after infection, again using three treatments of anthelmintic as for Litter A. Throughout the period from weaning to slaughter the animals were fed a commercial meal* containing 16 per cent crude protein. All animals were weighed weekly and the rations adjusted to the mean live-weight of the group according to Shinfield scales of feed. The animals were penned singly when they weighed approximately 12 Kg., and from then on had access to the food over the whole day. RESULTS
Animals infected with 20,000 H. rubidus larvae showed no clinical symptoms. Animals infected with 200,000 or 500,000 H. rubidus larvae had a slight fever, became listless, refused food and scoured from the third day to the fifth day of infection. The faeces were dark, rust-coloured and positive in the benzidine test (Wintrobe, 1956) for the presence of blood. Examination of the faeces revealed expelled exsheathed third stage larvae, many of which were alive. Mter the fifth day the animals recovered and appeared normal until the 19th day of infection when on, or shortly after, patency they again lost their appetite. They started to scour on the 20th day and by the 28th day all animals infected with 500,000 were again positive for blood. The animal in Litter B in which an infection with 500,000 larvae was terminated on the loth day did not scour subsequently. Animals of litter A which were reinfected did not scour or show other clinical symptoms, nor did the reinfection become patent. The mean live-weight gains of the pigs from Litter A are given in Fig. I. There was a lowered weight gain in animals infected with 200,000 or more larvae compared with those which were either uninfected or had the infection terminated on the 10th day or were infected with 20,000 larvae. The reduction in weight was most marked three weeks after infection, and at this time the heaviest infected animals were listless and refused food. The infected animals (200,000 or 500,000 larvae) remained poor feeders for two weeks but then recovered and their weight gain soon resembled those of uninfected animals. Between the fourth and fifth weeks of infection animals infected with 500,000 larvae were only two-thirds the weight of uninfected control littermates. In Litter B, the live-weight gain of two animals given 20,000 infective larvae remained similar to that of the uninfected control animal. The two animals given 500,000 infective larvae showed differing live-weight gains; the growth rate of both pigs was depressed for two weeks, after which the pig which had its
* Sow and Weaner Meal, B.O.C.M. Ltd.
H. RUBIDUS INFECTION AND WEIGHT GAIN IN PIGS 50
581
X X
40
1:
0>
'0; ~
'"
.~
30
0>
..:.:
20
10
-I
0
3
2
4
5
6
11
Weeks post infection
Fig. ~
G,~"
Live-weight increase of animals used in Trial A.
Indicates day of infection (Day Animal infected with
{
G,,",2 [
I.
500,000
° or week 6) or reinfection (week 6).
larvae in week
Mean of 2 animals infected twice with week 6. _ . _--
Animal infected with
200,000
larvae in week
Mean of 2 animals infected with larvae in week 6. x x xxxx Group 3
{
0.
500,000
larvae, in week
° and
0.
° and 500,000
200,000
larvae in week
500,000
larvae in week 6.
Uninfected animal. Mean of 2 animals infected with
infection terminated on day ten quickly recovered and regained the weight of its littermates. The animal in which the infection persisted continued to lose weight from four weeks post infection, and then started to gain weight slowly. DISCUSSION
Connan (1967) and Jacobs (1967) have suggested that gastritis due to H. rubidus might cause the same sort of protein digestive upset as is described in bovine ostertagiasis. Lean et at. (1969), however, reported that apparent digestibility and feed conversion efficiency did not differ between control animals and animals infected with 20,000 H. rubidus larvae. The reduced weight gain observed in the present study occurred during a period when animals had a mild fever, were listless, diarrhoeic and had little appetite. Where group feeding is routinely practised any reduction in appetite could mean a change in dominance within the group at the trough with the net result that certain animals would eat much more than others, thus accentuating the effect of the disease. This could explain the results reported by Davenport (1967). Where animals are penned singly, as in this experiment, the effect of
BRITISH VETERINARY JOURNAL, 126, I I
anorexia is not so marked since the animal can feed at leisure. I t is suggested therefore, that under commercial conditions the effect of infection may be accentuated, especially if other potential pathogens are also present which can exploit reduced host vigour due to H. rubidus infection. ACKNOWLEDGMENTS
The authors thank the Meat and Livestock Commission for a research grant. Castelino is grateful to the Commonwealth Scholarship Commission in the United Kingdom for a three-year scholarship. I. J. Lean was a Sir William Roberts postgraduate scholar.
J. B.
REFERENCES
CONNAN, R. M . (1967) . Vet. Rec., 80, 424. DAVENPORT, P. G. (1967) . Vet. Rec., 8I, 390. JACOBS, D. E . (1967). Vet. Rec., 81, 198. LEAN, I. j., CASTELINO, j . B. & HERBERT, I. V. (1969). Proc. 1St. Congr. Int. Pig Vet. Soc., Cambridge, p. 70. WINTROBE, M . M. (1956). Clinical Haematology. London: Kimpton. (Accepted for publication 26 May 1970) Le gain de poids de cochons en croissance infectes experiInentale:rnent par d es dos es :rnassives de larves d'Hyostrongylus rubidus (N e:rnatode) (Castelino et al. ) Reswne. On decrit pour la premiere fois les symptomes cliniques d'une fievre benigne, apathie, manque d'appetit, diarrhee et diIninution des gains de poids consecutifs a des infections pures par H. rubidus de cochons en croissance avec un minimum de maladies (M.D.). Les symptomes cliniques sont plus marques 3-5 et 20-28 jours apres infection par 200.000 ou 500.000 larves infectieuses. Des taux plus faibles d'infestation n'ont cause aucune debilite aux animaux en croissance. La diminution du taux de croissance est plus marquee 3-4 semaines apres infection. Gewichts zunah:rne bei heranwachs enden Schweinen, die experiInentelllllit lIlas siven Dosen v on Hyostrongylus rubidus (Ne:rnatoda) larvae infiziert worden waren (Castelino et al. ) Zusa:rn:rnenfassung. Leichtes Fieber, T eilnahmslosigkeit, verminderte Fresslust, geringere Zunahme werden zum ersten Male als klinische Symptome bei heranwachsenden "minimal disease (M .D.)" Schweinen nach alleiniger Infektion mit H. rubidus beschrieben. Am deutlichsten sind die klinischen Symptome 3-5 Tage und 20- 28 Tage nach I nfektionen mit 200 000 oder 500000 infektiosen Larven. Infektionen mit geringen Mengen verursachten keine Schwachung wachsender Tiere. Die herabgesetzte Entwicklung des Wachstums ist am deutlichsten 3-4 Wochen nach der Infektion. EI awnento del peso vivo de cerdos en des arrollo que fueron infectados experi:rnental:rnente con dosis :rnasivas de Hyostrongylus rubidus en for:rna larval (Ne:rnatoda) (Castelino et al. ) Resulllen. Se describen por vez primera los sintomas clinicos de fiebre ligera, apatia, falta de apetito, diarrea y aumentos de peso reducidos, todos ellos producidos por infecciones puras de H . rubidus en cerdos en desarrollo libres de la mayoria de enfermedades (M. D.). Los sintomas clinicos son mas marcados al cabo de 3-5 dias y de 20-28 dias despues de la infeccion con 200.000 6 500.000 larvas infectivas. R azones de infestacion menores no causaron debilidad a los animales en desarrollo. L a razon de creciIniento deprimid a es mas marcada de 3-4 semanas despues de la infecci6n.
THE LIVE-WEIGHT GAIN OF GROvVING PIGS EXPERIMENTALLY INFECTED WITH MASSIVE DOSES OF HYOSTRONGYLUS RUB/DUS (NEMATODA) LARVAE By
J.
B.
CAS TEL I NO,
* I. V.
HER B E R TAN D
I.
J.
LEA Nt
Department of Agricultural and Forest Zoology, University College of North Wales, Bangor
SUMMARY
Clinical symptoms of mild fever, listlessness, inappetite, diarrhoea, and reduced weight gains are described for the first time following pure infections of H. rubidus in minimal disease (M.D. ) growing pigs. Clinical symptoms are most marked 3-5 days and 20-28 days after infections with 200,000 or 500,000 infective larvae. Lower infestation rates have caused no debility to growing animals. The depressed growth rate is most marked 3-4 weeks after infection. INTRODUCTION
Numerous reports have suggested that Hyostrongylus rubidus, the red stomach worm of pigs, causes a number of clinical symptoms as varied as diarrhoea, constipation, inappetence, voracious appetite, anaemia, emaciation, loss in weight and death. The parasite has been found in animals showing the "thin sow syndrome". Lean, Castelino & Herbert (1969), in a study of hyostrongylosis in experimentally infected growing pigs, reported no clinical symptoms and no difference in weight gain between uninfected animals and their litter mates which were infected with larvae ranging in number from 20,000 to 150,000. In the present study the project was extended to cover higher infections, in order to see whether the above symptoms could be associated with pure infestations of H. rubidus and, if so, at what level of infection. MATERIALS AND METHODS
Two litters of conventionally reared Large White x Landrace M.D. (minimal disease) pigs were used. The animals were infected per os with infective larvae. Litter A, which was 56 days old, was divided into three groups of three animals each: Group I received 500,000 larvae each, Group 2 received 200,000 larvae each and Group 3 served as uninfected controls. The infection in two animals from each of Groups I and 2 was terminated with three treatments of anthelmintict given over three consecutive days, beginning 35 days after infection • Present address: Dept. of Zoology, University College, Nairobi, Kenya. t Present address: Dept. of Agriculture, Wye College, Nr. Ashford, Kent. t I dose of Thibenzole (Merck, Sharpe and Dohme) at 100 mg./Kg. liveweight followed by I dose of Atgard V (Shell Chemical Co. ) at 40 mg.JKg. liveweight, followed by a further dose of Thibenzole at the same dose rate as before. No signs of toxicity were seen.
580
BRITISH VETERINARY JOURNAL,
126, II
when the faecal egg counts were very low. These four animals were then reinfected one week after the last anthelmintic dose, each with 500,000 H. rubidus infective larvae. At the same time, two animals from Group 3 were infected for the first time with 500,000 H. rubidus larvae each. Litter B, 86 days old, consisted of five animals, divided into two groups of two, the fifth animal being used as the uninfected control. Groups I and 2 were infected with 500,000 and 20,000 larvae respectively. The infection in one of the animals in Group I was terminated on the tenth day after infection, again using three treatments of anthelmintic as for Litter A. Throughout the period from weaning to slaughter the animals were fed a commercial meal* containing 16 per cent crude protein. All animals were weighed weekly and the rations adjusted to the mean live-weight of the group according to Shinfield scales of feed. The animals were penned singly when they weighed approximately 12 Kg., and from then on had access to the food over the whole day. RESULTS
Animals infected with 20,000 H. rubidus larvae showed no clinical symptoms. Animals infected with 200,000 or 500,000 H. rubidus larvae had a slight fever, became listless, refused food and scoured from the third day to the fifth day of infection. The faeces were dark, rust-coloured and positive in the benzidine test (Wintrobe, 1956) for the presence of blood. Examination of the faeces revealed expelled exsheathed third stage larvae, many of which were alive. Mter the fifth day the animals recovered and appeared normal until the 19th day of infection when on, or shortly after, patency they again lost their appetite. They started to scour on the 20th day and by the 28th day all animals infected with 500,000 were again positive for blood. The animal in Litter B in which an infection with 500,000 larvae was terminated on the loth day did not scour subsequently. Animals of litter A which were reinfected did not scour or show other clinical symptoms, nor did the reinfection become patent. The mean live-weight gains of the pigs from Litter A are given in Fig. I. There was a lowered weight gain in animals infected with 200,000 or more larvae compared with those which were either uninfected or had the infection terminated on the 10th day or were infected with 20,000 larvae. The reduction in weight was most marked three weeks after infection, and at this time the heaviest infected animals were listless and refused food. The infected animals (200,000 or 500,000 larvae) remained poor feeders for two weeks but then recovered and their weight gain soon resembled those of uninfected animals. Between the fourth and fifth weeks of infection animals infected with 500,000 larvae were only two-thirds the weight of uninfected control littermates. In Litter B, the live-weight gain of two animals given 20,000 infective larvae remained similar to that of the uninfected control animal. The two animals given 500,000 infective larvae showed differing live-weight gains; the growth rate of both pigs was depressed for two weeks, after which the pig which had its
* Sow and Weaner Meal, B.O.C.M. Ltd.
H. RUBIDUS INFECTION AND WEIGHT GAIN IN PIGS 50
581
X X
40
1:
0>
'0; ~
'"
.~
30
0>
..:.:
20
10
-I
0
3
2
4
5
6
11
Weeks post infection
Fig. ~
G,~"
Live-weight increase of animals used in Trial A.
Indicates day of infection (Day Animal infected with
{
G,,",2 [
I.
500,000
° or week 6) or reinfection (week 6).
larvae in week
Mean of 2 animals infected twice with week 6. _ . _--
Animal infected with
200,000
larvae in week
Mean of 2 animals infected with larvae in week 6. x x xxxx Group 3
{
0.
500,000
larvae, in week
° and
0.
° and 500,000
200,000
larvae in week
500,000
larvae in week 6.
Uninfected animal. Mean of 2 animals infected with
infection terminated on day ten quickly recovered and regained the weight of its littermates. The animal in which the infection persisted continued to lose weight from four weeks post infection, and then started to gain weight slowly. DISCUSSION
Connan (1967) and Jacobs (1967) have suggested that gastritis due to H. rubidus might cause the same sort of protein digestive upset as is described in bovine ostertagiasis. Lean et at. (1969), however, reported that apparent digestibility and feed conversion efficiency did not differ between control animals and animals infected with 20,000 H. rubidus larvae. The reduced weight gain observed in the present study occurred during a period when animals had a mild fever, were listless, diarrhoeic and had little appetite. Where group feeding is routinely practised any reduction in appetite could mean a change in dominance within the group at the trough with the net result that certain animals would eat much more than others, thus accentuating the effect of the disease. This could explain the results reported by Davenport (1967). Where animals are penned singly, as in this experiment, the effect of
BRITISH VETERINARY JOURNAL, 126, I I
anorexia is not so marked since the animal can feed at leisure. I t is suggested therefore, that under commercial conditions the effect of infection may be accentuated, especially if other potential pathogens are also present which can exploit reduced host vigour due to H. rubidus infection. ACKNOWLEDGMENTS
The authors thank the Meat and Livestock Commission for a research grant. Castelino is grateful to the Commonwealth Scholarship Commission in the United Kingdom for a three-year scholarship. I. J. Lean was a Sir William Roberts postgraduate scholar.
J. B.
REFERENCES
CONNAN, R. M . (1967) . Vet. Rec., 80, 424. DAVENPORT, P. G. (1967) . Vet. Rec., 8I, 390. JACOBS, D. E . (1967). Vet. Rec., 81, 198. LEAN, I. j., CASTELINO, j . B. & HERBERT, I. V. (1969). Proc. 1St. Congr. Int. Pig Vet. Soc., Cambridge, p. 70. WINTROBE, M . M. (1956). Clinical Haematology. London: Kimpton. (Accepted for publication 26 May 1970) Le gain de poids de cochons en croissance infectes experiInentale:rnent par d es dos es :rnassives de larves d'Hyostrongylus rubidus (N e:rnatode) (Castelino et al. ) Reswne. On decrit pour la premiere fois les symptomes cliniques d'une fievre benigne, apathie, manque d'appetit, diarrhee et diIninution des gains de poids consecutifs a des infections pures par H. rubidus de cochons en croissance avec un minimum de maladies (M.D.). Les symptomes cliniques sont plus marques 3-5 et 20-28 jours apres infection par 200.000 ou 500.000 larves infectieuses. Des taux plus faibles d'infestation n'ont cause aucune debilite aux animaux en croissance. La diminution du taux de croissance est plus marquee 3-4 semaines apres infection. Gewichts zunah:rne bei heranwachs enden Schweinen, die experiInentelllllit lIlas siven Dosen v on Hyostrongylus rubidus (Ne:rnatoda) larvae infiziert worden waren (Castelino et al. ) Zusa:rn:rnenfassung. Leichtes Fieber, T eilnahmslosigkeit, verminderte Fresslust, geringere Zunahme werden zum ersten Male als klinische Symptome bei heranwachsenden "minimal disease (M .D.)" Schweinen nach alleiniger Infektion mit H. rubidus beschrieben. Am deutlichsten sind die klinischen Symptome 3-5 Tage und 20- 28 Tage nach I nfektionen mit 200 000 oder 500000 infektiosen Larven. Infektionen mit geringen Mengen verursachten keine Schwachung wachsender Tiere. Die herabgesetzte Entwicklung des Wachstums ist am deutlichsten 3-4 Wochen nach der Infektion. EI awnento del peso vivo de cerdos en des arrollo que fueron infectados experi:rnental:rnente con dosis :rnasivas de Hyostrongylus rubidus en for:rna larval (Ne:rnatoda) (Castelino et al. ) Resulllen. Se describen por vez primera los sintomas clinicos de fiebre ligera, apatia, falta de apetito, diarrea y aumentos de peso reducidos, todos ellos producidos por infecciones puras de H . rubidus en cerdos en desarrollo libres de la mayoria de enfermedades (M. D.). Los sintomas clinicos son mas marcados al cabo de 3-5 dias y de 20-28 dias despues de la infeccion con 200.000 6 500.000 larvas infectivas. R azones de infestacion menores no causaron debilidad a los animales en desarrollo. L a razon de creciIniento deprimid a es mas marcada de 3-4 semanas despues de la infecci6n.