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Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Consequences on milk production
veterinary parasitology ELSEVIER
Veterinary Parasitology 74 (1998) 43-54
Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Consequences on milk production H. Hoste
a, *, C . C h a r t i e r
b
a CR INRA Tours, Station de Pathologie AL,iaire et de Parasitologie, F37380 Nouzilly, France h C N E V A / S t a t i o n R~gionale de Pathologie Caprine, 60, rue de Pied-de-Fond, BP3081 F79012 Niort Cedex, France
Received 17 January 1997; accepted 27 May 1997
Abstract The objective of the study was to examine the ability of dairy goats to develop a response to nematode parasites of the digestive tract after a previous contact with the worms. One hundred dairy goats were initially divided into 2 groups. One remained free of parasites (not previously infected: NPI). The second group was infected thrice at 50 days interval with a mixture of H a e m o n c h u s contortus and Trichostrongylus colubriformis (previously infected: PI). After this initial exposure to nematodes, the goats were drenched with fenbendazole to eliminate the worms and remained free of parasites for 2 months around kidding. One month after kidding, 24 lactating dairy goats from each initial group were challenged with a mixture of H. contortus and T. colubriformis and parasitological, pathophysiological and milk production parameters were measured fortnightly to assess the effects of challenge infection and the response of the goats. No difference in parasite egg excretion was found between group NPI and PI after challenge infection. Similarly, no difference in worm counts was detected in 5 culled goats from each group killed one month post challenge. In contrast, differences between both groups were detected when considering the pathophysiological parameters (packed cell volume, inorganic phosphate and pepsinogen concentrations) with consequences of infection being more severe in the previously infected animals, Moreover, the milk production was also depressed in the PI group when compared to the NPI one. These results indicate that the response developed by adult dairy goats after the challenge infection was unable to limit the worm populations but could have pathophysiological repercussions and consequences on production. © 1998 Elsevier Science B.V. Keywords: Haemonchus contortus; Trichostrongylus colubriformis; Goat; Milk-production; Resistance
Corresponding author. Tel.: + 33-02-4742-7985; fax: + 33-02-4742-7774: e-mail: [email protected] 0304-4017/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0304-4017(97)001 30- 1
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H. Hoste, C. Chartier / Veterinar3' Parasitology 74 (1998) 43-54
1. Introduction
Several studies have been conducted to compare the level of parasitism with gastrointestinal nematodes in sheep and goats during mixed grazing (Le Jambre and Royal, 1976; Pomroy et al., 1986; Jallow et al., 1994). They have generally shown that goats were more infected than sheep as they exhibited higher worm burdens and egg excretion. This difference between host species has been attributed not only to a difference in feeding behaviour, but also to a lesser ability of goats to develop resistance to trichostrongyle infection. Few studies have been performed in experimental conditions to confirm these field observations and to analyze the response of goats to nematode infection (Pomroy and Charleston, 1989a,b; Huntley et al., 1995). In addition, these studies were mainly conducted in non-lactating goats and their results could not easily be applied to dairy goats since the hormonal perturbations related to the end of pregnancy and to early lactation have been shown to induce major interference on the response to parasitism (O'Sullivan and Donald, 1973; Barger, 1993; Rahman and Collins, 1992). As a consequence, no information is directly available on the resistance to trichostrongyles and its zootechnic consequences in goats bred for milk production despite their economic importance in several countries and the impact on milk yield due to nematodes demonstrated in naive animals (Hoste and Chartier, 1993). The objectives of the present study were therefore to assess the development of the response to parasitic nematodes of the gastrointestinal tract in dairy goats and to examine the pathophysiological consequences as well as the possible repercussions on milk production.
2. Material and methods
2.1. Experimental design One hundred French Alpine dairy goats were used initially in the study. They had been reared in a zero-grazing system and were free of gastrointestinal trichostrongyles at the start of the study. For all the goats, the lactation number was > 2. The goats were initially allocated randomly in 2 equal groups, 'Previously Infected ' (group PI) and 'Not Previously Infected' (group NPI) (Fig. 1). In the first part of the study, the 50 goats from the NPI group remained free of parasites. Goats from the PI group were infected 3 times at 50 days interval with a mixture of 10000 Trichostrongylus colubriformis and 5000 Haemonchus contortus third-stage larvae. Forty days after each infection, the goats were treated with fenbendazole (Panacur ND, 10 mg/kg). They remained free of parasites for 10 days before receiving the next infection. Blood and faeces were collected individually at the beginning and at the end of each infection to examine parasitological and pathophysiological parameters. This series of 3 consecutive infections ended approximately 1 month before kidding. The goats were then treated with fenbendazole and remained worm free for 2 months.
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
PREINFECTIONS (1: Infection, T: Treatment} Group
11
PI
T1 !2 40d
"1"2 la
45
CHALLENGE INFECTION
T3
I Cha,en *
...... I
10d
kiddin~ Group
Challenge
NPI
~ ' ~
5 months
~
2 '~ months
3 months
Fig. 1. Summary of the experimental treatment of the animals, in the first part of the study, the goats from the previously infected (PI) group received repeatedly 3 infections composed of a mixture of 5000 larvae of Haemonchus contortus and 10,000 larvae of Trichostrongylus colubriformis. The challenge infection was composed of 5000 larvae of H. contortus and 20000 larvae of 72 colubriformis.
The second part of the study began one month after kidding and the beginning of lactation. Twenty-four goats, randomly selected from groups PI and NPI, received a challenge infection composed of 20000 T. colubriformis and 5000 H. contortus infective larvae. Subsequently, the goats were sampled individually every 2 weeks for 3 months to assess parasitological, pathophysiological and milk production parameters. In addition, 5 culled goats of both groups were necropsied one month after challenge, in order to perform worm counts and to estimate the related histological changes. 2.1.1. Fecal examination Fecal nematode egg counts were performed according to the modified McMaster method (Raynaud, 1970) 2.1.2. Worm counts The abomasum and the small intestine of the goats were taken at necropsy for worm count. The organs were washed extensively to collect the parasites and the content fixed with 10% buffered formalin. The volume was then adjusted to 2000 ml and the populations of worms in the abomasum and the intestine were estimated by a 10% aliquot technique. 2.1.3. Hematological and serological examinations The PCV for each sample was measured by use of the capillary microhematocrit method. The serum pepsinogen concentrations were determined as described previously (Kerboeuf, 1975). The serum inorganic phosphate was measured according to the method described by Robinson et al. (1971) using a Technicon autoanalyser. The blood eosinophil count was determined as described by Dawkins et al. (1989) using the Carpentier's solution.
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H. Hoste, C. Chartier/ VeterinaryParasitology 74 (1998) 43-54
2.1.4. Histological examination Immediately after death, histological samples were taken from the abomasum and the duodenum and fixed either in 10% buffered formalin for 48 h or Carnoy's fluid for 24 h. Following dehydration, the tissues were embedded in paraffin wax and sectioned at 5 /xm thick. The formalin fixed samples were stained with Haematoxylin Eosin and used to assess the histological changes and to count the number of eosinophils in the mucosa. The C a r n o y ' s fixed sections were stained with alcyan blue (0.5% solution in 0.5 N HCI) and safranine acetate for mast cells (MC) counts. For the abomasal samples, the counts were performed both in the fundus and pylorus on 10 fields o f a reticulum square, randomly selected. In the small intestine, the counts were performed on 10 c r y p t / v i l l u s units as previously described (Miller and Jarrett, 1971).
2.1.5. Milk production data The milk yield and the fat and protein contents were recorded twice monthly at morning and afternoon milking. To estimate the difference between group PI and NPI in the total amount o f milk produced after the challenge infection, a graphic representation of the data was established and calculation of the surface under the curves was performed using a semi automatic digitalized analysing system (VIDS III, Shirehill, Safron Walden).
2.2. Statistical analyses In the first part of the study, comparisons were made between the different infections using a one-way analysis of variance ( A N O V A ) . In the second part of the study, the differences between both groups were analyzed using a one-way analysis of variance ( A N O V A ) except for PCV. For this parameter, covariance analysis was applied because significant differences were present between the two groups before the challenge infection.
3. Results 3.1. First part of the study 3.1.1. Parasitological data At the end o f the first initial infection, the level of egg excretion was approximately 4100 epg (Table 1). This level showed only a slight decrease following further infections Table 1 Values (Mean + S.D.) of the haematological and serological parameters measured at the end of each infection in the first part of the study Before infections End of the 1st infection End of the 2nd infection End of the 3rd infection EPG PCV Pepsinogen Inorganic phosphate
0 24.6a (2.7) 801.6a (392.6) 71.4a (17.3)
4134 (3120) 18.6b (2.9) 1523.5b (378.2) 61.5 b (13.3)
3726 (2551) 22.0 c (2.9) 1228.1c (463.0) 63.3b (16.3)
Different superscripts within each row indicate significant difference at P < 0.05.
3439 (2158) 28.0 d (4.2) 855.5a (424.6) 61.5 b (18.2)
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
47
such that at the end of the 3rd infection, the mean epg value was 3440. No statistical difference in egg output was detected between the 3 successive infections. Fenbendazole treatment, applied at the end of each infection, was highly efficient in removing worms as the epg, 7 days post treatment, was 0 on each occasion.
3.1.2. Haematological data At the end of the first infection, a significant depression was measured in the PCV values as compared to pre-infection values (Table 1). These changes in PCV were less severe after the 2nd infection but were still significantly depressed. However, the PCV values recovered after the third infection were in fact significantly higher than the values measured at the beginning of the experiment, before the goats received any infection. 3.1.3. Serological data The first infection was associated with a significant rise in the serum pepsinogen concentrations (Table 1). Following infection 2, the pepsinogen level remained significantly increased compared to the initial values, but the concentrations were lower than those detected at the end of the 1st infection. The pepsinogen concentrations measured after the third infection were not significantly different from pre-infection levels. A significant decrease was observed in the inorganic phosphate concentrations after each of the 1st, 2nd and 3rd infections (Table 1). 3.2. Second part of the study: Response to challenge infection 3.2• 1. Parasitological data After the challenge infection, a similar pattern in egg excretion was observed in both groups of goats and no statistical difference was observed between groups PI and NPI throughout the study (Fig. 2). The peak in egg excretion occurred in both groups on week 4 post challenge infection (PCI) and was followed thereafter, by a regular decrease until the end of the experiment. 35O0 3000t 2500 2000 L~J
1500 1000 5000
2
~
6
a
lO
Weeks post chal[engeirffection
12
14
Fig. 2. Parasite egg excreuon following the challenge infection in the previously infected (PI group) (""'i'm-) and non-previously infected goats (NPI group) (°°".".'~'°°).
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H. Hoste, C. Chattier/Veterinary Parasitology 74 (1998) 43-54
Table 2 Individual worm burdens in the 5 necropsied, culled goats from the PI and NPI groups one month after the challenge infection Group PI
Mean (S.D.)
Group NPI
H. contortus
T. colubriformis
H. contortus
T. colubr!formis
2 1129 19 48 85 2566 (488, 7)
13,540 10,960 4680 14,180 8040 10,280 (3, 926)
46 626 2748 23 362 761 (1138, 1)
6740 16,260 15,880 18,800 14,865 14,440 (5304)
No statistical difference was established in individual worm counts from the 5 culled goats from each group (PI and NPI), either for H. contortus or T. colubriformis (Table 2).
3.2.2. Histological data No major differences in the damage induced by the worms to the abomasal and the intestinal mucosae were assessed between group PI and NPI on the histological slides. The lesions observed in the abomasum were quite mild. Superficial abrasion of the mucus cells was associated with an increased depth of the mucosa due to oedema of the connective tissue. The main lesion noticed in the small intestine was a moderate abrasion of villi with a slight increase of cell density in the lamina propria. In addition, the number of mast cells and eosinophils in the fundic, pyloric and intestinal mucosa were not statistically different between group (Table 3).
3.2.3. Haematological data A similar evolution in the PCV values was observed in both groups. The PCV values dropped dramatically after 4 weeks post challenge and then began to stabilise. However, the decrease in PCV was more pronounced in the previously infected animals and statistical differences were established by covariance analysis on week 6 and 8 PCI ( P < 0.01) (Fig. 3).
Table 3 Number of eosinophils and mast cells in the digestive mucosa of 5 culled goats from group PI and NPI killed one month after the challenge infection Eosinophils
Group PI Group NPI
Mast cells
Fundus
Pylorus
Small intestine
Fundus
Pylorus
Small intestine
2.98 (1.62) 2.77 (0.39)
4.23 (1.91) 2.13 (0.91)
11.75 (5.16) 10.13 (2.03)
8.90 (9.67) 7.08 (3.60)
4.25 (2.44) 4.28 (3.32)
23.00 (3.90) 19.70 (5.65)
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
49
38 36 34 32
>~
×
~ 3o ~
28
26 24
..........x
22
.....................
2O
2
0
4
6
8
10
!2
"~
Weeks oost challenge infection Fig. 3. Packed cell volume values ( ~ ) and non-previously
following the challenge infection in the previously infected (P1 group) infected goats (NPI group) ( ° ° " ) ~ " ° ° ) . Significant differences were assessed by covariance analysis on week 6 and 8 post challenge ( * : P < 0.05; * * : P < 0.01).
Before the challenge infection, no difference was observed in blood eosinophil number in both groups of animals. This absence of difference persisted until week 8 post challenge. On week 12 post challenge, an increase in the number of blood eosinophil occurred in group PI (mean number: 43 X 103 cells per ml) but was not detected in group NPI (mean number: 15 × 103 cells per ml). This rise was due to a few number of goats. Nevertheless, the difference between both groups was statistically significant ( P < 0.01) (data not shown).
3.2.4. Serological data A similar evolution in the mean serum pepsinogen concentrations was observed in both groups PI and NPI as a rise in the values occurred as soon as 2 weeks PCI. The maximal values were reached on week 4 post challenge and were maintained until week 8 PCI. This increase in pepsinogen concentrations was however more marked in animals 1700160015001400 13004 t 1200
/," ,
1100)
w"
"".,
.,,..," ,-~ ',
,.,"
I 10001 gO0 i
/
800
Weeks post challenge infection
Pepsinogen values following the challenge infection in the previously infected (PI group) ( " " " ~ " ~ ) and non-previously infected goats (NPI group) ( ' ° " - ~ ° ° ° ) . Significance of statistical test: * P < 0.05;
Fig. 4.
* * P < 0.01.
50
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54 8.5
"..
/
,~" ........... ~-.
75 -
•
."
".
,/"
60-
r ss
0
2
S
6
~
I0
12
~4
Weeks post challenge infection
Fig. 5. Inorganic phosphate concentrations after challenge infection in the previously infected (PI group) (''"~"~) and non-previously infected goats (NPI group) (°°"-'~1~°=°). Significance of statistical test: *P<0.05; **P<0.01.
from group PI. On week 4 and 8 PCI, differences between groups PI and NPI were significant ( P < 0.05) (Fig. 4). The inorganic phosphate concentrations in the serum of goats from groups PI and NPI also showed a parallel evolution after challenge infection. Nevertheless, the phosphate concentrations measured in group PI were regularly lower than those in group NPI and statistical differences were established on weeks 4 ( P < 0.01) and 10 PCI ( P < 0.05) (Fig. 5).
3.2.5. Milk yield During the whole study, the milk yield in goats from group PI was lower than in the NPI animals (Fig. 6). Significant differences were observed on week 2 ( P < 0.0 1), 6 and 10 PCI ( P < 0.02). The estimation of milk yield in the 2 groups of goats for the 3-month study indicated a 10.6% total reduction in group PI compared to group NPI. 3,6. 3,4.
~. . . . .
/ ....
".
3,2
*
''",, ,,
i
3"~
2,8" 2,62,4" 2,2-
6
2
4We*~s
6
8
10
12
post chaJfenge ir~fectior~
Fig. 6. Milk yield data following the challenge infection in the previously infected (PI group) ( ~ ) and non-previously infected goats (NPI group) ( ° " ~ ° ° ° ) . Significance of statistical test: *P < 0.05; * *P < 0.01.
H. Hoste, C. Chartier/ Veterinary' Parasitology 74 (1998) 43-54
51
No differences were detected in the fat and protein contents of milk in both groups of goats (data not shown).
4. Discussion The parasitological, pathophysiological and production parameters examined in the present study provide information on the resistance and the resilience of dairy goats to challenge infection with H. contortus and T. colubriformis. Examination of nematode egg excretion clearly indicates a low ability of goats to develop a resistance to trichostrongyles. This conclusion was supported by the constant pattern in egg excretion following the 3 successive infections in the first part of the study and by the lack of difference in epg between the 2 groups of goats after the challenge infection. This absence of reduction in egg excretion in previously infected goats is in agreement with observations from field studies comparing the pasture contamination with goats and sheep. A reduction in faecal egg excretion during the grazing season was only detected in sheep (Pomroy et al., 1986). This difference between host species has been attributed both to a difference in feeding behaviour (Jallow et al., 1994), but also to a less efficient development of resistance to nematode parasites in goats (Le Jambre, 1984) In the present study, the goats received a mixed infection. Examination of egg excretion did not allow for analysis of any possible differential response to the 2 species, i.e, H. contortus and T. colubriformis. However, some indications can be obtained from the worm counts in the necropsied culled goats following the challenge infection and from the pathophysiological parameters specifically related either to the abomasal (pepsinogen and PCV) or to the intestinal (inorganic phosphate) infections. The results related to the T. colubriformis infection are unequivocal. No significant difference in the worm number was established between the PI and NPI necropsied goats and no concomitant difference in histological lesions and cellular infiltration of the mucosae was detected. Secondly, during the 1st part of the study, the levels of inorganic phosphate did not improve following the 3 successive infections. Lastly, after the challenge infection, the inorganic phosphate concentrations were depressed in the previously infected goats compared to the other group. All together, these results strongly suggest a lack of resistance to T.colubriformis. In a similar way, Huntley et al. (1995), examining feral goats challenged after a grazing season, did not find any evidence of acquired immunity to T. vitrinus in does when compared to ewes or even lambs. In contrast, Pomroy and Charleston (1989b) have demonstrated a strong resistance of young Saanen goats to T. colubriformis in experimental conditions. This last result, however, was obtained in non-lactating animals. In sheep, Dobson et al. (1990) have underlined the importance of the initial level of T. colubriformis pre infection in expression of resistance. This factor could possibly explain the discrepancy between the different studies. The data related to H. contortus infections are more difficult to interpret than those relevant to T. colubriformis. In the first part of the study, the evolution of PCV and pepsinogen values strongly indicated an improved ability of goats to withstand the negative effects of the successive infections. However, the lack of direct results on
52
14. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
worm populations made difficult to relate this better resilience to an improved resistance, i.e, a smaller establishment of worms. Paradoxically, results from the second part of the study were opposite to those from the first one. They showed evidence of a lack of resistance to H. contortus. The worm counts and the histopathological data from the challenged culled goats were comparable in the PI and NPI group and previous exposure to nematodes did not lead to any improved PCV and pepsinogen concentrations. These results observed after the challenge infection are in agreement with previous descriptions of goats failing to resist to H. contortus (Pomroy and Charleston, 1989a; Watson and Hosking, 1989). Nevertheless, the differences in response between the 2 parts of the present study remain outstanding. Two main events happened between the 2 periods of infection which could possibly be evoked to explain the differences (l) Kidding and beginning of lactation; (2) The drenching of goats at the end of the 1st period followed by 2 months without contact with the worms. A disruption of immunity to nematodes related to parturition and lactation has been strongly substantiated in ewes (O'Sullivan and Donald, 1973; Jeffcoate et al., 1992; Barger, 1993). In contrast, only little information on a similar relationship were available in Angora goats (Rahman and Collins, 1992). The possibility of more dramatic and prolonged perturbations in goats has to be considered and is worth to be documented. Concerning anthelmintic treatment, several studies in sheep (Barger, 1988; Luffau et al., 1985) and one in Saanen kids (Hosking and Watson, 1993) have examined possible interference between drenching and host immunity, especially with H. contortus. They have underlined the importance of the presence of an existing worm population in regulation of establishment of new incoming larvae. In the present study, comparison of results between the 2 periods tend to confirm a possible disturbing role of anthelmintic treatment on host immunity to H. contortus. The time the hosts remain free of parasites could also be an important factor to consider. Although no difference was observed in parasitological parameters between PI and NPI goats after the challenge infection, clear differences were observed in both pathophysiological and production parameters. Previous contact with the worms was associated with more severe disturbances in serological measurements related to both H. contortus (i,e., pepsinogen and PCV levels) and T. colubriformis (i,e, inorganic phosphate) infections. These consequences lasted for the 3 months after challenge and were concomitant with a 10.6% reduction in milk production in the PI goats when compared to the NPI ones. The reduction in milk yield detected in the previously infected goats could be attributed to decreased conditions and interference on preparation of lactation due to parasitism at the end of the previous lactation. No study are available in goats to substantiate this hypothesis of a long term effect of parasitic infection on subsequent lactation. On the other hand, it should be noticed that no difference between groups was observed on the first month of lactation before goats received the challenge. Moreover, this could not easily explain the differences detected in the pathophysiological parameters. The more severe impact of the challenge in the previously parasitised goats could alternatively be explained by some adverse consequences due to the host response.
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
53
Detrimental effects related to larval challenges in adult, immune sheep have been described previously. Several field studies have shown that reinfection of adult sheep after previous exposure to trichostrongyles was associated with major pathophysiological disturbances despite low egg output. The changes were associated with losses in wool production (Anderson, 1973; Barger and Southcott, 1975) a n d / o r lower body weight (Pullman et al., 1991) and sometimes with clinical signs (Larsen et al., 1994; Suttle and Brebner, 1995). These field observations were, to some extent, supported by conclusions from indoors studies with T. colubriformis or Teladorsagia circumcincta assessing the consequences of challenge infection in resistant animals (Yakoob et al.. 1983; Kimambo et al., 1988). The origin of these perturbations was not clearly identified, but the development of some hypersensitive reaction in the digestive mucosae following the larval challenge has been evoked (Larsen et al., 1994). Similar adverse effects related to the host response could also be evoked from the present data in goats. However, 2 main differences between the 2 host species have to be underlined. First, the detrimental effects in sheep were always associated with a resistance to infection which is not the case in the present study. Second, the possibility of an hypersensitivity reaction in the gut is not supported in goats by the lack of difference in mucosal cell populations found in the culled, challenged goats. To summarize, the response to challenge infection in previously infected dairy goats could lead, as in sheep, to pathophysiological disturbances and negative consequences on production traits. However, in contrast with results in sheep and paradoxically, this was not associated with any major effects on the biology of worm populations. The present results therefore underline the interest of comparative studies in the 2 small ruminants species which could provide valuable information on the immune response to nematodes in both species and the importance of various modulating factors on expression of immunity and the possible associated detrimental consequences.
Acknowledgements The authors are extremely grateful to Dr. P. Griers and the Socirt~ Distrivet for their financial support. They wish to thank Mrs. C. Benoit, C. Koch,, M.P. Pellet, I. Pors for their technical assistance. Special thanks are also due to Mr. J. Gautron for the help in the measurement of inorganic phosphate with Technicon autolab. We are also grateful to the technical staff of Lycre Agricole de Melle and particularly Mr. H. Coutineau who provided the facilities.
References Anderson, N., 1973. Trichostrongylidinfections of sheep in a winter rainfall region: II. Epizootilogicalstudies in the western district of Victoria, 1967-68. Aust. J. Agric. Res. 24, 599-611. Barger, I.A., 1988. Resistance of young lambs to Haemonchus contortus infection and its loss following anthelmintic treatment. Int. J. Parasitol. 18, 1107-1109. Barger, I.A., 1993. Influence of sex and reproductive status on susceptibility of ruminants to nematode parasitism. Int. J. Parasitol. 23, 463-469. Barger, I.A., Southcott, W.H., 1975. Trichostrongylosis and wool growth: 3. The wool growth response of resistant grazing sheep to larval challenge. Aust. J. Exp. Agric. Anim. Husb. 15, 167-172.
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Dawkins, H.J.S., Windon, R.G., Eagleson, G.K., 1989, Eosinophil responses in sheep selected for high and low responsiveness to Trichostrongylus colubriformis. Int. J. Parasitol. 19, 198-205. Dobson, R.J., Waller, P.J., Donald, A.D., 1990. Population dynamics of Trichostrongylus colubriformis in sheep: The effect of infection rate on the establishment of infective larvae and parasite fecundity. Int. J. Parasitol. 20, 347-352. Hosking, B.C., Watson, T.G., 1993. Development of resistance to Haemonchus contortus by Saanen goats. In: 14th conference of the WAAVP. Cambridge, UK p. 11 I. Hoste, H., Chartier, C., 1993. Comparison of the effects on milk production of concurrent infection with Haemonchus contortus and Trichostrongylus colubriformis in high-and low producing dairy goats. Am. J. Vet. Res. 54, 1886-1893. Huntley, J.F., Patterson, M., McKellar, A., Jackson, F., Stevenson, L.M., Coop, R.L., 1995. A comparison of the mast cell and eosinophil responses of sheep and goats to gastrointestinal nematode infections. Res. Vet. Sci. 58, 5-10. Jallow, O.A., McGregor, B.A., Anderson, N., Holmes, J.H.G, 1994. Intake of trichostrongylid larvae by goats and sheep grazing together. Aust. Vet. J. 71, 361-364. Jeffcoate, I.A., Wedrychowicz, H., Fishwick, G., Dunlop, E.M., Duncan, J.L., Holmes, P.H., 1992. Pathophysiology of the periparturient egg rise in sheep: A possible role for lgA. Res. Vet. Sci. 53, 212-218. Kerboeuf, D., 1975. Le dosage du pepsinogene sanguin. Pfizer Actualites 65, 9-16. Kimambo, A.E., McRae, J.C., Dewey, P.J.S., 1988. The effect of daily challenge with Trichostrongylus colubriformis larvae on the nutrition and performance of immunologically-resistant sheep. Vet. Parasitol. 28, 205-212. Larsen, J.W.A., Anderson, N., Vizard, A.L., Anderson, G.A., Hoste, H., 1994. Diarrhoea in Merino ewes during winter: Association with trichostrongylid larvae. Aust. Vet. J. 71,365-372. Le Jambre, L.F., Royal, W.M., 1976. A comparison of worm burdens in grazing Merino sheep and Angora goats. Aust. Vet. J. 52, 181-183. Le Jambre, L.F., 1984. Stocking rate effects on the worm burdens of Angora goats and Merino sheep. Aust. Vet. J. 61,280-282. Luffau, G., Pery, P., Carrat, C., 1985. Interf&ence entre vermifugation et immunit~ dans les strongyloses gastro-intestinales du mouton. Ann. Rech. Vet. 16, 17-23. Miller, H.R.P., Jarrett, W.F.H., 1971. Immune reactions in mucous membranes: 1. Intestinal mast cell response during helminth expulsion in the rat. Immunology 20, 277-288. O'Sullivan, B.M., Donald, A.D., 1973. Responses to infection with Haemonchus contortus and TrichostrongyIns colubriformis in ewes of different reproductive status. Int. J. Parasitol. 3, 521-530. Pomroy, W.E., Charleston, W.A.G., 1989a. Failure of young goats to acquire resistance to Haemonchus contortus. N.Z. Vet. J. 37, 23-26. Pomroy, W.E., Charleston, W.A.G., 1989b. Development of resistance to Trichostrongylus colubriformis in goats. Vet. Parasitol. 33, 283-288. Pomroy, W.E., Lambert, M.G., Betteridge, K., 1986. Comparison of faecal strongylate egg counts of goats and sheep on the same pasture. N.Z. Vet. J. 34, 36-37. Pullman, A.L., Beveridge, I., Martin, R.R., 1991. Effects of challenge with trichostrongylid nematode larvae on immunologically resistant grazing yearling sheep in South Australia. Vet. Parasitol. 38, 155-162. Raynand, J.P., 1970. Etude de l'efficacite d'une technique de coproscopie quantitative pour le diagnostic de routine et le controle des infestations parasitaires des bovins, ovins, equins et porcins. Ann. Parasitol. Hum. Comp. 45, 321-342. Rahman, W.A., Collins, G.H., 1992. An association of faecal egg counts and prolactin concentrations in sera of periparturient Angora goats. Vet. Parasitol. 45, 85-91. Robinson, R., Roughan, M.E., Wagstaff, D.F., 1971. Measuring inorganic phosphate without using a reducing agent. Ann. Clin. Biochem. 8, 168-170. Suttle, N., Brebner, J., 1995. A putative role for larval nematode infection in diarrhoeas of lambs which did not respond to anthelminthic drenches. Vet. Rec. 137, 311-316. Watson, T.G., Hosking, B.C., 1989. Observations on resistance and self-cure to nematode parasites exhibited by grazing lambs and Saanen kids. Proc. N.Z. Soc. An. Prod. 49, 179-182. Yakoob, A.. Holmes. P.H., Armour, J., 1983. Pathophysiology of gastrointestinal trichostrongyles in sheep: Plasma losses and changes in plasma pepsinogen levels associated with parasite challenge of immune animals. Res. Vet. Sci. 34, 305-309.
Veterinary Parasitology 74 (1998) 43-54
Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Consequences on milk production H. Hoste
a, *, C . C h a r t i e r
b
a CR INRA Tours, Station de Pathologie AL,iaire et de Parasitologie, F37380 Nouzilly, France h C N E V A / S t a t i o n R~gionale de Pathologie Caprine, 60, rue de Pied-de-Fond, BP3081 F79012 Niort Cedex, France
Received 17 January 1997; accepted 27 May 1997
Abstract The objective of the study was to examine the ability of dairy goats to develop a response to nematode parasites of the digestive tract after a previous contact with the worms. One hundred dairy goats were initially divided into 2 groups. One remained free of parasites (not previously infected: NPI). The second group was infected thrice at 50 days interval with a mixture of H a e m o n c h u s contortus and Trichostrongylus colubriformis (previously infected: PI). After this initial exposure to nematodes, the goats were drenched with fenbendazole to eliminate the worms and remained free of parasites for 2 months around kidding. One month after kidding, 24 lactating dairy goats from each initial group were challenged with a mixture of H. contortus and T. colubriformis and parasitological, pathophysiological and milk production parameters were measured fortnightly to assess the effects of challenge infection and the response of the goats. No difference in parasite egg excretion was found between group NPI and PI after challenge infection. Similarly, no difference in worm counts was detected in 5 culled goats from each group killed one month post challenge. In contrast, differences between both groups were detected when considering the pathophysiological parameters (packed cell volume, inorganic phosphate and pepsinogen concentrations) with consequences of infection being more severe in the previously infected animals, Moreover, the milk production was also depressed in the PI group when compared to the NPI one. These results indicate that the response developed by adult dairy goats after the challenge infection was unable to limit the worm populations but could have pathophysiological repercussions and consequences on production. © 1998 Elsevier Science B.V. Keywords: Haemonchus contortus; Trichostrongylus colubriformis; Goat; Milk-production; Resistance
Corresponding author. Tel.: + 33-02-4742-7985; fax: + 33-02-4742-7774: e-mail: [email protected] 0304-4017/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0304-4017(97)001 30- 1
44
H. Hoste, C. Chartier / Veterinar3' Parasitology 74 (1998) 43-54
1. Introduction
Several studies have been conducted to compare the level of parasitism with gastrointestinal nematodes in sheep and goats during mixed grazing (Le Jambre and Royal, 1976; Pomroy et al., 1986; Jallow et al., 1994). They have generally shown that goats were more infected than sheep as they exhibited higher worm burdens and egg excretion. This difference between host species has been attributed not only to a difference in feeding behaviour, but also to a lesser ability of goats to develop resistance to trichostrongyle infection. Few studies have been performed in experimental conditions to confirm these field observations and to analyze the response of goats to nematode infection (Pomroy and Charleston, 1989a,b; Huntley et al., 1995). In addition, these studies were mainly conducted in non-lactating goats and their results could not easily be applied to dairy goats since the hormonal perturbations related to the end of pregnancy and to early lactation have been shown to induce major interference on the response to parasitism (O'Sullivan and Donald, 1973; Barger, 1993; Rahman and Collins, 1992). As a consequence, no information is directly available on the resistance to trichostrongyles and its zootechnic consequences in goats bred for milk production despite their economic importance in several countries and the impact on milk yield due to nematodes demonstrated in naive animals (Hoste and Chartier, 1993). The objectives of the present study were therefore to assess the development of the response to parasitic nematodes of the gastrointestinal tract in dairy goats and to examine the pathophysiological consequences as well as the possible repercussions on milk production.
2. Material and methods
2.1. Experimental design One hundred French Alpine dairy goats were used initially in the study. They had been reared in a zero-grazing system and were free of gastrointestinal trichostrongyles at the start of the study. For all the goats, the lactation number was > 2. The goats were initially allocated randomly in 2 equal groups, 'Previously Infected ' (group PI) and 'Not Previously Infected' (group NPI) (Fig. 1). In the first part of the study, the 50 goats from the NPI group remained free of parasites. Goats from the PI group were infected 3 times at 50 days interval with a mixture of 10000 Trichostrongylus colubriformis and 5000 Haemonchus contortus third-stage larvae. Forty days after each infection, the goats were treated with fenbendazole (Panacur ND, 10 mg/kg). They remained free of parasites for 10 days before receiving the next infection. Blood and faeces were collected individually at the beginning and at the end of each infection to examine parasitological and pathophysiological parameters. This series of 3 consecutive infections ended approximately 1 month before kidding. The goats were then treated with fenbendazole and remained worm free for 2 months.
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
PREINFECTIONS (1: Infection, T: Treatment} Group
11
PI
T1 !2 40d
"1"2 la
45
CHALLENGE INFECTION
T3
I Cha,en *
...... I
10d
kiddin~ Group
Challenge
NPI
~ ' ~
5 months
~
2 '~ months
3 months
Fig. 1. Summary of the experimental treatment of the animals, in the first part of the study, the goats from the previously infected (PI) group received repeatedly 3 infections composed of a mixture of 5000 larvae of Haemonchus contortus and 10,000 larvae of Trichostrongylus colubriformis. The challenge infection was composed of 5000 larvae of H. contortus and 20000 larvae of 72 colubriformis.
The second part of the study began one month after kidding and the beginning of lactation. Twenty-four goats, randomly selected from groups PI and NPI, received a challenge infection composed of 20000 T. colubriformis and 5000 H. contortus infective larvae. Subsequently, the goats were sampled individually every 2 weeks for 3 months to assess parasitological, pathophysiological and milk production parameters. In addition, 5 culled goats of both groups were necropsied one month after challenge, in order to perform worm counts and to estimate the related histological changes. 2.1.1. Fecal examination Fecal nematode egg counts were performed according to the modified McMaster method (Raynaud, 1970) 2.1.2. Worm counts The abomasum and the small intestine of the goats were taken at necropsy for worm count. The organs were washed extensively to collect the parasites and the content fixed with 10% buffered formalin. The volume was then adjusted to 2000 ml and the populations of worms in the abomasum and the intestine were estimated by a 10% aliquot technique. 2.1.3. Hematological and serological examinations The PCV for each sample was measured by use of the capillary microhematocrit method. The serum pepsinogen concentrations were determined as described previously (Kerboeuf, 1975). The serum inorganic phosphate was measured according to the method described by Robinson et al. (1971) using a Technicon autoanalyser. The blood eosinophil count was determined as described by Dawkins et al. (1989) using the Carpentier's solution.
46
H. Hoste, C. Chartier/ VeterinaryParasitology 74 (1998) 43-54
2.1.4. Histological examination Immediately after death, histological samples were taken from the abomasum and the duodenum and fixed either in 10% buffered formalin for 48 h or Carnoy's fluid for 24 h. Following dehydration, the tissues were embedded in paraffin wax and sectioned at 5 /xm thick. The formalin fixed samples were stained with Haematoxylin Eosin and used to assess the histological changes and to count the number of eosinophils in the mucosa. The C a r n o y ' s fixed sections were stained with alcyan blue (0.5% solution in 0.5 N HCI) and safranine acetate for mast cells (MC) counts. For the abomasal samples, the counts were performed both in the fundus and pylorus on 10 fields o f a reticulum square, randomly selected. In the small intestine, the counts were performed on 10 c r y p t / v i l l u s units as previously described (Miller and Jarrett, 1971).
2.1.5. Milk production data The milk yield and the fat and protein contents were recorded twice monthly at morning and afternoon milking. To estimate the difference between group PI and NPI in the total amount o f milk produced after the challenge infection, a graphic representation of the data was established and calculation of the surface under the curves was performed using a semi automatic digitalized analysing system (VIDS III, Shirehill, Safron Walden).
2.2. Statistical analyses In the first part of the study, comparisons were made between the different infections using a one-way analysis of variance ( A N O V A ) . In the second part of the study, the differences between both groups were analyzed using a one-way analysis of variance ( A N O V A ) except for PCV. For this parameter, covariance analysis was applied because significant differences were present between the two groups before the challenge infection.
3. Results 3.1. First part of the study 3.1.1. Parasitological data At the end o f the first initial infection, the level of egg excretion was approximately 4100 epg (Table 1). This level showed only a slight decrease following further infections Table 1 Values (Mean + S.D.) of the haematological and serological parameters measured at the end of each infection in the first part of the study Before infections End of the 1st infection End of the 2nd infection End of the 3rd infection EPG PCV Pepsinogen Inorganic phosphate
0 24.6a (2.7) 801.6a (392.6) 71.4a (17.3)
4134 (3120) 18.6b (2.9) 1523.5b (378.2) 61.5 b (13.3)
3726 (2551) 22.0 c (2.9) 1228.1c (463.0) 63.3b (16.3)
Different superscripts within each row indicate significant difference at P < 0.05.
3439 (2158) 28.0 d (4.2) 855.5a (424.6) 61.5 b (18.2)
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
47
such that at the end of the 3rd infection, the mean epg value was 3440. No statistical difference in egg output was detected between the 3 successive infections. Fenbendazole treatment, applied at the end of each infection, was highly efficient in removing worms as the epg, 7 days post treatment, was 0 on each occasion.
3.1.2. Haematological data At the end of the first infection, a significant depression was measured in the PCV values as compared to pre-infection values (Table 1). These changes in PCV were less severe after the 2nd infection but were still significantly depressed. However, the PCV values recovered after the third infection were in fact significantly higher than the values measured at the beginning of the experiment, before the goats received any infection. 3.1.3. Serological data The first infection was associated with a significant rise in the serum pepsinogen concentrations (Table 1). Following infection 2, the pepsinogen level remained significantly increased compared to the initial values, but the concentrations were lower than those detected at the end of the 1st infection. The pepsinogen concentrations measured after the third infection were not significantly different from pre-infection levels. A significant decrease was observed in the inorganic phosphate concentrations after each of the 1st, 2nd and 3rd infections (Table 1). 3.2. Second part of the study: Response to challenge infection 3.2• 1. Parasitological data After the challenge infection, a similar pattern in egg excretion was observed in both groups of goats and no statistical difference was observed between groups PI and NPI throughout the study (Fig. 2). The peak in egg excretion occurred in both groups on week 4 post challenge infection (PCI) and was followed thereafter, by a regular decrease until the end of the experiment. 35O0 3000t 2500 2000 L~J
1500 1000 5000
2
~
6
a
lO
Weeks post chal[engeirffection
12
14
Fig. 2. Parasite egg excreuon following the challenge infection in the previously infected (PI group) (""'i'm-) and non-previously infected goats (NPI group) (°°".".'~'°°).
48
H. Hoste, C. Chattier/Veterinary Parasitology 74 (1998) 43-54
Table 2 Individual worm burdens in the 5 necropsied, culled goats from the PI and NPI groups one month after the challenge infection Group PI
Mean (S.D.)
Group NPI
H. contortus
T. colubriformis
H. contortus
T. colubr!formis
2 1129 19 48 85 2566 (488, 7)
13,540 10,960 4680 14,180 8040 10,280 (3, 926)
46 626 2748 23 362 761 (1138, 1)
6740 16,260 15,880 18,800 14,865 14,440 (5304)
No statistical difference was established in individual worm counts from the 5 culled goats from each group (PI and NPI), either for H. contortus or T. colubriformis (Table 2).
3.2.2. Histological data No major differences in the damage induced by the worms to the abomasal and the intestinal mucosae were assessed between group PI and NPI on the histological slides. The lesions observed in the abomasum were quite mild. Superficial abrasion of the mucus cells was associated with an increased depth of the mucosa due to oedema of the connective tissue. The main lesion noticed in the small intestine was a moderate abrasion of villi with a slight increase of cell density in the lamina propria. In addition, the number of mast cells and eosinophils in the fundic, pyloric and intestinal mucosa were not statistically different between group (Table 3).
3.2.3. Haematological data A similar evolution in the PCV values was observed in both groups. The PCV values dropped dramatically after 4 weeks post challenge and then began to stabilise. However, the decrease in PCV was more pronounced in the previously infected animals and statistical differences were established by covariance analysis on week 6 and 8 PCI ( P < 0.01) (Fig. 3).
Table 3 Number of eosinophils and mast cells in the digestive mucosa of 5 culled goats from group PI and NPI killed one month after the challenge infection Eosinophils
Group PI Group NPI
Mast cells
Fundus
Pylorus
Small intestine
Fundus
Pylorus
Small intestine
2.98 (1.62) 2.77 (0.39)
4.23 (1.91) 2.13 (0.91)
11.75 (5.16) 10.13 (2.03)
8.90 (9.67) 7.08 (3.60)
4.25 (2.44) 4.28 (3.32)
23.00 (3.90) 19.70 (5.65)
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
49
38 36 34 32
>~
×
~ 3o ~
28
26 24
..........x
22
.....................
2O
2
0
4
6
8
10
!2
"~
Weeks oost challenge infection Fig. 3. Packed cell volume values ( ~ ) and non-previously
following the challenge infection in the previously infected (P1 group) infected goats (NPI group) ( ° ° " ) ~ " ° ° ) . Significant differences were assessed by covariance analysis on week 6 and 8 post challenge ( * : P < 0.05; * * : P < 0.01).
Before the challenge infection, no difference was observed in blood eosinophil number in both groups of animals. This absence of difference persisted until week 8 post challenge. On week 12 post challenge, an increase in the number of blood eosinophil occurred in group PI (mean number: 43 X 103 cells per ml) but was not detected in group NPI (mean number: 15 × 103 cells per ml). This rise was due to a few number of goats. Nevertheless, the difference between both groups was statistically significant ( P < 0.01) (data not shown).
3.2.4. Serological data A similar evolution in the mean serum pepsinogen concentrations was observed in both groups PI and NPI as a rise in the values occurred as soon as 2 weeks PCI. The maximal values were reached on week 4 post challenge and were maintained until week 8 PCI. This increase in pepsinogen concentrations was however more marked in animals 1700160015001400 13004 t 1200
/," ,
1100)
w"
"".,
.,,..," ,-~ ',
,.,"
I 10001 gO0 i
/
800
Weeks post challenge infection
Pepsinogen values following the challenge infection in the previously infected (PI group) ( " " " ~ " ~ ) and non-previously infected goats (NPI group) ( ' ° " - ~ ° ° ° ) . Significance of statistical test: * P < 0.05;
Fig. 4.
* * P < 0.01.
50
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54 8.5
"..
/
,~" ........... ~-.
75 -
•
."
".
,/"
60-
r ss
0
2
S
6
~
I0
12
~4
Weeks post challenge infection
Fig. 5. Inorganic phosphate concentrations after challenge infection in the previously infected (PI group) (''"~"~) and non-previously infected goats (NPI group) (°°"-'~1~°=°). Significance of statistical test: *P<0.05; **P<0.01.
from group PI. On week 4 and 8 PCI, differences between groups PI and NPI were significant ( P < 0.05) (Fig. 4). The inorganic phosphate concentrations in the serum of goats from groups PI and NPI also showed a parallel evolution after challenge infection. Nevertheless, the phosphate concentrations measured in group PI were regularly lower than those in group NPI and statistical differences were established on weeks 4 ( P < 0.01) and 10 PCI ( P < 0.05) (Fig. 5).
3.2.5. Milk yield During the whole study, the milk yield in goats from group PI was lower than in the NPI animals (Fig. 6). Significant differences were observed on week 2 ( P < 0.0 1), 6 and 10 PCI ( P < 0.02). The estimation of milk yield in the 2 groups of goats for the 3-month study indicated a 10.6% total reduction in group PI compared to group NPI. 3,6. 3,4.
~. . . . .
/ ....
".
3,2
*
''",, ,,
i
3"~
2,8" 2,62,4" 2,2-
6
2
4We*~s
6
8
10
12
post chaJfenge ir~fectior~
Fig. 6. Milk yield data following the challenge infection in the previously infected (PI group) ( ~ ) and non-previously infected goats (NPI group) ( ° " ~ ° ° ° ) . Significance of statistical test: *P < 0.05; * *P < 0.01.
H. Hoste, C. Chartier/ Veterinary' Parasitology 74 (1998) 43-54
51
No differences were detected in the fat and protein contents of milk in both groups of goats (data not shown).
4. Discussion The parasitological, pathophysiological and production parameters examined in the present study provide information on the resistance and the resilience of dairy goats to challenge infection with H. contortus and T. colubriformis. Examination of nematode egg excretion clearly indicates a low ability of goats to develop a resistance to trichostrongyles. This conclusion was supported by the constant pattern in egg excretion following the 3 successive infections in the first part of the study and by the lack of difference in epg between the 2 groups of goats after the challenge infection. This absence of reduction in egg excretion in previously infected goats is in agreement with observations from field studies comparing the pasture contamination with goats and sheep. A reduction in faecal egg excretion during the grazing season was only detected in sheep (Pomroy et al., 1986). This difference between host species has been attributed both to a difference in feeding behaviour (Jallow et al., 1994), but also to a less efficient development of resistance to nematode parasites in goats (Le Jambre, 1984) In the present study, the goats received a mixed infection. Examination of egg excretion did not allow for analysis of any possible differential response to the 2 species, i.e, H. contortus and T. colubriformis. However, some indications can be obtained from the worm counts in the necropsied culled goats following the challenge infection and from the pathophysiological parameters specifically related either to the abomasal (pepsinogen and PCV) or to the intestinal (inorganic phosphate) infections. The results related to the T. colubriformis infection are unequivocal. No significant difference in the worm number was established between the PI and NPI necropsied goats and no concomitant difference in histological lesions and cellular infiltration of the mucosae was detected. Secondly, during the 1st part of the study, the levels of inorganic phosphate did not improve following the 3 successive infections. Lastly, after the challenge infection, the inorganic phosphate concentrations were depressed in the previously infected goats compared to the other group. All together, these results strongly suggest a lack of resistance to T.colubriformis. In a similar way, Huntley et al. (1995), examining feral goats challenged after a grazing season, did not find any evidence of acquired immunity to T. vitrinus in does when compared to ewes or even lambs. In contrast, Pomroy and Charleston (1989b) have demonstrated a strong resistance of young Saanen goats to T. colubriformis in experimental conditions. This last result, however, was obtained in non-lactating animals. In sheep, Dobson et al. (1990) have underlined the importance of the initial level of T. colubriformis pre infection in expression of resistance. This factor could possibly explain the discrepancy between the different studies. The data related to H. contortus infections are more difficult to interpret than those relevant to T. colubriformis. In the first part of the study, the evolution of PCV and pepsinogen values strongly indicated an improved ability of goats to withstand the negative effects of the successive infections. However, the lack of direct results on
52
14. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
worm populations made difficult to relate this better resilience to an improved resistance, i.e, a smaller establishment of worms. Paradoxically, results from the second part of the study were opposite to those from the first one. They showed evidence of a lack of resistance to H. contortus. The worm counts and the histopathological data from the challenged culled goats were comparable in the PI and NPI group and previous exposure to nematodes did not lead to any improved PCV and pepsinogen concentrations. These results observed after the challenge infection are in agreement with previous descriptions of goats failing to resist to H. contortus (Pomroy and Charleston, 1989a; Watson and Hosking, 1989). Nevertheless, the differences in response between the 2 parts of the present study remain outstanding. Two main events happened between the 2 periods of infection which could possibly be evoked to explain the differences (l) Kidding and beginning of lactation; (2) The drenching of goats at the end of the 1st period followed by 2 months without contact with the worms. A disruption of immunity to nematodes related to parturition and lactation has been strongly substantiated in ewes (O'Sullivan and Donald, 1973; Jeffcoate et al., 1992; Barger, 1993). In contrast, only little information on a similar relationship were available in Angora goats (Rahman and Collins, 1992). The possibility of more dramatic and prolonged perturbations in goats has to be considered and is worth to be documented. Concerning anthelmintic treatment, several studies in sheep (Barger, 1988; Luffau et al., 1985) and one in Saanen kids (Hosking and Watson, 1993) have examined possible interference between drenching and host immunity, especially with H. contortus. They have underlined the importance of the presence of an existing worm population in regulation of establishment of new incoming larvae. In the present study, comparison of results between the 2 periods tend to confirm a possible disturbing role of anthelmintic treatment on host immunity to H. contortus. The time the hosts remain free of parasites could also be an important factor to consider. Although no difference was observed in parasitological parameters between PI and NPI goats after the challenge infection, clear differences were observed in both pathophysiological and production parameters. Previous contact with the worms was associated with more severe disturbances in serological measurements related to both H. contortus (i,e., pepsinogen and PCV levels) and T. colubriformis (i,e, inorganic phosphate) infections. These consequences lasted for the 3 months after challenge and were concomitant with a 10.6% reduction in milk production in the PI goats when compared to the NPI ones. The reduction in milk yield detected in the previously infected goats could be attributed to decreased conditions and interference on preparation of lactation due to parasitism at the end of the previous lactation. No study are available in goats to substantiate this hypothesis of a long term effect of parasitic infection on subsequent lactation. On the other hand, it should be noticed that no difference between groups was observed on the first month of lactation before goats received the challenge. Moreover, this could not easily explain the differences detected in the pathophysiological parameters. The more severe impact of the challenge in the previously parasitised goats could alternatively be explained by some adverse consequences due to the host response.
H. Hoste, C. Chartier / Veterinary Parasitology 74 (1998) 43-54
53
Detrimental effects related to larval challenges in adult, immune sheep have been described previously. Several field studies have shown that reinfection of adult sheep after previous exposure to trichostrongyles was associated with major pathophysiological disturbances despite low egg output. The changes were associated with losses in wool production (Anderson, 1973; Barger and Southcott, 1975) a n d / o r lower body weight (Pullman et al., 1991) and sometimes with clinical signs (Larsen et al., 1994; Suttle and Brebner, 1995). These field observations were, to some extent, supported by conclusions from indoors studies with T. colubriformis or Teladorsagia circumcincta assessing the consequences of challenge infection in resistant animals (Yakoob et al.. 1983; Kimambo et al., 1988). The origin of these perturbations was not clearly identified, but the development of some hypersensitive reaction in the digestive mucosae following the larval challenge has been evoked (Larsen et al., 1994). Similar adverse effects related to the host response could also be evoked from the present data in goats. However, 2 main differences between the 2 host species have to be underlined. First, the detrimental effects in sheep were always associated with a resistance to infection which is not the case in the present study. Second, the possibility of an hypersensitivity reaction in the gut is not supported in goats by the lack of difference in mucosal cell populations found in the culled, challenged goats. To summarize, the response to challenge infection in previously infected dairy goats could lead, as in sheep, to pathophysiological disturbances and negative consequences on production traits. However, in contrast with results in sheep and paradoxically, this was not associated with any major effects on the biology of worm populations. The present results therefore underline the interest of comparative studies in the 2 small ruminants species which could provide valuable information on the immune response to nematodes in both species and the importance of various modulating factors on expression of immunity and the possible associated detrimental consequences.
Acknowledgements The authors are extremely grateful to Dr. P. Griers and the Socirt~ Distrivet for their financial support. They wish to thank Mrs. C. Benoit, C. Koch,, M.P. Pellet, I. Pors for their technical assistance. Special thanks are also due to Mr. J. Gautron for the help in the measurement of inorganic phosphate with Technicon autolab. We are also grateful to the technical staff of Lycre Agricole de Melle and particularly Mr. H. Coutineau who provided the facilities.
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