INHIBITION NEMATODES
PATTERNS AND SEASONAL AVAILABILITY OF FOR BEEF CATTLE GRAZING ON ARGENTINA’S WESTERN PAMPAS V. H. SUAREZ
I.N.T.A., Estacion Experimental Agropecuaria de Anguil, C.C. I I, 6326 Anguil, La Pampa, Argentina (Received 5 Junuary 1990; accepted 2 I Jwle 1990) hstract-SuAREz V. H. 1990. Inhibition patterns and seasonal availability of nematodes for beef cattle grazing on Argentina’s Western Pampas. Znternational Journa~~or Parasitology 20: 103 l-1036. The seasonal population trends of cattle nematodes in tracer calves are described from 1981 to 1987. Successive worm-free calves were grazed with growing beef cattle for 20-30 days at 6 week intervals and then slaughtered for nematode counts 2 weeks after their removal from pasture. Ostertgiu, Coop&u, Trichostrongylus and Haemonchus were the main genera recovered. O.ostertagi was the most often found and acquisition of inhibition-prone larvae began in late winter and reached a peak in spring, while maximum larval availability was in autumn. The seasonal inhibition and larval availability pattern for Z’.axei was similar to that of Ostertagia. Cooperia showed greatest inhibition during winter with maximum larval availability in autumn and spring. ~aemonch~s was more prevalent during summer to early autumn and no inhibition was observed. It was conchtded that infective larval availability for tracer calves was highest during autumn, and most reduced in summer. All predominant species were able to survive over summer on pasture.
INDEX KEY WORDS: Cattle gastro-intestinal nematodes; inhibition; tracer calves; Argentina.
nematode infections cause substantial economic losses in grazing beef cattle production in the semi-arid Pampeana region (Suarez & Medrano, 1984; Suarez, Ciminari, Bello, Busetti & Bedotti, 1987). Knowledge of the seasonal trends and availability of free-living stages of cattle nematodes is necessary for planning control programmes, Seasonal inhibition of development and general epidemiological patterns have been elucidated in Europe (Michel, 1974; Tharaldsen, 1976) and in southern areas of Australia and North America (Smeal, Hotson, Mylrea, Jackson, Campbell & Kirton, 1977; Williams, 1986). In Argentina there have been few attempts to define seasonal patterns of nematode infections from worm counts on serially slaughtered permanent grazing cattle or worm-free tracers, apart from the reports of Suarezet al. (1987), Fiel, Steffan, Vercesi, Ambrustolo, Catania, Casaro, Entrocasso & Biondani (1988), and Suarez & Busetti (1989). Previous studies in the Pampeana region have been made of the seasonal variability of nematodes from worm counts on serially killed fattening cattle (Suarez, in press), but not from tracer calves over several years with successive grazing periods. The use of worm-free calves as tracer animals during a short grazing period has been recognized as a satisfactory method to determine inhibition patterns and changes in the numbers of larvae on pasture ~ASTRO~I~ESTINAL
(Cabaret, Raynaud & Le Stang, 1982; Smeal, Fraser & Robinson, 1980). The purpose of the present paper was to determine, over 6 years, the intensity and seasonality of nematode larval inhibition and the seasonal availability of infective larvae on pasture as assessed from tracer calves. MATERIALS AND METHODS areas and grazing periods. The studies were conducted in the Western Pampeana region at Anguil (La Pampa province) and at Trenque-Lauquen (Buenos Aires province) from February 1981 to March 1987. Data from the following six sets of ‘fattening grazing periods’ (FGP) were obtained: 1981/1982, 1982/1983, 198311984, 1984j1985, 1985/1986 and 1986/1987. Each one had the same duration, from I February to 14 March of the next year; the FGP was subdivided into nine tracer intervals (TX)of 45 days. Experinrenral pastures and caitle contamination. The pastures were contaminated throughout each FGP by a naturally infected grazing herd, i.e. from I February to 1 April by calves and their dams or by an 18-20 month old herd, and then from 2 April to 14 March of the next year, by fattening weaned calves from 6 to 18 months of age. The management of beef animals was traditional for the region. Calves were born in spring and weaned in early autumn. Aberdeen Angus and Herefords predominated with some Zebu crossbred and Santa Gertrudis. None were treated with anthelmintics. Contaminating livestock were grazed on sown perennial pastures (mainly lucerne, clover, fescue, agropyrum and weeping lovegrass) or annual crops (oat, common rye, wheat and sorghum aftermath residues). Figure 1shows the experimental design with FGP, TI, pastures and
1031
experimental
1032
V. H. SUAREZ
I I
Inltlu
EXP. Looatlon
Fop.
L
6va2
Tr8cer
8.~.
-
2 c
Z:
Intervals
11 2 13 141
b
ANGUIL
TRENQUE
a2/aa
1.6 Q z:
am4
0.8 c
a4186
2.6 a
Pormanont
(11)
5 16 17 I8 19 S.R. .-_--.-.---.-._ 1.1 a .-_.--...~-._..___-.~. _._.._._-.-.._.__ -_..- . ..__..._.. -- ...
1.2 G 2.6 Q
LAUQUEN
I
1
66166
2.6 Q
1
1
2.6 Q
1
12 a
1
I
1.8 Q
I
1 a6187
IANGUIL
FQP=Fattoninp
FIG.
1.1a
praxlnp
pulod,
6R-6tooklng
rate
pw
hootwe.
C-Cow,
G=Fattenlnp
o&lo
1.Grazing systems. Initial S. R. stocking rate from I February S. R. stocking
to 2 April. Permanent rate from 2 April to 14 March of the next year.
0
EpAAINMLL
+
Ep.Y.Max.Rmp.
-+ -
Av.M.MxX.lwnp.
w
Av. RAINFALL
-8
Ep.M.Yln.Temp.
-+ -
Av.M.Mln.Temp.
r
36
140 120 100 60 -
m.m.
‘C SO 40 20 OJ
F
M
A
My
Jn
J
Ag
S
0
N
D
Month8
FIG. 2. Maximum (Ep. M. Max. Temp.) and minimum (Ep. M. Min. Temp) monthly mean temperature and mean monthly precipitation (Ep. Rainfall) during experimental periods (Ep) in relation to 40 year averages (Av) of the same parameters.
contaminating cattle stocking rates. Regional climare. The annual rainfall is around 650-720 mm with the highest incidence from October to April. Mean maximum summer temperature is around 30°C and mean minimum winter temperatures drop to 0°C and frosts are numerous. Temperature and rainfall averages from January 1981 to March 1987 and the average data over the last 30 years are presented in Fig. 2. Tracer calves. Aberdeen Angus or Hereford calves of 24 months of age were taken from their dams, treated with anthelmintics and reared under conditions free of helminth infections to 4-7 months of age. One tracer calf was introduced every interval (TI) of each FGP and was grazed alongside the contaminating grazing herd for 20-30 days.
After removal the tracer calves were held in confinement for 2 weeks before slaughter to assess the importance of arrested larvae. Worm COWIS. The abomasum, small and large intestine were examined separately for worm counts according to the standard methods of Anonymous (1982). The abomasal mucosa and the upper half of the small intestine were digested by the pepsin-HCl method (Herlich, 1956) and during the last two FGP this method was complemented by immersion in warm normal saline according to Downey (1981). Helminth identification was performed according to Ueno & Gutierres (1983) and for early fourth stage larvae (EL4) and developing fourth stage larvae (DL4) of Osfertagia, according to Hong (1989). Haemonchus contortus was
1033
Nematode populations in tracer calves TABLE I-WORM
COUNTSOFPREDOMINANT GENERARECOVERED FROM TRACER CALVES
Fattening grazing period (FGP)
Tl 1981/1982 Total EL4 W) Osterragia 1 0 2 1360 3 1320 4 0 5 0 6 155 7 575 8 120 9 40
0 0 0 0 0
1982/1983 Total EL4 W)
91 40 0 0
120 330 2780 355 2990 800 680 160 2210
60 300 3040 7296 0 130 130 300 0
0 0 0 20 0 12 0 0 0
0 0 0 0 0 0 0 0 0
0 35 1550 215 0 325 80 0 0
0 0 0 0 0 0 0 0 0
80 30 720 160 0 0 10 80 150
60 75 0 0
50 730 12,990 8500 0 2015 710 210 610
0 0 0 0 0 5 0 0 0
Trichostrongylus I 0 2 0 3 400 4 0 5 0 6 0 7 0 8 0 9 0 Haemonchus 1 0 2 120 3 50 4 0 5 0 6 0 7 180 8 200 9 70
Cooperia 1 2 3 4 5 6 7 8 9
0 1580 1800 0 0 155 875 480 180
0 0 0 0 0
1983/1984 Total EL4 W)
1984/1985 Total EL4 W)
0 0 0 0
31 50 76 0 9
4226 1320 9880 10,390 2520 120 10,588 230 90
43 20 918 115 50 0 200 610 3935
0 0 0 22 25 0 0 0 0
0 0 0 0 0 10 0 0 0
0 0 10 0 210 80 0 0 220
0 0 0 0 0 0 0 0 0
230 292 40 0 0 0 0 620 2400
0
1985/1986 Total EL4 W)
1986/1987 Total EL4 W) 0 0
65 76 0 0
690 5900 1270 450 15,390 12,195 6986 1540 100
0 0 0 0 17 78 27 16 0
50 35,240 77,657 28,965 46,148 12,795 1300 320 70
2 6 77 89 84 15 0
8960 2700 1210 425 113 0 2375 2760 1180
0 0 0 25 15 0 10 0 0
260 6100 300 70 1050 2400 7600 9542 500
0 0 0 20 14 9 20 0 0
420 17,700 28.372 4400 12,739 3492 1040 20 420
0 0 7 57 10 15 0 0 0
0 0 0 0 0 40 0 0 0
527 0 420 90 0 0 1924 10 130
0 0 0 0 0 0 21 0 0
240 800 100 55 825 1010 50 300 20
0 0 0 0 20 15 10 0 0
0 0 7094 570 316 338 200 0 0
0 0 0 0 0 38 40 0 0
0 0 0 0 0 0 0 0 0
2520 50 280 80 0 0 348 30 280
0 0 0 95 0 0 0 0 0
795 2950 0 0 0 60 115 180 200
0 0 0 0 0 0 98 0 0
290 2020 166 0 498 166 233 200 300
0 0 80 0 0 0 0 0 0
0
0 0 0
For Cooperia and Haemonchus EL4 percentages include DL4.
regarded as a synonym of H. placei according to Gibbons’ (1979)revision. Statistical methods. The significance of differences in seasonal patterns of worm counts of each species within TI and between FGP years was examined by analysis of variance, after transformation of the worm counts (x) as y = log,, (X + 1). For statistical analysis EL4 and DL4 were pooled with adult worms, but for hypobiosis analysis only DL4 were regrouped.
Table 1 presents
RESULTS the counts of predominant
worm
genera from individual tracers during the study. The overall prevalence of genera was: Ostertagia 92%, Cooperia 87%, Haemonchus 70% and Trichostrongylus 54%. The Cooperia species recovered were C. oncophora (80%) and C. punctata (20% with extreme frequencies of 40 and 5%). Ostertagia comprised 0. ostertagi (97%) and 0. lyrata (3% with extremes of 7 and 0%). Although Oesophagostomum radiatum and Trichuris spp. were found occasionally, numbers of these species were too low to draw useful conclusions. Ostertagia ostertagi was the most
1034
V. H. SUAREZ
Rlchortron6ylue
, 2
autumn
, ,
winier
, 6 Tracer Intbrwl* (TO t3vrlng Bummer
, 6
FIG. 3. Geometric mean numbers of genera recovered from tracer calves grazed across fattening grazing periods (FGP).
numerous species recovered, followed by Cooperia spp., Haemonchus contortus and Trichostrongylus axei. Figure 3 shows the geometric mean of each species recovered from tracers across FGPs. The total Ostertagia burdens acquired from different FGPs reached a peak in late autumn; a smaller peak in late spring was also seen (Fig. 3). Those acquired from whole perennial pasture grazing systems showed the greatest numbers from autumn to spring. Minimum acquisition was seen during summer. Ostertagia populations were almost exclusively adults until midwinter, but the percentage of EL4 increased significantly from late winter to spring, thereafter EL4 fell rapidly and remained low from early summer (Fig. 4). The total T. axei burdens acquired from different FGP reached significantly higher levels in late autumn (Fig. 3), and closely paralleled trends observed for Ostertagia, but at a lower level. The proportions of EL4 were small and irregular and were seen during spring (Fig. 4). Cooperia populations recovered from different FGP were significantly higher during autumn. After a winter decline numbers increased to a lesser peak during spring and early summer (Fig. 3). Cooperia showed a wider range in their occurrence between FGP systems and substantial numbers were available during winter to spring from whole perennial pasture systems. The number and proportion of L4 stages were relatively small and were seen from winter to early spring and thereafter fell rapidly to zero (Fig. 4). Haemonchus were more prevalent during midsummer to early autumn and remained significantly lower during winter and early spring. The number of L4 observed was negligible. Figure 5 presents the total worm burdens acquired for tracer calves during each FGP. Only for the first FGP system (1981/1982) were significant differences between FGP found, but higher worm burdens were recovered from whole perennial pasture FGP. All predominant nematode species were capable of surviving on pasture over summer. The greatest seasonal nematode availability for tracer calves was
1’ I
’
a)’ I’
7’
I’
FIG. 4. Seasonal occurrence
of inhibited larval development. EL4: Early fourth larvae stage; EL4, DL4: EL4 include developing fourth stage larvae; Adult: mature stage.
found during the autumn summer (Fig. 6).
and the smallest during the
DISCUSSION The most important seasonal changes in population structures were seen in Ostertagia. Occurrence of inhibited development reached a maximum in spring with EL4 comprising 27-9 1% of the total Ostertagia burden. This spring inhibition, previously noted for beefcattle in the Pampeana region (Suarez, V.H. 1985. Abstract in papers presented at the Eleventh Conference of the World Association for the Advancement of Veterinary Parasitology. Rio de Janeiro, pp. 41-42.; Suarez et al., 1987; Fiel et al., 1988), was confirmed by observation over several different grazing periods.
Nematode
populations
in tracer calves
1035
Worm* x 1000
1
1 ’ Autumn
FIG. 5. Total worms recovered
from tracer calves during
autumn
FIG. 6. Seasonal summary tracer calves during
of recovered nematodes each tracer interval (TI).
from
The spring arrest of development, also described in Australia and Louisiana, U.S.A. (Smeal et al., 1980; Williams, 1986) can be explained in various ways. Cessation of favourable autumn-winter conditions at spring, i.e. induction of inhibition by increasing temperature and increasing desiccation, may have some importance in Argentina’s semi-arid and subhumid conditions. By this means Ostertagia is able to survive over periods when environmental conditions are unsuitable for its free-living development. Resumed development of inhibited larvae when temperatures fall and moisture levels increase in late summer has been described in permanently grazing cattle in the Pampeana region (Fiel et al., 1988; Suarez, in press). Autumn inhibition of Ostertagia ostertagi in Great Britain was attributed to changes in larvae, induced by the external abrupt decrease in temperature (Armour & Bruce, 1974) and Michel, Lancaster & Hong (1975) have pointed out that the same larvae which became inhibited when ingested in autumn reverted to normal development after remaining on pasture until spring.
each fattening
grazing
period (FGPs).
In accordance with Sollod’s (1967) strain hypothesis, Smeal & Donald (1981) reported that seasonal changes in level of inhibition were due to changes in the relative frequency of inhibiting and non-inhibiting morphs, and that genetic worm factors were implicated in seasonal inhibition. Smeal & Donald (1981, 1984) and Frank, Herd, Marbury, Williams & Willis (1988) observed that this genetic determination of patterns of hypobiosis varies with climatic regions or cattle management systems. Another factor that could be involved in larval inhibition is degree of host acquired immunity. It was seen in continuously grazed beef cattle that older cattle showed a greater percentage of EL4 than younger ones, or that yearling tracers bore higher EL4 percentages than did 46 month old ones in spring (Suarez, unpublished results). T. axei seasonal trends of inhibited development appeared to be similar to those of 0. ostertagi, in accordance with the observation of Fiel et al. (1988) in the eastern part of Buenos Aires province. Cooperia exhibited an irregular and low frequency of EL4 and DL4 during winter and early spring; possibly associated with higher mid-winter burdens in accordance with previous (Suarez, in press) observations on continuous cattle grazing systems. Therefore it appeared that inhibition may be associated with immunological adaptive or densitydependent mechanisms rather than environmental stimuli, in contrast to Cooperiu strains in Britain (Michel et al., 1975). On pastures which were contaminated continuously, larval availability for tracer calves reached maximum levels from autumn to spring and it is suggested that the majority of these larvae were derived from autumn-winter contamination. In FGP with a high proportion of annual crops (no great initial contamination) or non-continuously contaminated
1036
V. H. SUAREZ
systems, larval availability reached maximum levels in late autumn and spring, with the exception of ~~g~o~e~us, which always reached maximum availability in late summer to mid-autumn. The studies suggest that a reduction in the initial nematode egg pasture contamination in autumnwinter could result in safer pastures. Acknowledgements-The
author wishes to express his grateful thanks to M. R. Busetti, D. 0. Bedotti, M. C. Fort and 0. E. Ciminari for their technical assistance and to INTA-Anguil ranch staff for their collaboration. I sincerely thank Dr Jacques Cabaret @NRA, Nouzilly, France) for his generous help. REFERENCE ANONYMOUS1982. Recuperation de nematodes adultos e inmaduros. In: Tecnicas de necropsiu y de laboratorio aphcadas en el Centro de Investigaciones Veterinarias, Buenos Aires, Remibiica Argentina (Edited bv I.N.T.A. CASTELAR,Jo&& S. A. C.-& JO&ON I.), pp. 33-34. ARMOURJ. & BRUCE R. G. 1974. The inhibition of development of Ostertagia ostertagi-a diapause phenomenon in a nematode. Parasitology 69: 161-174. CABARET J., RAYNAUD J. P. & LE STANG J. P. 1982.
Comparison between tracer calves and herbage samplings for the assessment of pasture infectivity in trichostrongylosis of cattle. Veterinary Parasitologj 10: 65-7 1. DOWNEYN. E. 1981. Recovery of Osiertagia from the bovine abomasal mucosa by immersion in warm normal saline. In:
~elminthoIog~~a1 Society of Washington 23: 102-103. HONG C. 1989. Inte~~tatio~ of abomasal worm burdens in cattle. Veterinary Record 28: 87-88. MICHEL J. F. 1974. Arrested development of nematodes and some related phenomena. Advances in Parasitology 12: 28&343. MICHEL J. F., LANCASTERM. B. & HONG C. 1975. Arrested development of Ostertagia ostertagi and Cooperia oncophora. Effect of temperature at the free-living stage. Journal of Comparative Pathoiogv 85: 133-138. SMEAL M. G., H~TSON 1. K., MYLREA P. J., JACKSONA. J., CAMPBELLN. J. & KRTON H. C. 1977. Studies of nematode infections of beef cattle in New South Wales. Australian Veterinary Journal 53: 566-573. SMEALM. G., FRAZERG. C. & ROBINSONG. G. 1980. Seasonal changes in the structure of nematode populations of cattle in New South Wales in relation to inhibited iarval development. Australian Veterinary Journal 56: 80-86. SMEALM. G. &DONALD A. D. 1981. Effects on inhibition of development of the transfer of Ostertugia ostertagi between geographical regions of Australia. Parasitofogy 82: 389399. SMEALM. G. & DONALDA. D. 1984. Inhibited development of Ostertagia ostertagi in Australia related to survival over summer in the host or on pasture. Parasitology 89: 597-602. SOLLODA. E. 1967. The possible existence of two strains of Ostertagia ostertagi. Veterinary RecordSI: 547-548. SUAREZ V. H. & MEDRANO C. A. 1984. Parasitism0 gastrointestinal en bovinos Aberdeen Angus en la Region Semiarida Pampeana. I Primeros 2 adios de observaciones. Therios 19: 336350. SU.+RE~V. H., CIMINARI0. E., BELLOE. M., BUSE~I M. R. & BELXXX D. 0. 1987. Parasitismos gastrointestinal en la
Current Topirs in Veterinary Medicine and Animal Science, Vol. 9 (Edited by NANSENP., JORGENSENR. J. & SOULSBYE. invernada de novillos Cruza-Zebu en la Region Subhumeda Pampeana. Veterinaria Argentina= 695-705. J. L.), pp. 69-73. Martinus Nijhoff, The Hague. FIEL C. A., STEFFAN P. E., VERCES~H., AMBRUSTOLOR. R., SUAREZV. H. & BUSE~TIM. R. 1989. Eaizootiolo!zia v efecto CATANIAP., CASAROA. P., ENTROCASSO C. M. & BLONDANI de 10s nematodes gastrointestinaies en la recrialde ferneras en la Region Semiarida Pampeana. Rev&a Argentina de C. A. 1988. Variation estacional del parasitism0 interno de Production Animal9: 149-158. bovinos en el sudeste de la Prov. de Buenos Aires SUAREZ V. H. (in press) Variation estacional de las (Argentina) con especial referencia al fenbmeno de ‘hipobiosis’. Revista de Medicina Veterinaria, Buenos Aires poblaciones de helmintos parasites de bovinos en sistemas de invernada en la Region Semiarida y Subhumeda 69: 51-64. Pampeana. Rev&a de Medicina Veterinaria, Buenos Aires. FRANK G. R., HERD R. P., MAR~URY K. S., WILLIAMSJ. C. & THARALDSENJ. 1976. The epidemiology of trichostrongylid WILLIS E. R. 1988. Additional investigations on hypobiosis infection in young cattle in Norway. Acta Veterinaria of Ostertagia ostertagi after transfer between northern and Scandinavica 17, Suppl. 61: l-21. southern U.S.A. Internationat Journal for Parasitology 18: UENO H. & GUTIERRE~V. C. 1983. ManuaIpara diagnostico 171-177. das heIm~nthoses de rum~nantes~pp. 118-129. Japan InterGIBBONS L. M. 1979. Revision of the genus ~~rnonc~~ Cobb, 1898, (~emafo~: Trjchostrongylidae). Systematic national Cooperation Agency, Tokyo. WILLIAMSJ. C. 1986. Epidemiologic patterns of nematodiasis FarasitoIogy 1: 3-24. in cattle. Veterinary Clinics of North America: Food Animal HERLICH H., 1956. A digestion method for post-mortem Practice 2: 235-246. recovery of nematodes from ruminants. Proceedings of the
PATTERNS AND SEASONAL AVAILABILITY OF FOR BEEF CATTLE GRAZING ON ARGENTINA’S WESTERN PAMPAS V. H. SUAREZ
I.N.T.A., Estacion Experimental Agropecuaria de Anguil, C.C. I I, 6326 Anguil, La Pampa, Argentina (Received 5 Junuary 1990; accepted 2 I Jwle 1990) hstract-SuAREz V. H. 1990. Inhibition patterns and seasonal availability of nematodes for beef cattle grazing on Argentina’s Western Pampas. Znternational Journa~~or Parasitology 20: 103 l-1036. The seasonal population trends of cattle nematodes in tracer calves are described from 1981 to 1987. Successive worm-free calves were grazed with growing beef cattle for 20-30 days at 6 week intervals and then slaughtered for nematode counts 2 weeks after their removal from pasture. Ostertgiu, Coop&u, Trichostrongylus and Haemonchus were the main genera recovered. O.ostertagi was the most often found and acquisition of inhibition-prone larvae began in late winter and reached a peak in spring, while maximum larval availability was in autumn. The seasonal inhibition and larval availability pattern for Z’.axei was similar to that of Ostertagia. Cooperia showed greatest inhibition during winter with maximum larval availability in autumn and spring. ~aemonch~s was more prevalent during summer to early autumn and no inhibition was observed. It was conchtded that infective larval availability for tracer calves was highest during autumn, and most reduced in summer. All predominant species were able to survive over summer on pasture.
INDEX KEY WORDS: Cattle gastro-intestinal nematodes; inhibition; tracer calves; Argentina.
nematode infections cause substantial economic losses in grazing beef cattle production in the semi-arid Pampeana region (Suarez & Medrano, 1984; Suarez, Ciminari, Bello, Busetti & Bedotti, 1987). Knowledge of the seasonal trends and availability of free-living stages of cattle nematodes is necessary for planning control programmes, Seasonal inhibition of development and general epidemiological patterns have been elucidated in Europe (Michel, 1974; Tharaldsen, 1976) and in southern areas of Australia and North America (Smeal, Hotson, Mylrea, Jackson, Campbell & Kirton, 1977; Williams, 1986). In Argentina there have been few attempts to define seasonal patterns of nematode infections from worm counts on serially slaughtered permanent grazing cattle or worm-free tracers, apart from the reports of Suarezet al. (1987), Fiel, Steffan, Vercesi, Ambrustolo, Catania, Casaro, Entrocasso & Biondani (1988), and Suarez & Busetti (1989). Previous studies in the Pampeana region have been made of the seasonal variability of nematodes from worm counts on serially killed fattening cattle (Suarez, in press), but not from tracer calves over several years with successive grazing periods. The use of worm-free calves as tracer animals during a short grazing period has been recognized as a satisfactory method to determine inhibition patterns and changes in the numbers of larvae on pasture ~ASTRO~I~ESTINAL
(Cabaret, Raynaud & Le Stang, 1982; Smeal, Fraser & Robinson, 1980). The purpose of the present paper was to determine, over 6 years, the intensity and seasonality of nematode larval inhibition and the seasonal availability of infective larvae on pasture as assessed from tracer calves. MATERIALS AND METHODS areas and grazing periods. The studies were conducted in the Western Pampeana region at Anguil (La Pampa province) and at Trenque-Lauquen (Buenos Aires province) from February 1981 to March 1987. Data from the following six sets of ‘fattening grazing periods’ (FGP) were obtained: 1981/1982, 1982/1983, 198311984, 1984j1985, 1985/1986 and 1986/1987. Each one had the same duration, from I February to 14 March of the next year; the FGP was subdivided into nine tracer intervals (TX)of 45 days. Experinrenral pastures and caitle contamination. The pastures were contaminated throughout each FGP by a naturally infected grazing herd, i.e. from I February to 1 April by calves and their dams or by an 18-20 month old herd, and then from 2 April to 14 March of the next year, by fattening weaned calves from 6 to 18 months of age. The management of beef animals was traditional for the region. Calves were born in spring and weaned in early autumn. Aberdeen Angus and Herefords predominated with some Zebu crossbred and Santa Gertrudis. None were treated with anthelmintics. Contaminating livestock were grazed on sown perennial pastures (mainly lucerne, clover, fescue, agropyrum and weeping lovegrass) or annual crops (oat, common rye, wheat and sorghum aftermath residues). Figure 1shows the experimental design with FGP, TI, pastures and
1031
experimental
1032
V. H. SUAREZ
I I
Inltlu
EXP. Looatlon
Fop.
L
6va2
Tr8cer
8.~.
-
2 c
Z:
Intervals
11 2 13 141
b
ANGUIL
TRENQUE
a2/aa
1.6 Q z:
am4
0.8 c
a4186
2.6 a
Pormanont
(11)
5 16 17 I8 19 S.R. .-_--.-.---.-._ 1.1 a .-_.--...~-._..___-.~. _._.._._-.-.._.__ -_..- . ..__..._.. -- ...
1.2 G 2.6 Q
LAUQUEN
I
1
66166
2.6 Q
1
1
2.6 Q
1
12 a
1
I
1.8 Q
I
1 a6187
IANGUIL
FQP=Fattoninp
FIG.
1.1a
praxlnp
pulod,
6R-6tooklng
rate
pw
hootwe.
C-Cow,
G=Fattenlnp
o&lo
1.Grazing systems. Initial S. R. stocking rate from I February S. R. stocking
to 2 April. Permanent rate from 2 April to 14 March of the next year.
0
EpAAINMLL
+
Ep.Y.Max.Rmp.
-+ -
Av.M.MxX.lwnp.
w
Av. RAINFALL
-8
Ep.M.Yln.Temp.
-+ -
Av.M.Mln.Temp.
r
36
140 120 100 60 -
m.m.
‘C SO 40 20 OJ
F
M
A
My
Jn
J
Ag
S
0
N
D
Month8
FIG. 2. Maximum (Ep. M. Max. Temp.) and minimum (Ep. M. Min. Temp) monthly mean temperature and mean monthly precipitation (Ep. Rainfall) during experimental periods (Ep) in relation to 40 year averages (Av) of the same parameters.
contaminating cattle stocking rates. Regional climare. The annual rainfall is around 650-720 mm with the highest incidence from October to April. Mean maximum summer temperature is around 30°C and mean minimum winter temperatures drop to 0°C and frosts are numerous. Temperature and rainfall averages from January 1981 to March 1987 and the average data over the last 30 years are presented in Fig. 2. Tracer calves. Aberdeen Angus or Hereford calves of 24 months of age were taken from their dams, treated with anthelmintics and reared under conditions free of helminth infections to 4-7 months of age. One tracer calf was introduced every interval (TI) of each FGP and was grazed alongside the contaminating grazing herd for 20-30 days.
After removal the tracer calves were held in confinement for 2 weeks before slaughter to assess the importance of arrested larvae. Worm COWIS. The abomasum, small and large intestine were examined separately for worm counts according to the standard methods of Anonymous (1982). The abomasal mucosa and the upper half of the small intestine were digested by the pepsin-HCl method (Herlich, 1956) and during the last two FGP this method was complemented by immersion in warm normal saline according to Downey (1981). Helminth identification was performed according to Ueno & Gutierres (1983) and for early fourth stage larvae (EL4) and developing fourth stage larvae (DL4) of Osfertagia, according to Hong (1989). Haemonchus contortus was
1033
Nematode populations in tracer calves TABLE I-WORM
COUNTSOFPREDOMINANT GENERARECOVERED FROM TRACER CALVES
Fattening grazing period (FGP)
Tl 1981/1982 Total EL4 W) Osterragia 1 0 2 1360 3 1320 4 0 5 0 6 155 7 575 8 120 9 40
0 0 0 0 0
1982/1983 Total EL4 W)
91 40 0 0
120 330 2780 355 2990 800 680 160 2210
60 300 3040 7296 0 130 130 300 0
0 0 0 20 0 12 0 0 0
0 0 0 0 0 0 0 0 0
0 35 1550 215 0 325 80 0 0
0 0 0 0 0 0 0 0 0
80 30 720 160 0 0 10 80 150
60 75 0 0
50 730 12,990 8500 0 2015 710 210 610
0 0 0 0 0 5 0 0 0
Trichostrongylus I 0 2 0 3 400 4 0 5 0 6 0 7 0 8 0 9 0 Haemonchus 1 0 2 120 3 50 4 0 5 0 6 0 7 180 8 200 9 70
Cooperia 1 2 3 4 5 6 7 8 9
0 1580 1800 0 0 155 875 480 180
0 0 0 0 0
1983/1984 Total EL4 W)
1984/1985 Total EL4 W)
0 0 0 0
31 50 76 0 9
4226 1320 9880 10,390 2520 120 10,588 230 90
43 20 918 115 50 0 200 610 3935
0 0 0 22 25 0 0 0 0
0 0 0 0 0 10 0 0 0
0 0 10 0 210 80 0 0 220
0 0 0 0 0 0 0 0 0
230 292 40 0 0 0 0 620 2400
0
1985/1986 Total EL4 W)
1986/1987 Total EL4 W) 0 0
65 76 0 0
690 5900 1270 450 15,390 12,195 6986 1540 100
0 0 0 0 17 78 27 16 0
50 35,240 77,657 28,965 46,148 12,795 1300 320 70
2 6 77 89 84 15 0
8960 2700 1210 425 113 0 2375 2760 1180
0 0 0 25 15 0 10 0 0
260 6100 300 70 1050 2400 7600 9542 500
0 0 0 20 14 9 20 0 0
420 17,700 28.372 4400 12,739 3492 1040 20 420
0 0 7 57 10 15 0 0 0
0 0 0 0 0 40 0 0 0
527 0 420 90 0 0 1924 10 130
0 0 0 0 0 0 21 0 0
240 800 100 55 825 1010 50 300 20
0 0 0 0 20 15 10 0 0
0 0 7094 570 316 338 200 0 0
0 0 0 0 0 38 40 0 0
0 0 0 0 0 0 0 0 0
2520 50 280 80 0 0 348 30 280
0 0 0 95 0 0 0 0 0
795 2950 0 0 0 60 115 180 200
0 0 0 0 0 0 98 0 0
290 2020 166 0 498 166 233 200 300
0 0 80 0 0 0 0 0 0
0
0 0 0
For Cooperia and Haemonchus EL4 percentages include DL4.
regarded as a synonym of H. placei according to Gibbons’ (1979)revision. Statistical methods. The significance of differences in seasonal patterns of worm counts of each species within TI and between FGP years was examined by analysis of variance, after transformation of the worm counts (x) as y = log,, (X + 1). For statistical analysis EL4 and DL4 were pooled with adult worms, but for hypobiosis analysis only DL4 were regrouped.
Table 1 presents
RESULTS the counts of predominant
worm
genera from individual tracers during the study. The overall prevalence of genera was: Ostertagia 92%, Cooperia 87%, Haemonchus 70% and Trichostrongylus 54%. The Cooperia species recovered were C. oncophora (80%) and C. punctata (20% with extreme frequencies of 40 and 5%). Ostertagia comprised 0. ostertagi (97%) and 0. lyrata (3% with extremes of 7 and 0%). Although Oesophagostomum radiatum and Trichuris spp. were found occasionally, numbers of these species were too low to draw useful conclusions. Ostertagia ostertagi was the most
1034
V. H. SUAREZ
Rlchortron6ylue
, 2
autumn
, ,
winier
, 6 Tracer Intbrwl* (TO t3vrlng Bummer
, 6
FIG. 3. Geometric mean numbers of genera recovered from tracer calves grazed across fattening grazing periods (FGP).
numerous species recovered, followed by Cooperia spp., Haemonchus contortus and Trichostrongylus axei. Figure 3 shows the geometric mean of each species recovered from tracers across FGPs. The total Ostertagia burdens acquired from different FGPs reached a peak in late autumn; a smaller peak in late spring was also seen (Fig. 3). Those acquired from whole perennial pasture grazing systems showed the greatest numbers from autumn to spring. Minimum acquisition was seen during summer. Ostertagia populations were almost exclusively adults until midwinter, but the percentage of EL4 increased significantly from late winter to spring, thereafter EL4 fell rapidly and remained low from early summer (Fig. 4). The total T. axei burdens acquired from different FGP reached significantly higher levels in late autumn (Fig. 3), and closely paralleled trends observed for Ostertagia, but at a lower level. The proportions of EL4 were small and irregular and were seen during spring (Fig. 4). Cooperia populations recovered from different FGP were significantly higher during autumn. After a winter decline numbers increased to a lesser peak during spring and early summer (Fig. 3). Cooperia showed a wider range in their occurrence between FGP systems and substantial numbers were available during winter to spring from whole perennial pasture systems. The number and proportion of L4 stages were relatively small and were seen from winter to early spring and thereafter fell rapidly to zero (Fig. 4). Haemonchus were more prevalent during midsummer to early autumn and remained significantly lower during winter and early spring. The number of L4 observed was negligible. Figure 5 presents the total worm burdens acquired for tracer calves during each FGP. Only for the first FGP system (1981/1982) were significant differences between FGP found, but higher worm burdens were recovered from whole perennial pasture FGP. All predominant nematode species were capable of surviving on pasture over summer. The greatest seasonal nematode availability for tracer calves was
1’ I
’
a)’ I’
7’
I’
FIG. 4. Seasonal occurrence
of inhibited larval development. EL4: Early fourth larvae stage; EL4, DL4: EL4 include developing fourth stage larvae; Adult: mature stage.
found during the autumn summer (Fig. 6).
and the smallest during the
DISCUSSION The most important seasonal changes in population structures were seen in Ostertagia. Occurrence of inhibited development reached a maximum in spring with EL4 comprising 27-9 1% of the total Ostertagia burden. This spring inhibition, previously noted for beefcattle in the Pampeana region (Suarez, V.H. 1985. Abstract in papers presented at the Eleventh Conference of the World Association for the Advancement of Veterinary Parasitology. Rio de Janeiro, pp. 41-42.; Suarez et al., 1987; Fiel et al., 1988), was confirmed by observation over several different grazing periods.
Nematode
populations
in tracer calves
1035
Worm* x 1000
1
1 ’ Autumn
FIG. 5. Total worms recovered
from tracer calves during
autumn
FIG. 6. Seasonal summary tracer calves during
of recovered nematodes each tracer interval (TI).
from
The spring arrest of development, also described in Australia and Louisiana, U.S.A. (Smeal et al., 1980; Williams, 1986) can be explained in various ways. Cessation of favourable autumn-winter conditions at spring, i.e. induction of inhibition by increasing temperature and increasing desiccation, may have some importance in Argentina’s semi-arid and subhumid conditions. By this means Ostertagia is able to survive over periods when environmental conditions are unsuitable for its free-living development. Resumed development of inhibited larvae when temperatures fall and moisture levels increase in late summer has been described in permanently grazing cattle in the Pampeana region (Fiel et al., 1988; Suarez, in press). Autumn inhibition of Ostertagia ostertagi in Great Britain was attributed to changes in larvae, induced by the external abrupt decrease in temperature (Armour & Bruce, 1974) and Michel, Lancaster & Hong (1975) have pointed out that the same larvae which became inhibited when ingested in autumn reverted to normal development after remaining on pasture until spring.
each fattening
grazing
period (FGPs).
In accordance with Sollod’s (1967) strain hypothesis, Smeal & Donald (1981) reported that seasonal changes in level of inhibition were due to changes in the relative frequency of inhibiting and non-inhibiting morphs, and that genetic worm factors were implicated in seasonal inhibition. Smeal & Donald (1981, 1984) and Frank, Herd, Marbury, Williams & Willis (1988) observed that this genetic determination of patterns of hypobiosis varies with climatic regions or cattle management systems. Another factor that could be involved in larval inhibition is degree of host acquired immunity. It was seen in continuously grazed beef cattle that older cattle showed a greater percentage of EL4 than younger ones, or that yearling tracers bore higher EL4 percentages than did 46 month old ones in spring (Suarez, unpublished results). T. axei seasonal trends of inhibited development appeared to be similar to those of 0. ostertagi, in accordance with the observation of Fiel et al. (1988) in the eastern part of Buenos Aires province. Cooperia exhibited an irregular and low frequency of EL4 and DL4 during winter and early spring; possibly associated with higher mid-winter burdens in accordance with previous (Suarez, in press) observations on continuous cattle grazing systems. Therefore it appeared that inhibition may be associated with immunological adaptive or densitydependent mechanisms rather than environmental stimuli, in contrast to Cooperiu strains in Britain (Michel et al., 1975). On pastures which were contaminated continuously, larval availability for tracer calves reached maximum levels from autumn to spring and it is suggested that the majority of these larvae were derived from autumn-winter contamination. In FGP with a high proportion of annual crops (no great initial contamination) or non-continuously contaminated
1036
V. H. SUAREZ
systems, larval availability reached maximum levels in late autumn and spring, with the exception of ~~g~o~e~us, which always reached maximum availability in late summer to mid-autumn. The studies suggest that a reduction in the initial nematode egg pasture contamination in autumnwinter could result in safer pastures. Acknowledgements-The
author wishes to express his grateful thanks to M. R. Busetti, D. 0. Bedotti, M. C. Fort and 0. E. Ciminari for their technical assistance and to INTA-Anguil ranch staff for their collaboration. I sincerely thank Dr Jacques Cabaret @NRA, Nouzilly, France) for his generous help. REFERENCE ANONYMOUS1982. Recuperation de nematodes adultos e inmaduros. In: Tecnicas de necropsiu y de laboratorio aphcadas en el Centro de Investigaciones Veterinarias, Buenos Aires, Remibiica Argentina (Edited bv I.N.T.A. CASTELAR,Jo&& S. A. C.-& JO&ON I.), pp. 33-34. ARMOURJ. & BRUCE R. G. 1974. The inhibition of development of Ostertagia ostertagi-a diapause phenomenon in a nematode. Parasitology 69: 161-174. CABARET J., RAYNAUD J. P. & LE STANG J. P. 1982.
Comparison between tracer calves and herbage samplings for the assessment of pasture infectivity in trichostrongylosis of cattle. Veterinary Parasitologj 10: 65-7 1. DOWNEYN. E. 1981. Recovery of Osiertagia from the bovine abomasal mucosa by immersion in warm normal saline. In:
~elminthoIog~~a1 Society of Washington 23: 102-103. HONG C. 1989. Inte~~tatio~ of abomasal worm burdens in cattle. Veterinary Record 28: 87-88. MICHEL J. F. 1974. Arrested development of nematodes and some related phenomena. Advances in Parasitology 12: 28&343. MICHEL J. F., LANCASTERM. B. & HONG C. 1975. Arrested development of Ostertagia ostertagi and Cooperia oncophora. Effect of temperature at the free-living stage. Journal of Comparative Pathoiogv 85: 133-138. SMEAL M. G., H~TSON 1. K., MYLREA P. J., JACKSONA. J., CAMPBELLN. J. & KRTON H. C. 1977. Studies of nematode infections of beef cattle in New South Wales. Australian Veterinary Journal 53: 566-573. SMEALM. G., FRAZERG. C. & ROBINSONG. G. 1980. Seasonal changes in the structure of nematode populations of cattle in New South Wales in relation to inhibited iarval development. Australian Veterinary Journal 56: 80-86. SMEALM. G. &DONALD A. D. 1981. Effects on inhibition of development of the transfer of Ostertugia ostertagi between geographical regions of Australia. Parasitofogy 82: 389399. SMEALM. G. & DONALDA. D. 1984. Inhibited development of Ostertagia ostertagi in Australia related to survival over summer in the host or on pasture. Parasitology 89: 597-602. SOLLODA. E. 1967. The possible existence of two strains of Ostertagia ostertagi. Veterinary RecordSI: 547-548. SUAREZ V. H. & MEDRANO C. A. 1984. Parasitism0 gastrointestinal en bovinos Aberdeen Angus en la Region Semiarida Pampeana. I Primeros 2 adios de observaciones. Therios 19: 336350. SU.+RE~V. H., CIMINARI0. E., BELLOE. M., BUSE~I M. R. & BELXXX D. 0. 1987. Parasitismos gastrointestinal en la
Current Topirs in Veterinary Medicine and Animal Science, Vol. 9 (Edited by NANSENP., JORGENSENR. J. & SOULSBYE. invernada de novillos Cruza-Zebu en la Region Subhumeda Pampeana. Veterinaria Argentina= 695-705. J. L.), pp. 69-73. Martinus Nijhoff, The Hague. FIEL C. A., STEFFAN P. E., VERCES~H., AMBRUSTOLOR. R., SUAREZV. H. & BUSE~TIM. R. 1989. Eaizootiolo!zia v efecto CATANIAP., CASAROA. P., ENTROCASSO C. M. & BLONDANI de 10s nematodes gastrointestinaies en la recrialde ferneras en la Region Semiarida Pampeana. Rev&a Argentina de C. A. 1988. Variation estacional del parasitism0 interno de Production Animal9: 149-158. bovinos en el sudeste de la Prov. de Buenos Aires SUAREZ V. H. (in press) Variation estacional de las (Argentina) con especial referencia al fenbmeno de ‘hipobiosis’. Revista de Medicina Veterinaria, Buenos Aires poblaciones de helmintos parasites de bovinos en sistemas de invernada en la Region Semiarida y Subhumeda 69: 51-64. Pampeana. Rev&a de Medicina Veterinaria, Buenos Aires. FRANK G. R., HERD R. P., MAR~URY K. S., WILLIAMSJ. C. & THARALDSENJ. 1976. The epidemiology of trichostrongylid WILLIS E. R. 1988. Additional investigations on hypobiosis infection in young cattle in Norway. Acta Veterinaria of Ostertagia ostertagi after transfer between northern and Scandinavica 17, Suppl. 61: l-21. southern U.S.A. Internationat Journal for Parasitology 18: UENO H. & GUTIERRE~V. C. 1983. ManuaIpara diagnostico 171-177. das heIm~nthoses de rum~nantes~pp. 118-129. Japan InterGIBBONS L. M. 1979. Revision of the genus ~~rnonc~~ Cobb, 1898, (~emafo~: Trjchostrongylidae). Systematic national Cooperation Agency, Tokyo. WILLIAMSJ. C. 1986. Epidemiologic patterns of nematodiasis FarasitoIogy 1: 3-24. in cattle. Veterinary Clinics of North America: Food Animal HERLICH H., 1956. A digestion method for post-mortem Practice 2: 235-246. recovery of nematodes from ruminants. Proceedings of the
