Efficacy of low doses of fenbendazole and its administration via drinking water in the prophylaxis of nematodiasis in grazing calves

Under experimental conditions, fenbendazole given at doses of 0.4 and 1.0 mg/kg body weight suppressed calves' faecal output of Ostertagia and Cooperia species eggs and Dictyocaulus viviparus larvae. Both dose levels were given in the form of small daily drenches and the higher level showed greater efficacy. In a grazing experiment, medication with fenbendazole at 1.0 mg/kg/day administered intermittently to calves using an automatic dose dispenser almost completely suppressed the output of trichostrongylid eggs. As a result, infection on the pasture and in the calves remained at a low level throughout the grazing season. By contrast, control pasture and control calves showed rather heavy infection from mid-August onwards with significantly lower weight gains and widespread signs of parasitic gastroenteritis. At post mortem examination of representative calves from each group in November, the medicated animals had 99 per cent less Ostertagia species, whether adults or larvae arrested at the early fourth stage, and 95 per cent less Cooperia species compared with controls. Medication in the drinking water suppressed the faecal output of D viviparus larvae for most of the grazing season by comparison with the controls but the medicated calves became infected with this parasite towards the end of the season. Until this problem is overcome, precautions against parasitic bronchitis are advised when this system of medication is adopted.     

Experimental infections with Dictyocaulus viviparus in vaccinated and unvaccinated red deer

Four of eight red deer calves which had been artificially reared and were lungworm free were vaccinated with bovine lungworm oral vaccine when eight weeks old; the other four were not vaccinated. Three of each category were challenged daily with 500 Dictyocaulus viviparus infective stage larvae per kg liveweight for 17 days when six months old while one in each category was left as an unchallenged control. The effects of challenge were monitored and all challenged deer and one control were killed for post mortem assessment. Challenge with D viviparus was associated with reduced food intakes and weight gains but vaccinated calves were less affected than unvaccinated ones. The reaction of the alveolar tissue of red deer lung to D viviparus was mild in vaccinated and unvaccinated animals and differed from that of bovine lung in that alveolar epithelialisation was limited and hyaline membrane formation and interstitial emphysema were not seen. The disease was most evident in and around airways and was less in vaccinated calves. It was concluded that young red deer are tolerant to D viviparus but will readily acquire infection.     

Comparison of vaccination and ivermectin treatment in the prevention of bovine lungworm

Three groups of calves were put out to graze on separate paddocks within a field known to be infected with Dictyocaulus viviparus and were also given a small initial trickle infection of the parasite. The first group were untreated controls, the second were immunised with live irradiated lungworm vaccine and the third were injected three times with ivermectin; the injections taking place after they had grazed for three, eight and 13 weeks. The subsequent infections of D viviparus were estimated by grazing a series of parasite-free tracer calves in the paddocks used by each group. The first group of such calves grazed from July 17 until August 7, the second from August 22 to September 29. During the first half of the grazing season all the untreated and three of the six immunised calves were observed to excrete D viviparus larvae, in contrast to none of the ivermectin-treated group. As a result all the tracer calves on the areas occupied by the untreated and immunised calves became infected with the parasite whereas only one worm was found in one of the 10 tracer calves grazing the area occupied by the ivermectin-treated calves.     

A comparison of interactions between vaccination against Dictyocaulus viviparus and anthelmintic suppression in immunised and unimmunised yearling cattle

Twenty parasite-naive calves aged approximately four months were divided randomly into four groups of five. Two groups were treated with oral lungworm vaccine. One immunised group plus another non-immunised group were put out to graze on May 1 on a pasture known to be contaminated with Dictyocaulus viviparus infective larvae during the previous autumn. All the calves both indoor and outdoor were treated with ivermectin at three, eight and 13 weeks after the first groups started to graze and again at housing at the end of September. After the winter housing period on April 27 of the following year all the calves were given an artificial challenge of D viviparus infective larvae at the rate of 15 larvae per kg bodyweight, and the clinical and parasitological reactions monitored. All the calves which had been vaccinated or exposed to field infection during year 1 reacted strongly in ELISAs using antigen prepared from fourth stage D viviparus larvae but much less strongly in similar tests using adult derived antigen. Clinically those calves exposed to previous field infections were less severely affected than the housed calves, although parasitologically all three groups with prior exposure to D viviparus appeared to have a similar functional level of immunity to the challenge infection in comparison to the unexposed calves of the same age.     

Seroprevalence of Dictyocaulus viviparus in first grazing season calves in Sweden

A serological survey was carried out to determine the prevalence and geographical distribution of Dictyocaulus viviparus in calves after their first grazing season in Sweden. A total of 754 animals from 76 randomly selected herds in seven geographical regions were examined between September 24 and December 19, 2001. To get an indication about the geographical distribution of the infection 41 herds with beef-suckler calves were investigated. On each farm, blood was collected from 8 to 10 animals after an average of 26 +/- 24 days post-housing to determine specific IgG1 levels against a possible lungworm sperm antigen that is highly specific against patent infections of D. viviparus. We also investigated the seroprevalence of lungworm infection in relation to cattle management. In one region additional samples were analysed from 35 herds either with: (a) beef-suckling calves that were dewormed at housing, (b) untreated organically raised dairy calves, and finally from conventionally raised dairy calves either, (c) with or, (d) without a prophylactic anthelmintic treatment programme against gastrointestinal parasites on pasture. A questionnaire was used to obtain information about herd size and management, including measures to control nematode parasites on the farm. A total of 86 (11.8%) out of 754 animals had antibodies against D. viviparus, and at least one infected individual was detected in 30 (39.5%) of the 76 herds examined. Lungworm infected animals were found throughout the country and there was no significant differences between regions, although in southern and southwestern Sweden 70.0% of the herds were infected. Furthermore, there were no major differences in the seroprevalence in relation to management. Between 40.0 and 44.4% of the herds were infected irrespective of management, with the exception of calves from organic herds where no seropositive samples were found (0%). This result is in contrast to previous findings of lungworms in Sweden, and indicates that the parasite status on organic farms is diverse.     

Comparison of the efficacy of dermal formulations of ivermectin and levamisole for the treatment and prevention of Dictyocaulus viviparus infection in cattle

Four groups of six parasite-naive calves were infected at seven day intervals with three doses of infective larvae of Dictyocaulus viviparus. Twenty-one days after the first dose three of the groups were treated either with an injectable formulation of ivermectin at a dose rate of 200 micrograms/kg bodyweight, or with pour-on preparations of levamisole at 10 mg/kg or ivermectin at 500 micrograms/kg. On day 28 two calves from each group were slaughtered and their burdens of lungworms counted. On day 35 the remaining calves were reinfected with D viviparus infective larvae at a rate of 80 L3/kg. The levamisole preparation was 94.6 per cent effective and both ivermectin preparations were 100 per cent effective against the initial infections. The ivermectin-treated calves were protected from the reinfection which subsequently became patent in the levamisole-treated and control calves.     

Comparison of early season suppressive anthelmintic prophylactic methods for parasitic gastroenteritis and bronchitis in calves

A comparison was made of the material costs and effectiveness of three methods of early season suppression by anthelmintic medication of Ostertagia species and two of Dictyocaulus viviparus in calves, each method suppressing faecal egg output for different lengths of time from the start of spring grazing. The anthelmintics used were: Morantel bolus administered five days before going to grazing; oxfendazole given three times at three, six and nine weeks after the start of grazing and ivermectin injected three, eight and 13 weeks after going to pasture. The effectiveness of each was estimated by comparison with worm numbers in untreated control calves. Oxfendazole, which was active for the shortest time (about 65 days) from the start of grazing (May 1), produced a 78.1 per cent reduction in Ostertagia species and an 84.4 per cent reduction in D viviparus. The morantel bolus was estimated to be active for 90 days and resulted in a 94.3 per cent reduction of Ostertagia species. The ivermectin treatment, which, because of the prolonged excretion of the chemical and different sensitivity of worm species, was estimated to suppress Ostertagia species for 105 days and D viviparus for 119 days, caused reductions of 98.7 per cent of the former and 97.4 per cent of the latter species. Material costs per calf were estimated at pounds 1.25 for oxfendazole, pounds 2.00 for ivermectin and pounds 10 for the morantel bolus.     

Management practices and use of anthelmintics on dairy cattle farms in The Netherlands: results of a questionnaire survey

In December 1996, a questionnaire about farm management and parasite control measures in calves was sent to 956 randomly chosen dairy cattle farmers in The Netherlands. Another 150 farmers in the vicinity of Deventer who had vaccinated their calves in 1995 against lungworm were approached with the same questions. Our objective was to investigate the consequences on worm control of the withdrawal of the lungworm vaccine from the market for reasons of possible BSE contamination of the vaccine. Of the returned questionnaires, 411 (43%) of the `at random' group and 89 (59.3%) of the `Deventer' group were valid. The most important data with regard to the farms of the `at random' group (411) were: mean area 31.6 ha, mean number of calves 23, heifers 23 and milking cows 53. Sheep (mean 37) were present on 18.3% of the farms. With regard to management: 74.5% of the farmers turned the calves in their first year onto pasture, 25.5% kept them indoors. The average time on pasture was ca. 5 months. Rotational grazing was practised on 81.4% of the farms, on 18.6% calves were set stocked. The first pasture of the calves was mown before turn-out on 72.9% of the farms. On 48.2% of these farms, calves were always moved to mown pastures. With regard to treatments: 33.8% of the farmers vaccinated their calves against lungworm in the years 1993, 1994 and 1995. Despite the withdrawal of the vaccine from the market in 1996, 7.2% of the farmers vaccinated their calves as recommended, with two doses, and 13.1% with a single dose. At turn-out, 41.5% of the farmers gave the calves a preventive anthelmintic treatment. Of these treatments, 66.9% were sustained of pulse release long acting devices. During the grazing season, 36.6% of the farmers treated their calves. After housing, 50.3% of the farmers gave a treatment. Signs of lungworm infection were noticed on 18.6% of the farms. Of the `Deventer' group (89 farmers), 96.6% turned the calves out. Of these farmers, 86.0% had used the lungworm vaccine in 1995. In 1996, 52.7% of the farmers had vaccinated the calves: 36.5% with a single dose and 16.2% with the double dose. Of the 35 farmers who did not vaccinate in 1996, 62.9% gave a preventive treatment at turn-out. Clinical signs of lungworm infection were not observed on the 12 farms which vaccinated the calves twice. On 11% of the farms which vaccinated once and on 14% of the farms which did not vaccinate, signs of lungworm infection were observed. It is concluded that more than 80% of Dutch dairy cattle farmers take appropriate measures to control gastrointestinal nematode and lungworm infections in calves in their first grazing season by grazing on aftermath, rotational grazing on mown pastures combined or not with preventive anthelmintic treatments. However, combinations of aftermath grazing and preventive treatment occurred on 30% of the farms. This may be overprotective and may prevent sufficient build up of immunity, causing worm problems at a later age. The withdrawal of the lungworm vaccine from the market did not cause a rise in lungworm problems. Some farmers did vaccinate, despite the withdrawal. The majority used other preventive treatment measures, mainly the application of long acting boli.     

Effect of naturally occurring nematode infections on growth performance of first-season grazing calves

Liveweight of calves on 89 dairy farms was measured at the end of the grazing season and related per herd to the level of exposure to nematode infection during the grazing season. There were significant between-herd variations in antibody titres against Ostertagia spp., Cooperia spp. and Dictyocaulus viviparus as well as in pepsinogen values. All but six herds (93.1%) had gastrointestinal nematode infections, as measured by faecal egg counts in September. Faecal samples of 17 herds (19.3%) contained lungworm larvae in September. Liveweight of calves per herd deviated from -68.1 kg to +84.1 kg from the age-adjusted population mean after their first grazing season. Growth performance up to the time of liveweight measurements was significantly correlated negatively with several serological and parasitological parameters. Data could be fitted by means of both linear and segmented curvilinear regression. Antibody titre against Cooperia spp. and gastrointestinal nematode egg output measured in September accounted for 3.1% (P less than 0.10) and 6.7% (P less than 0.05), respectively, of the variation in growth performance among herds. Certain infection parameters, when combined, accounted for 9.2% of this variation; these were antibody titre against Cooperia spp. and larval counts for both gastrointestinal nematodes and lungworm. Adding certain management factors to these infection parameters resulted in a model explaining 27.6% of the observed variation in growth performance among herds. These factors were supplementary feeding, lungworm vaccination, anthelmintic treatment at housing, date of housing and herd age.     

Efficacy of moxidectin against gastrointestinal nematodes of cattle.

Three groups of 11 naturally infected crossbred beef calves were injected subcutaneously with moxidectin 1 per cent injectable at 0.2 or 0.3 mg moxidectin/kg bodyweight or with the unmedicated vehicle. Nematode infections had been acquired during grazing from December to April. Based on the faecal egg counts and total worm counts of the control calves at necropsy (11 to 13 days after treatment) most of the calves had heavy parasitic burdens. Ostertagia ostertagi was predominant and the mean numbers of adults, developing fourth stage larvae (L4) and inhibited early L4 were 45,906, 10,061 and 68,918, respectively. Haemonchus placei and Trichostrongylus axei were also present in the abomasa. Three species of Cooperia, Oesophagostomum radiatum L4 and T colubriformis adults were found in the intestinal tract. Both dosages of moxidectin were equally effective (P < 0.05) against all the abomasal nematodes (99.9 to 100 per cent) and the intestinal tract nematodes (99.4 to 100 per cent). No adverse reactions to the moxidectin treatment were observed. Abomasal pathology characteristic of heavy O ostertagi infection was observed in the control calves, but not in the treated calves.     

Evaluation of a combined rotavirus and enterotoxigenic Escherichia coli vaccine in cattle

A vaccine of rotavirus and K99 antigen from enterotoxigenic Escherichia coli was emulsified in oil adjuvant and administered intramuscularly to pregnant cows. Calves born to and reared on vaccinated dams were protected against experimental rotavirus infection at five days old when compared with calves from unvaccinated control cows. Field trials of the vaccine were carried out in 40 commercial herds, in which half the cows in each herd were selected at random for vaccination and half were left unvaccinated. In 31 herds (2641 cows) there was no significant diarrhoea problem (less than 10 per cent morbidity); these herds were excluded from further analysis. The nine remaining herds did experience a calf diarrhoea problem of greater than 10 per cent morbidity, but on four farms the disease was associated with cryptosporidiosis and on a fifth no enteropathogens were detected; these five farms (461 cows) were also excluded from further analysis. Of the remaining four herds, two beef suckler herds (105 cows) had concurrent rotavirus and cryptosporidial infections, and vaccination was associated with a decreased excretion of rotavirus but not with a decreased incidence of diarrhoea. In the other two dairy herds (68 cows) with prevaccination rotavirus problems, there was a significantly decreased incidence of diarrhoea in calves born to vaccinated cows. No natural field challenge of enterotoxigenic E coli was encountered on any of the trial farms.     

Preventive vaccination of lactating and pregnant heifers against lungworm: safety and protection in three dairy herds

A study of the safety of a vaccine against lungworm was carried out with pregnant and lactating heifers from three dairy herds with a previous history of lungworm outbreaks in adult cows. Half of the heifers were vaccinated while the other half were not. A slight temporary cough following the vaccination was only observed in one herd. No adverse effects on pregnancy or milk production were seen. All heifers were serologically and coprologically examined before the first, before and after the second immunization, 3 months after introduction to pasture and at the end of the grazing season. Serological and faecal examination of the dairy cows before introduction into pasture confirmed the presence of at least one Dictyocaulus viviparus carrier in each herd. Lungworm infection occurred in all herds during the grazing season, most prominently in the herd with the highest number of heifers. In this herd, mild coughing associated with the lungworm infection was noticed, especially in the non vaccinated heifers. No other signs or symptoms were observed. It is concluded that a vaccine against D. viviparus can be used safely in heifers, before they are introduced into the adult herd, and that this vaccine can be used as a preventive measure against lungworm outbreaks in adult cattle.     

A survey on Dictyocaulus viviparus antibodies in bulk milk of dairy herds in Northern Germany

Parasitic bronchitis caused by the bovine lungworm, Dictyocaulus viviparus, occurs worldwide in temperate areas. The parasite is found predominantly in calves and heifers, but dairy cattle can suffer from lungworms when they become infected for the first time or if they have lost immunity due to lack of exposure to lungworm larvae during the grazing season. The present study was performed to determine the D. viviparus bulk milk antibody prevalence in dairy herds in the East Frisian region of northwestern Germany, Lower Saxony, by analysing bulk milk samples collected in January (860 samples), September (866 samples) and November (860 samples) 2008, thereby representing 906 dairy farms. These samples were tested for antibodies against D. viviparus by a milk ELISA. This test detects patent infections only since it is based on recombinant major sperm protein as antigen. While in January 12.8% of dairy farms were positive for D. viviparus antibodies, the bulk milk samples collected in September and November revealed 6.9% and 6.6% positive dairy herds. From the 906 dairy farms included in the study, 191 (21.1%) tested positive at least once for antibodies against lungworm. From 810 dairy farms from which bulk milk samples were obtained during all three samplings, 146 (18.0%) farms were positive at one sampling date, 27 (3.3%) at two, and 4 (0.5%) on all three sampling dates. The majority of the farms represented in the study belonged to four districts of East Frisia, which showed no significant difference in the proportion of positive dairy farms.     

Effect of naturally occurring nematode infections in the first and second grazing season on the growth performance of second-year cattle

Antibody titres against Ostertagia spp., Cooperia spp. and Dictyocaulus viviparus as well as pepsinogen values, reflecting exposure to nematode infection, differed significantly among herds of second-year cattle on 87 farms. Faecal examinations revealed that gastrointestinal nematode infections were present in all herds. Similar results were found in yearling-herds on the same farms a year earlier. Liveweight of yearlings per herd deviated from -64.7 kg to +94.4 kg from an age-adjusted population mean after the second grazing season. This mean herd weight deviation was significantly related negatively to antibody titre against Ostertagia spp. (linear regression, P less than 0.05; segmented curvilinear regression, P less than 0.01) and to antibody titre against Cooperia spp. (segmented curvilinear regression, P less than 0.05), both measured in the second grazing season. Antibody titre against Ostertagia spp. measured in the first grazing season, when yearlings were calves, was significantly correlated positively to age-adjusted body weights at the end of the second grazing season. The results suggested that immunity built up during the first year had a positive effect on growth performance in the second year, but that on average the acquired immunity was insufficient to prevent reduced weight gains in the second grazing season.     

Epidemiological study of bovine respiratory syncytial virus infections in calves: influence of maternal antibodies on the outcome of disease

A prospective epidemiological survey on bovine respiratory syncytial virus (BRSV) infections in calves was carried out on 21 dairy farms during one BRSV epidemic season. Special attention was paid to the role of maternal antibodies. On 15 farms the spread of the virus was demonstrated during the investigation period and on eight farms this was accompanied by an outbreak of acute respiratory disease. Disease seldom occurred in calves younger than two weeks old and the most severe disease was observed in calves from one to three months old. Although maternal antibodies did not effectively prevent the disease, both the incidence and severity of disease were inversely related to the level of specific maternal antibodies. Two serodiagnostic techniques were compared. In calves older than three months from herds with disease outbreaks associated with bovine respiratory syncytial virus the diagnosis was established in 80 per cent of the animals by an increase in IgG titre against BRSV and in 77 per cent by the detection of BRSV specific IgM. In comparison, only 10 per cent of the calves younger than three months were positive by IgG serodiagnosis, and 51 per cent by IgM serodiagnosis. On farms where the spread of the virus was accompanied by an outbreak of clinical disease more calves were present, a higher proportion of the calves was younger than three months, and calves of all ages were more often housed together.     

Dictyocaulus viviparus in calves: effect of rotational grazing on the development of infections.

A study was made of the possibility of reducing lungworm infections in young grazing calves by rotational grazing for weekly periods on six paddocks. For this purpose three groups of four calves each were grazed on separate pastures in 1989, whereas a fourth group served as a permanently housed control group. Two groups of calves were infected experimentally with six doses of 10 larvae of Dictyocaulus viviparus during the first 3 weeks on pasture. In the third group, low natural infections with overwintered larvae occurred. One of the experimentally infected groups was rotationally grazed for weekly periods on six small plots while both other groups were set-stocked. Faecal larval counts and worm counts in tracer calves demonstrated lower lungworm infections in the rotationally grazed group than in both set-stocked groups. However, the numbers of worms found after challenge infection and subsequent necropsy were relatively high in the rotationally grazed group, indicating that development of immunity was less than in both other groups. Owing to the dry weather conditions in the summer of 1989, no serious clinical signs of husk developed in any of the three groups. These dry conditions, however, did not prevent the build-up of heavy pasture infectivity with gastrointestinal nematodes resulting in heavy worm burdens and serious clinical signs in tracer calves grazing for 4 days in August and September-October, respectively. This implies that rotational grazing did not have a clear effect on build-up of gastrointestinal nematode infections.     

Comparison by experimental infections in cattle of a Dictyocaulus species occurring naturally in red deer and a dictyocaulus of bovine origin

Dictyocaulus species larvae were obtained from young red deer which had become infected on pastures considered to be carrying the Dictyocaulus species indigenous to the red deer of Scotland. These larvae were cultured to third stage and transmitted to five bovine calves. Five other bovine calves were infected with third stage Dictyocaulus viviparus larvae of bovine origin. Microscopic appearances of both groups of larvae were indistinguishable and their lengths were similar. Results indicated that the Dictyocaulus species derived from deer induced milder though similar clinical and pathological responses in cattle than did the D viviparus derived from cattle. It was concluded that there are strains of different pathogenicity within the species D viviparus, that the deer derived Dictyocaulus species was a strain of D viviparus, and that the hazards to animal health associated with infection by D viviparus in farming systems where red deer and cattle may graze alternately are likely to be acceptable.     

Grazing study in Ireland using the morantel sustained release bolus for controlling nematodiasis in calves

The morantel sustained release bolus was administered at turnout to first-season grazing calves in order to assess its efficacy in the seasonal control of infection by nematode parasites in Ireland. The pastures grazed by control calves showed a marked increase in gastrointestinal trichostrongylid infective larvae by September, while numbers of infective larvae on pasture grazed by bolus-treated calves remained at a low level throughout the grazing season. In consequence, the controls showed significantly higher worm egg counts in late season and significantly higher worm burdens (mainly Ostertagia spp) at necropsy carried out in November on representative number of principal animals selected from each group. These reduced worm burdens were attributed to the suppression of egg output during the early part of the season as a result of treatment with the morantel sustained release bolus at turnout in the spring. Pasture contamination with Dictyocaulus viviparus larvae was present on all treatment pastures. The bolus-treated calves however were subjected to an increase in D. viviparus infection which occurred on their pasture in late season after the active life of the bolus had expired. It was concluded that bolus treatment delayed (rather than prevented) the buildup of D. viviparus infection on the pasture by 60-90 days.     

Efficacy of a homoeopathic prophylaxis against experimental infection of calves by the bovine lungworm Dictyocaulus viviparus

Two groups of parasite-free calves, one of which had been treated with four doses of a homoeopathic oral vaccine for parasitic bronchitis due to Dictyocaulus viviparus and the other with a placebo, were infected at the rate of 25 infective larvae/kg bodyweight 18 days after the final dose. Both groups became severely affected by parasitic bronchitis, with clinical signs starting 13 days after infection. There were no discernible differences between the treated and control groups in their manifestations of resistance to D viviparus or their clinical responses to the disease produced.     

Observations on the epidemiology of Dictyocaulus viviparus in north west England

A five year ley pasture was used as a source of natural infection with Dictyocaulus viviparus for cattle in anthelmintic trials. Pasture larval counts, faecal larval counts of permanently grazing calves and lungworm burdens harboured by tracer calves were monitored in three grazing seasons to assess the pattern of infection. Carrier calves were introduced at the beginning of the grazing season in the first two years of the study but not in the third. In the fourth year the pasture was subdivided into two paddocks where overwintered infection with and without carrier infection were compared. A control paddock exposed to carrier infection but no overwintered infection was also monitored. Pasture larvae survived the winter but carrier infection appeared to make a larger contribution to pasture larval counts and the onset of parasitic bronchitis in susceptible calves. In the absence of grazing cattle at the end of the grazing season the concentration of D viviparus larvae on the herbage fell rapidly to undetectable levels. Discrepancies between contamination of herbage by infective D viviparus larvae and infectivity of pasture for susceptible cattle occurred in all years but were particularly marked on the third year when natural immunity appeared to influence the number of lungworms accumulating in tracer calves. Failure to recover lung worms from tracer calves cannot be regarded as an accurate indication of lungworm free pasture. In the first three years the proportion of the lungworm population which was inhibited in tracer calves was higher early and late in the grazing season and negligible in mid season. This suggests that a predisposition to inhibition in larvae which have overwintered on pasture may influence the time of onset of parasitic bronchitis in the next grazing season, but results from the fourth year did not support this hypothesis.