Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season

Gastrointestinal nematodes (GIN) infection can impair milk production (MP) in dairy cows. To investigate whether MP would be optimized by spring targeted-selective anthelmintic treatment in grazing cows, we assessed (1) the effect on MP of an anthelmintic treatment applied 1.5 to 2 months after turn-out, and (2) herd and individual indicators associated with the post-treatment MP response. A randomized controlled clinical trial was conducted in 13 dairy farms (578 cows) in western France in spring 2012. In each herd, lactating cows of the treatment group received fenbendazole orally, control cows remained untreated. Daily cow MP was recorded from 2 weeks before until 15 weeks after treatment. Individual serum pepsinogen and anti-Ostertagia antibody levels (expressed as ODR), faecal egg count and bulk tank milk (BTM) Ostertagia ODR were measured at treatment time. Anthelmintic treatment applied during the previous housing period was recorded for each cow. In each herd, information regarding heifers’ grazing and anthelmintic treatment history was collected to assess the Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving. The effect of treatment on weekly MP averages and its relationships with herd and individual indicators were studied using linear mixed models with two nested random effects (cow within herd). Unexpectedly, spring treatment had a significant detrimental effect on MP (-0.92 kg/cow/day on average). This negative MP response was particularly marked in high producing cows, in cows not treated during the previous housing period or with high pepsinogen levels, and in cows from herds with a high TEC or a high BTM ODR. This post-treatment decrease in MP may be associated with immuno-inflammatory mechanisms. Until further studies can assess whether this unexpected result can be generalized, non-persistent treatment of immunized adult dairy cows against GIN should not be recommended in early grazing season.     

Observations on parasitic gastroenteritis and bronchitis in grazing calves: Untreated calves

Pott J. M., Jpones R. M. and Cornwell R. L. 1978. Observations on parasitic gastroenteritis and bronchitis in grazing calves: untreated calves. International Journal for Parasitology8: 331–339. The epidemiology of parasitic gastroenteritis (p.g.e.) and incidental observations on lungworm infection were studied on two equal-sized paddocks of permanent pasture on a Kent farm in 1970. Groups of 10 Friesian calves were exposed for the first time to each paddock in May and grazed until the end of October. Faeces were monitored, body weights recorded and clinical signs observed. Herbage samples were examined for larvae throughout the year. Five ‘cumulative’ tracer calves exposed at the commencement were removed at monthly intervals and 5 ‘short term’ tracer calves exposed at successive monthly intervals for 1 month were killed for worm counts. A similar pattern of events occurred on both paddocks. Moderate herbage larval levels of Ostertagia and Cooperia fell to almost zero during April/May but rose quickly in July to high levels in August/September. Lower levels continued until the end of the year. Faecal egg excretion began in the test calves at the end of May, showed peaks in July and September and fell to low levels in October. D. viviparus larval excretion occurred in most calves with greater counts on Paddock 2. Clinical signs of p.g.e. complicated by lungworm infection occurred in August/September. Body weight gain which was initially rapid levelled off in June due partly to drought in addition to the parasitic infection. Weight loss occurred in August and there were 2 deaths on Paddock 1 and one on Paddock 2. Survivors gained weight again in September/October.Worm burdens in tracer calves showed quite heavy infections with Ostertagia and Cooperia as early as June/July. Massive infections complicated by lungworm disease accompanied clinical signs and death. There was evidence that aquisition of resistance to Cooperia and Dictyocaulus was acquired more readily than to Ostertagia. Inhibition of development of Ostertagia and Cooperia also became evident at the end of the trial period.     

Subclinical nematode parasitism affects activity and rumination patterns in first-season grazing cattle

Sickness behaviour has been suggested as an applicable indicator for monitoring disease. Deviating feeding behaviour and activity can provide information about animals’ health and welfare status. Recent advances in sensor technology enable monitoring of such behaviours and could potentially be utilized as an indicator of gastrointestinal nematode (GIN) infections. This study investigated activity and rumination patterns in first-season grazing steers exposed to subclinical infection levels of the GIN Ostertagia ostertagi and Cooperia oncophora. At turnout, animals were allocated to one of four experimental groups and were faced with “high” (H1, n = 15; H2, n = 17) or “low” (L1, n = 17; L2, n = 11) levels of parasite exposure by grazing in similar enclosures contaminated with overwintering third stage (L3) GIN larvae. Animals in H1 and H2 (HP) received a 1:1 mix of approximately 10,000 O. ostertagi and C. oncophora L3 at turnout; whereas the animals in L1 and L2 (LP) were treated monthly with ivermectin. Activity and rumination patterns were monitored by fitting animals with leg- (IceQube) and neck-mounted (Heatime) sensors. BW was recorded every fortnight, whereas faecal and blood samples were examined every four weeks for nematode faecal egg count and serum pepsinogen concentrations (SPCs). There was an interaction effect of exposure level and period (P < 0.0001) on average lying daily time across the entire grazing time. A higher mean daily lying time (P = 0.0037) was found in HP compared with LP during the first 40 days on pasture. There was also interaction effects of treatment and day since turnout on rumination time (P < 0.0001) and rumination change (P = 0.0008). Also mean daily steps (P < 0.0001) and mean daily motion index (P < 0.0001) were markedly higher in HP during days 62–69, coinciding with peaking SPC in HP. Strongyle eggs were observed both in HP and LP from 31 days after turnout. Eggs per gram (EPG) differed between parasite exposure levels (P < 0.0001), with mean EPG remaining low in LP throughout the experiment. Similarly, an increase in SPC was observed (P < 0.0001), but only in HP where it peaked at day 56. In contrast, no difference in BW gain (BWG) (P = 0.78) between HP and LP was observed. In conclusion, this study shows that behavioural measurements monitored with sensors were affected even at low infection levels not affecting BWG. These combined results demonstrate the potential of automated behavioural recordings as a tool for detection of subclinical parasitism.     

Novel epidemiological model of gastrointestinal nematode infection to assess grazing cattle resilience by integrating host growth,parasite, grass and environmental dynamics

Gastrointestinal nematode (GIN) infections are ubiquitous and often cause morbidity and reduced performance in livestock. Emerging anthelmintic resistance and increasing change in climate patterns require evaluation of alternatives to traditional treatment and management practices. Mathematical models of parasite transmission between hosts and the environment have contributed towards the design of appropriate control strategies in ruminants, but have yet to account for relationships between climate, infection pressure, immunity, resources, and growth. Here, we develop a new epidemiological model of GIN transmission in a herd of grazing cattle, including host tolerance (body weight and feed intake), parasite burden and acquisition of immunity, together with weather-dependent development of parasite free-living stages, and the influence of grass availability on parasite transmission. Dynamic host, parasite and environmental factors drive a variable rate of transmission. Using literature sources, the model was parametrised for Ostertagia ostertagi, the prevailing pathogenic GIN in grazing cattle populations in temperate climates. Model outputs were validated on published empirical studies from first season grazing cattle in northern Europe. These results show satisfactory qualitative and quantitative performance of the model; they also indicate the model may approximate the dynamics of grazing systems under co-infection by O. ostertagi and Cooperia oncophora, a second GIN species common in cattle. In addition, model behaviour was explored under illustrative anthelmintic treatment strategies, considering impacts on parasitological and performance variables. The model has potential for extension to explore altered infection dynamics as a result of management and climate change, and to optimise treatment strategies accordingly. As the first known mechanistic model to combine parasitic and free-living stages of GIN with host feed-intake and growth, it is well suited to predict complex system responses under non-stationary conditions. We discuss the implications, limitations and extensions of the model, and its potential to assist in the development of sustainable parasite control strategies.     

Development of Immunity to Ostertagia ostertagi (Trichostrongylidae: Nematoda) in Pastured Young Cattle

This experiment comprised 3 groups of calves, (+P2), (−P2) and (−P1), which all started their first grazing season as parasite-free calves. The (+P2)- and (−P2)-group grazed 2 seasons. In the first season the (−P2)-group of calves was grazing a pasture with no detectable trichostrongyles and treated with anthelmintics every second week. The untreated (+P2)-group grazed an Ostertagia ostertagi contaminated pasture. During the second grazing season these 2 original groups grazed together with a new group of first-year grazing calves (−P1) on paddocks infected with O.ostertagi. Parasitological analyses showed that (+P2)-group had negligible egg excretions in the second year in comparison with (−P2) and (−P1). This indicated, that the egg output may be regulated through acquired immunity. The difference in egg excretions was not reflected in the serum pepsinogen levels, which were only slightly elevated for all groups in the second year. Post mortem examination at the end of the experiment showed that only the (−P1)-group harboured relatively high numbers of worms in the abomasa at that time. Antibodies of 3 immunoglobulin classes were investigated: IgA, IgG1 and IgG2. The IgA and IgGl responses correlated with the presence of developing and adult worms in the abomasa and they remained elevated in the (+P2)-group throughout the experiment, perhaps indicating an involvement of these antibodies in a protective immune response. In the (−P2)-group the IgA and IgG1 showed fast and sharp rises during the second season that most likely were age-related and as such a result of maturation of the immune system. The role of IgG2 is unclear as the IgG2 response was weak in all groups of calves and difficult to relate to the parasitological data.     

Biological control of trichostrongylid infections in calves on pasture in Lithuania using Duddingtonia flagrans, a nematode-trapping fungus

The effect on the pasture contamination level with infective trichostrongylid larvae by feeding the nematode-trapping fungus, Duddingtonia flagrans at two dose levels to first time grazing calves was examined in Lithuania. Thirty heifer-calves, aged 3-6 months, were divided into three comparable groups, A, B and C. Each group was turned out on a 1.07 ha paddock (a, b and c). The paddocks were naturally contaminated with infective trichostrongylid larvae from infected cattle grazing the previous year. Fungal material was fed to the animals daily during a two month period starting 3 weeks after turnout. Groups A and B were given 10(6) and 2.5x10(5) chlamydospores per kg of live weight per day, respectively, while group C served as a non-dosed control group. Every two weeks the heifers were weighed and clinically inspected. On the same dates, faeces, blood and grass samples were collected. From mid-July onwards, the number of infective larvae in grass samples increased markedly (P<0.05)on paddock c, whereas low numbers of infective larvae were observed on paddocks a and b grazed by the fungus treated groups. However, the results indicate that administering fungal spores at a dose of 2.5x10(6)chlamydospores per kg live weight per day did not significantly prevent parasitism in calves, presumably due to insufficient suppression of developing infective larvae in the faeces. In contrast, a dose of 10(6) chlamydospores per kg lowered the parasite larval population on the pasture, reduced pepsinogen levels (P<0.05), and prevented calves from developing parasitosis.     

Tracking gastrointestinal nematode risk on cattle farms through pasture contamination mapping

Gastrointestinal nematode (GIN) parasites in grazing cattle are a major cause of production loss and their control is increasingly difficult due to anthelmintic resistance and climate change. Rotational grazing can support control and decrease reliance on chemical intervention, but is often complex due to the need to track grazing periods and infection levels, and the effect of weather on larval availability. In this paper, a simulation model was developed to predict the availability of infective larvae of the bovine GIN, Ostertagia ostertagi, at the level of individual pastures. The model was applied within a complex rotational grazing system and successfully reproduced observed variation in larval density between fields and over time. Four groups of cattle in their second grazing season (n = 44) were followed throughout the temperate grazing season with regular assessment of GIN faecal egg counts, which were dominated by O. ostertagi, animal weight and recording of field rotations. Each group of cattle was rotationally grazed on six group-specific fields throughout the 2019 grazing season. Maps and calendars were produced to illustrate the change in pasture infectivity (density of L3 on herbage) across the 24 separate grazing fields. Simulations predicted differences in pasture contamination levels in relation to the timing of grazing and the return period. A proportion of L3 was predicted to persist on herbage over winter, declining to similar intensities across fields before the start of the following grazing season, irrespective of contamination levels in the previous year. Model predictions showed good agreement with pasture larval counts. The model also simulated differences in seasonal pasture infectivity under rotational grazing in systems that differed in temperature and rainfall profiles. Further application could support individual farm decisions on evasive grazing and refugia management, and improved regional evaluation of optimal grazing strategies for parasite control. The integration of weather and livestock movement is inherent to the model, and facilitates consideration of climate change adaptation through improved disease control.     

Control of nematode parasites by grazing management—II. Decontamination of sheep and cattle pastures by varying periods of grazing with the alternate host

Commencing in December 1970, paddocks of a uniform series of sheep pastures were grazed for 6, 12 or 24 weeks by either yearling steers is or yearling ewes. Cattle pastures were treated similarly. All ewes and steers were pre-dosed with anthelmintic.At the conclusion of alternate grazing the effectiveness of the grazing treatments was evaluated by grazing each paddock for 1 month with either ten worm-free lambs (sheep pastures) or three wormfree calves (cattle pastures). The test animals were then slaughtered for total worm counts. The grazing of sheep pastures with cattle for 6, 12 or 24 weeks from December onwards resulted in reductions in numbers of Haemonchus contortus and Trichostrongylus colubriformis in test lambs. In comparison with continuous grazing by sheep, Nematodirus spp was only reduced after 24 weeks grazing by cattle. Cattle pastures grazed by sheep for 6 weeks showed no reduction in numbers of Ostertagia ostertagi or Cooperia oncophora in test calves. However after 12 weeks with sheep, numbers of O. ostertagi though not C. oncophora were reduced and after 24 weeks of alternate grazing both these species were reduced.Calves following the 6 week sheep treatments acquired both Haemonchus contortus and Trichostrongylus colubriformis and the calves from the 12 week sheep treatment paddock also carried H. contortus. For sheep the only evidence of cross-transmission was the occurrence of small numbers of Cooperia oncophora in test lambs from the 24 week cattle grazing treatment.The results provide evidence that sequential stocking with cattle and sheep in conjunction with anthelmintic treatment is an effective management strategy for preparing parasitologically safer pastures, but further information is required to determine the optimum timing of sequential stocking in farming situations.     

Effects of Chicory/Perennial Ryegrass Swards Compared with Perennial Ryegrass Swards on the Performance and Carcass Quality of Grazing Beef Steers

An experiment investigated whether the inclusion of chicory (Cichorium intybus) in swards grazed by beef steers altered their performance, carcass characteristics or parasitism when compared to steers grazing perennial ryegrass (Lolium perenne). Triplicate 2-ha plots were established with a chicory/ryegrass mix or ryegrass control. Forty-eight Belgian Blue-cross steers were used in the first grazing season and a core group (n = 36) were retained for finishing in the second grazing season. The experiment comprised of a standardisation and measurement period. During standardisation, steers grazed a ryegrass/white clover pasture as one group. Animals were allocated to treatment on the basis of liveweight, body condition and faecal egg counts (FEC) determined 7 days prior to the measurement period. The measurement period ran from 25 May until 28 September 2010 and 12 April until 11 October 2011in the first and second grazing year. Steers were weighed every 14 days at pasture or 28 days during housing. In the first grazing year, faecal samples were collected for FEC and parasite cultures. At the end of the first grazing year, individual blood samples were taken to determine O. ostertagi antibody and plasma pepsinogen levels. During winter, animals were housed as one group and fed silage. In the second grazing year, steers were slaughtered when deemed to reach fat class 3. Data on steer performance showed no differences in daily live-weight gain which averaged 1.04 kg/day. The conformation, fat grade and killing out proportion of beef steers grazing chicory/ryegrass or ryegrass were not found to differ. No differences in FEC, O. ostertagi antibody or plasma pepsinogen levels of beef steers grazing either chicory/ryegrass or ryegrass were observed. Overall, there were no detrimental effects of including chicory in swards grazed by beef cattle on their performance, carcass characteristics or helminth parasitism, when compared with steers grazing ryegrass.     

Divergence for residual feed intake of Holstein-Friesian cattle during growth did not affect production and reproduction during lactation

Residual feed intake (RFI) is the difference between actual and predicted dry matter intake (DMI) of individual animals. Recent studies with Holstein-Friesian calves have identified an ~20% difference in RFI during growth (calf RFI) and these groups remained divergent in RFI during lactation. The objective of the experiment described here was to determine if cows selected for divergent RFI as calves differed in milk production, reproduction or in the profiles of BW and body condition score (BCS) change during lactation, when grazing pasture. The cows used in the experiment (n=126) had an RFI of −0.88 and +0.75 kg DM intake/day for growth as calves (efficient and inefficient calf RFI groups, respectively) and were intensively grazed at four stocking rates (SR) of 2.2, 2.6, 3.1 and 3.6 cows/ha on self-contained farmlets, over 3 years. Each SR treatment had equal number of cows identified as low and high calf RFI, with 24, 28, 34 and 40/11 ha farmlet. The cows divergent for calf RFI were randomly allocated to each SR. Although SR affected production, calf RFI group (low or high) did not affect milk production, reproduction, BW, BCS or changes in these parameters throughout lactation. The most efficient animals (low calf RFI) lost similar BW and BCS as the least efficient (high calf RFI) immediately post-calving, and regained similar BW and BCS before their next calving. These results indicate that selection for RFI as calves to increase efficiency of feed utilisation did not negatively affect farm productivity variables (milk production, BCS, BW and reproduction) as adults when managed under an intensive pastoral grazing system.     

Monepantel-based anthelmintic combinations to optimize parasite control in cattle

Improvement in the use of existing anthelmintics is a high priority need for the pharmaco-parasitology research field, considering the magnitude and severity of anthelmintic resistance as an important issue in livestock production. In the work described here, monepantel (MNP) was given alone or co-administered with either macrocyclic lactone (ML) or benzimidazole (BZ) anthelmintics to calves naturally infected with ML- and BZ-resistant gastrointestinal (GI) nematodes on two different commercial cattle farms. Both pharmacokinetic (PK) and efficacy assessments were performed. On Farm A, male calves (n = 15 per group) were treated with either MNP orally (2.5 mg/kg), IVM s.c. (0.2 mg/kg), ricobendazole (RBZ) s.c. (3.75 mg/kg) or remained untreated. On Farm B, eight groups (n = 15) of male calves received treatment with either: MNP, abamectin (ABM, oral, 0.2 mg/kg), RBZ (s.c., 3.75 mg/kg), albendazole (ABZ, oral, 5 mg/kg), MNP+ABM, MNP+RBZ, MNP+ABZ (all at the above-mentioned routes and doses) or remained untreated. Seven animals from each treated group (Farm B) were randomly selected to perform the PK study. MNP and its metabolite monepantel sulphone (MNPSO₂) were the main analytes recovered in plasma after HPLC analysis. The combined treatments resulted in decreased systemic exposures to MNP parent drug compared with that observed after treatment with MNP alone (P < 0.05). However, the systemic availability of the main MNP metabolite (MNPSO₂) was unaffected by co-administration with either ABM, RBZ or ABZ. Efficacies of 98% (Farm A) and 99% (Farm B) demonstrated the high efficacy of MNP given alone (P < 0.05) against GI nematodes resistant to ML and BZ in cattle. While the ML (IVM, ABM) failed to control Haemonchus spp., Cooperia spp. and Ostertagia spp., MNP achieved 99% to 100% efficacy against those nematode species on both commercial farms. However, MNP alone failed to control Oesophagostomum spp. (60% efficacy) on Farm A. The co-administered treatments MNP+ABZ and MNP+RBZ reached a 100% reduction against all GI nematode genera. In conclusion, the oral treatment with MNP should be considered to deal with resistant nematode parasites in cattle. The use of MNP in combination with BZ compounds could be a valid strategy to extend its lifespan for use in cattle as well as to reverse its poor activity against Oesophagostomum spp.     

Effects on plasma pepsinogen, gastrin and pancreatic polypeptide of Ostertagia spp. transferred directly into the abomasum of sheep

Ostertagia spp. obtained at slaughter from the abomasa. of previously infected sheep and transferred via cannulae into the abomasa of previously worm-free sheep produced severe effects. This was shown with populations of mainly adult parasites given to three sheep and also when mixed populations of 4th stage larvae and adults were given to three other sheep. Although more severe effects were produced when both larval and adult worms were transferred, there were clearly effects when isolates composed predominantly of adults were transferred. Sheep of each group had reductions in food intake and elevations in plasma pepsinogen and gastrin within 24 h of transfer of the parasites. Further increase in plasma pepsinogen and gastrin occurred when abomasal pH rose 5–7 days after infection. Plasma pancreatic polypeptide varied but showed a general tendency to be markedly lower after infection. Ostertagia spp. eggs were detected in the faeces of infected sheep 48 h after transfer. The proportions of adults and inhibited larvae recovered from the abomasa were similar to those in the donor sheep, showing that inhibition, or arrested development of larvae, continued after their transfer to worm free sheep.     

Precision worm control in grazing lambs by targeting group treatment based on performance of sentinels

Given the economic impact of gastrointestinal nematode infection on livestock farming worldwide, and increasing anthelmintic resistance, it is imperative to develop practical, efficient and sustainable control strategies. Targeted selective treatment (TST), whereby anthelmintic treatments are administered to animals individually, based on selection criteria such as weight gain, has been shown to successfully maintain animal productivity whilst reducing the selection pressure for anthelmintic resistance and the economic cost of treatment in experimental and commercial settings. Despite the benefits of the TST approach, the equipment and time required to monitor animals individually make this strategy unsuitable for some farming enterprises. The sentinel group approach aims to maintain the benefits observed using TST whilst reducing these requirements. The study involved two experiments, each following a group of 80 lambs through their first grazing season. Anthelmintic treatment of the whole group was determined by monitoring the weight gain of identified sentinel lambs within it every 2 weeks: when 40% of the sentinel lambs failed to reach their weight gain targets, the whole group was treated. The sentinel lambs consisted of 45% of the group (n = 36) in experiment one and 20% (n = 16) in experiment two. A control group of 20 lambs was co-grazed with the main group during both experiments; in experiment one, the sentinel approach was compared with a TST approach, in which control lambs were treated on an individual basis in response to weight gain. In experiment two, the sentinel approach was compared with conventional prophylaxis, where all lambs in the control group were treated at strategic time points throughout the season (= strategic prophylactic treatment). The sentinel lambs were found to be representative of overall group performance regardless of the proportion of sentinels within the group: they recorded similar growth rates and reached weight gain targets simultaneously at each time point and overall. Live-weight gain was also similar between sentinel and control animals in both experiments. The findings of the current study suggest that monitoring sentinel lambs comprising 20% of a group of grazing lambs is sufficient to determine the need for anthelmintic treatment within the whole group, and that this approach maintains production in line with conventional or TST treatment regimes.     

Potential infection of grazing cattle via contaminated water: a theoretical modelling approach

Wastewater discharge and agricultural activities may pose microbial risks to natural water sources. The impact of different sources can be assessed by water quality modelling. The aim of this study was to use hydrological and hydrodynamic models to illustrate the risk of exposing grazing animals to faecal pollutants in natural water sources, using three zoonotic faecal pathogens as model microbes and fictitious pastures in Sweden as examples. Microbial contamination by manure from fertilisation and grazing was modelled by use of a hydrological model (HYPE) and a hydrodynamic model (MIKE 3 FM), and microbial contamination from human wastewater was modelled by application of both models in a backwards process. The faecal pathogens Salmonella spp., verotoxin-producing Escherichia coli O157:H7 (VTEC) and Cryptosporidium parvum were chosen as model organisms. The pathogen loads on arable land and pastures were estimated based on pathogen concentration in cattle faeces, herd prevalence and within-herd prevalence. Contamination from human wastewater discharge was simulated by estimating the number of pathogens required from a fictitious wastewater discharge to reach a concentration high enough to cause infection in cattle using the points on the fictitious pastures as their primary source of drinking water. In the scenarios for pathogens from animal sources, none of the simulated concentrations of salmonella exceeded the concentrations needed to infect adult cattle. For VTEC, most of the simulated concentrations exceeded the concentration needed to infect calves. For C. parvum, all the simulated concentrations exceeded the concentration needed to infect calves. The pathogen loads needed at the release points for human wastewater to achieve infectious doses for cattle were mostly above the potential loads of salmonella and VTEC estimated to be present in a 24-h overflow from a medium-size Swedish wastewater treatment plant, while the required pathogen loads of C. parvum at the release points were below the potential loads of C. parvum in a 24-h wastewater overflow. Most estimates in this study assume a worst-case scenario. Controlling zoonotic infections at herd level prevents environmental contamination and subsequent human exposure. The potential for infection of grazing animals with faecal pathogens has implications for keeping animals on pastures with access to natural water sources. As the infectious dose for most pathogens is more easily reached for calves than for adult animals, and young calves are also the main shedders of C. parvum, keeping young calves on pastures adjacent to natural water sources is best avoided.     

Reasons and risk factors for beef calf and youngstock on-farm mortality in extensive cow-calf herds

Raising calves and youngstock is an essential part of beef production. High on-farm mortality (unassisted death and euthanasia) is a consequence of poor animal health and welfare, and is economically unfavourable. The present study aimed to identify the reasons and risk factors for beef calf and youngstock on-farm mortality, using registry data for the years 2013 to 2015. Cox regression models were applied for the data of four age groups: calves up to 30 days (n=21 075), calves 1 to 5 months (n=21 116), youngstock 6 to 19 months (n=22 637) and youngstock ⩾20 months of age (n=9582). We found that dystocia, small birth weight and older parity of the mother increased the mortality hazard in calves up to 30 days of age. A summer birth was a common protective factor against mortality for calves up to 30 days and calves 1 to 5 months of age, compared with birth in other seasons. Among calves 1 to 5 months old, being the offspring of a first-parity cow was associated with significantly higher risk of death compared with calves who were the offspring of third- or higher-parity cows. A high herd-level stillbirth rate was associated with higher mortality hazard. The most commonly reported reasons for calf mortality were digestive disorders and respiratory disease. According to the models of youngstock from 6 months of age, male sex was a risk factor for mortality. Cattle having more than 10% dairy breed experienced a higher mortality risk in the ⩾20 months age group. No significant differences were found across regions, herd size or different breeds in any of the calf or youngstock groups. Metabolic and digestive disorders, as well as traumas and accidents, were the most common causes of mortality in beef youngstock older than 6 months. We can conclude that in young calves, animal-level factors associated with calving had a high impact on mortality. Further, timing calving for the warmer spring months would benefit calf survivability. Further studies including complementary information about farm factors adapted across the whole youngstock period is highly needed to provide sound recommendations in reducing on-farm mortality.     

The association between frequency of thiabendazole treatment and the development of resistance in field isolates of Ostertagia spp. of sheep

Martin P. J., Anderson N., Lwin T., Nelson G. and Morgan T. E. 1984. The association between frequency of thiabendazole treatment and the development of resistance in field isolates of Ostertagia spp. of sheep. International Journal for Parasitology14: 177–181. Isolates of Ostertagia spp. were obtained from grazing sheep 3,4 and 5 years after nil, planned (five per year) and regular (3-weekly) treatments with thiabendazole (TBZ). Levels of resistance to TBZ were measured by an in vitro egg hatch assay and a controlled anthelmintic efficiency assay. Isolates from planned treatment groups showed an increase in the level of resistance; the lethal concentrations of TBZ to 50% of eggs (LC₅₀s) were 3, 3 and 6 times the LC₅₀s of isolates from nil treatment groups for years 3, 4 and 5 respectively. The LC₅₀s of isolates from regular treatment groups were 14 times higher than those from nil treatment groups in each year. To assess the potential for an increase in level of resistance, additional egg assays were done 14 days after treatment with 44 mg kg^t?1 of TBZ on sheep infected with the planned group isolates for each year. This treatment raised the LC₅₀S for years 3, 4 and 5 respectively by 3, 2 and 1–5 times the LC₅₀s of the same isolates which had not been exposed to additional TBZ treatment. The controlled anthelmintic efficiency assay using 44 mg kg^t?1 of TBZ produced a significant reduction in the number of adult and immature worms from the nil isolate but failed significantly to reduce the number of worms from the planned and regular isolates. A three component analysis resolved the nonlinear trends of the log dose-probit plots in egg hatch assays for isolates from planned treatment groups into subpopulations of susceptible, hybrid and resistant individuals each with different levels of resistance. The proportions of these subpopulations changed in accordance with the level of resistance observed in each year.     

Predicting effects of naturally acquired abomasal nematode infections on growth rate and food intake in reindeer using serum pepsinogen levels

An experiment was performed on semiwild reindeer with naturally acquired parasite infections to assess whether measures of serum pepsinogen concentration and fecal egg counts can be used to predict effects of abomasal nematodes on reindeer weight gain and food intake. Food intake and weight gains were lower in infected calves compared with calves where parasites had been removed by anthelmintic treatment. Among the infected animals, concentration of pepsinogen in serum was correlated with food intake and weight gains. Concentration of abomasal nematode eggs in feces was not. Our results suggest that measures of pepsinogen levels in serum, but not fecal egg counts, may be used to predict the effects of abomasal nematodes on food intake and weight gain of reindeer.     

Effects of reproduction,genotype and anthelmintic treatment of ewes on Ostertagia spp. populations

Donald A. D., Morley F. H. W., Waller P. J., Axelsen A., Dobson R. J. and Donnelly J. R. 1982. Effects of reproduction, genotype and anthelmintic treatment of ewes on Ostertagia spp. populations. International Journal for Parasitology12: 403–411. Merino and Border Leicester × Merino (BL × M) ewes, nearly all of the same age and reared at the same site, were either unmated or mated to Border Leicester rams. Ewes of each genotype and reproductive status were untreated or were given a single pre-lambing drench with thiabendazole at 50 or 100 mg/kg a week before the start of lambing in spring on pastures at Canberra which had been contaminated during autumn and winter by adult sheep. The two genotypes grazed together within each combination of reproductive status and anthelmintic treatment which grazed separately. Thiabendazole was highly effective in removing both fourth stage larvae and adults of Ostertagia spp., the most abundant genus. Eight weeks after the pre-lambing drench lactating ewes carried larger Ostertagia spp. populations than did unmated ewes of both genotypes, but as a result of reinfection after treatment, differences between drenched and undrenched ewes were not significant. At this time lactating as well as unmated ewes harboured large populations of arrested early fourth stage larvae of Ostertagia spp. acquired during the last 8 weeks, showing that arrest of development is not prevented by lactation. There was strong evidence that some ingested larvae which became arrested in lactating ewes were rejected by unmated ewes. At all stages of the reproductive cycle studied, BL × M ewes were substantially more resistant to Ostertagia spp. infection than Merinos. No persistent benefits in parasite control or in animal production were detected from the pre-lambing drench.     

Effects of social learning on foraging behaviour and live weight gain in first-season grazing calves

When livestock are turned out to semi-natural grasslands, an effective onset of grazing is important both for animal productivity and for defoliation of the sward, which preserve the biodiversity of the vegetation. The aim of this study was to investigate whether foraging behaviour of naïve calves turned out to pasture was more intense, with a resulting diminished live weight loss, when experienced cattle accompanied them acting as social models. Twenty-six first-season grazing (FSG) dairy calves, allocated to groups with or without company of older, grazing-experienced steers, were turned out to semi-natural grasslands. Cattle behaviour was automatically recorded for 24 h during the first day on pasture and during 24 h after 1 month. Furthermore, the average live weight changes for the first day and for the first month on pasture were calculated. Calves turned out to pasture accompanied by grazing-experienced steers had similar grazing times (on average 42.7% of the day) to calves turned out to pasture in groups without older steers, but they had higher grazing activity during the first day on pasture (score 124 vs. 99, P = 0.005). Live weight changes were similar in calves kept with as in calves kept without company of grazing-experienced steers (?4.60 kg for the first day and ?0.30 kg day^?1 for the first month on pasture). In conclusion, the company of grazing-experienced conspecifics resulted in higher grazing activity in naïve calves, but their time spent grazing and live weight gains were unmodified. Hence, in this limited study we found no major positive effects on production of using grazing-experienced cattle as company to FSG calves on semi-natural grasslands.     

Cloning of the Authentic Bovine Gene Encoding Pepsinogen A and Its Expression in Microbial Cells

Bovine pepsin is the second major proteolytic activity of rennet obtained from young calves and is the main protease when it is extracted from adult animals, and it is well recognized that the proteolytic specificity of this enzyme improves the sensory properties of cheese during maturation. Pepsin is synthesized as an inactive precursor, pepsinogen, which is autocatalytically activated at the pH of calf abomasum. A cDNA coding for bovine pepsin was assembled by fusing the cDNA fragments from two different bovine expressed sequence tag libraries to synthetic DNA sequences based on the previously described N-terminal sequence of pepsinogen. The sequence of this cDNA clearly differs from the previously described partial bovine pepsinogen sequences, which actually are rabbit pepsinogen sequences. By cloning this cDNA in different vectors we produced functional bovine pepsinogen in Escherichia coli and Saccharomyces cerevisiae. The recombinant pepsinogen is activated by low pH, and the resulting mature pepsin has milk-clotting activity. Moreover, the mature enzyme generates digestion profiles with α-, β-, or κ-casein indistinguishable from those obtained with a natural pepsin preparation. The potential applications of this recombinant enzyme include cheese making and bioactive peptide production. One remarkable advantage of the recombinant enzyme for food applications is that there is no risk of transmission of bovine spongiform encephalopathy.