A bulk tank milk survey of Ostertagia ostertagi antibodies in dairy herds in Prince Edward Island and their relationship with herd management factors and milk yield

The objective of this study was to quantify the relationship of the levels of antibodies to Ostertagia ostertagi in bulk-tank milk samples from Prince Edward Island (PEI) dairy farms to milk production and to herd-management practices potentially related to gastrointestinal nematode infections. The milk samples were obtained from 289 to 322 dairy farms during 2000; production and management data were available from 197 and 200 farms, respectively. Cow exposure to pasture and whole-herd anthelmintic treatment were the only herd management variables significantly associated with antibody levels in the fall of 2000. An increase in antibody levels from the observed 25th percentile to the 75th percentile (interquartile range) was associated with a drop in milk production of 1.2 kg/cow/day. The results of this study indicate that the enzyme-linked immunosorbent assay for O. ostertagi antibody is a potentially useful technique to measure parasite exposure in adult dairy cows and that parasite burdens in lactating cattle in PEI have an important impact on milk production.     

A longitudinal study of gastrointestinal parasites in Canadian dairy farms. The value of an indirect Ostertagia ostertagi ELISA as a monitoring tool

The general objective of this study was to evaluate a crude Ostertagia ostertagi antigen enzyme-linked immunosorbent assay (ELISA) for monitoring gastrointestinal parasites in lactating dairy cattle. A longitudinal study of gastrointestinal parasites in lactating dairy cows was carried out in 38 herds in four provinces of Canada (Prince Edward Island, Quebec, Ontario and Saskatchewan) from September 1999 to October 2000. Bulk tank milk, cow milk, serum and fecal samples were collected monthly or quarterly from all these farms. Information on herd management factors was collected by a standard questionnaire and individual cow production data were obtained from an electronic database. The overall mean optical density ratio (ODR) was 0.30 and ranged from -0.05 to 1.55. Although a clear seasonal pattern was not observed, the ODR values tended to decrease during the housing period and start increasing in the spring before the cows went out to pasture. The second and third or greater lactation cows had significantly higher ODR values compared with first lactation animals. The individual cow ODR had a very low correlation with individual squared root fecal egg counts but showed a reasonably high correlation when herd averages values were computed (r=0.73). A moderate correlation (r approximately 0.50) between the bulk tank and herd average ODR was observed. Milk yield was negatively associated with individual cow milk ODR and a quadratic effect on ODR was observed for days in milk. Twenty-eight of the herds participated in a clinical trial of eprinomectin (Ivomec Eprinex) treatment at calving. The cow level ODR values determined late in the previous lactation had a marginally significant effect (P=0.07) on treatment response, suggesting that high OD cows responded better to the anthelmintic treatment. However, because of the small sample size available in this model, more research is needed to better understand this relationship. In conclusion, the indirect ELISA using an O. ostertagi crude antigen appears useful as a technique for monitoring gastrointestinal parasite burdens in adult dairy cows and holds promise as a potential predictor of response to anthelmintic treatment.     

Temporal and spatial dynamics of insecticide resistance in Myzus persicae (Hemiptera: Aphididae)

Advances in understanding insecticide resistance in the peach-potato aphid, Myzus persicae (Sulzer), at the genotypic, biochemical and molecular levels have led to rapid and precise methods for the detection of several resistance mechanisms (elevated carboxylesterase, modified acetylcholinesterase or MACE, and knockdown resistance or kdr) in individual insects, and for monitoring their frequencies over space and time. This paper summarises the results of two long-term surveys of resistance dynamics in M persicae in England, based on samples collected directly from field and glasshouse crops or from four 12.2-m suction traps. The study showed marked fluctuations in resistance frequencies that probably reflect the counteracting forces of selection imposed by insecticides for aphids possessing more copies of esterase resistance genes, and selection against these forms when insecticide use is relaxed. There is growing evidence that several different resistance mechanisms in M persicae have associated fitness costs. In the case of esterase and MACE, these costs are apparently strong enough to effect a decline in resistance frequency over winter, and a more prolonged decline over successive cropping seasons when aphid numbers are insufficient to trigger intensive chemical applications. Changes in the overall frequency of resistance genotypes may also be influenced by the predominance of year-round parthenogenesis in M persicae in the UK, leading to non-random associations between mechanisms and selection operating on clonal lineages rather than individual genotypes.     

New developments in insecticide resistance in the glasshouse whitefly (Trialeurodes vaporariorum) and the two-spotted spider mite (Tetranychus urticae) in the UK

A recent survey of insecticide resistance in two of the most problematic pests in UK glasshouses revealed some new developments. At least some individuals in all UK samples of Trialeurodes vaporariorum that were tested resisted the insect growth regulator (IGR) buprofezin. The most strongly resistant strains were unaffected by the field application rate of this compound, and even samples from populations that had never been exposed to buprofezin contained individuals that survived the highest concentration applied (10,000 mg litre-1). The field rate of buprofezin was shown to select for resistance through vapour action alone. The benzophenylurea teflubenzuron, an unrelated IGR, was cross-resisted by buprofezin-resistant individuals. There was no evidence of resistance to imidacloprid, but all T vaporariorum strains tested, regardless of origin, exhibited a high innate tolerance to nicotine, when compared with another whitefly species, Bemisia tabaci. Marked resistance to fenbutatin oxide and tebufenpyrad was found in single glasshouse populations of Tetranychus urticae, but these compounds and abamectin appeared to remain highly effective against all other strains collected.     

Use of age and milk production data to improve the ability of enzyme-linked immunosorbent assay test results to predict Mycobacterium avium ssp. paratuberculosis fecal culture status.

Cows from 2 California dairies were tested for paratuberculosis at the end of lactation by using fecal culture and a commercially available serum enzyme-linked immunosorbent assay (ELISA) test kit. Individual cow characteristics and production variables were evaluated along with ELISA testing results as predictors of fecal culture status. In multivariable logistic regression analysis, age and a herd-standardized version of 305-day mature equivalent (305 ME) milk production were significant predictors of fecal culture status after adjusting for herd, quarter of the study year, and ELISA sample-to-positive (S/P) ratio. The area under a nonparametric receiver operating characteristic curve was significantly greater for a multivariable model that included age and the level of milk production when compared with a model without these covariates. In conclusion, consideration of cow-level covariates was useful as an aid in predicting Mycobacterium avium ssp. paratuberculosis (MAP) fecal culture status. For a given ELISA S/P ratio, older cows and those with lower 305 ME milk production relative to other cows in the herd were significantly more likely to be shedding MAP in their feces at the end of lactation.     

Precision of estimated QTL positions in granddaughter designs using combined haplotype sharing TDT and linkage analysis

The aim of this study was to develop the linear haplotype sharing transmission disequilibrium test (LHS-TDT) method and combine this method with the simple regression method to estimate the precision of QTL positions in granddaughter designs. This precision was determined by Monte Carlo simulation in granddaughter designs. A single bi-allelic QTL at the midpoint of a linkage group and 26 markers with 1 cM intervals and with two alleles each were simulated. Three linear models, (i.e. the simple regression model, the linear haplotype sharing TDT method and the combination of these two models) were compared. The mean of absolute differences (A) between the estimated and true QTL position of each method was considered for six different scenarios consisting of combinations of a number of markers and the most frequent haplotypes. The mean of A, using the simple regression method, was 4.38 centimorgan (cM). The means of A using the LHS-TDT method were less than the simple regression method in all scenarios and ranged from 1.86 to 3.82 cM depending on the scenario. The mean of A using the combined method was more than the LHS-TDT method and less than the simple regression method. The means of A using the combined method ranged from 2.32 to 4.36 cM. Therefore, for populations similar to those population simulated in this study, the LHS-TDT was better than the simple regression method and the combined method for precision of estimated QTL position in granddaughter designs.     

Quantitative analysis of production traits in saltwater crocodiles (Crocodylus porosus): III. juvenile survival

Mortality records of 1302 juvenile crocodiles were available for analysis. Crocodiles that were slaughtered during this study were treated as censored (n = 2151). Additionally, records from animals that had neither died nor been slaughtered, i.e. were still alive in the production system (n = 1582), were censored at the last date of data collection. There were a total of 3733 censored records. The data were all full‐sib records from 29 parental pairs from Janamba Croc Farm (Northern Territory, Australia), collected over nine consecutive years. Data were analysed using an extension of Cox's proportional hazards model to include frailty (random) terms to account for genetic effects. Heritability of log survival time for juvenile crocodile survival was 0.15 (SE 0.04). The probability of a juvenile crocodile surviving to day 400 was estimated to be only 51%. These results are the first to quantify juvenile survival in a captive breeding situation. Also, this is the first heritability estimate of crocodile survival and is a fundamental element in the development of a genetic improvement programme.     

Landscape improvement, or ongoing degradation – reconciling apparent contradictions from the arid rangelands of Western Australia

Recent quantitative site-based monitoring and qualitative aerial and ground traverses provide contrasting assessments of the health of much of the arid shrublands of Western Australia extensively grazed by livestock (‘rangelands’). Although these results seem incompatible, we explain the apparent contradictions based on landscape succession processes operating at multiple levels of ecological organisation. Specifically, we suggest that the intact areas in which site-based monitoring is conducted are contracting as catchment canalisation and desiccation increase. However, the impacts of these processes have not yet become manifest at the site scale. The site-based system addresses important regional questions. These relate to the large, relatively intact areas away from most active surface flows, which should be a focus for resource conservation, given practical limits to repairing widespread degradation with low management inputs. We provide a complementary set of questions to provide a more comprehensive audit of rangeland dynamics in the context of underlying hierarchical landscape patterns and processes that might threaten intact areas. We recognise the need to match questions and levels of ecological organisation and the implications these have for sampling. We also recognise the difficulty in producing concise statements of change for clients when reporting on complex ecological issues and processes. Without a clearly articulated, and well understood, hierarchical model of pattern and process within which apparently contradictory findings can be reported meaningfully, policy makers may be confused by the results, with the consequent risk of policy inaction.     

Comparison of the Sensitivity of Landscape-fire-succession Models to Variation in Terrain, Fuel Pattern, Climate and Weather

The purpose of this study was to compare the sensitivity of modelled area burned to environmental factors across a range of independently-developed landscape-fire-succession models. The sensitivity of area burned to variation in four factors, namely terrain (flat, undulating and mountainous), fuel pattern (finely and coarsely clumped), climate (observed, warmer & wetter, and warmer & drier) and weather (year-to-year variability) was determined for four existing landscape-fire-succession models (EMBYR, FIRESCAPE, LANDSUM and SEM-LAND) and a new model implemented in the LAMOS modelling shell (LAMOS(DS)). Sensitivity was measured as the variance in area burned explained by each of the four factors, and all of the interactions amongst them, in a standard generalised linear modelling analysis. Modelled area burned was most sensitive to climate and variation in weather, with four models sensitive to each of these factors and three models sensitive to their interaction. Models generally exhibited a trend of increasing area burned from observed, through warmer and wetter, to warmer and drier climates with a 23-fold increase in area burned, on average, from the observed to the warmer, drier climate. Area burned was sensitive to terrain for FIRESCAPE and fuel pattern for EMBYR. These results demonstrate that the models are generally more sensitive to variation in climate and weather as compared with terrain complexity and fuel pattern, although the sensitivity to these latter factors in a small number of models demonstrates the importance of representing key processes. The models that represented fire ignition and spread in a relatively complex fashion were more sensitive to changes in all four factors because they explicitly simulate the processes that link these factors to area burned. The US Government's and the Canadian Government's right to retain a non-exclusive, royalty-free license is acknowledged