Herd Management Factors Research Articles

A model of the spread of the bovine viral-diarrhoea virus within a dairy herd

Wet BVDSim (a stochastic simulation model) was developed to study the dynamics of the spread of the bovine viral-diarrhoea virus (BVDV) within a dairy herd. This model took into account herd-management factors (common in several countries), which influence BVDV spread. BVDSim was designed as a discrete-entity and discrete-event simulation model. It relied on two processes defined at the individual-animal level, with interactions. The first process was a semi-Markov process and modelled the herd structure and dynamics (demography, herd management). The second process was a Markov process and modelled horizontal and vertical virus transmission. Because the horizontal transmission occurs by contacts (nose-to-nose) and indirectly, transmission varied with the separation of animals into subgroups. Vertical transmission resulted in birth of persistently infected (PI) calves. Other possible consequences of a BVDV infection during the pregnancy period were considered (pregnancy loss, immunity of calves). The outcomes of infection were modelled according to the stage of pregnancy at time of infection. BVDV pregnancy loss was followed either by culling or by a new artificial insemination depending on the modelled farmer’s decision. Consistency of the herd dynamics in the absence of any BVDV infection was verified. To explore the model behaviour, the virus spread was simulated over 10 years after the introduction of a near-calving PI heifer into a susceptible 38 cow herd. Different dynamics of the virus spread were simulated, from early clearance to persistence of the virus 10 years after its introduction. Sensitivity of the model to the uncertainty on transmission coefficient was analysed. Qualitative validation consisted in comparing the bulk-milk ELISA results over time in a sample of herds detected with a new infection with the ones derived from simulations.

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≈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.

Porcine proliferative enteropathy: a case-control study in swine herds in the United States

Objective: To describe epidemiologic characteristics of outbreaks of porcine proliferative enteropathy (PPE) and evaluate associations between herd production and management factors, and disease occurrence. Methods: A questionnaire about management factors was administered by telephone to the owners or managers of 30 PPE-affected herds (cases) and 18 unaffected herds (controls). Morbidity, mortality, and demographics of animals in affected herds were recorded. Fecal samples from approximately six pigs in each herd were tested by polymerase chain reaction (PCR) for Lawsonia intracellularis. Results: Porcine hemorrhagic enteropathy (PHE) occurred in 11 herds, and porcine intestinal adenomatosis (PIA) in 19 herds. In multivariable logistic regression analysis, use of a new building and recent mixing of pigs were associated (P<.05) with PPE. Management stressors such as overheating, chilling, number of times mixed, number of feeders per pen, and group size were not significantly associated with PPE. Fecal samples were more likely (P<.05) to be positive by PCR in case than control herds. Herds with PHE were more likely (P=.05) than herds with PIA to have at least one PCR-positive fecal sample. Implications: Placement of pigs into new facilities and commingling of groups of pigs significantly increase the risk of PPE. Production and management practices linked with high health status may not be associated with reduced risks of PPE outbreaks. Analysis of fecal samples by PCR is useful to detect L intracellularis in the population, but fecal samples are more likely to be PCR positive in herds with PHE than in herds with PIA.

Shiga toxin genes (stx) in Norwegian sheep herds.

The aim of this study was to describe the occurrence of shiga toxic genes (stx) in Norwegian sheep herds, and to identify herd management factors related to the occurrence of stx in herds. Faecal samples from 124 sheep-herds were collected at abattoirs in 1998. Pooled samples from lambs and from ewes were screened for stx by a PCR method directly on faeces. Of the 124 herds, 61 were positive for stx, giving an overall herd-prevalence of 49%. Twenty-one of the 61 positive herds were positive both in lamb and ewe samples, 24 only in lamb samples and 16 only in ewe samples. There was no difference in prevalence between regions. From the 21 herds positive both in lamb and ewe samples, stx encoding E. coli were detected in 18 herds using hydrophobic grid membrane filters and subsequent colony hybridization. Information about management factors was collected by telephone interviews. Having cattle at the same farm turned out to be a possible risk factor, with an Odds Ratio of 9.9 (CI 1.2 --> infinity).

Dealing with antimicrobial resistance – the Danish experience

Following the discovery in 1994 and 1995 that use of the glycopeptide antimicrobial avoparcin for growth promotion was associated with the occurrence of vancomycin resistant Enterococcus faecium in food animals and in food, the Danish Minister of Food, Agriculture and Fisheries banned the use of avoparcin in May 1995. The ban was later extended by the European Commission to include all EU member states. In May 1999, the EU Scientific Steering Committee recommended that use for growth promotion of antimicrobials, which are or may be used in human or veterinary medicine should be phased out as soon as possible and ultimately abolished. During the first half of the 1990s the consumption of tetracyclines, mainly in pig production, increased markedly. This was countered by severely reducing through legal means the financial enticement for veterinarians to prescribe medicines and by restricting the availability of tetracycline as non-registered speciality products. The focus on consumption of antimicrobials and on resistance prompted a number of initiatives by Danish authorities to limit the increase in antimicrobial resistance. One such initiative was the implementation of an integrated programme (DANMAP), which monitors resistance among bacteria from food animals, food and humans. A programme to monitor all use of prescription medicine in food animals at the herd level is presently being implemented. Another initiative was the elaboration of a series of practical recommendations to veterinarians on the prudent use of antimicrobials in order to reduce the development of resistance without compromising therapeutic efficacy. Our experience with avoparcin shows that a restrictive policy on the use of antimicrobials can curb the development of resistance. However, the occurrence and persistence of specific resistance phenotypes is the end-result of complex interactions of, among others, antimicrobial co-selection, clonal spread of resistant strains and various herd management factors. Key words: Antimicrobial resistance, Denmark, avoparcin, tetracycline

A Stochastic Model Simulating the Feeding-Health-Production Complex in a Dairy Herd

A dynamic, stochastic, and mechanistic Monte Carlo model, simulating a dairy herd with focus on the feeding-health-production complex is presented. By specifying biological parameters at cow level and a management strategy at herd level, the model can simulate the technical and economic consequences of scenarios at herd level. The representation of the feeding-health-production complex is aimed to be sufficiently detailed, to include relationships likely to cause significant herd effects, and to be sufficiently simple to enable a feasible parameterization of the model and interpretation of the results from the model. Consequently, diseases are defined as four disease types: two metabolic disease types, an udder disease type, and a reproductive disease type. Risk factors for the diseases were defined as parity, yield capacity, disease recurrence, disease interrelationships, lactation stage, and season. Direct effects of the diseases were defined according to milk yield, feed intake, feed utilization, conception, culling, involuntary removal, and death.Scenarios differing in base risks of milk fever and ketosis, heat detection rate, and culling strategy were simulated for describing the model behavior. Annual milk yield per cow was decreased by increased risk of ketosis and by increased risk of milk fever, even though no direct effect of milk fever on milk yield was modeled at the cow level. The indirect effect from milk fever is a consequence of increased replacement rate (relatively lower milk yield from younger cows). By ignoring the history of milk fever in insemination and replacement decisions, a significantly reduced net income per cow was found in some herds. We concluded that important benefits from using such a herd model are the capability of accounting for herd management factors and the advantage of avoiding to double count the indirect effects from disease, such as increased risk of other diseases, poorer reproduction results, and increased risk of culling and death.

Association of Herd Management Factors with Colonization of Dairy Cattle by Shiga Toxin-Positive Escherichia coli O157

Management factors in 36 Pacific Northwest dairy herds were evaluated for their association with the prevalence of Shiga toxin-positive Escherichia coli O157 (E. coli O157) in dairy cattle. The within-herd prevalence of E. coli O157 was estimated by bacteriological culture of fecal pat samples, collected monthly for 6 months (approximately 60 per visit), from heifer cattle. During the first visit to each farm, a management questionnaire was administered that covered a broad range of animal husbandry practices. On each subsequent visit, a brief questionnaire was administered to detect changes in management practices. A significantly higher prevalence of E. coli O157 was noted in herds that fed com silage to heifers compared to herds that did not feed com silage. More tentative associations of E. coli O157 prevalence were observed for weaning method, protein level of calf starter, feeding of ionophores in heifer rations, feeding of grain screens to heifers, and feeding of animal by-products to cows.

Associations Between Winter Herd Management Factors and Milk Protein Yield in Ontario Dairy Herds

A questionnaire was used to investigate associations between farm management practices in winter and milk protein yield. The questionnaire was completed by 500 dairy producers in Ontario, Canada in March 1994. A high positive correlation (0.96) existed between herd mean for protein yield per day per cow and herd mean for milk yield per day per cow. Therefore, most management practices that were associated with the farm mean for protein yield per day per cow were also associated with the farm mean for milk yield per day per cow. After adjustment for farm mean milk and fat yields, farms that housed dry cows as a separate group had higher mean protein yields than did herds that housed dry cows with the milking herd or the bred heifers. A positive association existed between herd mean for days of lactation and protein yield. Because of the correlation between milk and protein yields, these associations were of small magnitude. Thus, the potential benefit of progressive practices in herd management are primarily related to increased yields of milk and milk components in general rather than specifically to an increase in protein yield.

Associations of Ascaris suum and Oesophagostomum spp. infections of sows with management factors in 83 Danish sow herds

Associations of the occurrence of Ascaris suum and Oesophagostomum spp. in sows with herd management factors were examined using logistic-binomial regression. The information used was from 11 to 78 sows sampled from each of 83 breeding herds (2961 sows in total) and examined for eggs per gram of faeces (EPG). A sow excreting at least 20 EPG was defined as ‘infected’. Management factors of the study herds were recorded using a questionnaire. A total of 263 sows from 50 herds (8.9% of sows) and 375 sows from 20 herds (12.7% of sows) were infected with A. suum and Oesophagostomum spp., respectively. For A. suum, sows from herds with more than 85 sows had significantly higher odds of being infected compared with those from 30 to 85 sows ( P < 0.05). When bedding was provided for sows, the odds of A. suum infection was 5.4 compared with sows from herds in which bedding was not provided ( P < 0.05). For Oesophagostomum spp., sows from herds with different specific pathogen free status had about one tenth the odds of being infected compared with those from conventional herds ( P < 0.05). Sows that had been treated with anthelmintics had very low odds of being infected with Oesophagostomum spp. compared with those that were not treated ( P < 0.05). The effects of these management factors in both final models did not differ when the definition of an ‘infected’ sow was changed. The present results suggest the importance of disposal of bedding material from pens in reducing the prevalence of A. suum in larger sow herds. Anthelmintic treatment is important in reducing the prevalence of Oesophagostomum spp. infection of sows.

The Key Role of Records in a Production Medicine Practice

The needs of dairy farmers for veterinary assistance have changed and are still changing. It appears that many future opportunities in dairy practice will involve active consultation on herd management factors. The ability to evaluate herd records will be crucial to this effort. This article discusses organizing and then utilizing a production medicine program based on systematic records analysis.

Sire by Herd Environment Interaction for Milk Production

The importance of interaction between estimates of breeding values of dairy sires and ten contrasting herd environments in which their daughters made records was investigated by estimating variance components for interaction between sires and herd management factors and by correlating sire proofs in contrasting herd environments. Artificial insemination sires were evaluated by a within-season and environmental category contemporary comparison, adjusted for the number of daughters and contemporaries involved. Each environmental factor was studied independently, and the sire proofs constituted observations. Herd environment and season effects were assumed to be fixed, while sire effects were assumed to be random. No interactions of practical importance between sire proofs and herd environments were found when herds were grouped in categories with respect to the extent of use of artificial insemination sires, price received for milk, source of water on pasture, forage feeding methods in winter and in summer, amount of exercise received by cows in winter, and herd size. Results of interaction of sire proofs with grain-feeding levels in winter, and with housing systems were inconclusive. A highly significant interaction involving sire proofs and level of grain feeding in summer was found. The interaction component of variance accounted for 17% of the total variance in sire proofs. Genetic correlations between proofs of the same sires based on their daughters in herds with different levels of grain feeding in summer ranged from 0.54 to 0.79.