Henrik Stryhn

University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada

Are you Henrik Stryhn?

Claim your profile

Publications (98)153 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Compared with blanket dry cow therapy (DCT), the selective antimicrobial treatment of cows based upon on-farm culture results has the potential to reduce the amount of antimicrobials used in dairy production. The objective of the current study was to determine the effect of a Petrifilm (3M Canada, London, Ontario) on-farm culture-based selective DCT program on milk yield and somatic cell count (SCC) in the following lactation. A total of 729 low-SCC (<200,000 cells/mL) cows from 16 commercial dairy herds with a low bulk tank SCC (<250,000 cells/mL) were randomly assigned to receive either blanket DCT or Petrifilm-based selective DCT. Cows belonging to the blanket DCT group were infused with a commercial DCT product and an internal teat sealant (ITS) at drying off. Using composite milk samples collected on the day before drying off, cows in the selective DCT group were treated at drying off based on the results obtained by the Petrifilm on-farm culture system with DCT and ITS (Petrifilm culture positive) or ITS alone (Petrifilm culture negative). Milk test-day records for the following lactation were obtained from Dairy Herd Improvement for all cows enrolled in the trial. Repeated measures linear mixed models were used to assess the effect of study group (blanket or selective DCT) on test-day milk production and natural logarithm of SCC over the first 180 d of the subsequent lactation. According to the final multivariable models, when low-SCC cows were selectively treated with DCT at drying off based on results obtained using the Petrifilm on-farm culture system, no effect on milk production (least squares means for blanket DCT = 39.3 kg vs. selective DCT = 39.0 kg) or natural logarithm of SCC (least squares means for blanket DCT = 3.95 vs. selective DCT = 3.97) was observed in the subsequent lactation when compared with cows receiving blanket DCT. The results of this study indicate that selective DCT based on results obtained by the Petrifilm on-farm culture system enabled a reduction in the use of DCT without negatively affecting milk production and milk quality. Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.
    Journal of dairy science. 01/2015;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In Eastern Canada, an increasing number of pests, predators and pathogens in downriver areas (close to the ocean) have led the aquaculture industry to consider growing oysters in upriver areas (close to the river source). In this study, oyster growth performance was compared between downriver and upriver environments by means of stock transfer experiments within the Richibucto estuary. In May 2009, seed oysters (~26 mm shell height) originating from two downriver sites (salinity ~20–30 ‰) were transferred upriver (salinity ~5–20 ‰). Follow-up measurements in October 2009 revealed that the seed transferred upriver grew and survived as well as seed that remained downriver, while the mortality rates of adult oysters (shell height ~66 mm) were lower at the upriver site. Meat content was unaffected in adult oysters transferred upriver. However, there were indications that the upriver environment promoted shell growth (mm) in adult oysters. Oysters transferred upriver had a gain in shell height (LSM ± SE) over the oysters that remained downriver (2.7 ± 0.5 vs. 1.8 ± 0.5 mm) and in shell width [Median (95 % CI); 2.8 mm (1.9, 3.6) vs. 1.0 mm (0.3, 1.2)]. Therefore, the holding of adult oysters upriver during the spring–summer period confers productivity advantages on top of protection from diseases and predation. By contrast, productivity losses were recorded when relocating adult oysters originating from the upriver environment. More specifically, final organic meat content were approximately 35 % less in adult oysters transferred downriver compared to those that remained upriver (0.48 ± 0.04 vs. 0.74 ± 0.04 g). Results suggest that transfers along the river impact physiological processes such as gametogenesis and shell formation in adult oysters.
    Aquaculture International 12/2014; · 0.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mastitis is a complex disease affecting dairy cows and is considered to be the most costly disease of dairy herds. The hazard of mastitis is a function of many factors, both managerial and environmental, making its control a difficult issue to milk producers. Observational studies of clinical mastitis (CM) often generate datasets with a number of characteristics which influence the analysis of those data: the outcome of interest may be the time to occurrence of a case of mastitis, predictors may change over time (time-dependent predictors), the effects of factors may change over time (time-dependent effects), there are usually multiple hierarchical levels, and datasets may be very large. Analysis of such data often requires expansion of the data into the counting-process format–leading to larger datasets–thus complicating the analysis and requiring excessive computing time. In this study, a nested frailty Cox model with time-dependent predictors and effects was applied to Canadian Bovine Mastitis Research Network data in which 10,831 lactations of 8,035 cows from 69 herds were followed through lactation until the first occurrence of CM. The model was fit to the data as a Poisson model with nested normally distributed random effects at the cow and herd levels. Risk factors associated with the hazard of CM during the lactation were identified, such as parity, calving season, herd somatic cell score, pasture access, fore-stripping, and proportion of treated cases of CM in a herd. The analysis showed that most of the predictors had a strong effect early in lactation and also demonstrated substantial variation in the baseline hazard among cows and between herds. A small simulation study for a setting similar to the real data was conducted to evaluate the Poisson maximum likelihood estimation approach with both Gaussian quadrature method and Laplace approximation. Further, the performance of the two methods was compared with the performance of a widely used estimation approach for frailty Cox models based on the penalized partial likelihood. The simulation study showed good performance for the Poisson maximum likelihood approach with Gaussian quadrature and biased variance component estimates for both the Poisson maximum likelihood with Laplace approximation and penalized partial likelihood approaches.
    Preventive Veterinary Medicine 12/2014; · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Piscirickettsiosis (SRS) is an endemic bacterial disease of high economic importance and is the primary reason for antibiotic usage in the aquaculture industry in Chile. Understanding the epidemiology of this disease is important in order to develop better control strategies for the Chilean aquaculture industry. The objectives of this project were to 1) describe the epidemiology of SRS on Atlantic salmon and rainbow trout farms, and 2) to identify factors that impact the severity of SRS outbreaks. Special attention was given to vaccine strategies currently used by the industry. Production data from 14 Atlantic salmon farms (252 cages) and 11 rainbow trout farms (216 cages) that had completed their production cycles between 2010 and 2012 were investigated. Regression models were used to evaluate time-to-first outbreak of SRS and total mortality attributed to SRS mortality. The factors evaluated in our models were: vaccine type (control and 5 vaccines), smolt weight and cumulative mortality within the first 4 weeks in saltwater, season of smolt introduction, infection with other pathogens during the production cycle, SRS treatments, and total number of sea lice treatments. The prevalence of SRS-affected cages on infected farms was high for both species; however, outbreaks appeared more severe (i.e. higher mortalities) on rainbow trout farms. Onset of SRS outbreaks was, on average, for fish in different vaccine groups, between 2480 degree-days (dd) and 3829 dd for Atlantic salmon, and between 1696 dd and 2241 dd for rainbow trout. For both species, none of the vaccines evaluated completely prevented SRS, although there were significant variations in the time-to-first outbreak and the severity of SRS outbreaks associated with vaccines after controlling for farm effect and other predictors. Specifically, a booster vaccine strategy in Atlantic salmon had significantly lower mortalities associated with SRS and a delay in the onset of disease compared to several of the other vaccines evaluated. Whether the differences observed between vaccines are economically significant is unknown. In rainbow trout, time-to-first outbreak was significantly delayed for vaccinated fish compared to the unvaccinated fish after we controlled for other factors in our model; however, total SRS mortality of vaccinated rainbow trout was not significantly different than unvaccinated rainbow trout. Consistent for both species was that mortality during the first 4 weeks post-salt water entry was associated with time-to-outbreak of SRS, and this effect was dependent on the vaccine used.
    Aquaculture 09/2014; 433:288–294. · 1.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A cross-classified and multiple membership Cox model was applied to calf mortality data from Western Canada, where 23,409 calves from 174 herds were followed for up to 180 days after calving. The herds were cross-classified by 49 veterinary clinics and 9 ecological regions and in a multiple membership relation to the veterinary clinics, resulting in a 3-level cross-classified and multiple membership data structure. The model was formulated in a mixed-effects Poisson model framework with normally distributed random effects, and was fitted to the data by Bayesian Markov Chain Monte Carlo (MCMC) estimation. Important fixed effects included whether the calf was a twin, calf gender, assistance at calving, cow age, average temperature the first week after calving, the percentage of the herd that had already calved, whether calf shelters were provided, whether cow-calf pairs were moved to a nursery area, and whether any animals were purchased into the herd at or near the time of calving. The analysis demonstrated a greater variation among herds than among both ecological regions and veterinary clinics. Further, a simulation study for a setting similar to the real data gave evidence that the used approach provides valid estimates.
    Preventive Veterinary Medicine 07/2014; · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Control of sea lice in Chile is largely based on antiparasitic treatments, synthetic pyrethroids being the most used drugs. In recent years, farmers in Chile have reported decreased performance of pyrethroid-based treatments. The aim of this study was to assess the performance of two deltamethrin-based (Alphamax® and a generic product) and one cypermethrin-based (Betamax®) product on the different life stages of Caligus rogercresseyi, while controlling potential confounders. We found that both deltamethrin products and the cypermethrin product had a significant effect on the reduction of juvenile, mobile adult, and gravid female lice, compared with untreated pens; however, the effect on juvenile lice was less than on mobile stages. There was no evidence that pyrethroids performed better on certain mobile life stages, such as gravid females. When the three products were compared, no significant differences were observed in the numbers of juvenile, adult male, and non-gravid female lice after we controlled for potential confounders; however, cypermethrin exhibited a small, yet significantly greater effect on the gravid female group when compared with one of the deltamethrin-based products. We also confirmed that other factors besides the product choice, such as the pre-treatment sea lice abundance, water temperature and salinity, and time elapsed to the post-treatment sample, affect the post-treatment sea lice level as well, and therefore, they should be taken into consideration when assessing the effect of immersion treatments.
    Aquaculture 04/2014; s 426–427:231–237. · 1.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study was designed to assess the physiological impact of transferring oysters between upriver and downriver aquaculture sites, a common practice in North America that is primarily aimed at reducing disease infections and predation on cultured stocks. In May 2009, oysters (Crassostrea virginica) were reciprocally transferred between an upriver and a downriver site in the Richibucto estuary in eastern Canada. Mortality, tissue and cellular stress responses were subsequently evaluated in August and October 2009. Overall, oyster mortality remained low (~5%) throughout the 5-month study period with no significant difference between sites or oyster sources. However, by October oysters reared at the upriver site, regardless of their origin, had significantly higher levels of lysosomal membrane destabilization (63.6%, SE = 1.9) and digestive tubule atrophy (33.3–42.4%, SE = 3.6) than oysters reared at the downriver site (47.5%, SE = 1.8; 15.6–19.1%, SE = 3.8 respectively). They also exhibited a greater salinity differential between their mantle/haemolymph fluids and the ambient seawater, possibly indicating more restricted exchange with the environment. In general, the transfer of upriver oysters to a downriver site had a positive impact, i.e. lower levels of lysosomal destabilization and tubule atrophy, whereas transfer of downriver oysters upriver had the opposite effect. These results suggest that upriver environmental conditions negatively impact cellular and tissue integrity in oysters without leading to mortality during the summer–autumn period.
    Aquaculture Research 03/2014; · 1.42 Impact Factor
  • Henrik Stryhn, Jette Christensen
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper discusses statistical modelling for data with a hierarchical structure, and distinguishes in this context between three different meanings of the term hierarchical model: to account for clustering, to investigate variability and separate predictive equations at different hierarchical levels (multi-level analysis), and in a Bayesian framework to involve multiple layers of data or prior information. Within each of these areas, the paper reviews both past developments and the present state, and offers indications of future directions. In a worked example, previously reported data on piglet lameness are reanalyzed with multi-level methodology for survival analysis, leading to new insights into the data structure and predictor effects. In our view, hierarchical models of all three types discussed have much to offer for data analysis in veterinary epidemiology and other disciplines.
    Preventive Veterinary Medicine 10/2013; · 2.51 Impact Factor
  • Source
    Elmabrok Masaoud, Henrik Stryhn
  • Source
    Elmabrok Masaoud, Henrik Stryhn
  • Source
    Henrik Stryhn, Elmabrok Masaoud
  • Source
    Henrik Stryhn, Elmabrok Masaoud
  • Source
    Elmabrok Masaoud, Henrik Stryhn
  • Source
    Henrik Stryhn, Elmabrok Masaoud
  • Source
  • Source
    Elmabrok Masaoud, Henrik Stryhn
  • Source
    Elmabrok Masaoud, Henrik Stryhn
  • Source
  • Source
    Elmabrok Masaoud, Henrik Stryhn
  • Source
    Elmabrok Masaoud, Henrik Stryhn

Publication Stats

933 Citations
153.00 Total Impact Points

Institutions

  • 2004–2015
    • University of Prince Edward Island
      • Department of Health Management
      Charlottetown, Prince Edward Island, Canada
  • 2011
    • University of Adelaide
      • School of Animal and Veterinary Sciences
      Adelaide, South Australia, Australia
    • University of Zawia
      • Faculty of Science
      Zawia, Az Zāwiyah, Libya
  • 2008
    • University of Saskatchewan
      • Western College of Veterinary Medicine
      Saskatoon, Saskatchewan, Canada
  • 2004–2005
    • Ghent University
      • Department of Obstetrics, Reproduction and Herd Health
      Gand, Flemish, Belgium