Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Predicting survival in dairy cattle by combining genomic breeding values and phenotypic information
    Heide, E.M.M. van der; Veerkamp, R.F. ; Pelt, M.L. van; Kamphuis, C. ; Ducro, B.J. - \ 2020
    Journal of Dairy Science 103 (2020)1. - ISSN 0022-0302 - p. 556 - 571.
    dairy cow - individual prediction - longevity - survival

    Advances in technology and improved data collection have increased the availability of genomic estimated breeding values (gEBV) and phenotypic information on dairy farms. This information could be used for the prediction of complex traits such as survival, which can in turn be used in replacement heifer management. In this study, we investigated which gEBV and phenotypic variables are of use in the prediction of survival. Survival was defined as survival to second lactation, plus 2 wk, a binary trait. A data set was obtained of 6,847 heifers that were all genotyped at birth. Each heifer had 50 gEBV and up to 62 phenotypic variables that became gradually available over time. Stepwise variable selection on 70% of the data was used to create multiple regression models to predict survival with data available at 5 decision moments: distinct points in the life of a heifer at which new phenotypic information becomes available. The remaining 30% of the data were kept apart to investigate predictive performance of the models on independent data. A combination of gEBV and phenotypic variables always resulted in the model with the highest Akaike information criterion value. The gEBV selected were longevity, feet and leg score, exterior score, udder score, and udder health score. Phenotypic variables on fertility, age at first calving, and milk quantity were important once available. It was impossible to predict individual survival accurately, but the mean predicted probability of survival of the surviving heifers was always higher than the mean predicted probability of the nonsurviving group (difference ranged from 0.014 to 0.028). The model obtained 2.0 to 3.0% more surviving heifers when the highest scoring 50% of heifers were selected compared with randomly selected heifers. Combining phenotypic information and gEBV always resulted in the highest scoring models for the prediction of survival, and especially improved early predictive performance. By selecting the heifers with the highest predicted probability of survival, increased survival could be realized at the population level in practice.

    Influence of larval density and dietary nutrient concentration on performance, body protein, and fat contents of black soldier fly larvae (Hermetia illucens)
    Barragan-Fonseca, Karol B. ; Dicke, Marcel ; Loon, Joop J.A. van - \ 2018
    Entomologia Experimentalis et Applicata 166 (2018)9. - ISSN 0013-8703 - p. 761 - 770.
    detritivory - diet quality - Diptera - growth - nutritional value - ration - Stratiomyidae - survival

    Performance and body composition of insect larvae depend on quality and quantity of their diet, and on biotic factors such as larval density. We investigated the effect of dietary nutrient concentration and larval rearing density on survival, development, growth, and protein and fat contents of larvae of the black soldier fly (BSF), Hermetia illucens L. (Diptera: Stratiomyidae). Neonate larvae were fed with a low (NC1), intermediate (NC2), or high nutrient concentration (NC3), and with four rearing densities (50, 100, 200, or 400 larvae per container). Two feeding regimes (FR) were tested: in FR1, the amount of diet added during the experiment was based on the visually estimated larval mass present, whereas in FR2, a fixed feeding ration of 0.6 g of food per larva was applied at the start. FR1 resulted in food limitation, resulting in significantly lower body crude protein content on diet NC1 than on NC2 at larval densities 100 and 200. Larval crude fat content was higher on diets with higher nutrient concentration and at lower larval densities. For FR2, development time was shorter on diets with higher nutrient concentration and at lower larval densities. Individual larval weight and total larval yield increased with higher nutrient concentration at all four larval densities. At lower nutrient concentration, higher larval density resulted in higher individual larval weight and total larval yield, revealing an interaction between larval density and dietary quality. Larval crude protein content was higher at lower densities and lower nutrient concentration. Larval crude fat was higher at higher larval densities and nutrient concentrations. This study indicates that larval protein content is regulated within narrow limits, whereas larval crude fat content is strongly affected by nutrient concentration and by larval density.

    Genetic improvement of longevity in dairy cows
    Pelt, Mathijs van - \ 2017
    Wageningen University. Promotor(en): Roel Veerkamp, co-promotor(en): T.H.E. Meuwissen. - Wageningen : Wageningen University - ISBN 9789463430821 - 188
    dairy cows - longevity - genetic improvement - breeding value - genetic analysis - survival - animal models - animal genetics - melkkoeien - gebruiksduur - genetische verbetering - fokwaarde - genetische analyse - overleving - diermodellen - diergenetica

    Improving longevity helps to increase the profit of the farmer, and it is seen as an important measure of improved animal welfare and sustainability of the sector. Breeding values for longevity have been published since in 1999 in the Netherlands. For AI-companies and farmers it is necessary that breeding values are accurately estimated and will remain stable for the rest of life. However, current breeding values for longevity of bulls seem to fluctuate more than expected. The main aim of this thesis was to revisit the genetics of longevity and develop a genetic evaluation model for longevity, where breeding values reflect the true breeding value quicker during early life and therefore breeding values become more stable. Genetic parameters were estimated for survival up to 72 months after first calving with a random regression model (RRM). Survival rates were higher in early life than later in life (99 vs. 95%). Survival was genetically not the same trait across the entire lifespan, because genetic correlations differ from unity between different time intervals, especially when intervals were further apart. Survival in the first year after first calving was investigated more in depth. Survival of heifers has improved considerably in the past 25 years, initially due to the focus on a high milk production. More recently, the importance of a high milk production for survival has been reduced. Therefore functional survival was defined as survival adjusted for within-herd production level. For survival the optimum age at first calving was around 24 months, whereas for functional survival calving before 24 months resulted in a higher survival. Over years, genetic correlations between survival in different 5-yr intervals were below unity, whereas for functional survival genetic correlations did not indicate that survival changed over years. This suggested that a genetic evaluation using historical data should analyze functional survival rather than survival. A new genetic evaluation system for longevity was developed based on a RRM analyzing functional survival. Based on the correlation between the first breeding value of a bull and his later breeding values, the ranking of bulls was shown to be more stable for RRM than the current genetic evaluation. Bias in breeding value was observed, mainly for bulls with a large proportion of living daughters. Adjusting for within-herd production level reduced this bias in the breeding values greatly. Before implementing this new model for genetic evaluation, the cause of this bias needs to be further investigated.

    Data from: Plant quantity affects development and survival of a gregarious insect herbivore and its endoparasitoid wasp
    Fei, Minghui ; Gols, R. ; Zhu, F. ; Harvey, Jeffrey A. - \ 2016
    Wageningen University & Research
    development - group-living - herbivore - mortality - parasitiod - phenology - starvation - survival
    Data for the paper of plant quantity represents a greater constraint than quality for a gregarious insect herbivore and its endoparasitoid wasp
    Genetic changes of survival traits over the past 25 yr in Dutch dairy cattle
    Pelt, M.L. van; Ducrocq, V. ; Jong, G. de; Calus, M.P.L. ; Veerkamp, R.F. - \ 2016
    Journal of Dairy Science 99 (2016)12. - ISSN 0022-0302 - p. 9810 - 9819.
    genetic correlation - longevity - survival

    Genetic correlations and heritabilities for survival were investigated over a period of 25 yr to evaluate if survival in first lactation has become a different trait and if this is affected by adjusting for production level. Survival after first calving until 12 mo after calving (surv_12mo) and survival of first lactation (surv_1st_lac) were analyzed in Dutch black-and-white cows. The data set contained 1,108,745 animals for surv_12mo and 1,062,276 animals for surv_1st_lac, with first calving between 1989 and 2013. The trait survival as recorded over 25 yr was split in five 5-yr intervals to enable a multitrait analysis. Bivariate models using subsets of the full data set and multitrait and autoregressive models using the full data set were used. Survival and functional survival were analyzed. Functional survival was defined as survival adjusted for within-herd production level for 305-d yield of combined kilograms of fat and protein. Mean survival increased over time, whereas genetic variances and heritability decreased. Bivariate models yielded large standard errors on genetic correlations due to poor connectedness between the extreme 5-yr intervals. The more parsimonious models using the full data set gave nonunity genetic correlations. Genetic correlations for survival were below 0.90 between intervals separated by 1 or more 5-yr intervals. Genetic correlations for functional survival did not indicate that definition of survival changed (≥0.90). The difference in genetic correlations between survival and functional survival is likely explained by lower emphasis of dairy farmers on culling in first lactation for low yield in more recent years. This suggests that genetic evaluation for longevity using historical data should analyze functional survival rather than survival.

    Demographic Changes Underpinning the Population Decline of Starlings Sturnus vulgaris in the Netherlands
    Versluijs, Martijn ; Turnhout, Chris A.M. van; Kleijn, David ; Jeugd, Henk P. van der - \ 2016
    Ardea 104 (2016)2. - ISSN 0373-2266 - p. 153 - 165.
    LTRE - mark-recovery - population matrix model - reproduction - survival

    Declines in farmland bird populations are often linked to changes in agricultural practices, but little is known about the demographic changes underlying these adverse trends. Identifying the demographic drivers of population change is critical for understanding why populations are declining. In this study we assessed the demographic changes in the declining Dutch Starling Sturnus vulgaris population. We estimated productivity per breeding attempt and survival rates over a period of 52 years (1960-2012). The results show that juvenile survival decreased significantly over time. Adult survival fluctuated between years, with (non-significant) lower survival rates between 1990 and 2012. No trend in reproductive output was found over the study period. A population model was built for three different phases of population change within the study period: 1960-1978, 1978-1990 and 1990-2012. The contribution of changes in demographic parameters to population growth rate (lambda) between the different periods was examined by performing a life table response experiment (LTRE). The LTRE analysis showed that changes in juvenile survival explained most of the differences in population growth rate between periods. Our results therefore suggest that a decline in juvenile survival rather than changes in adult survival or reproductive success is the most important cause of the decline of the Starling population in The Netherlands.

    Post-release effects on reintroduced populations of hihi
    Panfylova, Julia ; Bemelmans, Ellis ; Devine, Chris ; Frost, Peter ; Armstrong, Doug - \ 2016
    Journal of Wildlife Management 80 (2016)6. - ISSN 0022-541X - p. 970 - 977.
    capture-mark-recapture - hihi - MARK - New Zealand - Notiomystis cincta - post-release effects - reintroduction - survival

    Modeling survival of reintroduced populations is critical for understanding population dynamics and therefore making appropriate management decisions. We analyzed survival data collected over the first 2 years after a reintroduction of hihi (Notiomystis cincta), an endangered New Zealand forest bird, to Bushy Park, a conservation reserve in New Zealand enclosed by a predator-exclusion fence. We constructed a set of candidate models representing different hypotheses about the effects of age, sex, and post-release acclimation on survival, and used model averaging to obtain parameter estimates reflecting the relative support for the models. In combination with fecundity data, we constructed a stochastic population model incorporating uncertainty in parameter estimation, and used this to project population dynamics over the next 10 years. The survival analysis indicated that female survival was unusually low over a 6-month acclimation period; hence, this initial low survival was not reflected in the estimates of long-term survival obtained through model averaging. The resulting projections showed that although population growth was highly uncertain, there was a negligible probability of extinction over the next 10 years, therefore indicating that the existing management regime (i.e., supplementary feeding and nest box maintenance) should be continued. In contrast, if post-release effects had not been accounted for, the projections would have shown a high probability of decline under this management regime.

    Changes in the genetic level and the effects of age at first calving and milk production on survival during the first lactation over the last 25 years
    Pelt, M.L. van; Jong, G. de; Veerkamp, R.F. - \ 2016
    Animal 10 (2016)12. - ISSN 1751-7311 - p. 2043 - 2050.
    age at first calving - dairy cattle - longevity - survival - within-herd production level

    Survival during the first year after first calving was investigated over the last 25 years, 1989–2013, as well as how the association of survival with season of calving, age at first calving (AFC) and within-herd production level has changed over that period. The data set contained 1 108 745 Dutch black-and-white cows in 2185 herds. Linear models were used to estimate (1) effect of year and season and their interaction and (2) effect of AFC, within-herd production level, and 5-year intervals and their two-way interactions, and the genetic trend. All models contained AFC and percentage of Holstein Friesian as a fixed effect, and herd-year-season, sire and maternal grandsire as random effects. Survival and functional survival were analysed. Functional survival was defined as survival adjusted for within-herd production level. Survival rate increased by 8% up to 92% in the last 25 years. When accounting for pedigree, survival showed no improvement up to 1999, but improved since then. Genetically, survival increased 3% to 4% but functional survival did not increase over the 25 years. We found an interesting difference between the genetic trends for survival and functional survival for bulls born between 1985 and 1999, where the trend for survival was still increasing, but was negative for functional survival. Since 1999, genetic trend picked up again for both survival and functional survival. AFC, season of calving and within-herd production level affected survival. Survival rate decreased 0.6%/month for survival and 1.5% for functional survival between AFC of 24 and 32 months. Calving in summer resulted in 2.0% higher survival than calving in winter. Within herd, low-producing cows had a lower survival rate than high-producing cows. However, these effects became less important during the recent years. Based on survival optimum AFC is around 24 months, but based on functional survival it is better to have an AFC

    Overleving van discard platvis: vaststellen en verhogen
    Marlen, B. van; Molenaar, P. ; Reijden, K.J. van der; Goudswaard, P.C. ; Bol, R.A. ; Glorius, S.T. ; Theunynck, R. ; Uhlmann, S.S. - \ 2016
    IMARES (Rapport / IMARES C180/15) - 116
    pleuronectiformes - overleving - discards - zeevisserij - visserijbeheer - nederland - pleuronectiformes - survival - discards - marine fisheries - fishery management - netherlands
    Consequences of discard survival under the landing obligation : Reporting validation and reprocessing project outcomes of "demersal discard processing"
    Verkempynck, R. ; Machiels, M.A.M. - \ 2015
    IJmuiden : IMARES (Report / IMARES C176/15) - 16
    discards - bycatch - demersal fisheries - demersal fishes - survival - solea - plaice - discards - bijvangst - demersale visserij - demersale vissen - overleving - solea - schol
    This report describes the results of a short and medium term forecast over the period 2016-2019 given different scenarios of discard survival rates (10-50%) of North Sea plaice and North Sea sole. Additionally, average value of landings over the year 2019 is calculated per scenario using the landings derived from the biomass and the average price per kg of both stocks. Potential loss in average gross revenue from value of landings can be inferred from these.
    Hartpillen maken gezond eten niet overbodig
    Ramaker, R. ; Sijtsma, F.P.C. - \ 2015
    Resource: weekblad voor Wageningen UR 10 (2015)7. - ISSN 1874-3625 - p. 9 - 9.
    hartziekten - patiënten - gezondheidsvoedsel - dieetadvisering - voeding en gezondheid - overleving - heart diseases - patients - health foods - diet counseling - nutrition and health - survival
    Hartpatiënten hebben een kleinere kans te overlijden naarmate ze gezonder eten, zelfs als ze de beste medicijnencocktail krijgen. Dat stelt Femke Sijtsma in haar proefschrift. Deze uitkomsten laten volgens Sijtsma zien dat gezonde voeding een verschil blijft maken, ook naast de beste zorg met bijvoorbeeld bloeddrukverlagers, cholesterolverlagers en antistollingsmiddelen.
    Quantifying strain variability in modeling growth of Listeria monocytogenes
    Aryani, D. ; Besten, H.M.W. den; Hazeleger, W.C. ; Zwietering, M.H. - \ 2015
    International Journal of Food Microbiology 208 (2015). - ISSN 0168-1605 - p. 19 - 29.
    lactic-acid concentration - minimal water activity - bacillus-cereus - escherichia-coli - microbial-growth - lag time - temperature - ph - fermentation - survival
    Prediction of microbial growth kinetics can differ from the actual behavior of the target microorganisms. In the present study, the impact of strain variability on maximum specific growth rate (µmax) (h- 1) was quantified using twenty Listeria monocytogenes strains. The µmax was determined as function of four different variables, namely pH, water activity (aw)/NaCl concentration [NaCl], undissociated lactic acid concentration ([HA]), and temperature (T). The strain variability was compared to biological and experimental variabilities to determine their importance. The experiment was done in duplicate at the same time to quantify experimental variability and reproduced at least twice on different experimental days to quantify biological (reproduction) variability. For all variables, experimental variability was clearly lower than biological variability and strain variability; and remarkably, biological variability was similar to strain variability. Strain variability in cardinal growth parameters, namely pHmin, [NaCl]max, [HA]max, and Tmin was further investigated by fitting secondary growth models to the µmax data, including a modified secondary pH model. The fitting results showed that L. monocytogenes had an average pHmin of 4.5 (5–95% prediction interval (PI) 4.4–4.7), [NaCl]max of 2.0 mM (PI 1.8–2.1), [HA]max of 5.1 mM (PI 4.2–5.9), and Tmin of - 2.2 °C (PI (- 3.3)–(- 1.1)). The strain variability in cardinal growth parameters was benchmarked to available literature data, showing that the effect of strain variability explained around 1/3 or less of the variability found in literature. The cardinal growth parameters and their prediction intervals were used as input to illustrate the effect of strain variability on the growth of L. monocytogenes in food products with various characteristics, resulting in 2–4 log CFU/ml(g) difference in growth prediction between the most and least robust strains, depending on the type of food product. This underlined the importance to obtain quantitative knowledge on variability factors to realistically predict the microbial growth kinetics. Keywords: Quantitative microbiology; Growth parameters; Heterogeneity; Pathogen
    Genetic and Non-Genetic Inheritance of Natural Antibodies Binding Keyhole Limpet Hemocyanin in a Purebred Layer Chicken Line
    Berghof, T.V.L. ; Klein, S.A.S. van der; Arts, J.A.J. ; Parmentier, H.K. ; Poel, J.J. van der; Bovenhuis, H. - \ 2015
    PLoS ONE 10 (2015)6. - ISSN 1932-6203 - 13 p.
    laying hens - immune-responses - parameters - iga - survival - isotypes - associations - sensitivity - disease - cells
    Natural antibodies (NAb) are defined as antibodies present in individuals without known antigenic challenge. Levels of NAb binding keyhole limpet hemocyanin (KLH) in chickens were earlier shown to be heritable, and to be associated with survival. Selective breeding may thus provide a strategy to improve natural disease resistance. We phenotyped 3,689 white purebred laying chickens for KLH binding NAb of different isotypes around 16 weeks of age. Heritabilities of 0.12 for the titers of total antibodies (IgT), 0.14 for IgM, 0.10 for IgA, and 0.07 for IgG were estimated. We also estimated high, positive genetic, and moderate to high, positive phenotypic correlations of IgT, IgM, IgA, and IgG, suggesting that selective breeding for NAb can be done on all antibody isotypes simultaneously. In addition, a relatively substantial non-genetic maternal environmental effect of 0.06 was detected for IgM, which may reflect a transgenerational effect. This suggests that not only the genes of the mother, but also the maternal environment affects the immune system of the offspring. Breaking strength and early eggshell whiteness of the mother’s eggs were predictive for IgM levels in the offspring, and partly explained the observed maternal environmental effects. The present results confirm that NAb are heritable, however maternal effects should be taken into account.
    With the Help of Kin? Household Composition and Reproduction in The Netherlands, 1842-1920
    Rotering, P.P.P. ; Bras, H. - \ 2015
    Human Nature-An Interdisciplinary Biosocial Perspective 26 (2015)1. - ISSN 1045-6767 - p. 102 - 121.
    dutch fertility transition - demographic-transition - birth intervals - reproductive-behavior - historical krummhorn - genetical evolution - child-mortality - netherlands - survival - success
    Relatives play an important role in human reproduction according to evolutionary theories of reproductive behavior, but previous empirical studies show large differences in the effects of kin on fertility outcomes. In our paper we examine the effect of co-resident kin and non-kin on the length of birth intervals over the reproductive life course of Dutch women born between 1842 and 1920. We estimate Cox proportional hazard models for parity progression based on the presence of kin and non-kin in the household while controlling for a large number of individual and community-level characteristics. We find that couples living with their brothers experienced shorter birth intervals whereas couples residing with a widowed father had relatively longer birth intervals. The effects of these types of kin on reproduction were most pronounced up to the birth of the fifth child, but not thereafter. We found no effect for mothers or other types of kin.
    First clinical results of a personalized immunotherapeutic vaccine against recurrent, incompletely resected, treatment-resistant glioblastoma multiforme (GBM) tumors, based on combined all- and auto-immune tumor reactivity
    Schijns, V.E.J.C. ; Pretto, C. ; Devillers, L. ; Pierre, D. ; Hofman, F.M. ; Chen, T.C. ; Mespouille, P. ; Hantos, P. ; Glorieux, P. ; Bota, D.A. ; Stathopolous, A. - \ 2015
    Vaccine 33 (2015)23. - ISSN 0264-410X - p. 2690 - 2696.
    colony-stimulating factor - survival - melanoma - cells - cyclophosphamide - adjuvant - immunity - glioma
    Glioblastoma multiforme (GBM) patients have a poor prognosis. After tumor recurrence statistics suggestan imminent death within 1–4.5 months. Supportive preclinical data, from a rat model, provided therational for a prototype clinical vaccine preparation, named Gliovac (or ERC 1671) composed of autologousantigens, derived from the patient’s surgically removed tumor tissue, which is administered together withallogeneic antigens from glioma tissue resected from other GBM patients. We now report the first resultsof the Gliovac treatment for treatment-resistant GBM patients.Nine (9) recurrent GBM patients, after standard of care treatment, including surgery radio- andchemotherapy temozolomide, and for US patients, also bevacizumab (AvastinTM), were treated under acompassionate use/hospital exemption protocol. Gliovac was given intradermally, together with humanGM-CSF (Leukine®), and preceded by a regimen of regulatory T cell-depleting, low-dose cyclophos-phamide.Gliovac administration in patients that have failed standard of care therapies showed minimal toxicityand enhanced overall survival (OS). Six-month (26 weeks) survival for the nine Gliovac patients was 100%versus 33% in control group. At week 40, the published overall survival was 10% if recurrent, reoperatedpatients were not treated. In the Gliovac treated group, the survival at 40 weeks was 77%. Our datasuggest that Gliovac has low toxicity and a promising efficacy. A phase II trial has recently been initiatedin recurrent, bevacizumab naïve GBM patients (NCT01903330).
    Indirect interactions among tropical tree species through shared rodent seed predators: a novel mechanism of tree species coexistence
    Garzon-Lopez, C.X. ; Ballesteros-Mejia, L. ; Ordonez, A. ; Bohlman, S.A. ; Olff, H. ; Jansen, P.A. - \ 2015
    Ecology Letters 18 (2015)8. - ISSN 1461-023X - p. 752 - 760.
    rain-forest tree - apparent competition - density-dependence - spatial autocorrelation - plant recruitment - dispersal - palm - herbivores - diversity - survival
    The coexistence of numerous tree species in tropical forests is commonly explained by negative dependence of recruitment on the conspecific seed and tree density due to specialist natural enemies that attack seeds and seedlings (‘Janzen–Connell’ effects). Less known is whether guilds of shared seed predators can induce a negative dependence of recruitment on the density of different species of the same plant functional group. We studied 54 plots in tropical forest on Barro Colorado Island, Panama, with contrasting mature tree densities of three coexisting large seeded tree species with shared seed predators. Levels of seed predation were far better explained by incorporating seed densities of all three focal species than by conspecific seed density alone. Both positive and negative density dependencies were observed for different species combinations. Thus, indirect interactions via shared seed predators can either promote or reduce the coexistence of different plant functional groups in tropical forest.
    Evaluation of the Dutch Eel Management Plan 2015: status of the eel population in the periods 2005 - 2007, 2008 - 2010 and 2011 - 2013
    Wolfshaar, K.E. van de; Tien, N.S.H. ; Griffioen, A.B. ; Winter, H.V. ; Graaf, M. de - \ 2015
    IJmuiden : IMARES Wageningen UR (Report / IMARES Wageningen UR C078/15) - 104
    european eels - palingen - visserijbeheer - nederland - visbestand - overleving - visvangsten - ecologisch herstel - eu regelingen - anguillidae - european eels - eels - fishery management - netherlands - fishery resources - survival - fish catches - ecological restoration - eu regulations - anguillidae
    Evaluatie van het Nederlandse aalbeheerplan: maatregelen hebben in eerste instantie geleid tot een substantiële verbetering van de overleving tussen de perioden 2005-2007 en 2008-2010 gevolgd door een bescheiden verbetering in overleving tussen de perioden 2008-2010 en 2011-2013; positieve effecten op de aalpopulatie kunnen pas na vele jaren zichtbaar worden en blijven onzeker, omdat de aal pas na vele jaren terug zwemt naar zee om zich voort te planten en omdat niet goed bekend is welke de oorzaken zijn van de achteruitgang in de aalpopulatie.
    High natural antibody titers of indigenous chickens are related with increased hazard in confinement
    Wondmeneh, E. ; Arendonk, J.A.M. van; Waaij, E.H. van der; Ducro, B.J. ; Parmentier, H.K. - \ 2015
    Poultry Science 94 (2015)7. - ISSN 0032-5791 - p. 1493 - 1498.
    laying hens - responses - survival - immunity - corticosterone - population - strains - stress - innate - plasma
    Natural antibody (NAb) levels and survival rates were evaluated in 4 breeds of laying hens in Ethiopia: indigenous, improved indigenous, exotic layer, and crossbred. Titers of NAb isotypes IgG and IgM binding keyhole limpet hemocyanin (KLH) in serum were measured at 20, 26, 35, and 45 wk age. Repeated-measure ANOVA showed that IgG and IgM levels vary with time within each breed (P <0.05). Indigenous chickens had significantly (P <0.05) higher NAb levels at all ages. The Cox proportional hazard analysis showed increased hazard with increased levels of NAbs in the exotic layers (P <0.05). However, the reduced hazards with increased levels of NAbs were not significant in the improved indigenous and crossbred chickens. Indigenous chickens showed increased hazard with increasing levels of NAb (P > 0.05). We concluded that not only the NAb levels but also the effect of Nabs on survival vary between indigenous and improved breeds. The results indicate that NAb levels are associated with survival in elite (improved) breeds, but are associated with increased hazard in indigenous chickens.
    Extending the moral economy beyond households: Gendered livelihood strategies of single migrant women in Accra, Ghana
    Tufuor, T. ; Niehof, A. ; Sato, C. ; Horst, H.M. van der - \ 2015
    Women's Studies International Forum 50 (2015). - ISSN 0277-5395 - p. 20 - 29.
    institutions - migration - survival - poverty - porters
    This article highlights how single migrant women (SMW) from rural northern Ghana generate livelihoods through the adoption of both market and non-market based strategies by extending and then prioritising moral obligations to community members beyond their immediate households instead of focusing on maximisation of profits. The setting is the Old Fadama market in Accra, Ghana. Communities of old and new SMW build a “moral community economy” through, amongst others, engaging in reciprocal labour, gift giving, childcare and food sharing. Our study reveals the importance of this moral community economy to SMW's livelihood generation and how it is sustained through social relations amongst women, in which also generation, ethnicity and regional background, play crucial roles. SMW give support to and receive benefits from the community through moral obligations and ethnic commitment. The analysis of these strategies contributes to the understanding of the intersections of household, livelihood strategies, gender and markets in urban settings.
    Genetic relations between natural antibodies binding keyhole limpet hemocyanin and production traits in a purebred layer chicken line
    Klein, S.A.S. van der; Berghof, T.V.L. ; Arts, J.A.J. ; Parmentier, H.K. ; Poel, J.J. van der; Bovenhuis, H. - \ 2015
    Poultry Science 94 (2015)5. - ISSN 0032-5791 - p. 875 - 882.
    red-blood-cells - sheep erythrocytes - laying hens - immune-response - selection experiments - parameters - survival - isotypes - responsiveness - sensitivity
    Natural antibodies (NAb) are an important component of the first line of immune defense. Selective breeding for enhanced NAb levels in chickens may improve general disease resistance. It is unknown what the consequences of selection for NAb will be on the productive performance of laying hens. In this paper we describe the genetic relations between NAb titers binding keyhole limpet hemocyanin at 19 wk age and production traits in a white purebred leghorn chicken line observed in several time periods. A linear animal model was used to estimate (co)variance components, heritabilities, and correlations. Negative genetic correlations were found between egg weight and NAb titers, and between egg breaking strength and NAb titers. Positive genetic correlations were found between the feed conversion ratio (consumed feed/egg mass produced) and NAb titers, and egg production and NAb titers. Negative phenotypic correlations were found between body weight and NAb titers, between egg weight and NAb titers, and between egg breaking strength and NAb titers. Positive phenotypic correlations were found between egg production and NAb titers, and feed conversion ratio and NAb titers. In general, phenotypic correlations were more often significant, but less pronounced than genetic correlations. Other production traits were not found to be significant related to NAb titers. These findings suggest that there is a genetic tradeoff between levels of immunity and some production traits, although the underlying mechanism(s) remain(s) unclear. The results suggest possible consequences for production efficiency as a result of selective breeding for improved general disease resistance by natural antibodies.
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