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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    Eikwaliteit bij welzijnskooien niet beter ondanks maatregelen
    Reuvekamp, B.F.J. ; Niekerk, Th.C.G.M. van - \ 1996
    Praktijkonderzoek voor de Pluimveehouderij 7 (1996)2. - ISSN 0924-9087 - p. 11 - 15.
    huisvesting, dieren - dierlijke producten - dierenwelzijn - batterijhuisvesting - hennen - ovipositie - kwaliteit - animal housing - animal products - animal welfare - battery husbandry - hens - oviposition - quality
    Over het algemeen zijn de legprestaties van de hennen in de welzijnskooien goed. Helaas is de eikwaliteit ronduit slecht te noemen. Door de nesten aan te passen is getracht de positie van de hennen in het legnest te beonvloeden. Dit zou tot een verbetering van de eikwaliteit moeten leiden.
    Vleeskuikenouderdieren: het gebruik van een automatisch dierweegsysteem bij het voeren naar legpercentage en groei
    Haar, J.W. van der - \ 1996
    Praktijkonderzoek voor de Pluimveehouderij 7 (1996)1. - ISSN 0924-9087 - p. 22 - 26.
    diervoedering - automatisering - weegschalen - ontwikkeling - eierproductie - groei - mechanisatie - ovipositie - weegapparaten - vleeskuikenouderdieren - animal feeding - automation - balances - development - egg production - growth - mechanization - oviposition - weighers - broiler breeders
    Bij vleeskuikenouderdieren komt een belangrijk deel van de kosten voor rekening van het voer. Om de voerkosten laag te houden moet de voergift afgestemd worden op het legpercentage en de groei van de dieren. Naast een goed inzicht in de eiproduktie moet men ook een goed inzicht hebben in de gewichtsontwikkeling van de dieren. Bij Praktijkonderzoek Pluimveehouderij (PP) is onderzocht welke rol een automatisch dierweegsysteem hierbij kan spelen.
    Legnest in batterijkooi
    Niekerk, Th.G.C.M. van - \ 1995
    Praktijkonderzoek voor de Pluimveehouderij 6 (1995)4. - ISSN 0924-9087 - p. 13 - 18.
    dierlijke producten - batterijhuisvesting - eierproducten - eieren - nesten - ovipositie - pluimveehokken - kwaliteit - animal products - battery husbandry - egg products - eggs - nests - oviposition - poultry housing - quality
    In dit artikel wordt ingegaan op het inbrengen van een legnest in een batterijkooi. De resultaten tot nu toe geven aan, dat de hennen graag gebruik maken van het nest, maar dat er nog duidelijke problemen zijn met betrekking tot de eikwaliteit.
    Vroegrijpheid bij vleeskuikenouderdieren
    Haar, J.W. van der - \ 1994
    Beekbergen : Praktijkonderzoek Pluimveehouderij (PP uitgave : praktijkonderzoek pluimveehouderij 17) - 21
    ovipositie - vleesproductie - vleeskuikens - productiviteit - rentabiliteit - dierhouderij - vleeskuikenouderdieren - oviposition - meat production - broilers - productivity - profitability - animal husbandry - broiler breeders
    Bij Praktijkonderzoek Pluimveehouderij is onderzocht of het vroeger leg- en geslachtsrijp maken van vleeskuikenouderdieren voordelen oplevert.
    Soort opfokvoer geen invloed op legresultaten
    Reuvekamp, B.F.J. - \ 1994
    Praktijkonderzoek voor de Pluimveehouderij 5 (1994)2. - ISSN 0924-9087 - p. 6 - 8.
    diervoedering - eierproductie - hennen - ovipositie - jonge dieren - animal feeding - egg production - hens - oviposition - young animals
    Gedurende de 2e ronde met leghennen onderzoeken we of het soort voer, dat verstrekt is tijdens de opfok invloed heeft op de resultaten in de legperiode. Op een kleine uitzondering na zijn er geen verschillen in legprestaties.
    Multiphasic growth in the layer pullet : effects of nutrient restrictions during rearing
    Kwakkel, R.P. - \ 1994
    Agricultural University. Promotor(en): M.W.A. Verstegen; G. Hof. - S.l. : Kwakkel - ISBN 9789054852445 - 189
    hennen - diervoedering - jonge dieren - gerantsoeneerde voeding - groei - ontwikkeling - productiviteit - rentabiliteit - dierhouderij - ovipositie - eieren - eierproducten - hens - animal feeding - young animals - restricted feeding - growth - development - productivity - profitability - animal husbandry - oviposition - eggs - egg products

    Traditionally, layer pullets are reared on a least-cost basis. Feeding regimens, that allow pullets to consume a restricted amount of nutrients, have been designed to control body growth towards a 'target' weight and age. It was questioned whether the pattern of body growth in relation to the rate of development of particular organs during rearing interferes with the productive potential of the young hen. For the present study, it was hypothesized that the supply of nutrients for some organs may be critical at certain ages, as a result of their individual growth patterns. In this thesis, growth and development of the pullet body and its constituents has been studied by means of multiphasic growth functions. It was found that body weight at end of rearing ('target weight') is less important than type (which nutrient?) and phase (what age?) of restriction in determining egg performance. Furthermore, a pronounced growth spurt in the body growth curve was distinguished at around 19 wk of age ('the maturity growth spurt'), that appeared to be related to both the development of the reproductive organs and the onset of lay. The assessment of this growth spurt in a flock may help the producer in taking nutritional decisions. A certain amount of fat-free tissue in the body is suggested to be critical for the initiation of sexual growth. Fat growth at early rearing seemed to be functionally related to growth of the fat-free body: pullets on a low-lysine diet did not increase their fat-to-protein ratio at that stage of development. Fat growth at late rearing is stored as an energy buffer (abdominal fat pad). The composition of the fat-free body was not affected by dietary treatment. It was concluded that the fatfree body of pullets is a better measure of physiological age than body weight. Effects of nutrient restrictions on growth of body constituents should be presented relative to the fat-free body. Multiphasic analyses of pullet growth quantified some growth relationships between body components which had not been revealed if a simple monophasic growth approach had been used.

    Tussentijdse resultaten leghennen
    Niekerk, Th.G.C.M. van - \ 1992
    Praktijkonderzoek voor de Pluimveehouderij 3 (1992)3. - ISSN 0924-9087 - p. 9 - 11.
    lucht - luchtverontreiniging - ammoniak - dierlijke meststoffen - emissie - voer - hennen - hygiëne - massa - voedingswaarde - ovipositie - pluimveehokken - drijfmest - vervluchtiging - gewicht - air - air pollution - ammonia - animal manures - emission - feeds - hens - hygiene - mass - nutritive value - oviposition - poultry housing - slurries - volatilization - weight
    De eerste ronde in de nieuwe batterijstal van het Praktijkonderzoek is nu halverwege. Hoewel nog niet van alle proeven evenveel resultaten bekend zijn, lijkt het toch een goed moment om de stand van zake te bekijken.
    Vergelijking etage- en batterijhuisvesting, de vierde ronde
    Hiskemuller, W.G.M. - \ 1992
    Praktijkonderzoek voor de Pluimveehouderij 3 (1992)2. - ISSN 0924-9087 - p. 13 - 15.
    huisvesting, dieren - dierhouderij - dierenwelzijn - batterijkooien - kleur - hennen - ovipositie - pluimveehokken - productiviteit - rentabiliteit - groepshuisvesting - animal housing - animal husbandry - animal welfare - battery cages - colour - hens - oviposition - poultry housing - productivity - profitability - group housing
    De vierde ronde is, voor wat de legperiode betreft, ingegaan op 17 oktober 1991. Dit is dus een tussentijds verslag tot en met week 46. Naast de vergelijking van etage- en batterijhuisvesting speelt nu ook het verschil tussen witte en bruine hennen een belangrijke rol in deze proef.
    Laatste ronde legnestenonderzoek in Delden
    Haar, J.W. van der - \ 1992
    Praktijkonderzoek voor de Pluimveehouderij 3 (1992)1. - ISSN 0924-9087 - p. 20 - 22.
    huisvesting, dieren - dierenwelzijn - hennen - nesten - ovipositie - pluimveehokken - animal housing - animal welfare - hens - nests - oviposition - poultry housing
    Op het Pluimveeteeltproefbedrijf in Delden is al meerdere jaren onderzoek verricht naar de bruikbaarheid van automatische legnesten in de vermeerderingssector. In de laatste ronde van het onderzoek in Delden werden met het Jansen nest weer de beste resultaten behaald.
    Gecontroleerd voeren bij slachtkuikenouderdieren
    Haar, J.W. van der - \ 1991
    Praktijkonderzoek voor de Pluimveehouderij 2 (1991)4. - ISSN 0924-9087 - p. 19 - 22.
    dierhouderij - dierlijke meststoffen - voedingsrantsoenen - vruchtbaarheid - bevruchting - infertiliteit - ovipositie - productiviteit - rentabiliteit - gerantsoeneerde voeding - drijfmest - vleeskuikenouderdieren - animal husbandry - animal manures - feed rations - fertility - fertilization - infertility - oviposition - productivity - profitability - restricted feeding - slurries - broiler breeders
    Bij slachtkuikenouderdieren wordt de voergift meestal vastgesteld aan de hand van het legpercentage. Door ook rekening te houden met het lichaamsgewicht kan er wellicht bespaard worden op de voerkosten.
    Invloed van legnesten op economische resultaten
    Meijerhof, R. ; Horne, P.L.M. van - \ 1991
    Praktijkonderzoek voor de Pluimveehouderij 2 (1991)4. - ISSN 0924-9087 - p. 15 - 18.
    dierhouderij - hennen - nesten - ovipositie - productiviteit - rentabiliteit - grondeieren - animal husbandry - hens - nests - oviposition - productivity - profitability - floor eggs
    In de vermeerderingssector staat het gebruik van automatische legnesten al jarenlang sterk in de belangstelling. Vooral de arbeidsbesparing, de flexibiliteit in tijdstip van werken en de verbetering van de werkomstandigheden wordt als voordeel gezien
    Een geautomatiseerd legnest kan goede resultaten geven
    Haar, J.W. van der - \ 1991
    Praktijkonderzoek voor de Pluimveehouderij 2 (1991)2. - ISSN 0924-9087 - p. 13 - 14.
    huisvesting, dieren - dierenwelzijn - eierproducten - eieren - hennen - nesten - ovipositie - pluimveehokken - animal housing - animal welfare - egg products - eggs - hens - nests - oviposition - poultry housing
    Op het Pluimveeteeltproefbedrijf in Delden wordt al meerdere jaren onderzoek verricht naar de bruikbaarheid van automatische legnesten in de vermeerderingssector. Met één type wegrolnest zijn in de laatste proef goede resultaten behaald.
    Gedragsonderzoek legnesten slachtkuikenmoederdieren
    Haar, J.W. van der - \ 1990
    Praktijkonderzoek voor de Pluimveehouderij 1 (1990)2. - ISSN 0924-9087 - p. 8 - 9.
    diergedrag - huisvesting, dieren - dierenwelzijn - kippen - nesten - ovipositie - pluimvee - pluimveehokken - vleeskuikenouderdieren - grondeieren - animal behaviour - animal housing - animal welfare - fowls - nests - oviposition - poultry - poultry housing - broiler breeders - floor eggs
    Op het Pluimveeteeltproefbedrijf in Delden wordt onderzoek uitgevoerd naar verschillende typen geautomatiseerde legnesten. De resultaten van de nesttypen zijn verschillend. Bij dit onderzoek zijn gedragswaarnemingen verricht om meer inzicht te krijgenin de oorzaken van deze verschillen.
    Waterrantsoenering bij leghennen
    Niekerk, Th. van - \ 1990
    Praktijkonderzoek voor de Pluimveehouderij 1 (1990)1. - ISSN 0924-9087 - p. 14 - 15.
    dierlijke meststoffen - drinken - drinkwater - voer - hennen - ovipositie - gerantsoeneerde voeding - drijfmest - water - animal manures - drinking - drinking water - feeds - hens - oviposition - restricted feeding - slurries - water
    Uit voorlopige resultaten blijkt, dat waterrantsoenering bij leghennen wellicht leidt tot een betere voederconversie en drogere mest, terwijl er geen nadelige invloed is op de eiproduktie.
    Legnestenonderzoek slachtkuikenouderdieren
    Meijerhof, R. - \ 1990
    Praktijkonderzoek voor de Pluimveehouderij 1 (1990)1. - ISSN 0924-9087 - p. 10 - 11.
    huisvesting, dieren - dierenwelzijn - automatisering - kippen - mechanisatie - nestelen - nesten - ovipositie - pluimvee - pluimveehokken - vleeskuikenouderdieren - animal housing - animal welfare - automation - fowls - mechanization - nesting - nests - oviposition - poultry - poultry housing - broiler breeders
    Op het Pluimveeteeltproefbedrijf in Delden wordt praktijkonderzoek uitgevoerd voor de vermeerderingssector. Het onderzoek naar verschillende verschillende typen van geautomatiseerde legnesten neemt hierbij een belangrijke plaats in.
    The development of egg-laying behaviour and nest-site selection in a strain of white laying hens
    Rietveld - Piepers, B. - \ 1987
    Agricultural University. Promotor(en): P.R. Wiepkema, co-promotor(en): E.H. Ketelaars. - Apeldoorn : Rietveld-Piepers - 141
    rassen (dieren) - kippen - uitbroeden - hennen - nesten - ovipositie - sociaal gedrag - instinct - breeds - fowls - hatching - hens - nests - oviposition - social behaviour - instinct

    Since World War II livestock husbandry has been highly intensificated. This trend was most obvious in the poultry industry. Laying hens used to be housed outdoors in free-range systems, but nowadays these systems have almost entirely been replaced by the battery-cage. In the early sixties scientists and the general public started to express much concern for the well-being of hens kept for egg-production in battery cages. In reaction to this concern for the well-being of farm animals, several research programs were started. One of them concentrated on the objective assessment of welfare. Moreover, investigations to improve existing systems and to develop alternative floor-systems were started (chapter 1). However, a problem common to all floor-systems is the reluctancy of a various percentage of hens to use the laying nests provided. This has considerable economic implications, such as loss of eggs , dirty eggs and time consuming eggcollection. Acceptation of alternatives will be promoted if such a problem is solved. The general aim of the present study was to trace factors that cause floor-laying.

    Chapter 2 reviews some literature on the physiology and the normal nesting behaviour of domestic hens. It is concluded that irregularities during, for example, the hormonal control of ovulation may easily lead to abnormalities in egg-production and nesting behaviour and thus to flooreggs, as well. In chapter 7 these parameters were used in order to find out to what extent floor-laying is caused by physiological irregularities (see below).

    Chapter 3 presents a description of the rearing and experimental housing conditions and of the hens used in this study. Furthermore, it provides a definition of the behavioural elements scored.

    In chapter 4 the development of egg-laying behaviour and nest-site choice is described in seven flocks of hens housed in small floor-pens (2 x 2 square meter). Special interest is directed towards social dominance and the effect of the presence of a cock on the hen's nest-site choice.

    In the weeks before the hens came into lay they frequently examined the nests, whereas nest-entries only occurred some days before or in the hours preceding the first oviposition. It was postulated that the early examinations serve the selection of a suitable nest-site.

    In order to study perseverence in nest-box choice, two parameters were used: a perseverence index defined as the number of the same choices on successive oviposition days divided by the total number of choices and a frequency index, defined as the number of the same choices divided by the total number of choices. Hens were judged to persevere in their choice if both measures reached values larger than 0.7.

    Only one of the 13 observed hens persevered in nest-box choice within clutches; she nearly always chose the same box on subsequent days, but started another egg-laying sequence in another nest-box. The other hens frequently changed nest-boxes. Consistency in nest-choice increased, if three boxes along one side of the pen were regarded as one nest; four of the 13 hens nearly always used the same side of the pen. Four other birds did choose the same side of the pen on successive oviposition days, but started another egg-laying sequence on the other side of the pen. One hen used nest-boxes on one side of the pen more frequently, although not on subsequent oviposition days. The remaining four hens did not show any consistency in their nest-choice behaviour. It was concluded that individual hens involved different factors in their nest-site choice.

    Furthermore, individual hens were consistent in using either the floor or a nest-box as a nesting site. No relationship was found between social status and nest-box choice, nor between social status and using the floor or a nest-box for laying. Some evidence was provided that the presence of a cock could reduce the percentage of floor-eggs in a pen provided with rollaway boxes.

    Chapter 5 presents the results of an experiment designed to investigate the effect of rearranging the sites of four different nest-boxes on the nest-examination duration in the weeks before and during the egg-laying period. Two types of examinations were distinguished: inspections and glances. Moreover, the development of inspections and glances in the weeks before laying is described and compared (experiment 1). Finally, in the first and in a second experiment the nest-examination pattern in the weeks before laying and its relationship with the final nest-choice is studied.

    In the first experiment sixteen white laying hens were placed in 8 round floor-pens (1.5 m Ø); two hens per pen. Each pen was provided with four different nest-boxes; nest-floors were covered with astroturf, wood- shavings, buckwheat husks or a wire basket. In the weeks before laying the hens were exposed to an exploration test in their home pen. During the first two weeks of the experiment the positions of the nests never changed. Subsequently the positions of the nests in four of the 8 pens were changed 3-4 times a week (=experimental group). In the other four pens nests were always in the same position (=control group). Exposing hens to an exploration test was continued in the egg-laying period.

    No differences were present in the total time spent in inspections and glances in the period before the rearrangement of the nests between control and experimental hens. However, as a result of changing the positions of the nests regularly, experimental hens spent more time in nest-inspections than did control hens. Likewise, the inspection duration increased in the experimental group if days without a change were followed by days with a change and, vice versa, decreased if days with a change were followed by days without a change. From these results it was concluded that inspections during the weeks before laying serve the acquisition of information.

    The total time spent in glancing at the nests remained unaffected by the treatment. Moreover, glances and inspections followed a different temporal pattern over time. In the course of time (in the weeks before laying) the glance duration decreased, whereas the time spent in inspections showed an increase. Apparently glances and inspections do not represent the same type of exploration. Glancing at the nests was regarded to be a passive form of exploration, which is initially elicited by a change in the environment. Nest-inspections were regarded as an active form of exploration during which information is gathered from the nests, which may be used for the final selection of a nesting-site.

    Moving the nests to new places during the laying period did not result in an increase in the inspection duration. Obviously nest-inspections during this period do not serve the same function as those during the weeks before laying. Inspections in the hours before oviposition were supposed to represent intention movements to enter a nest-box. In the hours before oviposition glances were almost never performed.

    To study the relation between nest-examinations in the weeks before laying and later nest-preference a correlation coefficient was computed between nest-preference in the weeks before and during laying. In none of the hens a significant coefficient was found. Apparently the final nestchoice could not be predicted by the amount of attention paid to the nest boxes during the period considered.

    In the second experiment the nest-examination pattern and its relation to later nest-preference is studied in five hens that had been observed until the day of first oviposition. Experimental conditions were the same as described for experiment 1, however, nest-boxes were always in the same position. The results revealed that one day before the day of first oviposition all hens showed the tendency to spent most time in inspecting the nest they preferred for the oviposition of the first series of eggs. Apparently the final nest-choice was established one day before the day of first oviposition.

    Chapter 6 presents the results of two experiments designed to reduce the percentage of floor-eggs. The effect of the properties of the nests (factor 1) and the moment the hens got access to the nests (factor 2) on the percentage of floor-eggs is investigated. Moreover, in experiment 1 the interrelationship between these two factors is examined. In both experiments the effect of the treatments are described over time. The effectiveness of a treatment was judged according to the percentage of floor-eggs laid during the whole 6-week egg-laying period and during the 6th week of the egg-laying period.

    In the first experiment twenty-four flocks of white laying hens were housed at an age of 16 weeks in small floor-pens. Two types of nests were used (litter and roll-away nests); the nests were opened at two different moments (on the day the first egg appeared in a f1ock=late, or on the day the flocks were housed in the pens = early). A main effect was present of the properties of the nests: more floor-eggs were found in pens provided with roll-away nests than in pens provided with litter nests, indicating that litter was preferred over a wire basket. Furthermore, a significant interaction was present between the two factors under study; opening rollaway boxes late resulted in fewer floor-eggs than opening these boxes early, whereas no differences were found between opening litter nests early and late. It was concluded that the extent to which early experience with nests affects the incidence of floor-laying depends upon the type of nestbox used.

    In order to reduce the percentage of floor-eggs even more as compared to opening roll-away nests late, the influence of converting litter nests into roll-away nests at about 15 and 35 % of lay on the percentage of floor-eggs was studied (experiment 2). For this purpose sixteen flocks of white laying hens were housed in floor-pens at an age of 16 weeks. In 8 pens litter nests were converted into roll-away nests at an average laying percentage of 17.7 % (group LT1) and in the remaining 8 at an average laying percentage of 38.6 % (group LT2). More floor-eggs were found in group LT1 than in group LT2 , not only if the total period after the nestchange is considered, but also during the last egg-laying week.

    A comparison of the results within and between both experiments showed that replacing the litter with a wire basket at 17.7 % of lay resulted in more floor-eggs during the 6th egg-laying week than opening roll-away nests at the start of the egg-laying period. Obviously the latter treatment did not reduce the incidence of floor-laying further. In contrast, it appeared to have a negative effect. In the week immediately following the nestchange the percentage of floor-eggs in group LT1 significantly increased. From this it was concluded that if hens have only been able to inspect nests visually in the weeks before laying, they are less likely to start using roll-away nests later on.

    Changing litter nests into roll-away nests at about 38.6 % of lay resulted in a comparable percentage of floor-eggs as opening roll-away nests late, if the 6th egg-laying week is considered. Thus the first mentioned treatment did not reduce floor-laying further as compared with opening roll-away nests late.

    Replacing the litter with a wire basket at 38.6 % of lay (LT2) resulted, as expected, in fewer floor-eggs during the 6th egg-laying week as compared with changing the nests at 17.7 % of lay (LT1). Postponing the moment of the nest-change allowed a larger number of hens to start using the litter nests. Probably these hens were trained in the use of a nest-box and continued in doing so, even after the replacement of wood-shavings with a wire basket.

    As had become evident in chapter 4, some hens always used the floor for laying, while other hens, kept under the same circumstances always used a nest-box. Chapter 7 concentrates on the question which factors may cause individual differences in site use. Two possibilities that might explain such differences are considered. First, in order to detect whether floorlaying is caused by physiological irregularities, egg-laying records of floor-and nest-layers are described and compared. The following parameters were used: daily egg-production per hen, egg-shell quality, lag duration and consistency in site use. No differences were found with respect to each of these measures between floor-and nest-layers. It was concluded that physiological irregularities are uncommon in this laying strain. Therefore this factor was not supposed to account for the differences in site use between individual hens.

    Second, to find out whether floor-and nest-layers react differently to environmental stimuli or whether floor-layers simply prefer the floor for laying, the pre-laying behaviour of five floor-and five nest-layers is described and compared. The results indicated that floor-layers performed more behaviour indicative of frustration due to the nesting situation than the nest-layers. Furthermore, floor-layers spent like nest-layers some time in inspecting and entering nest-boxes during egg-laying sessions. Therefore the results did not support the view that floor-layers simply prefer the floor for laying. It is more likely that the nesting tendency in these hens is frustrated by particular properties of the (roll-away) nests or perhaps by the inability to move away from the flock.

    In chapter 8 the development of nesting behaviour, the selection of a nest and factors that appeared to affect floor-laying are discussed in some detail. It was concluded that the selection of a nest is a process which starts in the weeks before laying. In order to reduce floor-laying it is recommended to take all factors, that affect the hen's nest-site choice, into account.

    Furthermore recommendations to reduce the percentage of floor-eggs are derived from the results obtained in this and other studies concerning nest-site choice in domestic hens and their practical significance is discussed.

    Tijdige beschikbaarstelling van legnesten: effect op leggedrag niet altijd positief
    Rietveld-Piepers, B. - \ 1984
    De Pluimveehouderij 14 (1984)45. - ISSN 0166-8250 - p. 10 - 11.
    huisvesting, dieren - dierenwelzijn - hennen - nesten - ovipositie - pluimveehokken - grondeieren - animal housing - animal welfare - hens - nests - oviposition - poultry housing - floor eggs
    In kleine koppels leghennen in grondhokken werden of legnesten met strooisel of legnesten met een (gazen) wegrolbodem geplaatst. De dieren werden op 16 weken leeftijd geplaatst in deze afdelingen. In de helft van de groepen werden de nesten direkt ter beschikking gesteld, in de andere helft werden de nesten pas open gesteld wanneer het eeste ei in de groep verscheen. In de groepen met strooiselnesten (12) werden minder grondeieren geplaatst dan in de groepen met wegrolnesten, het maakte daarbij niet uit of de nesten vroeg dan wel laat waren geopend. In de groepen met wegrolnesten werden minder grondeieren geraapt wanneer de nesten later werden geopend
    Physiological and genetical aspects of egg production in White Plymouth Rock pullets
    Middelkoop, J.H. van - \ 1974
    Landbouwhogeschool Wageningen. Promotor(en): M. van Albada. - Wageningen : Pudoc, Centre for Agricultural Publishing and Documentation - ISBN 9789022004999 - 76
    rassen (dieren) - kippen - genetische variatie - genetica - heritability - ovipositie - pluimvee - zoölogie - breeds - fowls - genetic variation - genetics - heritability - oviposition - poultry - zoology

    White Plymouth Rock pullets selected for a high 8-week bodyweight have an unsatisfactory production of hatching eggs, but this is not the only problem. In addition a great proportion of ovulated yolks are lost for the formation of normal eggs, because they are laid in abnormal eggs. In a study on the relationship between yolk production and egg formation, abnormal eggs were found to be laid when ovulation rate exceeded the limit of one ovulation per egg formation period.

    Research on the genetic background showed that laying of double-yolked eggs, of two eggs a day, and of normal eggs only is genetically controlled to a large extent. Correlations were calculated between these laying traits and 8-week bodyweight, but those estimates did not provide a conclusive answer.

    Economically, first eggs of a pair have also to be seen as abnormal, because they proved almost unhatchable.

    With the help of the sex-linked dwarfing gene dw , it was shown that a reduction of yolk production in the ovary can result in an increase in normal egg laying in hens whose ovulation rate is too high. There seems therefore to be the relationship between total yolk production and the laying of abnormal or normal eggs.

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