Browsing by Subject "Rabbit"

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Determination of Laterality in the Rabbit Embryo: Studies on Ciliation and Asymmetric Signal Transfer
(2007) Feistel, Kerstin; Blum, Martin
The midline of the vertebrate embryo plays a pivotal role in the regulation of left-right (LR) asymmetry. In mammals recent interest has focused on a structure situated at the caudal part of the notochord, the posterior notochord (PNC), which is homologous to Kupffer?s vesicle (KV) in fish and the gastrocoel roof plate (GRP) in frog. Despite highly diverging embryonic architecture, the PNC/KV/GRP is the site where motile monocilia set up a directional fluid flow, an event indispensable for the generation of LR asymmetry. Signals created at the PNC/KV/GRP need to be transferred to the periphery of the embryo, where they initiate the left-specifying program in the left lateral plate mesoderm (LPM). In this study morphogenesis and ciliogenesis of the notochordal plate as well as the signaling processes between midline and LPM were studied in the rabbit embryo. Rabbit development progresses through a flat blastodisc phase and represents the typical mode of mammalian embryogenesis. Transcription of ciliary marker genes, the first sign of beginning ciliogenesis, initiated in Hensen?s node and persisted in the nascent notochord. Cilia emerged on cells leaving Hensen?s node anteriorly to form the notochordal plate. Cilia lengthened to about 5µm and polarized from an initially central position to the posterior pole of cells. Electron microscopic analysis revealed 9+0 and 9+2 cilia and a novel 9+4 axoneme intermingled in a salt-and-pepper-like fashion. These data showed that the ciliogenic gene program essential for laterality determination is conserved at the midline of the rabbit embryo. The present study also provided evidence that initiation as well as repression of the Nodal cascade crucially depended on communication between midline and lateral plate (LP). Separation of LP tissue from the midline before, during and after the 2 somite stage demonstrated that signals from the PNC induced and maintained the competence of LPM to express Nodal. Signals from the midline were necessary after the 2 somite stage to maintain a right-sided identity, i.e. absence of Nodal expression. Gap-junction-dependent intercellular communication (GJC) was shown to play a central role in this process. Previously, GJC had been involved in LR axis determination in cleavage stage frog embryos and early blastodisc stages in chick. This study for the first time demonstrates the role of GJC in mammalian embryos. GJs regulate the signaling between midline and periphery: permeable gap junctions were required specifically at the 2 somite stage to repress Nodal induction in the right LPM, whereas closed GJs were a prerequisite for Nodal signaling on the left side. Establishment of the right-sided fate depended on FGF8, the signaling of which was regulated by the opening status of GJs. A 3-step model is proposed for symmetry breakage and induction of the LR signaling cascade in vertebrates: (1) Nodal protein synthesized at the lateral edges of the PNC diffuses bilaterally and confers competence for the induction of the Nodal cascade to the LPM, (2) at the same time the left-specific cascade is actively repressed by action of the GJC/FGF8 module, and (3) following the onset of leftward flow at the PNC repression gets released specifically on the left side at the 2 somite stage, presumably by transient inhibition of GJC. This model not only is consistent with the presented data, but also with published work in other model organisms.
Establishment of a new in vitro culture system and functional analysis of sonic hedgehog and FGF8 in the determination of laterality in the rabbit embryo
(2008) Bitzer, Eva; Blum, Martin
Cilia-driven leftward flow plays a pivotal role in the determination of left-right (LR) asymmetry. In mammals, this extracellular fluid flow is produced by motile monocilia situated on the posterior notochordal plate (PNC). The PNC is homologous to superficial mesoderm derived structures of other species like the gastrocoel roof plate (GRP) in frog and Kupffer's vesicle (KV) in fish. Directional fluid flow created at these structures subsequently leads to the initiation of the left-specifying Nodal signalling cascade in the left lateral plate (LPM). The rabbit develops via a flat blastodisc phase representing the archetypical mode of mammalian embryogenesis. These specific advantages of the rabbit were employed in this study to further examine the role of two central determinants of laterality, namely Sonic hedgehog (Shh) and FGF8, and also extended by the design of a new in vitro culture technique. In this new method, the so-called ring culture, a medium-filled plastic ring was placed upon the extraembryonic tissue of the explanted embryo. In contrast to the semi-dry standard culture method, this setting corresponded more to the in vivo conditions of gastrulating/neurulating rabbit embryos in the uterus. It therefore facilitated stable development of laterality in most cases also when presomite stages were taken into culture. Subsequent analysis showed that this was due to improved development of the PNC. Conversely, in standard-cultured embryos showing altered LR marker gene expression, maturation of the PNC was impaired leading to a disturbance of leftward flow. This study also provided evidence that cilia-driven leftward flow is indispensable for the determination of laterality in rabbit embryos. When the flow was blocked during culture by methylcellulose-containing medium embryos displayed altered LR marker gene expression in a very high proportion. The unilateral gain-of-function of Shh revealed important differences between rabbit and chick embryos. In rabbit, Shh induced right-sided marker gene expression only in the 2 somite stage, whereas in chick this inductive effect lasted from stage 4 until up to the 1-2 somite stage. This indicated that in rabbit Shh works in conjunction with the flow, which has not been described up to now in chick. The systemic inhibition of Shh signalling by cyclopamine led to bilateral expression of LR marker genes in rabbit. This was due to disruption of the floor plate and therefore the loss of the restrictive midline barrier function of Lefty expression as described in Shh mutant mice. FGF8 has a right-sided repressive function in the rabbit implicated in the transfer of laterality cues. In the present study it could be shown that this repressive effect is epistatic to cilia-driven leftward flow, because it also functioned when the flow was blocked. The systemic inhibition of FGF8 signalling with SU5402 caused loss of LR marker gene expression prior to the 2 somite stage but did not influence ciliogenesis or the setup of cilia-driven leftward flow. Taken together, this suggested a dual function for FGF8 signalling: First, it is needed to confer competence to the lateral plate and second, during the 2 somite stage, it is needed for the transfer of LR cues.
Ethologische und klinische Untersuchungen zur Käfig- und Bodenhaltung bei Mastkaninchen
(2010) Toplak, Andrej; Reiter, Klaus
The aim of this project was to evaluate the effect of different rearing systems on the basis of ethological and clinical parameters in young domestic rabbits kept for meat production. Newly developed pen housing was compared with the conventional cage-rearing. Four experiments were performed between June 2005 and July 2006 with total 1349 animals. ZIKA-hybrid rabbits were assigned into different rearing systems after weaning. The fattening period lasted eight weeks. In the cages the group size was four animals (8.3 animals/m2) and in pens 24 animals (7.8 animals/m2). In experiment A the conventional cage rearing was compared with the pen rearing on plastic perforated floor and with pen rearing with straw litter. The effect of the elevated ledges was analysed in experiment B. The influence of straw as enrichment was studied in experiment C. The possibility of separated fattening of male and female growing rabbits was tested in the experiment D. The housing had a significant effect on some important behavioural traits of the animals. The frequencies of locomotion in pens were compared with cages significantly higher. This could be due to the restricted possibility of movement in the conventional cages compared to the pens. The intensive locomotion was performed very seldom and less markedly in the cages, very likely due to the lack of space. As opposed to that, the intensive multiple hops could be observed very frequently in the pens. In the cages only modified single hops could be performed. The elevated slates had no significant effect on the frequency of locomotion. In the cages with elevated slates the frequencies of locomotion were still significantly lower compared to the pens. The results obtained by peripheral computed tomography confirmed the behavioural observations of locomotory frequences. The pQCT-parameters were higher in pen reared animals. The differences between the animals without the elevated ledges and the pen reared animals were especially significant. Particularly the strain-strength-index was bigger when it comes to the animals in the pens. The major differences were determined in the diaphysis of the analysed bones. The aggressive interactions occurred very rarely and were not intensive. The majority of aggressive interactions resulted only in minor bite wounds. By clinical examinations predominantly small scratches and small superficial bite wounds were found. No clear differences could be determined between different rearing systems. Animals can bear easily minor scratches and bite wounds without any long-term residual effects. Severe aggression and problematic wounds were observed very seldom. In experiment D the percentage of the animals with injuries was higher in pens than in cages. The percentage of the animals with lesions was especially high in the mixed groups with males and females in the experiment. In general more males than females had bite injuries. Bare cage environment may be averse to animals. The animals may be unable to adapt, and show abnormalities of behaviour. Abnormal behaviour was shown independently of the housing system. The rate of abnormal behaviour decreased in pens. However, it is also important to note that the pen-raising was not sufficient to completely prevent the development of abnormal behaviour. The frequency of the scratching and gnawing on the equipment could be significantly reduced with straw as enrichment. Only minor differences were found between the tested rearing systems regarding blood parameters. Although some of these differences were significant. Mortality did not differ between the treatments. Most of the mortality was caused by diarrhoea in the second and third week of the experiment. The daily weight gain was significantly different between the treatments in experiments A, B and C. The animals in pens with litter achieved the lowest daily weight gains. On the other hand, the daily weight gains of the animals in pens with perforated floor were comparable with the daily weight gains of the animals reared in cages. In experiment D no differences were found in this respect. In all four experiments no differences between the treatments were found in daily feed intake and feed conversion ratio. The rabbits showed only a weak interest for straw litter. This may be due to the attraction towards the cleanliness and dryness of the perforated plastic floor compared to the litter. The use of litter may also depend on the environmental temperature. Especially the pen housing on plastic perforated floor with straw in the wire container showed positive effects on the behaviour of the rabbits without reduction of performance. More studies are needed before any final conclusion about the appropriateness of the group housing in developed pens can be made. These results have to be proven in further field studies under commercial conditions.
Untersuchungen zum Einfluss eines Auslaufes in einer strukturierten Bodenhaltung auf ethologische, klinische und leistungsbezogene Parameter bei Mastkaninchen
(2014) Woodrow, Julia; Reiter, Klaus
The aim of the study was to investigate and evaluate the effect of a covered outdoor run in a structured pen housing system, on both ethological and clinical parameters as well as productive performance of growing rabbits. During this study new insights were gained into the use of the outdoor runs as well as into the optimization of the slaughter age, taking the frequency and severity of sexual and aggression based injuries as well as the productive performance of the bucks into account. 960 hybrid rabbits were used for this study over four experiments. During the first and second experiments the type of housing was primary investigated in male and female groups. In the third and fourth experiment only bucks were housed and the slaughter date was varied between 11, 12 and 13 weeks of age. Each group consisted of 24 animals, with an available space of 1275 cm2 per animal in the structured pen housing system. Rabbits with access to an outdoor run had an available area of 2317 cm2. The animals were weaned at an age of 5 weeks and assigned into the housing systems, where they remained to a maximum age of 13 weeks. The pen housing system had fully perforated plastic flooring and was structured with raised platforms, gnawing sticks and racks for straw and hay. The runs were littered. The ethological parameters collected during this study included information of the use of the outside run with RFID technique as well as the observed behaviour monitored and recorded via video cameras. The clinical parameters captured the mortality and the aggression related injuries as well as the blood tests. Additionally the productive performance was measured and the carcass traits were analysed. The experiments showed that the rabbits spent on average two hours a day in the run. 95% of the rabbits visited the run at least once during the day. The use of the outdoor run was lower during the winter months when the temperatures were lower in comparison to the spring and summer. The penned housing system with access to an outdoor run had a positive impact, as higher levels of slow movement were observed during all four experiments in this type of system. In comparison fast movements were shown rarely and there was no difference in regards to behaviour between the housing systems. When using sawdust as a litter in the run there was no significant difference in the exploratory behaviour between the two housing systems. The use of straw however had a positive impact on the occurrences of exploratory behaviour in the groups held in the pen housing system with an outside run. The frequency of sexual and aggressive behaviour resulting in injuries was significantly higher in the male rabbits in contrast to the female. There was a continual increase in the sexual and aggressive behaviour of the bucks observed between the age of 8 and 13 weeks. The mortality varied between the different experiments as well as individual groups. Over the course of all the experiments the average mortality was 9.5% for the animals held in the pen housing system and 13.0% of the animals held in the system with additional outdoor run. Over all four experiments the housing system showed no significant effect on the mortality. The percentage of injured rabbits increased from the 10th to the 13th week of age for both the males as well as the females. However at an age of 12 weeks a significantly higher number of bucks were injured in comparison to female rabbits. The percentage of heavily injured bucks increased on average over all four experiments from 0.2% at 10 weeks of age to 6.2% at 13 weeks of age. However the pen housing system with an outdoor run showed significantly lower numbers of heavy injured bucks in comparison to the groups with no access to an outdoor run at an age of 13 weeks. The productive performance did not significantly differ across all four experiments when considering the structured pen housing systems with or without an outdoor run. The daily weight gain of the male rabbits increased and peaked at the age of eight weeks where it held till ten weeks and then began to decrease again. The weight gain was the lowest and the feed conversion at its worst between 12 and 13 weeks of age. The carcass traits of the bucks were not influenced by the housing system at all three slaughtering ages. The absolute weights of the back and the hind legs did not differ significantly between 12 and 13 weeks of age. The structured pen housing system with an outdoor run has a positive effect on the welfare of the animals and is an alternative to the housing in cages. A covered outdoor run in the structured pen housing system is positive in regards to animal welfare. With an earlier slaughtering age of bucks with 12 weeks, the frequency and severity of animal welfare specific injuries were reduced whilst maintaining the same carcass quality and reducing the economic effect of lower growth performance within the last fattening week.