Rabbit Kittens Research Articles

External negative pressure improves lung aeration in near-term rabbit kittens at risk of developing respiratory distress

IntroductionAs airway liquid is cleared into lung interstitial tissue after birth, the chest wall must expand to accommodate this liquid and the incoming air. We examined the effect of applying external positive and negative pressures to the chest wall on lung aeration in near-term rabbit kittens at risk of developing respiratory distress.MethodsRabbit kittens (30 days; term ∼31 days) were randomised into Control and Elevated Liquid (EL) groups. Lung liquid was drained in Control kittens to simulate expected volumes following vaginal delivery. EL kittens had lung liquid drained before 30 ml/kg was returned to simulate expected volumes after caesarean section. Kittens were delivered, placed in a water-filled plethysmograph and the external pressure was adjusted to −6 (negative), 0 (atmospheric), or +6 (positive) cmH2O. Kittens were ventilated with an 8 ml/kg tidal volume and PEEP of 0 cmH2O and lungs imaged using phase contrast x-ray imaging.ResultsCompared to external atmospheric pressures, external negative pressures expanded the chest (by 2100 ± 43 vs. 1805 ± 59 mm2; Control kittens; P = 0.028), directed tidal ventilation into lower, larger lung regions and increased functional residual capacity (FRC) levels in both Control (26.7 ± 2.0 vs. 12.6 ± 2.2 ml/kg; P < 0.001) and EL (19.6 ± 1.6 vs. 10.0 ± 2.9 ml/kg; P < 0.01) kittens. External positive pressures reduced FRC levels in Control (6.3 ± 0.8 vs. 12.6 ± 2.2 ml/kg; P < 0.05), but not in EL kittens, and directed tidal ventilation into upper lung regions.DiscussionExternal negative pressures increased lung aeration and resulted in a more evenly distributed tidal ventilation immediately after birth in near-term rabbit kittens, whereas external positive pressures reduced lung aeration and compliance.

The effect of vibrotactile stimulation on hypoxia-induced irregular breathing and apnea in preterm rabbits.

Manual tactile stimulation is used to counteract apnea in preterm infants, but it is unknown when this intervention should be applied. We compared an anticipatory to a reactive approach using vibrotactile stimulation to prevent hypoxia induced apneas. Preterm rabbit kittens were prematurely delivered and randomized to either group. All kittens breathed spontaneously with a positive airway pressure of 8 cmH2O while they were imaged using phase contrast X-ray. Irregular breathing (IB) was induced using gradual hypoxia. The anticipatory group received stimulation at the onset of IB and the reactive group if IB transitioned into apnea. Breathing rate (BR), heart rate (HR) and functional residual capacity (FRC) were compared. Anticipatory stimulation significantly reduced apnea incidence and maximum inter-breath intervals and increased BR following IB, compared to reactive stimulation. Recovery in BR but not HR was more likely with anticipatory stimulation, although both BR and HR were significantly higher at 120 s after stimulation onset. FRC values and variability were not different. Anticipated vibrotactile stimulation is more effective in preventing apnea and enhancing breathing when compared to reactive stimulation in preterm rabbits. Stimulation timing is likely to be a key factor in reducing the incidence and duration of apnea. Anticipated vibrotactile stimulation can prevent apnea and stimulate breathing effort in preterm rabbits. Anticipated vibrotactile stimulation increases the likelihood of breathing rate recovery following hypoxia induced irregular breathing, when compared to reactive stimulation. Automated stimulation in combination with predictive algorithms may improve the treatment of apnea in preterm infants.

The effect of adding garlic powder to the feed of local fatted rabbits on production parameters and blood biochemical traits

Abstract The aim was to evaluate the effect of the addition of garlic powder to the feed of young rabbits (kittens) on production parameters (incl. growth) and blood biochemical traits. Twelve local Iraqi rabbit kittens were selected (4-5 weeks of age) with an average weight of 330±5 grams. Each kitten was housed individually in a cage (1.5 x 2.0m) to ensure they had free access to feed and water. The kittens were divided into three groups of four according to three feeding trials (T1, T2 and T3) to evaluate production efficiency. The kittens were fed a controlled ration containing crude protein (16.6%) and metabolizable energy (2791Kcal/kg feed), with 1% garlic powder (dry weight; g/kg) added to the control ration of T2, and 2% to T3 (T1 was the control group, i.e. without garlic powder). The total weight gain, feed consumption rate and feed conversion ratio were calculated. Blood samples were obtained from all the kittens at the end of the trial period to determine specific blood biochemical traits, including total protein, triglyceride, cholesterol and glucose. At the end of experiment, the control ration was found to have a statistically significant (p≤0.05) effect on almost all production parameters and blood biochemical traits. It was shown that there was a statistically significant (p≤0.05) reduction in total weight gain, cholesterol, glucose, triglyceride, ALT and AST in those kittens fed with the added garlic powder.

Increased end-expiratory pressures improve lung function in near-term newborn rabbits with elevated airway liquid volume at birth.

Approximately 53% of near-term newborns admitted to intensive care experience respiratory distress. These newborns are commonly delivered by cesarean section and have elevated airway liquid volumes at birth, which can cause respiratory morbidity. We investigated the effect of providing respiratory support with a positive end-expiratory pressure (PEEP) of 8 cmH2O on lung function in newborn rabbit kittens with elevated airway liquid volumes at birth. Near-term rabbits (30 days; term = 32 days) with airway liquid volumes that corresponded to vaginal delivery (∼7 mL/kg, control, n = 11) or cesarean section [∼37 mL/kg; elevated liquid (EL), n = 11] were mechanically ventilated (tidal volume = 8 mL/kg). The PEEP was changed after lung aeration from 0 to 8 to 0 cmH2O (control, n = 6; EL, n = 6), and in a separate group of kittens, PEEP was changed after lung aeration from 8 to 0 to 8 cmH2O (control, n = 5; EL, n = 5). Lung function (ventilator parameters, compliance, lung gas volumes, and distribution of gas within the lung) was evaluated using plethysmography and synchrotron-based phase-contrast X-ray imaging. EL kittens initially receiving 0 cmH2O PEEP had reduced functional residual capacities and lung compliance, requiring higher inflation pressures to aerate the lung compared with control kittens. Commencing ventilation with 8 cmH2O PEEP mitigated the adverse effects of EL, increasing lung compliance, functional residual capacity, and the uniformity and distribution of lung aeration, but did not normalize aeration of the distal airways. Respiratory support with PEEP supports lung function in near-term newborn rabbits with elevated airway liquid volumes at birth who are at a greater risk of suffering respiratory distress.NEW & NOTEWORTHY Term babies born by cesarean section have elevated airway liquid volumes, which predisposes them to respiratory distress. Treatments targeting molecular mechanisms to clear lung liquid are ineffective for term newborn respiratory distress. We showed that respiratory support with an end-expiratory pressure supports lung function in near-term rabbits with elevated airway liquid volumes at birth. This study provides further physiological understanding of lung function in newborns with elevated airway liquid volumes at risk of respiratory distress.

Higher CPAP levels improve functional residual capacity at birth in preterm rabbits.

Preterm infants are commonly supported with 4-8 cm H2O continuous positive airway pressures (CPAP), although higher CPAP levels may improve functional residual capacity (FRC). Preterm rabbits delivered at 29/32 days (~26-28 weeks human) gestation received 0, 5, 8, 12, 15 cm H2O of CPAP or variable CPAP of 15 to 5 or 15 to 8 cm H2O (decreasing ~2 cm H2O/min) for up to 10 min after birth. FRC was lower in the 0 (6.8 (1.0-11.2) mL/kg) and 5 (10.1 (1.1-16.8) mL/kg) compared to the 15 (18.8 (10.9-22.4) mL/kg) cm H2O groups (p = 0.003). Fewer kittens achieved FRC > 15 mL/kg in the 0 (20%), compared to 8 (36%), 12 (60%) and 15 (73%) cm H2O groups (p = 0.008). While breathing rates were not different (p = 0.096), apnoea tended to occur more often with CPAP < 8 cm H2O (p = 0.185). CPAP belly and lung bulging rates were similar whereas pneumothoraces were rare. Lowering CPAP from 15 to 5, but not 15 to 8 cm H2O, decreased FRC and breathing rates. In all, 15 cm H2O of CPAP improved lung aeration and reduced apnoea, but did not increase the risk of lung over-expansion, pneumothorax or CPAP belly immediately after birth. FRC and breathing rates were maintained when CPAP was decreased to 8 cm H2O. Although preterm infants are commonly supported with 4-8 cm H2O CPAP at birth, preclinical studies have shown that higher PEEP levels improve lung aeration. In this study, CPAP levels of 15 cm H2O improved lung aeration and reduced apnoea in preterm rabbit kittens immediately after birth. In all, 15 cm H2O CPAP did not increase the risk of lung over-expansion (indicated by bulging between the ribs), pneumothorax, or CPAP belly. These results can be used when designing future studies on CPAP strategies for preterm infants in the delivery room.

Improving lung aeration in ventilated newborn preterm rabbits with a partially aerated lung.

Preterm newborns commonly receive intermittent positive pressure ventilation (iPPV) at birth, but the optimal approach that facilitates uniform lung aeration is unknown, particularly in a partially aerated lung. As both inflation time and exogenous surfactant facilitate uniform lung aeration, we investigated whether they can improve lung aeration and lung mechanics in a partially aerated lung immediately after birth. Preterm rabbit kittens (29 days of gestation, term ~32 days) were delivered by caesarean section and partial lung aeration was created by intubating and mechanically ventilating the right lung. The tube was then withdrawn to ventilate both lungs using inflation times of 0.2 s or 1.0 s, with or without exogenous surfactant (200 mg/kg; Curosurf) and a tidal volume (Vt) of 8 mL/kg. Simultaneous phase contrast X-ray imaging and plethysmography were used to measure lung aeration and mechanics. Kittens ventilated with longer inflation times (1.0 s) reached their target Vt with fewer inflations, required lower inflation pressures (28.5 ± 1.1 vs. 33.5 ± 1.3 cmH2O, P = 0.01) and had higher dynamic lung compliances (0.54 ± 0.3 vs. 0.40 ± 0.3 cmH2O·mL-1·kg-1, P = 0.003). Surfactant increased functional residual capacity (FRC; 31.9 ± 3.2 vs. 18.0 ± 3.9 mL/kg, P = 0.02) and the proportion of the Vt entering the previously unaerated lung but had no effect on dynamic lung compliance. Combining early surfactant treatment with longer inflation times increases FRC levels, improves dynamic lung compliance, reduces inflation pressures and markedly increases the proportion of the lungs being ventilated during iPPV in preterm kittens with a partially aerated lung.NEW & NOTEWORTHY Preterm newborns commonly receive intermittent positive pressure ventilation (iPPV) at birth, but the optimal approach that facilitates uniform lung aeration is unknown, particularly in a partially aerated lung. Using phase contrast X-ray imaging, we showed that combining a long inflation time (1.0 s) with surfactant improved lung mechanics and aeration in the immediate newborn period. The current clinical practice of using short inflation times during iPPV might be suboptimal and a different approach is needed.

Increasing Respiratory Effort With 100% Oxygen During Resuscitation of Preterm Rabbits at Birth.

Background: Spontaneous breathing is essential for successful non-invasive respiratory support delivered by a facemask at birth. As hypoxia is a potent inhibitor of spontaneous breathing, initiating respiratory support with a high fraction of inspired O2 may reduce the risk of hypoxia and increase respiratory effort at birth.Methods: Preterm rabbit kittens (29 days gestation, term ~32 days) were delivered and randomized to receive continuous positive airway pressure with either 21% (n = 12) or 100% O2 (n = 8) via a facemask. If apnea occurred, intermittent positive pressure ventilation (iPPV) was applied with either 21% or 100% O2 in kittens who started in 21% O2, and remained at 100% O2 for kittens who started the experiment in 100% O2. Respiratory rate (breaths per minute, bpm) and variability in inter-breath interval (%) were measured from esophageal pressure recordings and functional residual capacity (FRC) was measured from synchrotron phase-contrast X-ray images.Results: Initially, kittens receiving 21% O2 had a significantly lower respiratory rate and higher variability in inter-breath interval, indicating a less stable breathing pattern than kittens starting in 100% O2 [median (IQR) respiratory rate: 16 (4–28) vs. 38 (29–46) bpm, p = 0.001; variability in inter-breath interval: 33.3% (17.2–50.1%) vs. 27.5% (18.6–36.3%), p = 0.009]. Apnea that required iPPV, was more frequently observed in kittens in whom resuscitation was started with 21% compared to 100% O2 (11/12 vs. 1/8, p = 0.001). After recovering from apnea, respiratory rate was significantly lower and variability in inter-breath interval was significantly higher in kittens who received iPPV with 21% compared to 100% O2. FRC was not different between study groups at both timepoints.Conclusion: Initiating resuscitation with 100% O2 resulted in increased respiratory activity and stability, thereby reducing the risk of apnea and need for iPPV after birth. Further studies in human preterm infants are mandatory to confirm the benefit of this approach in terms of oxygenation. In addition, the ability to avoid hyperoxia after initiation of resuscitation with 100% oxygen, using a titration protocol based on oxygen saturation, needs to be clarified.

Elevated airway liquid volumes at birth: a potential cause of transient tachypnea of the newborn.

Excessive liquid in airways and/or distal lung tissue may underpin the respiratory morbidity associated with transient tachypnea of the newborn (TTN). However, its effects on lung aeration and respiratory function following birth are unknown. We investigated the effect of elevated airway liquid volumes on newborn respiratory function. Near-term rabbit kittens (30 days gestation; term ~32 days) were delivered, had their lung liquid-drained, and either had no liquid replaced (control; n = 7) or 30 ml/kg of liquid re-added to the airways [liquid added (LA); n = 7]. Kittens were mechanically ventilated in a plethysmograph. Measures of chest and lung parameters, uniformity of lung aeration, and airway size were analyzed using phase contrast X-ray imaging. The maximum peak inflation pressure required to recruit a tidal volume of 8 ml/kg was significantly greater in LA compared with control kittens (35.0 ± 0.7 vs. 26.8 ± 0.4 cmH2O, P < 0.001). LA kittens required greater time to achieve lung aeration (106 ± 14 vs. 60 ± 6 inflations, P = 0.03) and had expanded chest walls, as evidenced by an increased total chest area (32 ± 9%, P < 0.0001), lung height (17 ± 6%, P = 0.02), and curvature of the diaphragm (19 ± 8%, P = 0.04). LA kittens had lower functional residual capacity during stepwise changes in positive end-expiratory pressures (5, 3, 0, and 5 cmH20). Elevated lung liquid volumes had marked adverse effects on lung structure and function in the immediate neonatal period and reduced the ability of the lung to aerate efficiently. We speculate that elevated airway liquid volumes may underlie the initial morbidity in near-term babies with TTN after birth.NEW & NOTEWORTHY Transient tachypnea of the newborn reduces respiratory function in newborns and is thought to result due to elevated airway liquid volumes following birth. However, the effect of elevated airway liquid volumes on neonatal respiratory function is unknown. Using phase contrast X-ray imaging, we show that elevated airway liquid volumes have adverse effects on lung structure and function in the immediate newborn period, which may underlie the pathology of TTN in near-term babies after birth.

Lung hypoplasia in newborn rabbits with a diaphragmatic hernia affects pulmonary ventilation but not perfusion

BackgroundA congenital diaphragmatic hernia (DH) can result in severe lung hypoplasia that increases the risk of morbidity and mortality after birth; however, little is known about the cardiorespiratory transition at birth.MethodsUsing phase-contrast X-ray imaging and angiography, we examined the cardiorespiratory transition at birth in rabbit kittens with DHs. Surgery was performed on pregnant New Zealand white rabbits (n=18) at 25 days’ gestation to induce a left-sided DH. Kittens were delivered at 30 days’ gestation, intubated, and ventilated to achieve a tidal volume (Vt) of 8 ml/kg in control and 4 ml/kg in DH kittens while they were imaged.ResultsFunctional residual capacity (FRC) recruitment and Vt in the hypoplastic left lung were markedly reduced, resulting in a disproportionate distribution of FRC into the right lung. Following lung aeration, relative pulmonary blood flow (PBF) increased equally in both lungs, and the increase in pulmonary venous return was similar in both control and DH kittens.ConclusionThese findings indicate that nonuniform lung hypoplasia caused by DH alters the distribution of ventilation away from hypoplastic and into normally grown lung regions. During transition, the increase in PBF and pulmonary venous return, which is vital for maintaining cardiac output, is not affected by lung hypoplasia.

Vagal denervation inhibits the increase in pulmonary blood flow during partial lung aeration at birth.

Lung aeration at birth significantly increases pulmonary blood flow, which is unrelated to increased oxygenation or other spatial relationships that match ventilation to perfusion. Using simultaneous X-ray imaging and angiography in near-term rabbits, we investigated the relative contributions of the vagus nerve and oxygenation to the increase in pulmonary blood flow at birth. Vagal denervation inhibited the global increase in pulmonary blood flow induced by partial lung aeration, although high inspired oxygen concentrations can partially mitigate this effect. The results of the present study indicate that a vagal reflex may mediate a rapid global increase in pulmonary blood flow in response to partial lung aeration. Air entry into the lungs at birth triggers major cardiovascular changes, including a large increase in pulmonary blood flow (PBF) that is not spatially related to regional lung aeration. To investigate the possible underlying role of a vagally-mediated stimulus, we used simultaneous phase-contrast X-ray imaging and angiography in near-term (30days of gestation) vagotomized (n=15) or sham-operated (n=15) rabbit kittens. Rabbits were imaged before ventilation, when one lung was ventilated (unilateral) with 100% nitrogen (N2 ), air or 100% oxygen (O2 ), and after all kittens were switched to unilateral ventilation in air and then ventilation of both lungs using air. Compared to control kittens, vagotomized kittens had little or no increase in PBF in both lungs following unilateral ventilation when ventilation occurred with 100% N2 or with air. However, relative PBF did increase in vagotomized animals ventilated with 100% O2 , indicating the independent stimulatory effects of local oxygen concentration and autonomic innervation on the changes in PBF at birth. These findings demonstrate that vagal denervation inhibits the previously observed increase in PBF with partial lung aeration, although high inspired oxygen concentrations can partially mitigate this effect.

Milkweed control by food imprinted rabbits

Many species of invasive plants are spreading out rapidly in Europe. The common milkweed occupies increasingly more area. Being poisonous, most animals will not graze on it however rabbits would be an effective organism for the biological control of milkweed. Rabbit kittens can learn the maternal diet in various ways. They prefer aromatic foods which their mother had eaten during pregnancy or lactation period, -even if it is poisonous- but they can also learn the maternal diet from the fecal pellets deposited by the mother into the nest during the nursing events. The present study was aimed to investigate if rabbit kittens can learn that the common milkweed is a potential food also. In the first 10days of their lives kits got fecal pellets originating from individuals having fed on common milkweed previously. When weaned on day 28 postpartum, these pups preferred the milkweed in the 3-way food choice test, opposite to the control group. Most surprisingly in a second experiment it was also shown that the common milkweed was also preferred by the kittens if their mother ate it not during, but one month before pregnancy.

Effect of betamethasone, surfactant, and positive end-expiratory pressures on lung aeration at birth in preterm rabbits.

Antenatal glucocorticoids, exogenous surfactant, and positive end-expiratory pressure (PEEP) ventilation are commonly provided to preterm infants to enhance respiratory function after birth. It is unclear how these treatments interact to improve the transition to air-breathing at birth. We investigated the relative contribution of antenatal betamethasone, prophylactic surfactant, and PEEP (3 cmH2O) on functional residual capacity (FRC) and dynamic lung compliance (CDL) in preterm (28 day GA) rabbit kittens at birth. Kittens were delivered by cesarean section and mechanically ventilated. FRC was calculated from X-ray images, and CDL was measured using plethysmography. Without betamethasone, PEEP increased FRC recruitment and CDL Surfactant did not further increase FRC, but significantly increased CDL Betamethasone abolished the benefit of PEEP on FRC, but surfactant counteracted this effect of betamethasone. These findings indicate that low PEEP levels are insufficient to establish FRC at birth following betamethasone treatment. However, surfactant reversed the effect of betamethasone and when combined, these two treatments enhanced FRC recruitment irrespective of PEEP level.

X-ray specks: low dose in vivo imaging of lung structure and function

Respiratory health is directly linked to the structural and mechanical properties of the airways of the lungs. For studying respiratory development and pathology, the ability to quantitatively measure airway dimensions and changes in their size during respiration is highly desirable. Real-time imaging of the terminal airways with sufficient contrast and resolution during respiration is currently not possible. Herein we reveal a simple method for measuring lung airway dimensions in small animals during respiration from a single propagation-based phase contrast x-ray image, thereby requiring minimal radiation. This modality renders the lungs visible as a speckled intensity pattern. In the near-field regime, the size of the speckles is directly correlated with that of the dominant length scale of the airways. We demonstrate that Fourier space quantification of the speckle texture can be used to statistically measure regional airway dimensions at the alveolar scale, with measurement precision finer than the spatial resolution of the imaging system. Using this technique we discovered striking differences in developmental maturity in the lungs of rabbit kittens at birth.

Real-time measurement of alveolar size and population using phase contrast x-ray imaging.

Herein a propagation-based phase contrast x-ray imaging technique for measuring particle size and number is presented. This is achieved with an algorithm that utilizes the Fourier space signature of the speckle pattern associated with the images of particles. We validate this algorithm using soda-lime glass particles, demonstrating its effectiveness on random and non-randomly packed particles. This technique is then applied to characterise lung alveoli, which are difficult to measure dynamically in vivo with current imaging modalities due to inadequate temporal resolution and/or depth of penetration and field-of-view. We obtain an important result in that our algorithm is able to measure changes in alveolar size on the micron scale during ventilation and shows the presence of alveolar recruitment/de-recruitment in newborn rabbit kittens. This technique will be useful for ventilation management and lung diagnostic procedures.

Comparative quantitative monitoring of rabbit haemorrhagic disease viruses in rabbit kittens.

BackgroundOnly one strain (the Czech CAPM-v351) of rabbit haemorrhagic disease virus (RHDV) has been released in Australia and New Zealand to control pest populations of the European rabbit O. cuniculus. Antigenic variants of RHDV known as RHDVa strains are reportedly replacing RHDV strains in other parts of the world, and Australia is currently investigating the usefulness of RHDVa to complement rabbit biocontrol efforts in Australia and New Zealand. RHDV efficiently kills adult rabbits but not rabbit kittens, which are more resistant to RHD the younger they are and which may carry the virus without signs of disease for prolonged periods. These different infection patterns in young rabbits may significantly influence RHDV epidemiology in the field and hence attempts to control rabbit numbers.MethodsWe quantified RHDV replication and shedding in 4–5 week old rabbits using quantitative real time PCR to assess their potential to shape RHDV epidemiology by shedding and transmitting virus. We further compared RHDV-v351 with an antigenic variant strain of RHDVa in kittens that is currently being considered as a potential RHDV strain for future release to improve rabbit biocontrol in Australia.ResultsKittens were susceptible to infection with virus doses as low as 10 ID50. Virus growth, shedding and transmission after RHDVa infection was found to be comparable or non-significantly lower compared to RHDV. Virus replication and shedding was observed in all kittens infected, but was low in comparison to adult rabbits. Both viruses were shed and transmitted to bystander rabbits. While blood titres indicated that 4–5 week old kittens mostly clear the infection even in the absence of maternal antibodies, virus titres in liver, spleen and mesenteric lymph node were still high on day 5 post infection.ConclusionsRabbit kittens are susceptible to infection with very low doses of RHDV, and can transmit virus before they seroconvert. They may therefore play an important role in RHDV field epidemiology, in particular for virus transmission within social groups during virus outbreaks.

Several Immunological Parameters in Rabbit Kittens Born to S. japonicum -infected Mothers

Several Immunological Parameters in Rabbit Kittens Born to S. japonicum -infected Mothers

Several Immunological Parameters in Rabbit Kittens Born to &amp;lt;i&amp;gt;S. japonicum&amp;lt;/i&amp;gt;-Infected Mothers

In this study we explored the rabbit as an animal model for the congenital infection of schistosomiasis japonica and assessed the effect of a congenital S. japonicum infection on the resistance of rabbit kittens to a postnatal challenge infection. Kittens were challenged 17-19 weeks after the primary infection of their mothers. Perfusion was undertaken six weeks after the challenge. At this time parasitological, pathological and immunological parameters, worm reduction rate, granuloma size reduction rate, egg reduction rate, IgG and IgM responses were assessed and compared to that of kittens born to un-infected mothers. The overall prevalence of congenital infection in kittens of infected mothers was 20% (12/60). After a postnatal challenge infection, prenatally infected kittens had a 54.66% worm reduction rate, 41.45% egg reduction rate, and 51.76% granuloma size reduction rate compared to naive kittens. Congenital infection decreases the IgM responses by 39.47% while it increases the IgG responses by 56.22%. Together, these results indicate that congenital infection induce long-term effects on pathology and immune response patterns in rabbits’ subsequently challenge with S. japonicum cercariae.

Expired CO2 Levels Indicate Degree of Lung Aeration at Birth

As neonatal resuscitation critically depends upon lung aeration at birth, knowledge of the progression of this process is required to guide ongoing care. We investigated whether expired CO2 (ECO2) levels indicate the degree of lung aeration immediately after birth in two animal models and in preterm infants. Lambs were delivered by caesarean section and ventilated from birth. In lambs, ECO2 levels were significantly (p<0.0001) related to tidal volumes and CO2 clearance/breath increased exponentially when tidal volumes were greater than 6 mL/kg. Preterm (28 days of gestation; term = 32 days) rabbits were also delivered by caesarean section and lung aeration was measured using phase contrast X-ray imaging. In rabbit kittens, ECO2 levels were closely related (p<0.001) to lung volumes at end-inflation and were first detected when ∼7% of the distal lung regions were aerated. ECO2 levels in preterm infants at birth also correlated with tidal volumes. In each infant, ECO2 levels increased to >10 mmHg 28 (median) (21–36) seconds before the heart rate increased above 100 beats per minute. These data demonstrate that ECO2 levels can indicate the relative degree of lung aeration after birth and can be used to clinically assess ventilation in the immediate newborn period.

Vertical transmission of Schistosoma japonicum in the rabbit.

The aim of the present study was to confirm observations on the vertical transmission of Schistosoma japonicum in the rabbit. S. japonicum-infected pregnant rabbits were used in this study. Perfusion of mother rabbits was done 9 weeks after infection in order to obtain worm burdens in relation to their initial cercarial dose. Anti-schistosoma specific IgM antibodies in serum samples collected from rabbit kittens were detected by ELISA. Our results showed that gestation period lasted the normal 29-31 days. All the exposed mother rabbits became infected with S. japonicum. Positive IgM antibody OD values were detected in 12 out of the 60 kittens examined (20.0%). In group C and A, 40.0% and 17.9% of the kitten were congenitally infected, respectively. 18.1% of the kittens born to mothers infected with a single dose of 200 cercariae per rabbit were positives; this is not significantly different from that obtained for the 600 dose group (22.2%). Three randomly selected IgM+ kittens harbored between one and two adult worms. The livers of these kittens displayed granulomatous lesions. It is concluded that congenital S. japonicum infection does occur in the rabbit and is affected by the mother stage of pregnancy and to a lesser extent by its infection load.

Statistical models for the effect of age and maternal antibodies on the development of rabbit haemorrhagic disease in Australian wild rabbits

Statistical models have been developed to explain the influence of age and maternal antibody on the outcome of rabbit haemorrhagic disease virus (RHDV) infection of Australian wild rabbit kittens in terms of survival, survival time in those that failed to survive, and pyrexia (temperature response, or fever). Similar models describing survival and survival time were derived by substituting mass for age, owing to their high correlation. The models were developed from data obtained following the inoculation of 78 kittens 5–11 weeks old born to does with varying levels of α-RHDV immunoglobulin (IgG) antibody as measured by enzyme-linked immunosorbent assay (ELISA). A significant correlation was found between survival and doe titre but not between survival and kitten titre. It was deduced that maternal antibody in kittens can fall below the level of detection in the ELISA but still be protective. The model describing the influence of age and doe titre had the form logit(SURVIVAL) = 5.98 – 0.944(AGE) + 0.000473(DOE TITRE), and showed, for example, that kittens born to seronegative does had a 50% probability of survival at about 6 weeks old and, with a doe titre of 10 240, a 50% probability of survival at about 11 weeks old. There was a significant influence of kitten titre on pyrexia, and the model developed had the form logit(TEMPERATURE RESPONSE) = 1.436 – 0.0531(KITTEN TITRE). The influence of age and maternal antibody on survival time was fitted using Cox proportional hazard models. A parametric regression gave rise to a final model of the form S(t | AGE, DOE TITRE) = exp[–(t/ηAGE)1.7979], where ηAGE = exp[7.1838 – 0.2976(AGE) + 0.000227(DOE TITRE)]. The model showed that survival time decreased with age, but for each age category there was an increase in survival time with increasing doe titre. Kitten titre had only a marginally significant effect on seroconversion; there was no effect of kitten age or mass, or of doe titre. No kitten with a titre of 60 or more seroconverted.