Birth In Rabbits Research Articles

Influence of males of the paternal line with different weight index on the productivity of rabbits of the maternal form of the Hyla Cross

The maternal form of modern rabbit crosses is obtained by crossing ancestral lines. Therefore it is relevant to investigate the effect of using males of the parental line of the Hyla cross with different weight indices on the performance of the main breeding traits of the female rabbits of the parental form of the cross. The purpose of the study was to investigate the level of productivity of rabbits of the maternal form of cross by reproduction signs and to consider the dynamics of the main breeding traits for a number of births. The experiments used 223 rabbits of the maternal form of the Hyla cross, which came from males with different weight indices. To achieve this goal, groups of rabbits were formed, depending on the value of their father's weight Index – Group 1 – ≤ 100 units, Group 2 – from 100 to 120 units, Group 3 – ≥ 120 units. The live weight of rabbits after kindling, multiparity, the weight of newborn rabbits, milk yield, and the live weight of rabbits at the time of weaning were determined. Female rabbits that came from males with a high weight index at first kindling significantly outnumbered their peers in multiparity by 1.16-1.23 animal units (p ≤ 0.05), and in milk yield – by 6-6.5%. Rabbits whose parents were males with a high weight index according to the results of the 3rd kindling prevailed over their peers from other males in multiparity (p ≤ 0.05), milk yield (p ≤ 0.05), and also had significantly higher values of complex indices (p≤0.05). From the 1st to the 3rd kindling, the multiparity of rabbits increases, on average, by 6.5%. Live weight at birth of rabbits in Groups 2 and 3 had a positive trend and increased by 3.2% and 4.2%, respectively. On average, the milk yield of rabbits increased by 38.6% from the first to the third kindling. The practical significance of the results lies in the fact that to obtain highly productive rabbits of the maternal cross form, it is advisable to use males of the ancestral form with a weight index ≥ 120 units

INDICATORS OF FERTILITY OF SOVIET CHINCHELLA RABBITS AND THE DEVELOPMENT OF THEIR OFFSPRING IN THE URALS

The conducted studies established that the fertility of young rabbits,for one okrol brought 6.28 rabbits, their survival rate on the 21st day was 92.7%. During the year, the rabbits were bred 6.05 times, the total number of rabbits was 32-33 heads. The live weight at birth of rabbits is 68.9-69.2 g, on the 21st day an average of 279.3 g, the growth rate of 0-150 days was 54.07 times. In winter, the body temperature was 37.50 C, in summer 38.90 C, the respiratory rate was 56.7 and the pulse rate was 142.5 minutes. Hematological parameters of young animals were determined and established: hemoglobinins 96.05 g/l, erythrocytes 7.98 1012 /l and leukocytes 6.49109 / ml, blood biochemical parameters: total proteins 96.88%, albumins 47.86%, gamma-globulins 21.89%, beta-globulins 13.92%, alpha-globulins 10.21%. In young rabbits, the ratio of calcium to phosphorus was 1.81. Concluding the study, we note a high multiplicity of rabbits, intensive growth of young animals, therefore they can be grown in farms in the Urals.

Закономірності кількісної динаміки тканинних компонентів лімфатичних вузлів кролів м’ясного напрямку використання

Метою роботи було визначити закономірності вікової динаміки відносної площі строми, компонентів лімфоїдної паренхіми та системи внутрішньовузлового лімфатичного русла деяких соматичних та вісцеральних лімфатичних вузлів кролів м’ясного напрямку використання. Проведено комплексний аналіз гістоархітектоніки лімфатичних вузлів на різних етапах постнатального онтогенезу. Подано результати комплексного дослідження структурно-функціональних особливостей соматичних (підколінних, підщелепних) та вісцеральних (каудальних брижових та середостінних) лімфатичних вузлів від 1- до 90-добового віку. Наведено морфометричні показники кількісної динаміки тканевих компонентів (стромального апарату, функціональних зон паренхіми та системи синусів) з особливостями їхнього співвідношення в межах функціональних сегментів. З’ясовано, що на структурно-функціональному рівні організації всі без винятку лімфатичні вузли кролів представлені скупченням компартментів, кожен з яких складається з лімфатичних вузликів та прилеглих до них територій паренхіми, мозкових тяжів, що продовжуються в глибину мозкової речовини, та розвиненої системи синусів. Проведеними дослідженнями встановленно, що у лімфатичних вузлах переважає відносна площа лімфоїдної паренхіми, найбільш розвиненими структурно-функціональними зонами якої є одиниці глибокої кори та мозкові тяжі. Визначено, що в момент народження у кролів лімфатичні вузли представленні скупченням лімфоїдної тканини та стромою. Зі збільшенням віку тварин в лімфатичних вузлах збільшується кількість сполучної тканини, потовщується капсула та трабекули. Одночасно з цим у вузлах зменшується кількість кіркової речовини і відносно збільшується кількість мозкової. Встановлено, що активне формування лімфатичних вузликів починається з 20-денного віку, а остаточна зональна диференціація лімфатичних вузлів у кролів досягається після 30-го дня. Кількісна вікова динаміка паренхіми на пізніх етапах онтогенезу по досягненню 90 днів визначається переважанням розвитку лімфатичних вузликів з центрами розмноження, особливо у вісцеральних лімфатичних вузлах, які мають різнорівневий характер розташування та розміщуються на бокових поверхнях одиниць глибокої кори, на їх полюсах, а також в глибоких шарах паренхіми. Мозкові синуси широкі та займають більшу площу, ніж підкапсулярні та проміжні як в соматичних, так і в вісцеральних лімфатичних вузлах, незалежно від віку тварин.

A 100-Year Review: Reproductive technologies in dairy science

Reproductive technology revolutionized dairy production during the past century. Artificial insemination was first successfully applied to cattle in the early 1900s. The next major developments involved semen extenders, invention of the electroejaculator, progeny testing, addition of antibiotics to semen during the 1930s and 1940s, and the major discovery of sperm cryopreservation with glycerol in 1949. The 1950s and 1960s were particularly productive with the development of protocols for the superovulation of cattle with both pregnant mare serum gonadotrophin/equine chorionic gonadotrophin and FSH, the first successful bovine embryo transfer, the discovery of sperm capacitation, the birth of rabbits after in vitro fertilization, and the development of insulated liquid nitrogen tanks. Improved semen extenders and the replacement of glass ampules with plastic semen straws followed. Some of the most noteworthy developments in the 1970s included the initial successes with in vitro culture of embryos, calves born after chromosomal sexing as embryos, embryo splitting resulting in the birth of twins, and development of computer-assisted semen analysis. The 1980s brought flow cytometric separation of X- and Y-bearing sperm, in vitro fertilization leading to the birth of live calves, clones produced by nuclear transfer from embryonic cells, and ovum pick-up via ultrasound-guided follicular aspiration. The 20th century ended with the birth of calves produced from AI with sexed semen, sheep and cattle clones produced by nuclear transfer from adult somatic cell nuclei, and the birth of transgenic cloned calves. The 21st century has seen the introduction of perhaps the most powerful biotechnology since the development of artificial insemination and cryopreservation. Quick, inexpensive genomic analysis via the use of single nucleotide polymorphism genotyping chips is revolutionizing the cattle breeding industry. Now, with the introduction of genome editing technology, the changes are becoming almost too rapid to fully digest.

Embryo transfer manipulation cause gene expression variation in blastocysts that disrupt implantation and offspring rates at birth in rabbit

ObjectiveIn the current study we aimed to evaluate the effect of embryo transfer on gene expression during pre-implantation development and its consequences on implantation rate, offspring rate at birth and embryonic and fetal losses in the rabbit model. Study designThe mRNA expressions of 8 candidate genes were compared between 6-day-old in vivo-produced embryos (non-manipulated embryos) to those of 6-day-old embryos previously recovery at the third day of development and transferred into recipient rabbit females (manipulated embryos). Furthermore, we compared between both experimental groups the implantation rate and offspring rate at birth and embryonic and fetal losses. ResultsDifferences in transcript abundance of OCT4, C1qTNF1, EMP1 and TNFAIP6 were observed in transferred embryos. In addition, lower implantation and offspring rates at birth were obtained in transferred embryos than in the control group. In addition, embryonic losses were significantly higher in the transferred group than in the control. However, fetal losses were similar between groups. ConclusionThe findings of the current study show that embryo transfer manipulation influenced mRNA expression of late blastocysts prior to implantation, resulting in higher gestational losses as a consequence of faulty embryonic implantation.

Influence of zona pellucida thickness on fertilization, embryo implantation and birth

Defective sperm–zona pellucida binding and penetration are the main causes of IVF failure. The purpose of this study was to evaluate the effect of zona pellucida thickness in fertilization failure and test the influence of zona pellucida thickness on implantation and birth in rabbits. Embryos and oocytes were collected from 72 females on Day 2 post-insemination. A total of 559 normal embryos were recovered; 402 embryos were transferred by laparoscopy and 157 embryos were used to measure the zona pellucida thickness using the ImageJ program. Laparoscopies were also performed on all does at Day 12 of gestation to record the number of implanted embryos. Litter size at birth was recorded. The mean zona pellucida thickness of the 157 embryos and of the 64 control group oocytes (18.3±0.2 and 18.5±0.3μm, respectively) was significantly less than the zona pellucida thickness of the 74 failed fertilization oocytes (19.2±0.3μm). The probabilities of the regression coefficient being positive were 0.72 and 0.74 for implantation and birth, respectively, and the subsequent means of the coefficient were 2.92 and 0.03 for implantation and birth, respectively. In conclusion, the zona pellucida thickness has an important influence on in vivo fertilization and implantation processes, but not on birth.

Effect of different number of frozen spermatozoa inseminated on the reproductive performance of rabbit does

The relationship between the number of frozen spermatozoa inseminated and fertility rate and litter size at birth in rabbit does was investigated. Six hundred artificial inseminations (AI) were performed on multiparous lactating does with three spermatozoa concentrations: 10, 25, 50 × 10 6 spermatozoa/AI. All the does were synchronized with 20 UI of eCG 2 days before AI. The estimated sexual receptivity was 87%. The freezing–thawing procedure strongly reduced kinetic and functional traits (acrosome integrity, capacitation) of the spermatozoa. The number of spermatozoa inseminated did not affect the reproductive performance: the mean fertility rate and litter size values were 51.5% and 7.6%, respectively. Sexually receptive does ( n = 522) inseminated with frozen spermatozoa showed a 58.0% fertility rate whereas, non-receptive does ( n = 78), had a very poor fertility rate (7.8%).

Effect of number of motile sperms inseminated on reproductive performance of rabbit does.

The relationship between the number of motile sperms inseminated and fertility rate and litter size at birth in rabbits was investigated. A total of 651 artificial inseminations on multiparous rabbit does in different physiological states (lactating or not; sexually receptive or not) were inseminated with a number of motile cells/dose varying from about 1-20 x 10(6). The statistical model computed the following traits: maximum expected value (a), rate of approach to this value (b) and number of motile spermatozoa/dose needed to obtain threshold level (95% of the maximum). The physiological condition of the doe affected the reproductive performance. The sexual receptivity had significant effect during lactation: non-receptive does had the lowest fertility (a: 43.70%; P < 0.05) while no significant differences were found in non-lactating ones (73.80 vs. 89.11%). Also the rate of approach to this maximum was different: non-receptive does showed a higher dependence on spermatozoa number than receptive females (b: 0.69 and 0.58, respectively, in lactating and non-lactating does) and consequently more spermatozoa (13.1 and 11.1 x 10(6) motile/dose) were needed to reach the threshold value. The physiological state of the does did not affect litter size and only 4.1 x 10(6) of motile spermatozoa/dose are needed to reach the threshold value.

Biochemical characterization and purification of sperm agglutination antigen-1, A human sperm surface antigen implicated in gamete interactions

Reproductive technology revolutionized dairy production during the past century. Artificial insemination was first successfully applied to cattle in the early 1900s. The next major developments involved semen extenders, invention of the electroejaculator, progeny testing, addition of antibiotics to semen during the 1930s and 1940s, and the major discovery of sperm cryopreservation with glycerol in 1949. The 1950s and 1960s were particularly productive with the development of protocols for the superovulation of cattle with both pregnant mare serum gonadotrophin/equine chorionic gonadotrophin and FSH, the first successful bovine embryo transfer, the discovery of sperm capacitation, the birth of rabbits after in vitro fertilization, and the development of insulated liquid nitrogen tanks. Improved semen extenders and the replacement of glass ampules with plastic semen straws followed. Some of the most noteworthy developments in the 1970s included the initial successes with in vitro culture of embryos, calves born after chromosomal sexing as embryos, embryo splitting resulting in the birth of twins, and development of computer-assisted semen analysis. The 1980s brought flow cytometric separation of X- and Y-bearing sperm, in vitro fertilization leading to the birth of live calves, clones produced by nuclear transfer from embryonic cells, and ovum pick-up via ultrasound-guided follicular aspiration. The 20th century ended with the birth of calves produced from AI with sexed semen, sheep and cattle clones produced by nuclear transfer from adult somatic cell nuclei, and the birth of transgenic cloned calves. The 21st century has seen the introduction of perhaps the most powerful biotechnology since the development of artificial insemination and cryopreservation. Quick, inexpensive genomic analysis via the use of single nucleotide polymorphism genotyping chips is revolutionizing the cattle breeding industry. Now, with the introduction of genome editing technology, the changes are becoming almost too rapid to fully digest.

GABA and GABA-A receptors are maximally expressed in association with cone synaptogenesis in neonatal rabbit retina

Previous studies have shown the cone photoreceptors form reciprocal synapses with horizontal cells during the first week after birth in rabbits. These synapses constitute pioneering elements of the developing outer plexiform layer. We now report that antibodies against the α-1 and against the β- 2 3 subunits of the GABA-A receptor label a highly restricted sublamina in the developing outer plexiform layer known to contain nascent cone photoreceptor terminals. Staining is relatively weak at birth, increases to maximal levels between postnatal days 5 and 7, and is significantly reduced in the adult. These results support recent calcium imaging studies which have shown that the activation of GABA-A receptors causes an increase in intracellular free calcium in cones, an effect which is observed only at 3–9 days after birth. The transient expression of GABA-A receptors in this region coincides with the period of peak expression of GABA immunoreactivity in horizontal cells. A direct functional link between GABAergic transmission and cone synaptogenesis is suggested by previous reports that GABA-A receptor antagonists cause disruption of cone synaptogenesis. Together these findings support the notion that GABA functions as a developmental neurotransmitter which is produced by horizontal cells and interacts with developing cone axons in order to facilitate synaptic linkage between these two cells types.

Evaluation of frequency of ultrasonically guided follicle aspiration on bovine ovarian dynamics

Reproductive technology revolutionized dairy production during the past century. Artificial insemination was first successfully applied to cattle in the early 1900s. The next major developments involved semen extenders, invention of the electroejaculator, progeny testing, addition of antibiotics to semen during the 1930s and 1940s, and the major discovery of sperm cryopreservation with glycerol in 1949. The 1950s and 1960s were particularly productive with the development of protocols for the superovulation of cattle with both pregnant mare serum gonadotrophin/equine chorionic gonadotrophin and FSH, the first successful bovine embryo transfer, the discovery of sperm capacitation, the birth of rabbits after in vitro fertilization, and the development of insulated liquid nitrogen tanks. Improved semen extenders and the replacement of glass ampules with plastic semen straws followed. Some of the most noteworthy developments in the 1970s included the initial successes with in vitro culture of embryos, calves born after chromosomal sexing as embryos, embryo splitting resulting in the birth of twins, and development of computer-assisted semen analysis. The 1980s brought flow cytometric separation of X- and Y-bearing sperm, in vitro fertilization leading to the birth of live calves, clones produced by nuclear transfer from embryonic cells, and ovum pick-up via ultrasound-guided follicular aspiration. The 20th century ended with the birth of calves produced from AI with sexed semen, sheep and cattle clones produced by nuclear transfer from adult somatic cell nuclei, and the birth of transgenic cloned calves. The 21st century has seen the introduction of perhaps the most powerful biotechnology since the development of artificial insemination and cryopreservation. Quick, inexpensive genomic analysis via the use of single nucleotide polymorphism genotyping chips is revolutionizing the cattle breeding industry. Now, with the introduction of genome editing technology, the changes are becoming almost too rapid to fully digest.

Morphologic and molecular changes during the post-natal development of the rabbit vitreous

Rabbits aged 1, 4, 10, 15, and 20 days, and 4 months were anesthetized and perfused with 4% formaldehyde. One eye of each rabbit was processed for paraffin embedding, while the other eye was embedded intact in methacrylate. Rabbits aged 1 and 15 days and 4 months were perfused with 2·5% glutaraldehyde, and the eyes were processed for Epon embedding. The paraffin sections were immunostained to allow detection of a high molecular weight cartilage matrix glycoprotein (CMGP), which is synthesized by the ciliary body and found in the vitreous in adult animals, using a specific mouse monoclonal antibody. CMGP was identified in the vitreous and in the inner layer of the ciliary epithelium only after the fifteenth day of life in amounts comparable to those detected in adult rabbits. Before this time immunostaining with the monoclonal antibody was seen only in the apical region of the inner ciliary epithelial cells. However, electron microscopic observations revealed that the cytoplasmic organelles responsible for the secretion of glycoproteins, i.e. the rough endoplasmic reticulum, Golgi apparatus, and vesicles, were present in the inner layer of ciliary epithelial cells as early as the first day of life. Anteroposterior sections of whole eyes embedded in methacrylate revealed a relatively dense meshwork of vitrous fibrils on the first day of life. The blood vessels were concentrated at the posterior region of the lens, and isolated cells were visible. The blood vessels were not seen after the age of 15 days, and the fiber meshwork and cells were inconspicuous by then. Electron microscopy demonstrated that the isolated cells had morphologic features similar to macrophages and were considered to be hyalocytes. The blood vessels were formed by a continuous layer of non-fenestrated endothelial cells and by a discontinuous layer of pericyte-like cells. No evidence was found for the participation of the hyalocytes in the synthesis of the components of the vitreous. It is likely that the amorphous components of the vitreous, which include hyaluronic acid and glycoproteins, e.g. CMGP, are produced at greater rates than type II collagen fibrils after birth in rabbits. Thus, the fibrils were a minor component by volume of the vitreous of adult rabbits in comparison to the amorphous portion of the vitreous.

口輪筋に対する酵素組織化学的研究 家兎口輪筋のｌａｃｔａｔｅ ｄｅｈｙｄｒｏｇｅｎａｓｅとｇｌｙｃｅｒａｌｄｅｈｙｄｅ‐３‐ｐｈｏｓｐｈａｔｅ ｄｅｈｙｄｒｏｇｅｎａｓｅの活性の成長に伴う変化

The author did experimental zymohystochemical studies on the developmental stages (from immediately after birth to 180 days) of rabbit's orbicularis oris muscles to determine the optimal time for cleft lip and palate operation.The results were as follows:1. The activity of lactate dehydrogenase was high for 30 days after birth, but it had no differential activities for the developmental stages as the marker.2. Orbicularis oris muscle fibers showed both dark and light glyceraldehydc-3-phosphate dehydrogenase staining for 60 days after birth.3. When lip plasty was done after differentiation of orbicularis oris muscle, it seems that the appropriate stage for the lip plasty is later than 60 days after birth in rabbits, and later than one year and 4 months after birth in humans.

Respiratory effects of cigarette smoke, dust, and histamine in newborn rabbits.

We studied the respiratory effects of cigarette smoke, 5% histamine aerosol, and dust in unanesthetized 1- to 7-day-old rabbits in a body plethysmograph. Cigarette smoke immediately provoked the animal's arousal and irregular breathing. Histamine and dust had no effect in some of the youngest animals. In others, 5-15 s from the onset of the exposure to either of the two stimuli, respiratory rate increased and the depth of breathing decreased. These changes were more pronounced with age. The fact that effects of dust and aerosol lessened with time of exposure showed adaptation to the stimuli. The age dependence of the reflex response was also observed after injection of 50 micrograms of histamine per kilogram into the external jugular vein in anesthetized (50 mg ketamine + 3 mg acepromazine per kg) and tracheostomized rabbits during the 1st wk of life. In 1-day-old animals, a short-lasting excitation was followed by apnea or a prolongation of expiratory phase. Peak amplitude of the diaphragmatic EMG (EMGdi) increased in all animals, but only in the youngest was the EMGdi increase paralleled by an increase in tidal volume. In vagotomized animals or animals pretreated with H1-blocker, histamine never affected timing parameters in animals greater than 1 day old. In the youngest animals, respiratory depression due to histamine was not abolished after vagotomy or promethazine. The results imply that inputs from the upper airways and the rapidly adapting pulmonary mechanoreceptors exert their effects on the pattern of breathing immediately after birth in rabbits. The importance of those inputs increases with maturation.

口輪筋の成長に関する生化学的研究 ｍｙｏｓｉｎ Ｃａ｀２＋´‐ＡＴＰａｓｅを指標とした口輪筋の成長と分化について

In Japan, about 3 to 4 months after birth is widely accepted as the appropriate stage of lip plasty but some insist on operating a few days after birth or after 6 months. Natsume of our department investigated the orbicularis oris muscle which plays and important role in lip plasty morphometrically during development of rabbits. He suggested human lip plasty should not be performed before 3 months after birth.Subsequtently the author intended to examine the stage of lip plasty biochemically by analyzing the myosin changes during development, and then to clarify the growth process of orbicularis oris muscle in rabbits.Total activity of myosin Ca2+-ATPase in pure orbicularis oris muscle from the median area of lower lip was taken up as an index of the muscle development, and myosin Ca2+-ATPase activity per mg muscle protein was used as an index of its differentiation.The results were as follows:1. The variance of total activity of myosin Ca2+-ATPase during development was approximately the same as that of the weight of orbicularis oris muscle.2. The variance of myosin Ca2+-ATPase activity per mg muscle protein which was considered the important factor of muscle differentiation, presented the figure of 3 peaks. This suggested that there were differences in the stage and the rate of accumulation between myosin and other muscle proteins.3. Myosin of gastrocnemius muscle was chiefly accumulated in the growing stage. So it was supposed that orbicularis oris muscle was differentiated in the early stage.4. Supposing that lip plasty should be done after differentiation of orbicularis oris muscle, it seemed that the appropriate stage of the lip plasty was more than 40 days after birth in rabbits and more than one year after birth in human.

The production of monozygotic twins of preselected parentage by micromanipulation of non-surgically collected cow embryos

Reproductive technology revolutionized dairy production during the past century. Artificial insemination was first successfully applied to cattle in the early 1900s. The next major developments involved semen extenders, invention of the electroejaculator, progeny testing, addition of antibiotics to semen during the 1930s and 1940s, and the major discovery of sperm cryopreservation with glycerol in 1949. The 1950s and 1960s were particularly productive with the development of protocols for the superovulation of cattle with both pregnant mare serum gonadotrophin/equine chorionic gonadotrophin and FSH, the first successful bovine embryo transfer, the discovery of sperm capacitation, the birth of rabbits after in vitro fertilization, and the development of insulated liquid nitrogen tanks. Improved semen extenders and the replacement of glass ampules with plastic semen straws followed. Some of the most noteworthy developments in the 1970s included the initial successes with in vitro culture of embryos, calves born after chromosomal sexing as embryos, embryo splitting resulting in the birth of twins, and development of computer-assisted semen analysis. The 1980s brought flow cytometric separation of X- and Y-bearing sperm, in vitro fertilization leading to the birth of live calves, clones produced by nuclear transfer from embryonic cells, and ovum pick-up via ultrasound-guided follicular aspiration. The 20th century ended with the birth of calves produced from AI with sexed semen, sheep and cattle clones produced by nuclear transfer from adult somatic cell nuclei, and the birth of transgenic cloned calves. The 21st century has seen the introduction of perhaps the most powerful biotechnology since the development of artificial insemination and cryopreservation. Quick, inexpensive genomic analysis via the use of single nucleotide polymorphism genotyping chips is revolutionizing the cattle breeding industry. Now, with the introduction of genome editing technology, the changes are becoming almost too rapid to fully digest.

Clearance of liquid from lungs of newborn rabbits.

Apparent inconsistencies in the results of previous studies led us to reexamine the process by which fluid leaves the lungs of newborn rabbits after birth. We measured pulmonary blood volume, extravascular lung water, and the size of perivascular cuffs of fluid in frozen sections of lung obtained from 166 full-term rabbits (31 days gestation) born vaginally or by cesarean section. We killed the rabbits by giving them barbiturate intraperitoneally and immersing them in liquid nitrogen before they breathed or at randomly predetermined intervals from 5 min to 24 h after birth. We found that a) pulmonary blood volume of both groups of rabbits increased soon after birth, b) extravascular lung water per gram of dry lung tissue was greater at birth in rabbits born by cesarean section than in those born vaginally, c) extravascular lung water did not begin to decrease in either group of animals until 30-60 min postnatally, after which it decreased progressively for 24 h, and d) the rate of fluid clearance and pattern of puddling around pulmonary vessels was similar in both groups of rabbits, with maximal perivascular cuffs 30 min after birth, followed by diminution of cuff size as the lungs shed water.

The effect of prolonged cold exposure on heat production in new-born rabbits.

1. The rates of oxygen consumption and the colonic temperatures were monitored from birth in rabbits delivered by Caesarean section at term. The rates of oxygen consumption at 25 and 36 degrees C rose over the first 12 hr of life.2. Thirty rabbits were kept unfed in an environment of 25 degrees C from birth. Extra oxygen consumption, in response to cold exposure, failed 24-34 hr later. Twenty-four of these rabbits were allowed to recover in an environment of 36 degrees C. The metabolic response to cold exposure did not return in those kept unfed or given glucose but those fed with rabbit's milk showed significant recovery when re-exposed to cold 4 or 18 hr later.3. The tissue glyceride content of brown and white adipose tissue and the liver were greatly reduced once the animals failed to respond to cold exposure and no significant rise was detected during the recovery period after a milk feed.4. Another twelve rabbits were kept unfed in an environment of 36 degrees C. These animals showed a poor metabolic response to cold exposure after 48 hr, although their brown adipose tissue was still replete with fat and the blood glucose rose to normal values during cold exposure.5. These results suggest that an increase in oxygen consumption in response to cold exposure can occur even though brown adipose tissue is largely depleted of glyceride provided that an alternative supply of fuel is available. Glucose alone is not an adequate source of energy.