Body size, body temperature and age in relation to the metabolic rate of the pig in the first five weeks after birth

Frequent Occurrence of Simultaneous Infection with Multiple Rotaviruses in Swiss Pigs

Rotavirus (RV) infections are the most important viral cause of diarrhea in piglets in Switzerland and are thought to cause substantial economic losses to the pig industry. However, no data are available on the occurrence and dynamics of the main porcine RV species, namely RVA, RVB, and RVC, and the diversity of the circulating strains. We therefore tested fecal samples from a cross-sectional (n = 95) and a longitudinal (n = 48) study for RVA, RVB, and RVC by real-time RT-PCR and compared the results of the cross-sectional study to postmortem findings. In addition, eight samples were fully genotyped by using next-generation sequencing. In the cross-sectional study, triple RV infections significantly correlated with diarrhea and wasting and were most frequent in the weaned age group. In the longitudinal study, the shedding of RV peaked one week after weaning and decreased thereafter. Here, mainly double infections were seen, and only a few animals showed diarrhea. The full-genome sequencing revealed a genotype pattern similar to other European countries and, importantly, co-infection by up to four RVA strains. Our results imply that the weaning of piglets may trigger not only RV shedding but facilitate co-infection of multiple RV species and strains in the same host.

Safety and immunogenicity in piglets of two immunization schedules initiated at two or three weeks of age with PorvacÒ, a classical swine fever subunit marker vaccine

Classical swine fever is a highly contagious viral disease with a significant impact on food production worldwide. It currently represents one of the main limitations for the development of the pig industry in Cuba. PorvacÒ is a subunit marker vaccine that confers a very rapid onset of protection. Since there are different production systems in pig breeding, readjustments in the vaccination program are often required. This study compares the safety and efficacy in piglets of two vaccination schedules with PorvacÒ (0-2 weeks and 0-3 weeks), initiated at two or three weeks of age. Clinical monitoring was conducted, and a neutralization peroxidase-linked assay was used to measure the neutralization titers. All immunization regimens were safe and well-tolerated, without local or systemic adverse reactions in the vaccinated animals. Geometric mean neutralizing antibody titers higher than 1/1500 were detected in all groups during the six months of the trial. One month after the second immunization, piglets primed at two weeks of age, and boostered three weeks later, developed significantly higher neutralization titers (1/15644) compared to those vaccinated at a similar age but with a two-week interval between doses (1/5760). However, no significant differences in the titers were found three and six months after vaccination among the four regimens. In summary, all the variants studied are effective, but it is recommended to start vaccination at two weeks old, with the second dose at either two or three weeks later, depending on the production system and the purpose of the farm.

Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals

Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.

Immediate hypothermia reduces cardiac troponin I after hypoxic-ischemic encephalopathy in newborn pigs

Neonatal hypoxic-ischemic encephalopathy (HIE) is a clinically defined neurological condition after lack of oxygen and often associated with cardiac dysfunction in term infants. Therapeutic hypothermia (HT) after birth is neuroprotective in infants with HIE. However, it is not known whether HT is also cardioprotective. Four newborn pigs were used in the pilot study and a further 18 newborn pigs [randomly assigned to 72 h normothermia (NT) or 24 h HT followed by 48 h NT] were subjected to global HIE insults. Serum cTnI was measured before and post the HIE insult. Blood pressure, inotropic support, blood gases, and heart rate (HR) were recorded throughout. Cardiac pathology was assessed from histological sections. Cooling reduced serum cTnI levels significantly in HT pigs by 6 h (NT, 1.36 ± 0.67; HT, 0.34 ± 0.23 ng/mL; p = 0.0009). After rewarming, from 24 to 30 h postinsult, HR and cTnI increased in the HT group; from HR[24 h] = 117 ± 22 to HR[30 h] = 218 ± 32 beats/min (p = 0.0002) and from cTnI[24 h] = 0.23 ± 0.12 to cTnI[30 h] = 0.65 ± 0.53 ng/mL, (p = 0.05). There were fewer ischemic lesions on cardiac examination (37%) in the HT group compared with the NT group (70%). HT (24 h) pigs did not have the postinsult cTnI increase seen in NT-treated pigs. There was a trend that HT improved cardiac pathology in this 3-d survival model.

Environmental cooling of the newborn pig brain during whole-body cooling

AIM

Therapeutic hypothermia after perinatal asphyxia decreases brain injury in newborns, whereas hyperthermia worsens the brain injury. We examined how different clinical practices influence regional brain temperatures during hypothermia.

METHODS

Six newborn pigs, which have comparable physiology and brain maturation to human term infants, were maintained at hypothermia (33.5°C) or normothermia with a servo-controlled whole-body cooling device that is in clinical use. Pigs were anesthetized and fully instrumented for cardiovascular and temperature (rectal and regional brain) monitoring. Changes in brain temperatures were measured during four different paradigms to mimic different clinical practices.

RESULTS

Inserting an insulating pillow between the head and the heated surface reduced cortex temperature by 1 or 2°C during normothermia (core temperature T(core) 37°C) or hypothermia, T(core) 33.5°C. Reducing ambient temperature from 28°C to 23°C reduced cortex temperature by 3.9 ± 1.9°C. Without a hat and overhead heater at normothermia, cortex and deep brain temperatures were reduced by 1.2 ± 0.8 and 0.7 ± 0.7°C, respectively. Direct overhead heating abolished the normal cortex to deep brain temperature gradient that was maintained if using a head shield.

CONCLUSION

Brain temperature may differ from core temperature during therapeutic hypothermia influenced by different clinical practices.

Scaled cortical impact in immature swine: effect of age and gender on lesion volume

The piglet scaled cortical impact model creates a focal contusion using a skull-mounted, spring-loaded blunt indentation device scaled to achieve identical tissue strains in subjects with different brain sizes. Preliminary data showed that contusion size increased proportional to subject age. This study details the results from a new, larger series of subjects of three ages, and compares the effect of age and additional host and physiologic variables on injury response. Sixty-seven subjects, including infant (5- to 7-day-old), "toddler" (1-month-old), and early adolescent (4-month-old) swine underwent scaled cortical impact under strict anesthetic protocols. Serum glucose, testosterone, and 17beta-estradiol levels were measured. Lesion size was measured at 1 week post injury, as the ratio of the lesion area over the area of the contralateral hemisphere. Adolescent subjects had lesions over eight times larger than infants (p < 0.0001). Lesion volumes were larger in toddlers than in infants, most significantly for males (p < 0.05). Adolescent subjects were warmer on average, but there was no correlation between temperature and lesion volume within any age group. Serum glucose did not differ among ages. Infant males had the highest levels of circulating sex steroids. In this model, age was the most robust predictor of lesion size. Temperature had an effect, but did not explain all the variability seen among age groups. There was an interaction among gender, hormone levels, and lesion size in younger subjects. Characterization of these variables allows use of this model for treatment trials for subjects at different stages of maturation.

Analysis of neuronal, glial, endothelial, axonal and apoptotic markers following moderate therapeutic hypothermia and anesthesia in the developing piglet brain

Hypothermia (HT) by whole body (WBC) or selective head cooling (SHC) reduces hypoxic-ischemic (HI) brain injury; however, whether prolonged hypothermia and/or anesthesia disrupts immature brain development, eg, increases apoptosis, is unknown. Anesthesia increases apoptosis in immature animals. We investigated whether neuroprotective hypothermia and anesthesia disrupts normal brain development. Thirty-eight pigs <24 h old were randomized between five groups and were killed after 72 h: eighteen received a global hypoxic-ischemic insult under anesthesia, eight subsequently cooled by SHC with WBC to T(rectal) 34.5 degrees C for 24 h, followed by 48 h normothermia (NT) at T(rectal) 39.0 degrees C, while 10 remained normothermic. Sixteen underwent anesthetized sham hypoxic-ischemic, six then following normothermia and 10 following hypothermia protocols. There were four normothermic controls. The hypothermia groups demonstrated significant brain hypothermia. In the hypoxic-ischemic groups this conferred approximately 60% neuroprotection reducing histological injury scores in all brain areas. Immunohistochemical/histochemical analyses of neuronal, glial, endothelial, axonal, transcriptional apoptotic markers in areas devoid of histological lesions revealed no hypothermia/normothermia group and differences whether exposed to hypoxic-ischemic or not. Neither 36-h anesthesia nor 24-h hypothermia produced adverse effects at 4-day survival on a panel of brain maturation/neural death markers in newborn pigs. Longer survival studies are necessary to verify the safety of hypothermia in the developing brain.

Twenty-four hours of mild hypothermia in unsedated newborn pigs starting after a severe global hypoxic-ischemic insult is not neuroprotective

Three to 12 h of mild hypothermia (HT) starting after hypoxia-ischemia is neuroprotective in piglets that are anesthetized during HT. Newborn infants suffering from neonatal encephalopathy often ventilate spontaneously and are not necessarily sedated. We aimed to test whether mild posthypoxic HT lasting 24 h was neuroprotective if the animals were not sedated. Thirty-nine piglets (median weight 1.6 kg, range 0.8-2.2 kg; median age 24 h, range 7-48 h) were anesthetized and ventilated and subjected to a 45-min hypoxic (FiO(2) approximately 6%) global insult (n = 36) or sham hypoxia (n = 3). On reoxygenation, 18 were maintained normothermic (NT, 39.0 degrees C) for 72 h, and 21 were cooled from 39 (NT) to 35 degrees C (HT) for the first 24 h before NT was resumed (18 experimental, three sham hypoxia). Cardiovascular parameters and intermittent EEG were documented throughout. The brain was perfusion fixed for neuropathology and five main areas examined using light microscopy. The insult severity (duration in minutes of EEG amplitude < 7 microV) was similar in the NT and HT groups, mean +/- SD (28 +/- 7.2 versus 27 +/- 8.6 min), as was the mean FiO(2) (5.9 +/- 0.7 versus 5.8 +/- 0.8%) during the insult. Six NT and seven HT piglets developed posthypoxic seizures that lasted 29 and 30% of the time, respectively. The distribution and degree of injury (0.0-4.0, normal-maximal damage) within the brain (hippocampus, cortex/white matter, cerebellum, basal ganglia, thalamus) were similar in the NT and HT groups (overall score, mean +/- SD, 2.3 +/- 1.5 versus 2.4 +/- 1.3) as was the EEG background amplitude at 3 h (13 +/- 3.5 versus 10 +/- 3.3 microV). The HT animals shivered and were more active. The sham control group (n = 3) shivered but had normal physiology and neuropathology. Plasma cortisol was significantly higher in the HT group during the HT period, 766 +/- 277 versus 244 +/- 144 microM at 24 h. Mild postinsult HT for 24 h was not neuroprotective in unsedated piglets and did not reduce the number of animals that developed posthypoxic seizures. Cortisol reached 3 times the NT value at the end of HT. We speculate that the stress of shivering and feeling cold interfered with the previously shown neuroprotective effect of HT. Research on the appropriateness of sedation during clinical HT is urgent.

Mild hypothermia after severe transient hypoxia-ischemia reduces the delayed rise in cerebral lactate in the newborn piglet

This study tested the hypothesis that mild hypothermia after severe transient hypoxia-ischemia reduces the subsequent delayed rise in cerebral lactate peak-area ratios as determined by proton (1H) magnetic resonance spectroscopy (MRS) in the newborn piglet. Nine piglets aged < 24 h underwent temporary occlusion of the common carotid arteries and hypoxemia. Resuscitation was started when cerebral [phosphocreatine]/[inorganic phosphate] had fallen close to zero and [nucleotide triphosphate (NTP)]/[exchangeable phosphate pool (EPP)] was below about a third of baseline. On resuscitation rectal and tympanic temperatures were lowered to 35 degrees C for 12 h after which normothermia (38.5 degrees C) was resumed. 1H MRS data collected over 48 or 64 h after resuscitation were compared with concurrently established data from 12 piglets similarly subjected to transient cerebral hypoxia-ischemia, but maintained normothermic, and six sham-operated controls. The severity of the primary insult (judged from the time integral of depletion of [NTP]/[EPP]) was similar in the hypothermic and normothermic groups. The maximum lactate/N-acetylaspartate ratio observed between 24 and 48 h after resuscitation in the hypothermic group was 0.10 (0.05-0.97), median (interquartile range), which was significantly lower than that observed in the normothermic group, 1.28 (0.97-2.14), and not significantly different from that observed in the control group, 0.08 (0.06-0.11). Similar results were obtained for lactate/choline and lactate/total creatine. We conclude that mild hypothermia after a severe acute cerebral hypoxic-ischemic insult reduces the delayed elevation in lactate peak-area ratios, thus reflecting reduced lactate accumulation.

MAC for halothane and isoflurane during normothermia and hypothermia in the newborn piglet

BACKGROUND

Halothane and isoflurane are frequently used in studies of perinatal hypoxia and ischemia. Little information exists on the minimum alveolar concentration (MAC) necessary to prevent movement to a painful stimulus in newborn pigs and no information on the effects of hypothermia on MAC in pigs. Hypothermia is currently investigated as a posthypoxic neuroprotective intervention.

METHODS

The MAC of halothane and isoflurane necessary to prevent movement when a 25 cm hemostatic clamp was applied to the tail were determined in six 20-48-hour-old piglets, and when the same stimulus was applied to the hoof. MAC for halothane was first determined at 39 degrees C, then at 35 degrees C, whereafter halothane was discontinued and MAC for isoflurane determined first at 35 degrees C and then at 39 degrees C.

RESULTS

In all six piglets MAC was lower at 35 degrees C than at 39 degrees C for both anesthetics with both tail and hoof determination, lower for halothane than isoflurane for both stimuli at both temperatures, and lower for tail than hoof determination for both anesthetics at both temperatures. For halothane at 39 degrees C, mean (SD) MAC hoof was 0.82 (0.05)% vs tail 0.60 (0.12)%, and at 35 degrees C, hoof 0.65 (0.06)% vs tail 0.42 (0.10)%. For isoflurane at 39 degrees C, MAC hoof was 2.47 (0.28)% vs tail 1.83 (0.28)%, and at 35 degrees C, hoof was 1.83 (0.18)% vs tail 0.85 (0.25)%.

CONCLUSION

In the newborn piglet, MAC should be determined by hoof clamp, MAC of isoflurane is approximately three times that of halothane, and both are reduced during hypothermia.

Postnatal development of the cerebral blood flow velocity response to changes in CO2 and mean arterial blood pressure in the piglet

Cerebral blood flow velocity was studied during changes (haemorrhage) in mean arterial blood pressure or P(a)CO2 in 56 (aged 0-26 days) anaesthetized and ventilated piglets. The CO2 reactivity increased with age from 6.5% kPa-1 (< 1 day) to adult levels of 25% kPa-1 for piglets over 4 days old. The mean arterial blood pressure reactivity was reduced from 1.3% mmHg-1 (< 1 day old) to 0.0%/mmHg (> 4 days old). The reactivities were similar with two different anesthetics: chloralose/urethane or pentobarbital. To validate the cerebral blood flow velocity data, both electromagnetic flow and precerebral Doppler ultrasound velocity were recorded from the same common carotid artery with extracranial branches tied off. There were no differences between the results with these two methods nor between these results and those obtained when the cerebral blood flow velocities were recorded from an intracerebral artery and the electromagnetic flowmeter recorded from the carotid artery. The vessel diameter appears stable during these interventions. In conclusion, the autoregulatory response and the reaction to P(a)CO2 appear poorly developed in the newborn piglet, but rapidly mature during the first 4 days of life.

Morphometry of postnatal development in the porcine lung

Alveolar regions of normal pig lungs (newborn to 60-day-old) were characterized morphometrically to provide a basis for comparison in future investigations of porcine respiratory diseases. Endotracheal installation of fixative was done to expand the lungs uniformly at total capacity. Differential effects of lobar variations were determined by stratified random sampling of lung lobes. A stereologic study was done by point and intersection counts on electron micrographs. At birth, the lungs were remarkably well developed. Relative alveolar and capillary surface densities and air-blood tissue barrier thicknesses were at adult levels. In allometric regressions, volumes and surfaces of lung components regressed directly to lung volume, but monoexponentially (to the 3/4 power) with body weight. In the first postnatal week, however, relative volume densities of cellular interstitium in septal tissue and of capillary lumina in parenchyma increased at statistically significant levels. Composition of lung parenchyma and septa was changed, although without statistically significant direct impact on parameters related to gas exchange. Type II pneumocytes had increased nuclear to cytoplasmic volume ratios in 7- to 14-day-old pigs, probably reflecting cell activation and increased surfactant production. Age (postnatal lung growth) created the most substantial variance of results; interanimal variation in pigs of the same age was less important and no consistent lobar variations were seen.

Respiratory studies in foals from birth to seven days old

Respiratory measurements and blood-gas and acid-base values are reported in nine term induced foals. Measurements were performed at 2, 15, 30 and 60 mins, 4, 12, 24 and 48 h, and four and seven days after birth. Minute respiratory volume was significantly lower at birth than values from 12 h old. Tidal volume peaked at 60 mins old, while respiration rate decreased significantly at 15 mins after birth. Oxygen consumption was high at birth and decreased to its lowest values at 24 and 48 h. The respiratory exchange ratio and ventilatory equivalent showed few significant changes to seven days, as did the minute alveolar ventilation and physiological deadspace. The blood-gas and acid-base values indicated that the foals rapidly establish adequate pulmonary ventilation within minutes of birth, and that those values changed little from 12 h to seven days after birth. Body position had a significant effect on arterial oxygen tension with Pao2 values in lateral recumbency being, on average, 14 mmHg lower than when the foals were standing.

Quantitative lung morphology in newborn mammals

We have examined the lungs of eleven species of newborn mammals by quantitative morphometric techniques and related the findings to body weight (BW) and O(2) consumption (Vo2 is found to be proportional to BW(0.88); this exponent is significantly greater than the value of about 0.73, repeatedly found for adult mammals. Lung volume (LV) is essentially proportional to BW, and neonatal alveolar size - as indicated by mean chord length - is nearly constant among species and independent of BW. Thus the respiratory surface area (SA) is not proportional to Vo2, as in adult mammals, but to Vo2(1.23). Neonates of small species have lower SA/Vo2 ratios than adult mammals, possibly owing to constraints of surface forces on alveolar size. Newborn members of larger species have SA/Vo2 values in excess of the adult range. Published data on human newborn lung dimensions suggest that the human infant may have an unexpectedly low SA/Vo2 value in relation to BW. Whether this is a valid finding, or whether it derives from methodological differences between studies cannot be ascertained from the available data.

The relation between body size and maximum and minimum metabolic rates in the new-born pig

1. Measurements of rates of oxygen consumption were made on a total of sixty-two Large White pigs aged between 1 hr and 6 days, with a range of body weight from 0.75 to 2.40 kg.2. The maximum rate was determined from the continuous estimation of oxygen consumption as the environmental temperature fell past the point at which the maximum occurred.3. The minimum rate was determined both as the environmental temperature rose through the zone of thermal neutrality, and from measurements at thermal neutrality.4. In animals aged 1-6 days the mean maximum rate was 49.0 ml. O(2)/kg.min, and the mean minimum was 15.3 ml. O(2)/kg.min. Both rates were proportional to body weight and not to surface area.5. Pigs less than 1 day old exhibited lower maximum and minimum rates than the older pigs.