Variability in tracheal mucociliary transport is not controlled by beating cilia in lambs in vivo during ventilation with humidified and nonhumidified air.

Mucociliary transport in the respiratory epithelium depends on beating of cilia to move a mucus layer containing trapped inhaled particles toward the mouth. Little is known about the relationship between cilia beat frequency (CBF) and mucus transport velocity (MTV) in vivo under normal physiological conditions and when inspired air is dry or not fully humidified. This study was designed to use video-microscopy to simultaneously measure CBF and MTV in the tracheal epithelium through an implanted optical window in mechanically ventilated lambs. The inspired air in 6 animals was heated to body temperature and fully saturated with water for 4 hours as a baseline. In another series of experiments, 5 lambs were ventilated with air at different temperatures and humidities and the mucosal surface temperature was monitored with infrared macro-imaging. In the baseline experiments, during ventilation with fully humidified air at body temperature, CBF remained constant, mean 13.9 ± 1.6 Hz but MTV varied considerably between 0.1 and 26.1 mm/min with mean 11.0 ± 3.9 mm/min, resulting in a maximum mucus displacement of 34.2 µm/cilia beat. Fully humidified air at body temperature prevented fluctuations in the surface temperature during breathing indicating a thermodynamic balance in the airways. When lambs were ventilated with dryer air, the mucosal surface temperature and MTV dropped without a significant change in CBF. When inspired air was dry, mainly latent heat (92%) was transferred to air in the trachea, reducing the surface temperature by 5 °C. Reduced humidity of the inspired air lowered the surface temperature and reduced MTV in the epithelium during ventilation.

A Bayesian threshold-linear model evaluation of perinatal mortality, dystocia, birth weight, and gestation length in a Holstein herd.

The objective of this research was to estimate genetic parameters for a multiple-trait evaluation of dystocia (DYS), perinatal mortality (PM), birth weight (BWT), and gestation length (GL) in Holsteins. The data included 5,712 calving records collected between 1968 and 2005 from the Iowa State University dairy breeding herd in Ankeny. The incidence of PM was 8.8% and that of DYS 28.8%; mean BWT was 40.5 kg, and GL was 279 d. A threshold-linear animal model included the effects of year, season, sex of calf, parity, sire group, direct genetic, maternal genetic, and maternal permanent environment. Direct heritabilities for DYS, PM, BWT, and GL were 0.11 (0.04), 0.13 (0.05), 0.26 (0.04), and 0.51 (0.05), respectively. Maternal heritabilities were 0.14 (0.04), 0.15 (0.03), 0.08 (0.01), and 0.08 (0.02), for DYS, PM, BWT, and GL, respectively. The heritabilities are the posterior means of the Gibbs samples with their standard deviations in parentheses. The direct genetic correlation between PM and DYS was estimated at 0.67 (0.19), whereas the maternal genetic correlation was 0.45 (0.16). Direct and maternal PM and DYS are partially controlled by the same genes. Selection on only calving ease is not sufficient to control PM. With moderate genetic correlations between all 4 traits, BWT and GL should be included with DYS and PM in an evaluation of calving performance.

Experimental triggering of reproduction in a natural population of Microtus montanus.

A nonbreeding winter population of Microtus montanus was given limited supplements of fresh green wheatgrass over a 2-week period. The population was sampled at the end of the feeding period and compared to an adjacent population receiving no grass supplements. All of the experimental females were pregnant, while animals from the control area remained in nonbreeding condition. Replication of the experiment during the next winter produced similar results. The data suggest that Microtus montanus cues reproductive effort from chemical signals in the plant food resources.

Chemical triggering of reproduction in Microtus montanus.

In a replicated experiment, nonbreeding winter populations of Microtus montanus were given supplements of rolled oats coated with 6-methoxybenzoxazolinone, a naturally occurring plant derivative. After 3 weeks of this feeding regime, samples from the populations demonstrated a high incidence of pregnancy in females and testicular hypertrophy in males. Control populations receiving rolled oats coated only with the solvent showed no reproductive activity. These results demonstrate that the presence of 6-methoxybenzoxazolinone in the plant food resource acts as the ultimate cue to trigger reproductive effort in Microtus montanus.

Phenolic plant compounds functioning as reproductive inhibitors in Microtus montanus.

Naturally occurring cinnamic acids and their related vinylphenols were found to inhibit reproductive function in Microtus montanus. When fed on these compounds, the rodents exhibited decreased uterine weight, inhibition of follicular development, and a cessation of breeding activity. It is suggested that these animals utilize plant compounds as a cue to terminate their reproductive effort in natural populations.

Genome-wide scan for bovine twinning rate QTL using linkage disequilibrium.

Twinning is a complex trait with negative impacts on health and reproduction, which cause economic loss in dairy production. Several twinning rate quantitative trait loci (QTL) have been detected in previous studies, but confidence intervals for QTL location are broad and many QTL are unreplicated. To identify genomic regions or genes associated with twinning rate, QTL analysis based on linkage combined with linkage disequilibrium (LLD) and individual marker associations was conducted across the genome using high-throughput single nucleotide polymorphism (SNP) genotypes. A total of 9919 SNP markers were genotyped with 200 sires and sons in 19 half-sib North American Holstein dairy cattle families. After SNPs were genotyped, informative markers were selected for genome-wide association tests and QTL searches. Evidence for twinning rate QTL was found throughout the genome. Thirteen markers significantly associated with twinning rate were detected on chromosomes 2, 5 and 14 (P < 2.3 x 10(-5)). Twenty-six regions on fourteen chromosomes were identified by LLD analysis at P < 0.0007. Seven previously reported ovulation or twinning rate QTL were supported by results of single marker association or LLD analyses. Single marker association analysis and LLD mapping were complementary tools for the identification of putative QTL in this genome scan.

Graphical approach to evaluate genetic estimates of calf survival.

Genetic variation and resemblance among relatives are fundamentals of quantitative genetics. Our purpose was to identify bulls with a bimodal pattern of inheritance in the quest for new discoveries about the inheritance of calf survival. A bimodal pattern of inheritance for calf survival was identified in sons of Holstein bulls. A bimodal pattern of inheritance indicates 2 groups of sons resulting from an allele effect, a grandsire effect, or some other common factor. Different combinations (AA, Aa, aa) of 2 alleles at a locus cause varying phenotypes to be expressed. Bulls that are heterozygous for loci affecting reproductive performance may have a bimodal pattern of inheritance if the difference in effect of the 2 alleles is large. If the bimodal pattern is caused by an allele effect, then molecular markers can be identified for use in marker-assisted selection breeding programs. Data on predicted transmitting ability for perinatal survival for the first parity of 8,678 sons of 599 sires were collected from 1984 through 1997 from the National Association of Animal Breeders calving ease database, which included 7 Midwestern states. Sixteen bulls were identified with a potential bimodal pattern of inheritance because they had 2 distinct groups of sons. The 2 groups of sons were separated by calculating the coefficient of variation for each possible combination of sons; the combination that gave the smallest coefficient of variation difference between the 2 groups was considered the correct distribution of the sons into those groups. Bulls with a bimodal distribution were analyzed to determine the distribution of the grandsons among the maternal grandsires (MGS) of the 2 groups of the bimodal distribution. The bimodal distribution may be a result of heterozygous sires or MGS that are homozygous for low or high survival. If the bimodal distribution is caused by a MGS effect, then marker-assisted selection can still be used by evaluating the MGS instead of the sires.

A small family of elements with long inverted repeats is located near sites of developmentally regulated DNA rearrangement in Tetrahymena thermophila.

Extensive DNA rearrangement occurs during the development of the somatic macronucleus from the germ line micronucleus in ciliated protozoans. The micronuclear junctions and the macronuclear product of a developmentally regulated DNA rearrangement in Tetrahymena thermophila, Tlr1, have been cloned. The intrachromosomal rearrangement joins sequences that are separated by more than 13 kb in the micronucleus with the elimination of moderately repeated micronucleus-specific DNA sequences. There is a long, 825-bp, inverted repeat near the micronuclear junctions. The inverted repeat contains two different 19-bp tandem repeats. The 19-bp repeats are associated with each other and with DNA rearrangements at seven locations in the micronuclear genome. Southern blot analysis is consistent with the occurrence of the 19-bp repeats within pairs of larger repeated sequences. Another family member was isolated. The 19-mers in that clone are also in close proximity to a rearrangement junction. We propose that the 19-mers define a small family of developmentally regulated DNA rearrangements having elements with long inverted repeats near the junction sites. We discuss the possibility that transposable elements evolve by capture of molecular machinery required for essential cellular functions.

Type and amount of dietary fat affect relative concentration of cholesterol in blood and other tissues of rats.

The effects of diet on tissue cholesterol disposition in the rat were studied. Growing rats were fed a nonfat dry milk supplemented with two levels of soy-bean oil (SBO) and tallow (T) such that either 30% or 50% of total dietary calories came from fat. Two of four groups of rats fed the diets with 50% of calories from fat were supplemented with 20% ground whole oats. Considering all diets, rats fed SBO had higher blood and kidney cholesterol than did rats fed T; supplementation of the diet with oats increased the plasma cholesterol of the "50%" SBO rats and , conversely, decreased plasma cholesterol of the "50%" T rats. Muscle cholesterol content was not affected by variations in dietary fat and oats. In all treatments, cholesterol concentration of epididymal fat and liver were greater in the SBO-fed than in the T-fed rats.

Functional importance of a highly elastic ligament on the mammalian diaphragm.

The diaphragm of mammals is a musculotendinous dome separating the thoracic and abdominal cavities. With no skeletal elements to stretch it, the diaphragm has the problem of positioning its muscle fibres at a length appropriate for the onset of an inspiratory contraction. This is achieved through a negative intrapleural pressure, resulting from the opposing elastic recoil of the ribcage and lungs, which sucks the diaphragm into the thorax and extends the muscle fibres. A consequence of this negative pressure is that the diaphragm muscle is under tension when inactive during expiration. This is an unusual condition for skeletal muscles, which can suffer irreversible changes when stretched to long length, or they may respond by growing longer. We now describe a highly elastic and resilient diaphragmatic ligament which sets a sarcomere length enabling the muscle to use its full operating range, reduces stress on the diaphragm muscle fibres, and assists shortening of the diaphragm muscle at the onset of inspiration by means of elastic recoil.

Uterotropic 6-methoxybenzoxazolinone is an adrenergic agonist and a melatonin analog.

6-Methoxybenzoxazolinone (MBOA) is a compound isolated from grasses which has gonadotropic effects in a variety of animals. The weak beta-adrenergic agonist character of MBOA is shown by its in vitro stimulation of adenylate cyclase from several tissues. Tritiated MBOA bound specifically to particulate fractions from uterus is also displaced by alpha- and beta-adrenergic compounds. The adrenergic properties of MBOA suggest it may exert diverse effects including direct actions on gonadotropin synthesis and release. The mixed adrenergic agonist ephedrine and the antidepressant imipramine were also found to be uterotropic in the vole Microtus montanus following injection protocols used with MBOA. MBOA is structurally similar to melatonin (5-methoxy-N-acetyltryptamine); [3H]melatonin which binds to uterine and pineal membranes is displaced by MBOA and by other adrenergic agents. The fact that MBOA is a beta-adrenergic agonist and a melatonin analog can account for stimulatory and inhibitory effects of this compound on sexual development.

Decline in lung liquid volume before labor in fetal lambs.

The volume of liquid in the fetal lung depends on the amount of liquid secreted across the pulmonary epithelium and the amount flowing through the trachea. Lung liquid volume (V1) and secretion rate Vs) were determined using an indicator-dilution technique, while tracheal flow rate (Vtr) was measured simultaneously with a bubble flowmeter. Least-squares regression analysis showed that in 10 chronically instrumented fetal lambs, V1 increased from 51.0 ml at 119 days to 104.6 ml at 135 days (V1 = -347.65 + 3.35 X days; 95% confidence limits on slope: 1.89-4.81) before declining to 70.2 ml at 142 days gestation (V1 = 768.8 - 4.92 X days; 95% confidence limits on slope: -2.55 to -7.30). Similarly Vs increased from 7.4 ml/h at 119 days to 16.8 ml/h at 133 days (Vs = -72.35 + 0.67 X days; 95% confidence limits on slope: 0.21-1.14), before declining to 7.1 ml/h at 142 days (Vs = 159.07 - 1.07 X days; 95% confidence limits on slope: -0.56 to -1.57). Vtr did not change significantly with gestation. We conclude that V1 increases until 135 days gestation, after which it falls substantially. This fall in volume, which occurs well before the onset of labor, results predominantly from the decline in Vs.

State-related changes in lung liquid secretion and tracheal flow rate in fetal lambs.

The volume of liquid in the fetal lungs depends on the rate of liquid secretion (Vs) across the pulmonary epithelium and the rate of flow out of the trachea (Vtr). We measured Vs, by an isotope-dilution technique, and Vtr, with a bubble flowmeter, during low-voltage (LV) and high-voltage (HV) electrocortical activity. In nine chronically instrumented fetal lambs, Vtr was greater during the transition to and at LV (16.98 +/- 1.98 ml/h, mean +/- SE, n = 23) than values during the transition to and at HV (8.69 +/- 0.8 ml/h). A pronounced peak in Vtr of 22.3 +/- 1.8 ml/h (n = 197) occurred at the transition to LV and early in the LV state. Ten minutes or more into LV, Vtr had declined to 10.3 +/- 1.8 ml/h (n = 235). Vtr remained low throughout the HV state. Vs values were not significantly different throughout the LV (11.83 +/- 1.34 ml/h, n = 216) and the HV (13.61 +/- 2.34 ml/h, n = 174) states. Diaphragmatic burst rate during LV (146.9 +/- 6.7 bursts/5 min, n = 432) was greater than during HV (26.5 +/- 4.6 bursts/5 min, n = 348), but burst rate was not correlated with Vtr. In summary, Vtr reaches a peak during the early part of LV when breathing commences and Vs remains constant throughout the behavioral cycle. As a result, lung liquid volume increases slightly during HV and decreases by a similar amount in the early part of LV.

Errors in estimating lung liquid volume in fetal lambs when using radiolabeled serum albumin and blue dextran.

Fetal lung liquid volume is usually determined by using radio-iodinated serum albumin (RISA) or blue dextran (BD) as volume tracers. We tested the reliability of both tracers at 124 (G124) and 142 days of gestation (G142; term = G147) when the labels were employed simultaneously. We measured the proportion of label bound reversibly to the lung, or apparently lost from the lung compartment, by washing out the lung with saline and 5% albumin. At G124, volume estimates with the two labels were similar. At G142, the volume estimate with BD (36.3 +/- 8.7 ml/kg of body wt) was higher (P < 0. 05) than with RISA (22.3 +/- 3.5 ml/kg). This difference resulted from reversible binding of BD, because 5% albumin washout released 38.5 +/- 4.0% of the BD added at the start of the experiment but a lesser amount of RISA (9.8 +/- 0.7%; P < 0.05). At G142, when RISA was used alone, its reversible binding was 1.3 +/- 0.2%. Background absorbance increased during experiments, giving rise to an apparent increase in BD concentration. We conclude that RISA is an effective tracer for lung liquid volume determination in the fetal lamb, whereas our findings of substantial epithelial binding of BD and large changes in background absorbance demonstrate that, under the conditions of our experiments, BD is a poor tracer close to term.

Easily-implantable electrodes for chronic recording of electromyogram activity in small fetuses.

A method is described for the construction of simple, robust electrodes suitable for obtaining long-term chronic recordings of electromyogram activity from delicate muscles of small experimental animals. The electrodes are equipped with small, gold-plated barbed tips which have the form of harpoons that may be pushed directly into a muscle, where they remain without being sutured into place. These features greatly facilitate the instrumentation of muscles which are very thin or of limited accessibility. The electrodes have been used successfully to obtain chronic recordings of respiratory muscle activity from early gestation fetal lambs in utero.

Precursor of respiratory pattern in the early gestation mammalian fetus.

Recordings of respiratory muscle activity in fetal lambs from early in gestation provide insight into the organization of the central pattern generator for respiration in mammals. Evidence presented here is consistent with the recent hypothesis that production of the respiratory pattern involves two separate neural modules: one, the 'rhythm' module, which specifies the respiratory cycle and another, the 'form' module, which creates the characteristic shape of each burst of activity within this cycle. The rhythm module is already functional when gestation is 35% complete while the form module appears to be constructed gradually over the second half of gestation.

Origin of tonic electrical activity patterns in the diaphragm of the fetal lamb.

The respiratory pattern generator in fetal and postnatal life activates the phrenic nucleus and diaphragm muscle with phasic bursts of activity. In the fetus, diaphragmatic activity is also characterized by tonic activity patterns of unknown origin. We have examined whether such activity is diaphragmatic, or radiated from nearby ribcage muscles, by placing two sets of electrodes side-by-side in the costal portion of the diaphragm in five fetuses. The rationale for this approach is that if tonic activity, radiates to the diaphragm it should be recorded by both sets of electrodes and there should be no delay between the action potentials from each set of electrodes. Of 24 single tonic units identified, 15 were recorded from only one of the two sets of electrodes in the diaphragm. In the 9 tonic units recorded from both sets of electrodes, there was a time delay between the appearance of the action potentials in the two recordings (mean +/- S.E.M. 1.6 +/- 0.2 ms). This is the expected conduction delay along the muscle fibres separating the two electrodes. Since tonic diaphragmatic activity persisted in fetuses with the spinal cord transected rostral or caudal to the phrenic nucleus, we conclude that the spinal cord alone is sufficient to produce the tonic activity recorded from the fetal diaphragm but that the brain may also generate such activity.

Properties of threshold model predictions.

Estimation of genetic parameters and accuracy of threshold model genetic predictions were investigated. Data were simulated for different population structures by using Monte Carlo techniques. Variance components were estimated by using threshold models and linear sire models applied to untransformed data, logarithmically transformed data, and transformation to Snell scores. Effects of number of categories (2, 5, and 10), incidence of categories (extreme, moderate, and normal), heritability in the underlying scale (.04, .20, and .50), and data structure (unbalanced and balanced) on accuracy of genetic prediction were investigated. The real importance of using a threshold model was to estimate genetic parameters. An expected heritability of .20 was estimated to be .22 and .10 by a threshold model and a linear model, respectively. Accuracy increased significantly with a larger number of categories, a more normal distribution of incidences, increased heritability, and more balanced data. Even threshold models were shown to be more efficient with more than two categories (e.g., binomial). Transformation of scale did not accomplish the purpose intended.

Population parameter estimates for performance and reproductive traits in Polish Large White nucleus herds.

Performance test records from on-farm tests of young Polish Large White boars and reproductive records of Polish Large White sows from 94 nucleus farms during 1978 to 1987 were used to estimate population parameters for the measured traits. The number of boar performance records after editing was 114,347 from 3,932 sires, 21,543 dams, 44,493 litters and 1,075 herd-year-seasons. Reproductive performance records of sows involved 41,080 litters from 2,348 sires, 18,683 dams and 1,520 herd-year-seasons. Both data sets were analyzed by using restricted maximum-likelihood programs. The model used for the performance records included fixed herd-year-seasons, random sires, dams and error effects, and covariances for the year of birth of sire and year of birth of dam. The model used for the reproduction data set was the same as the performance data with parity as an additional fixed effect. Estimated heritabilities were .27, .29, .26, .07, .06, .06 for average daily gain standardized to 180 d (ADG), backfat thickness standardized to 110 kg BW (BF), days to 110 kg (DAYS), litter size at birth born alive (NBA), litter size at 21 d (N21) and litter weight at 21 d (W21), respectively. Estimated common environmental effects for the same traits were .09, .10, .09, .06, .07 and .08, respectively. Genetic correlations were .25 (ADG and BF), -.99 (ADG and DAYS), -.21 (BF and DAYS), .91 (NBA and N21), .68 (NBA and W21) and .80 (N21 and W21). The respective phenotypic correlations were .23, -.99, -.20, .88, .75, .86. These population parameters for Polish Large White pigs are similar to those for breeds in other countries.