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.

Factors associated with sow stayability in 6 genotypes.

The purpose of this study was to determine the association of production factors with stayability to parity 4 (STAY4) under controlled experimental conditions. Data were from 2,293 female pigs, sampled from 6 genetic lines that were entered into the National Pork Producers Council Maternal Line National Genetic Evaluation Program. Genetic lines evaluated included Newsham (NH), National Swine Registry (NSR), American Diamond Swine Genetics (ADSG), Danbred (DAN), and 2 Dekalb-Monsanto lines (DK44 and GPK347). Stepwise logistic regression was utilized in the analysis of STAY4. All effects were nested within genetic line. Categorical effects in the model were arrival date to the wean-to-finish unit (entry date) and breed-gestation-farrowing facility (farm). Continuous effects in the model were gilt backfat, LM depth, ADG, age at puberty, age at first farrowing, and traits recorded before the last litter of the sow (prefarrow backfat, number born alive, number weaned, litter weaning weight, lactation feed intake, lactation backfat loss, and lactation length). Factors significant for STAY4 included farm, entry date, age at first farrowing, ADG, gilt backfat, and lactation before removal effects, as well as feed intake, number born alive, and lactation length. Age at first farrowing and lactation feed intake affected all genetic lines. Regression coefficients for STAY4 on age at first farrowing were -0.014, -0.022, -0.017, -0.016, -0.011, and -0.021 (all P < 0.05), respectively, for NH, NSR, ADSG, DK44, GPK347, and DAN genetic lines. Regression coefficients for STAY4 on lactation feed intake were 0.043, 0.049, 0.051, 0.061, 0.120, and 0.097 (all P < 0.05), respectively, for NH, NSR, ADSG, DK44, GPK347, and DAN females. Age at puberty, age at first farrowing, and lactation feed intake had the greatest effect on STAY4.

Fine-mapping quantitative trait loci for twinning rate on Bos taurus chromosome 14 in North American Holsteins.

A previous genome-wide search with a moderate-density 10,000-SNP set identified many marker associations with twinning rate on BTA14 through either single-marker analysis or combined linkage-linkage disequilibrium (LLD; haplotype) analysis. The objective of the current study was to fine-map putative QTL using a more densely populated marker map and both a larger and an independent set of phenotypic data. Holstein bulls (n = 921) from 100 paternal half-sib families were genotyped for 129 SNP markers that included both original and additionally selected markers for increasing marker density in the targeted 34 megabase region. Twinning rate predicted transmitting abilities were calculated using calving records from 1994 to 1998 (data I) and 1999 to 2006 (data II), and the underlying liability scores from threshold model analysis were used as the trait in marker association analyses. The previous analysis used 201 bulls with daughter records in data I. In the current analysis, this was increased to 434, providing a revised estimate of effect and significance. Bulls with daughter records in data II totaled 851, and analysis of these data provided an opportunity for an independent analysis separate from data I. Single-marker association and LLD analyses were performed. Fifteen significant single-marker associations were found (minimally exceeding P < 8.74 x 10(-3)) to concur between data sets. Three and 12 regions in data I and data II, respectively, showed positive results for the presence of QTL from LLD analysis (P < 0.001) within the respective data sets. After combining results from single-marker association, LLD analysis, and model-building strategies, 3 QTL were identified on BTA14. Based on single-marker results from data II, BTA14 harbors QTL responsible for approximately 24% of the variation in twinning rate predicted transmitting ability.

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.

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.

Refined mapping of twinning-rate quantitative trait loci on bovine chromosome 5 and analysis of insulin-like growth factor-1 as a positional candidate gene.

Twinning in cattle is a complex trait that is associated with economic loss and health issues such as abortion, dystocia, and reduced calf survival. Twinning-rate QTL have been detected previously on BTA5 in the North American Holstein and Norwegian dairy cattle populations and in a USDA herd selected for high twinning rate. In previous work with the North American Holstein population, the strongest evidence for a QTL was obtained from analysis of an extended, multiple-generation family. Using additional animals, an increased density of SNP marker association tests, and a combined linkage and linkage disequilibrium mapping method, we refined the position of this QTL in the North American Holstein population. Two sets of twinning-rate predicted transmitting abilities estimated during 2 different time periods in the North American dairy cattle population were used to provide validation of results. A total of 106 SNP and 3 microsatellites were used to scan the genomic region between 5 and 80 Mb on BTA5. Combined linkage-linkage disequilibrium analysis identified significant evidence for QTL within the 25- to 35-Mb and 64- to 70-Mb regions of BTA5. The IGF-1 gene (IGF1) was examined as a positional candidate gene and an SNP in intron 2 of IGF1 was significantly associated with twinning rate by using both data sets (P = 0.003 and P = 1.05 x 10(-6)). Replication of this association in other cattle populations will be required to examine the extent of linkage disequilibrium with the underlying quantitative trait nucleotide across breeds.

Genome screen for twinning rate QTL in four North American Holstein families.

The objective of this study was to identify twinning rate quantitative trait loci (QTL) by typing pooled samples in a preliminary screening followed by interval mapping to test QTL effects. Four elite North American Holstein half-sib sire families with high twinning rate predicted transmitting abilities (PTA) were used in this study. Chromosomes 5, 7, 19 and 23 were not genotyped as these chromosomes were scanned for QTL in these families in a previous study. DNA was extracted from phenotypically extreme sons in each sire family. Two pools were prepared from sons of sires in each phenotypic tail, two each for high and low PTA levels for twinning rates. Each pool contained DNA from 4 to 15% of all sons of the sire depending on family. A total of 268 fluorescently labelled microsatellite markers were tested for heterozygosity in sires. About 135--170 informative markers per family were genotyped using pooled DNA samples. Based on the preliminary evidence for potential twinning rate QTL from pooled typing, interval mapping was performed subsequently on 12 chromosomal regions by family combinations. Evidence of QTL for twinning rate was found in one family on BTA 21 and 29 at a chromosome-wide P<0.05 and on BTA 8, 10 and 14 with a chromosome-wide P<0.01.

Evidence for quantitative trait loci affecting twinning rate in North American Holstein cattle.

Twinning in dairy cattle has been associated with many negative health and reproductive events that cause economic loss to the producer. Reports have suggested that twinning rates are increasing and that there may be a positive relationship between milk production and twinning frequency. Putative quantitative trait loci (QTL) for twinning and ovulation rate on bovine chromosomes 5, 7, 19 and 23 have been previously identified in other populations. The objective of this study was to detect and possibly confirm the existence and effects of these QTL in the North American Holstein population. Half-sib families of 20 North American Holstein sires with above average twinning rate predicted transmitting abilities (PTA) comprised the sample population under investigation. Twinning rate PTA values had been estimated from calving data. DNA extracted from semen samples was analysed using 45-61 microsatellite markers across the four chromosomes. Marker heterozygosity of the patriarchs averaged 62%. Evidence of twinning QTL was found in multiple families on chromosomes 5, 7 and 23 and in one family on chromosome 19. Four of the sires formed one three-generation family: one sire and three half-sib sons with sons of their own. This extended family was analysed with additional markers confirming a twinning QTL of significant size on chromosome 5.

Birth weight as a predictor of calving ease and perinatal mortality in Holstein cattle.

The objective of this research was to determine the effect of birth weight on perinatal mortality (PM) (alive or dead at 48 h of age) and dystocia (unassisted or assisted). Data were 4528 records of births between 1968 and 1999 from the Iowa State University research dairy farm in Ankeny. The incidence of PM was 7.1%; dystocia was 23.7%. A logistic regression model was used to predict both PM and dystocia. The PM model included effects of year of birth, season (summer or winter), dystocia, parity (first or later), birth weight (kg), ratio of calfs birth weight to dam's weight (%), and gestation length (d). Odds of PM increased by 2.1%/yr. Calves born in the winter have a 36% higher risk of PM than calves born in the summer. Difficult births tend to result in PM 2.7 times more often than unassisted births. First-parity cows have a 2.4 times higher risk of PM than cows in later parities. Probabilities of PM for birth weights of 29, 35, 40, 46, and 52 kg were 2.1, 2.5, 3.4, 5.1, and 9.6%, respectively, when other factors were set at their average value. Similarly, ratios of calf to cow weight of 4.5, 5.7, 6.9, 8.1, and 9.3% yield probabilities of PM at 8.2, 4.2, 3.1, 3.5, and 5.7%, respectively. Finally, gestation lengths of 268, 273, 279, 284, and 290 d yield probabilities of PM of 5.5, 3.9, 3.1, 3.1, and 3.6%, respectively. The dystocia model included effects of year of birth, season, sex of calf, PM, parity, birth weight, and pelvic area (externally measured). Odds for dystocia decreased by 4.7%/yr. Calves born in the winter have a 15% higher risk of dystocia than calves born in the summer. Odds of male calves needing assistance were 25% greater than female calves. If a calf died in the first 48 h, then it is 2.7 times more likely that the calf needed assistance. First-parity cows have a 4.7 times higher risk of dystocia than cows in later parities. Odds of dystocia increase by 13%/kg increase in birth weight. An 11% decrease in odds for dystocia is associated with a one square decimeter (dm2) increase in pelvic area.

Design and standards for genetic evaluation of swine seedstock populations.

The purpose of this article is to describe a program for evaluation of seedstock populations in the swine industry. Differences among seedstock populations for economically important traits must be identified in order for pork producers to efficiently use available genetic resources. National genetic evaluation programs have the potential to identify the important differences among populations and to increase the rate of genetic improvement in a population. Program results provide performance benchmarks that stimulate testing and selection procedures by seedstock suppliers that further increase the rate of genetic improvement. A Terminal Sire Line Genetic Evaluation Program was designed and conducted in the United States by the National Pork Producers Council (Des Moines, IA) to compare seedstock populations for use in crossbreeding systems. High levels of statistical accuracy for program results were established; the ability to detect differences of 0.25 SD per trait, a power of test of 75%, and a 5% significance level were selected. Pure breeds and breeding company sire lines were nominated for the program. Semen was collected from nominated boars and distributed to cooperating commercial producers during eight 1-wk breeding periods. Pigs were produced in 136 commercial herds and transported to testing facilities at 8 to 23 d of age. Nine of the 11 sire lines originally entered in the program completed the sampling requirements for statistical analysis. High levels of statistical accuracy and a large, representative sample of boars with restrictions on genetic relationships ensured that the program results included unbiased, highly accurate sire line data for growth, carcass, meat quality, and eating quality traits of economic importance. This program has shown commercial producers that they have several choices of sire lines for changing their crossbreeding programs in desired trait areas. Commercial product evaluation must be an ongoing process, and this program serves as a model for future testing and evaluation of diverse genetic seedstock populations.

Volume and secretion rate of lung liquid in the final days of gestation and labour in the fetal sheep.

1. Most of the liquid that fills the lung of the fetal sheep in late gestation is cleared by the end of labour. Clearance of this liquid has a beneficial effect on postnatal gas exchange and therefore represents an important adaptation for postnatal life. Despite its importance, there is disagreement about whether clearance begins prior to labour, or occurs entirely within labour. 2. To address this issue, we made serial determinations of lung liquid volume by indicator dilution during late gestation and labour in the fetal sheep. 3. Regression analysis demonstrated that lung liquid volume exhibited a plateau level in the near-term fetus before it began to decline. Two models provided a fit to the decline in volume. In one, lung liquid clearance occurred in two linear phases, the first beginning 70 h before the study was terminated when the ewe was in advanced labour, the second occupying the last 8 h of the study period. In the initial phase, average lung liquid volume fell from 38.3 to 26.4 ml x kg(-1) before a rapid decline in the second phase reduced the volume to 13.8 ml x kg(-1). An exponential decay model was also found to fit the data; this showed a gradual decline in lung liquid volume in the 2 days preceding onset of labour, followed by a much more rapid decline within labour. 4. The rate of lung liquid secretion also declined in two linear phases, both of which commenced earlier than the changes in lung liquid volume. An exponential decay model also gave a significant fit to the data, but the fit was significantly weaker than that achieved with the two-slope model. 5. We conclude that clearance of lung liquid begins well before commencement of labour in the full term fetal sheep, and then accelerates once labour is established. In our study, lung liquid volume fell even in the absence of reabsorption of liquid across the pulmonary epithelium, indicating that outflow of liquid through the trachea must have occurred at a rate in excess of the secretion rate.

Genetic evaluation of Holstein sires and maternal grandsires in the United States for perinatal survival.

Stillbirth, defined as a calf that dies just prior to, during, or within 48 h of parturition, represents a reoccurring concern among breeders of dairy cattle in the United States. About 11% of parturitions of primiparous Holstein cows result in the death of a calf; 5.7% in multiparous cows. Genetic evaluations can be reported as perinatal survival to 48 h to emphasize the positive information about the trait. The purpose of this research was to: 1) estimate genetic parameters by restricted maximum likelihood for perinatal survival rates; 2) characterize the genetic evaluation of sires for the perinatal survival of their progeny and maternal grandsires for the perinatal survival of their daughters progeny; and 3) estimate genetic trends from 1984 to 1994. Data (n = 666,339) were from the National Association of Animal Breeders calving ease database. Over 600 new young sires were available each year. The binomial response variable, 1 = alive, 0 = stillborn within 48 h of parturition was analyzed by using a sire-maternal grandsire linear mixed model. The model included fixed effects for sex of calf, dystocia, and season of birth, and gestation length as a covariate; correlated random effects of sire and maternal grandsire; and uncorrelated random effects of herd-years. Parturitions of primiparous and multiparous cows were analyzed separately. In primiparous cows, heritability estimates were 1.1 and 2.2% for sire of the calf and maternal grandsire, respectively. The genetic correlation between sire and maternal grandsire predicted transmitting ability (PTA) for perinatal survival, was 0.31; simple product moment correlations among sire-MGS PTA were 0.43 and 0.46 for primiparous and multiparous cows, respectively. The PTA for sire of the calf ranged from -2.9 (lower survival) to 2.8% (higher survival). Mean PTA from 1984 to 1994 was quite variable from year to year. Evidence showed a slightly negative, but nonsignificant, genetic trend in perinatal survival (-0.04% per year for sires and -0.02% per year for maternal grandsires). Estimates of genetic parameters and genetic trends for data from multiparous cows are also reported. Correlations among PTA for perinatal survival, milk yield, and calving ease are given.

Phenotypic trends in incidence of stillbirth for Holsteins in the United States.

The objectives for this study were to determine 1) if there was a trend in stillbirths for the U.S. Holstein population, 2) if stillbirths are the same trait in primiparous and multiparous cows, and 3) what was the role of dystocia in stillbirths. A sample of 666,341 births from the MidStates Dairy Records Processing Center and the National Association of Animal Breeders was used to examine the influence of sire, herd, year, season, sex of calf, parity of dam, calving ease, and gestation length on the survival of the calf. Parity was scored as an ordered variable (1, 2, 3+). Calving ease was scored on a scale of 1 (no assistance) to 3+ (needed assistance). An increasing trend in stillbirths was found in primiparous and multiparous cows. The percentage of stillborn calves in primiparous cows increased from 9.5 in 1985 to 13.2 in 1996. Stillbirths in multiparous cows increased from 5.0 to 6.6% from 1985 to 1996. Variation about the trend was greater in primiparous cows than in multiparous cows. Dystocia was a major determinant of stillbirth incidence, but the association was stronger in primiparous cows. Sex of calf had different associations with stillbirth incidence in primiparous and multiparous cows. Gestation length and season of birth also had significant associations with stillbirth incidence. Logistic regression models with fixed and random effects were fit to the data to preserve the binary nature of the stillbirth response. The expected probability of stillbirths for an average herd and sire was 10% for primiparous cows and 5% for multiparous cows. Replacement of stillborn calves is a substantial cost to the dairy industry at more than $125.3 million per year. Because of the increasing incidence of stillbirths, these costs have increased by $75.9 million from 1985 to 1996.

Interactions among factors affecting stillbirths in Holstein cattle in the United States.

Each year about 7% of the Holstein calves born in the United States die within 48 h of birth. The exact cause of death is unknown. The purpose of this article is to examine the complex interactions among factors (e.g., parity, season of birth, dystocia, year) contributing to stillbirth rates. A modified chi-squared automated interaction detection algorithm was used to develop classification trees explaining the most likely sequence of factors that result in a stillborn calf. The data were 666,341 births from the MidStates Dairy Records Processing Center and the National Association of Animal Breeders. Primiparous and multiparous cows clearly differ in the rate of stillbirths, 11.0 and 5.7%, respectively. Dystocia followed parity as the next most important factor within both primiparous and multiparous cows. In primiparous cows, season, year of birth, or gestation length ranked third as an important predictor for dystocia equal to 1, 2, or 3+, respectively. Gestation length ranked third in importance among the factors that affect stillbirth rates for all levels of dystocia in multiparous cows. Among multiparous cows needing assistance (dystocia 3+), stillbirth rates were greatest for shorter gestations less than the average of 280 d, 55.3% for -15 to -12 d, 45.5% for -11 to -9 d, 33.7% for -8 to -5 d, 23.8% for -4 to 13 d, and 35.4% for 14 to 15 d. Gestation length pinpointed the time when stillbirths occurred, as indicated by the increase from 23.8% stillbirth rate among calves born at or above the mean gestation length to 55.3% for those calves born -15 to -12 d below the mean gestation. Further investigation of the relationship between stillbirth rates and gestation length is needed to develop a more complete understanding of the biological processes resulting in the loss of calves at birth.

Influence of prenatal adrenaline infusion on arterial blood gases after caesarean delivery in the lamb.

The efficacy of pulmonary gas exchange immediately after delivery is inversely related to the volume of liquid in the lung at birth, but aspiration of as much liquid as possible from the lung before Caesarean delivery fails to improve postnatal oxygenation (Pa,O2) to the level achieved after spontaneous term delivery. We hypothesised that the differing respiratory benefit of aspiration and vaginal delivery results from the differing volume of lung liquid remaining after aspiration (17 ml (kg body weight)-1) and labour (7 ml kg-1). We addressed this hypothesis by reducing lung liquid volume to an estimated 7 ml kg-1 by infusing adrenaline to seven fetal lambs at 140 days gestation (term is 147 days) before performing Caesarean delivery and obtaining postnatal blood gases for comparison with samples from lambs delivered vaginally. Infusion of adrenaline to fetuses caused a progressive decline in arterial O2 saturation (Sa, O2), pH and base excess, but no change in arterial partial pressure of O2 (Pa,O2) or CO2 (Pa,CO2). After birth, Pa,O2 rapidly rose to the same level in adrenaline-treated and vaginal-delivery groups. A severe acidosis occurred in the adrenaline-treated group and this appeared to be related to a higher Pa,CO2 and a transiently lower Sa, O2 in this group. We conclude that adrenaline infusion can enhance postnatal Pa,O2 levels in the newborn lamb, but this beneficial effect may be outweighed by the severe acidosis that develops after prolonged prenatal adrenaline treatment.

Unusual respiratory response to oxygen in an infant with repetitive cyanotic episodes.

High inspired oxygen concentrations have recently been recommended to control Cheyne-Stokes respiration in adults, with the intention of averting periodic apnea and its attendant arterial desaturation. We report a case study on an infant presenting with recurrent apnea and cyanosis in which oxygen treatment led to a gross form of respiratory instability we call episodic breathing, in which a breathing phase of 60 to 90 s alternated with an apnea lasting up to 60 s. When oxygen was discontinued, a profound arterial desaturation developed before breathing recommenced and restored oxygen levels. We propose that episodic breathing is an unusual respiratory pattern that involves the central chemoreceptors and results from the ventilatory threshold (the central PCO(2) at which breathing starts) lying considerably above the apneic threshold (the central PCO(2 )at which breathing stops). This feature predisposes to lengthy periods of hyperpnea alternating with lengthy periods of apnea. We suggest that when the case infant returned to air during episodic breathing, termination of apnea was entirely dependent upon carotid body activity, which reached a sufficient level to restart breathing only when arterial desaturation was severe. We conclude that oxygen therapy involves potential risks when employed to treat respiratory disorders involving unstable breathing patterns in the infant.

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.

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.

Genetic and phenotypic parameters for 305-day yield, fertility, and survival in Holsteins.

A data file containing 122,715 lactation records of Holstein cows distributed across 11,374 herd-year-season groups was analyzed to obtain (co)variance estimates for yield, fertility and cow survival. Milk, fat, and protein yields were adjusted to 305 d. Days open was truncated to 305 d, and the number of services was truncated to 9. Survival of a cow during a full lactation (305 d) was recorded as 0 (died) or 1 (alive). Variance components for the six traits were estimated using a multiple-trait animal model and the REML procedure. The model included herd-year-season, parity (three groups), age (three groups nested within parity), sex of calf (1 = male, 2 = female), and dystocia score (1 = no problem,..., 5 = extreme difficulty) as fixed effects and animal and permanent environment as random effects. Heritabilities for milk, fat, and protein yields, days open, number of services and cow survival were 0.2, 0.18, 0.18, 0.04, 0.03, and 0.002, respectively. The corresponding repeatabilities were 0.42, 0.41, 0.41, 0.12, 0.08, and 0.009, respectively. Genetic and phenotypic correlations between yield traits were high and positive, and correlations between yields and reproduction traits were high and antagonistic. Phenotypic correlations between survival and yields were about 0.1, and their genetic counterparts were slightly negative. Thus, management practices seem to keep mortality rates of high producing cows lower even though those cows have lower genetic potential for survival than do the low producers. Fertility traits showed a slightly undesirable (e.g., 0.1 to 0.3) genetic relationship with survival, but phenotypic correlations were essentially 0. For heifers, yields increased significantly with age. For cows in other parities, the significant changes with age were reduced fertility and reduced survival.