The effect of selective reporting on estimates of weaning weight parameters in beef cattle

The effect of selective reporting on estimates of weaning weight parameters in beef cattle was evaluated by comparing REML estimates from unaltered and altered simulated data. Selective reporting reduced estimates of weaning weight direct (WWD), maternal milk (MAT), and error variances. However, heritability estimates were not greatly affected because the reductions in variance estimates were relatively proportionate. When the true value for the direct-maternal (DM) correlation was zero or negative, selective reporting caused estimates of DM to be less positive or more negative in 50 of 62 comparisons, with an average change of -.136. When the true value for DM was positive, selective reporting increased the positive magnitude of DM estimates in 12 of 20 comparisons, with an average change of +.040. In BLUP of unaltered data with a true DM value of -.09, using a -.28 and a zero DM correlation reduced the correlation of MAT EPD with true values .065 and .041, respectively. These results suggest that the reliability of parameter estimates (and BLUPs) would be improved by estimating parameters from representative subsets of data free of reporting bias.     

Parameter estimates for direct, maternal, and grandmaternal genetic effects for birth weight and weaning weight in Hereford cattle

Birth and weaning weights adjusted for age of dam from four lines of Hereford cattle were analyzed to determine the relationships among grandmaternal, maternal, and direct genetic effects. Three lines were selected for 1) weaning weight (WWL), 2) yearling weight (YWL), and 3) an index of yearling weight and muscle score (IXL). The fourth line was an unselected control line (CTL). Numbers of observations ranged from 1,699 (CTL) to 2,811 (WWL), and number of animals in the pedigree file ranged from 2,266 to 3,192. Two animal models were used to obtain estimates by REML using an average information method. Model 1 included random direct and maternal genetic, permanent maternal environmental, and residual environmental effects, and fixed sex x year effects. Model 2 additionally included random grandmaternal genetic and permanent grandmaternal environmental effects. For birth weight, Models 1 and 2 gave almost identical estimates for direct and maternal heritability, and for the fraction of variance that was due to maternal permanent environmental effects. Estimates for grandmaternal heritability could be obtained only for IXL (.03) and CTL (.01). For weaning weight, estimates for direct heritability were similar from both models. Estimates for maternal heritability from Model 1 were .18, .20, .13, and .20, and corresponding estimates from Model 2 were .34, .31, .13, and .34 for WWL, YWL, IXL, and CTL, respectively. For IXL, estimates for variances that were due to grandmaternal genetic and grandmaternal permanent environmental variances could not be obtained and were set to zero. Grandmaternal heritability estimates for WWL, YWL, and CTL were .05, .09, and .12. Estimates of correlations between direct and maternal genetic effects were -.13, -.44, -.11, and -.26 for WWL, YWL, IXL, and CTL. Estimates of correlations between direct and grandmaternal genetic effects were .21, .83, and .55, and those between maternal and grandmaternal genetic effects were -.99, -.84, and -.76 for WWL, YWL, and CTL, respectively. These results indicate that grandmaternal effects may be important for weaning weight and that maternal heritability may be underestimated if grandmaternal effects are not included in the model.     

Application of an autoregressive process to estimate genetic parameters and breeding values for daily milk yield in a tropical herd of Lucerna cattle and in United States Holstein herds

The objectives of this study were to estimate from test day records the genetic and environmental (co)variance components, correlations, and breeding values to increase genetic gain in milk yield of Lucerna and US Holstein cattle. The effects of repeated observations (within cow) were explained by first-order autoregressive processes within and across lactations using an animal model. Estimates of variance components and correlation coefficients between test days were obtained using derivative-free REML methodology. The autoregressive structure significantly reduced the model error component by disentangling the short-term environmental effects. The additional information and the more heterogeneous environmental variances between lactations in the multiple-lactation test day model than in the first lactation model provided substantially larger estimates of additive genetic variance (0.62 kg2 for Lucerna; 14.73 kg2 for Holstein), heritability (0.13 for Lucerna; 0.42 for Holstein), and individual genetic merit. Rank correlations of breeding values from multiple lactations and from first lactations ranged from 0.18 to 0.37 for females and from 0.73 to 0.89 for males, respectively. Consequently, more selection errors and less genetic gain would be expected from selection decisions based on an analysis of first lactation only, and greater accuracy would be achieved from multiple lactations. Results indicated that substantial genetic gain was possible for milk yield in the Lucerna herd (34 kg/yr). Estimates of genetic variance for Holsteins were larger than previously reported, which portends more rapid genetic progress in US herds also; under our assumptions, increases would be from 173 to 197 kg/yr.     

Estimation of genetic parameters for growth, feed consumption, and conformation traits for double-muscled Belgian blue bulls performance-tested in Belgium

For 1,442 Belgian Blue bulls performance-tested at the Centre de Sélection de la Race Blanc-Bleue Belge, nine traits were observed: height at withers at 7 mo, height at withers at 13 mo, weight at 7 mo, weight at 13 mo, average feed consumption of concentrates, average daily gain, average feed consumption of concentrates per average daily gain, average feed consumption of concentrates per mean metabolic weight, and price per kilogram of live weight. This price is based on muscle conformation and is therefore used as muscle conformation score. Restricted maximum likelihood with a derivative-free algorithm was used to estimate (co)variance components because there were different models and missing values per trait. Estimates of heritabilities were above .50 except for average feed consumption per average daily gain (.16) and average feed consumption per mean metabolic weight (.33). Estimates of genetic and phenotypic correlations between height at withers and weight traits were positive and moderate to high. Average daily gain showed a negative genetic correlation with weight at 7 mo (-.68) but had positive correlations with height at withers at 13 mo and weight at 13 mo (.22 and .43). Muscle conformation expressed as price per kilogram of live weight was related to low average feed consumption per average daily gain. Average feed consumption showed high correlations with weight at 7 mo and weight at 13 mo. Average feed consumption per average daily gain had a high negative genetic correlation with average daily gain (-.89).     

Sulfur distribution in bacteriorhodopsin from multiple wavelength anomalous diffraction near the sulfur K-edge with synchrotron x-ray radiation

Estimates of variance components for test day records in an animal model that considered multiple traits over multiple lactations were calculated using REML methodology. Test day records were classified into 11 periods within first and later lactations. Missing ancestors in the relationship matrix were classified in genetic groups. Data were collected from Costa Rican dairy farms. Estimates of components for total and additive genetic variance were clearly heterogeneous during the lactation. Heritabilities for traits in later parities were slightly higher than those for traits in first parity. Heritabilities were highest for records of midlactation. Phenotypic and genetic correlations for adjacent test days were close to 1. Phenotypic correlations were lower than genetic correlations. Heterogeneity of variances during the lactation suggests the adequacy of the multiple-trait test day model to describe milk yield during the lactation. When missing ancestors were allocated to a single base population instead of genetic groups, the estimates of residual variance were lower, and the estimates of genetic variance and genetic correlations were higher. When standardized records were used instead of actual test day records, the estimates of residual and total variance were lower, and the estimates of genetic variance were higher. Consequently, estimates of heritability and genetic correlations were also higher. Use of standardized data obtained by interpolation procedures is not advised for estimation of genetic variance components in a test day model.     

Genetic parameters for sex-specific traits in beef cattle

Data from 3,593 beef heifers and 4,079 of their steer paternal half-sibs were used to estimate genetic parameters of and among female growth and reproductive traits and male carcass traits. Estimates of heritability for adjusted 205-d weight, adjusted 365-d weight, age at puberty, calving rate, and calving difficulty measured on females were .16, .38, .47, .19, and .18, respectively; estimates for calving rate and calving difficulty were expressed on a normal scale. Estimates of heritability for hot carcass weight; retail product percentage; fat percentage; bone percentage; rib eye area; kidney, pelvic, and heart fat percentage; adjusted fat thickness; marbling score; Warner-Bratzler shear force; taste panel tenderness; taste panel juiciness; and taste panel flavor that were measured on steers at an average age of 447 d (weaning age = 185, days on feed = 262) were .50, .66, .58, .54, .61, .48, .66, .71, .26, .31, .00, and .04, respectively. Genetic correlations were positive for heifer weights with hot carcass weight, fat percentage, rib eye area, adjusted fat thickness, marbling score, and Warner-Bratzler shear force, and they were negative with retail product percentage and kidney, pelvic, and heart fat percentage of steers. Age at puberty was genetically correlated with taste panel tenderness but not with other carcass traits. Calving rate had positive genetic correlations with fat percentage, rib eye area, adjusted fat thickness, and taste panel flavor, and it had negative genetic correlations with retail product percentage; bone percentage; and kidney, pelvic, and heart fat percentage. Calving difficulty had favorable genetic correlations with hot carcass weight, retail product percentage, and measures of carcass tenderness, but it was unfavorably correlated with traits that involve carcass fatness. These results indicate that selection for some traits expressed in one sex of beef cattle may result in undesirable responses in traits expressed in the opposite sex.     

Bayesian analysis of twinning and ovulation rates using a multiple-trait threshold model and Gibbs sampling

The Multiple-Trait Gibbs Sampler for Animal Models programs were extended to allow analysis of ordered categorical data using a Bayesian threshold model. The algorithm is based on data augmentation, where a value on the unobserved underlying normally distributed variable (liability) is generated in each round of iteration for each categorical observation. The programs allow analysis of several continuous and ordered categorical traits. Categorical traits can have any number of response levels. Models can be different for each trait. The programs were used to analyze twinning and ovulation rates from a herd of cattle selected for twinning rate at the U.S. Meat Animal Research Center. Data included number of calves born at each parturition for the lifetime of a cow and number of eggs ovulated for several estrous cycles before first breeding as heifers. A total of 6,411 calvings was recorded for 2,087 cows with 83.2% single and 16.8% multiple births. A total of 19,849 ovulations was recorded for 2,332 heifers with 85.2% single and 14.8% multiple ovulations. Mean posterior estimates of heritability and fraction of variance accounted for by permanent environmental effects (PE) were .128 and .103 for twinning rate and .168 and .079 for ovulation rate. Mean posterior estimate of genetic correlation was .808, and correlation of PE effects was .517. Use of a threshold model could allow for more rapid genetic improvement of the twinning herd through improved identification and selection of genetically superior animals because of higher heritability on the underlying scale.     

Variances of direct genetic effects, maternal genetic effects, and cytoplasmic inheritance effects for milk yield, fat yield, and fat percentage

Milk yield, fat yield, and fat percentage during the first three lactations were studied using New York Holsteins that were milked twice daily over a 305-d, mature equivalent lactation. Those data were used to estimate variances from direct and maternal genetic effects, cytoplasmic effects, sire by herd interaction, and cow permanent environmental effects. Cytoplasmic line was traced to the last female ancestor using DHI records from 1950 through 1991. Records were 138,869 lactations of 68,063 cows calving from 1980 through 1991. Ten random samples were based on herd code. Samples averaged 4926 dams and 2026 cytoplasmic lines. Model also included herd-year-seasons as fixed effects and genetic covariance for direct-maternal effects. Mean estimates of the effects of maternal genetic variances and direct-maternal covariances, as fractions of phenotypic variances, were 0.008 and 0.007 for milk yield, 0.010 and 0.010 for fat yield, and 0.006 and 0.025 for fat percentage, respectively. Average fractions of variance from cytoplasmic line were 0.011, 0.008, and 0.009 for milk yield, fat yield, and fat percentage. Removal of maternal genetic effects and covariance for maternal direct effects from the model increased the fraction of direct genetic variance by 0.014, 0.021, and 0.046 for milk yield, fat yield, and fat percentage; little change in the fraction was due to cytoplasmic line. Exclusion of cytoplasmic effects from the model increased the ratio of additive direct genetic variance to phenotypic variance by less than 2%. Similarly, when sire by herd interaction was excluded, the ratio of direct genetic variance to phenotypic variance increased 1% or less.     

Effect of inaccurate parameter estimates on genetic response to marker-assisted selection in an outbred population

The effect of inaccurate estimates of variance and of the location of the quantitative trait locus on the genetic response to marker-assisted selection was studied by simulation of an adult multiple ovulation and embryo transfer nucleus breeding scheme. Two genetic models were simulated for the quantitative trait locus: a total of 10 alleles or 2 distinct alleles per base parent. For both models, the locus explained either 5 or 10% of phenotypic variance. A polygenic component was simulated, and the two genetic components were summed to 35% heritability for a trait measured on females. Overestimation of variance of the quantitative trait locus had minimal effect on genetic gain for marker-assisted selection over the short term, but decreased long-term response. The long-term loss was reduced when variance of the quantitative trait locus was reestimated after four generations of marker-assisted selection. Selection for favorable alleles at a nonexistent quantitative trait locus resulted in first generation losses of 3 and 7% for postulated quantitative trait loci, explaining 5 and 10% of variance, respectively. The larger the degree of error in location, the larger was the genetic loss compared with the correct location scenario. For the largest simulated location error of 15 cM, genetic superiority of marker-assisted selection was reduced by 80% in the first generation. We concluded that studies should be undertaken to verify estimates of quantitative trait locus and location to make optimal use of marker-assisted selection.     

Effects of inbreeding and heterozygosity on preweaning traits in a closed population of Herefords under selection

Records of five inbred lines at the Livestock and Range Research Laboratory were used to evaluate effects of inbreeding and heterozygosity on preweaning traits. Members of each line were descendants of a single founder Hereford bull. A total of 8,065 records of birth weight and 7,380 records of preweaning daily gain and weaning weight were analyzed by derivative-free REML using a model that included fixed effects of sex, combination of year and month of birth and parity of dam, with covariates for direct and maternal genetic fractions of inheritance from the genetic groups, inbreeding, and heterozygosity fractions. Heterozygosity fractions were computed for crosses between lines. The random model effects were direct and maternal genetic and uncorrelated maternal permanent environmental and temporary environmental. Direct inbreeding and heterozygosity fractions averaged .098 and .343, and maternal inbreeding and heterozygosity fractions averaged .075 and .294. Regression coefficients of traits on direct and maternal inbreeding fractions were -5.8 +/- 1.1 and -4.7 +/- 1.3 for birth weight, -.189 +/- .031 and -.252 +/- .039 for preweaning daily gain, and -44.5 +/- 6.6 and -56.1 +/- 8.4 kg for weaning weight. Estimates for direct heritability, maternal heritability, and direct-maternal genetic correlations were .37, .12, and -.01 for birth weight; .16, .25, and -.27 for daily gain; and .17, .26, and -.21 for weaning weight. Results suggest that heterosis represents recovery of accumulated inbreeding depression. Results also indicate that selection can overcome inbreeding depression and antagonism exists between direct and maternal genetic effects for preweaning traits.     

Genetic and environmental influences on antisocial behavior: A meta-analysis of twin and adoption studies.

A meta-analysis of 51 twin and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on antisocial behavior. The best fitting model included moderate proportions of variance due to additive genetic influences (.32), nonadditive genetic influences (.09), shared environmental influences (.16), and nonshared environmental influences (.43). The magnitude of familial influences (i.e., both genetic and shared environmental influences) was lower in parent-offspring adoption studies than in both twin studies and sibling adoption studies. Operationalization, assessment method, zygosity determination method, and age were significant moderators of the magnitude of genetic and environmental influences on antisocial behavior, but there were no significant differences in the magnitude of genetic and environmental influences for males and females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of sire breed solutions for growth traits adjusted by mean expected progeny differences to a 1993 base

Records on growth traits were obtained from five Midwestern agricultural experiment stations as part of a beef cattle crossbreeding project (NC-196). Records on birth weight (BWT, n =3,490), weaning weight (WWT, n = 3,237), and yearling weight (YWT, n = 1,372) were analyzed within locations and pooled across locations to obtain estimates of breed of sire differences. Solutions for breed of sire differences were adjusted to the common base year of 1993. Then, factors to use with within-breed expected progeny differences (EPD) to obtain across-breed EPD were calculated. These factors were compared with factors obtained from similar analyses of records from the U. S. Meat Animal Research Center (MARC). Progeny of Brahman sires mated to Bos taurus cows were heaviest at birth and among the lightest at weaning. Simmental and Gelbvieh sires produced the heaviest progeny at weaning. Estimates of heritability pooled across locations were .34, .19, and .07 for BWT, WWT, and YWT, respectively. Regression coefficients of progeny performance on EPD of sire were 1.25+/-.09, .98+/-.13, and .62+/-.18 for BWT, WWT, and YWT, respectively. Rankings of breeds of sire generally did not change when adjusted for sire sampling. Rankings were generally similar to those previously reported for MARC data, except for Limousin and Charolais sires, which ranked lower for BWT and WWT at NC-196 locations than at MARC. Adjustment factors used to obtain across-breed EPD were largest for Brahman for BWT and for Gelbvieh for WWT. The data for YWT allow only comparison of Angus with Simmental and of Gelbvieh with Limousin.     

Genetic and phenotypic (co)variances for production traits of intact male populations of purebred and composite beef cattle

Least squares means, genetic (sigma g) and phenotypic (sigma p) standard deviations, and phenotypic coefficients of variation (CV) were estimated for growth traits of intact males from 12 breed groups combined, for nine purebreds combined, and for the F1, F2, F3, and F4 generations of three composite populations to which the nine purebreds contributed. Heritabilities (h2) and genetic (rg) and phenotypic (rp) correlations were estimated for growth traits, calving difficulty of calves with dams of different ages, and gestation length. Coefficients of variation and sigma g generally were similar for composites and contributing purebreds. Generally, estimates of h2 were similar for all breed groups combined, contributing purebreds combined, and composites combined. Estimates of h2 for calving difficulty were higher for calves with 2-yr-old dams than for calves with dams > or = 3 yr old and were sufficiently high (.27 and .31) to be a useful selection criterion for reducing calving difficulty. Mean h2 pooled within all breed groups ranged from .35 for 200-d weight and 368-d weight to .48 for 368-d height. Estimates of h2 for subjective scores of anatomical traits were only slightly lower than those for growth and size traits. The h2 of scrotal circumference (.43) was similar to those for growth and size traits. Genetic correlations between birth weight and calving difficulty were similar for 1) calves with dams of all ages, 2) calves with 2-yr-old dams, and 3) calves with dams > or = 3 yr old.(ABSTRACT TRUNCATED AT 250 WORDS)     

Germ-line origins of mutation in families with hemophilia B: the sex ratio varies with the type of mutation

Previous epidemiological and biochemical studies have generated conflicting estimates of the sex ratio of mutation. Direct genomic sequencing in combination with haplotype analysis extends previous analyses by allowing the precise mutation to be determined in a given family. From analysis of the factor IX gene of 260 consecutive families with hemophilia B, we report the germ-line origin of mutation in 25 families. When combined with 14 origins of mutation reported by others and with 4 origins previously reported by us, a total of 25 occur in the female germ line, and 18 occur in the male germ line. The excess of germ-line origins in females does not imply an overall excess mutation rate per base pair in the female germ line. Bayesian analysis of the data indicates that the sex ratio varies with the type of mutation. The aggregate of single-base substitutions shows a male predominance of germ-line mutations (P < .002). The maximum-likelihood estimate of the male predominance is 3.5-fold. Of the single-base substitutions, transitions at the dinucleotide CpG show the largest male predominance (11-fold). In contrast to single-base substitutions, deletions display a sex ratio of unity. Analysis of the parental age at transmission of a new mutation suggests that germ-line mutations are associated with a small increase in parental age in females but little, if any, increase in males. Although direct genomic sequencing offers a general method for defining the origin of mutation in specific families, accurate estimates of the sex ratios of different mutational classes require large sample sizes and careful correction for multiple biases of ascertainment. The biases in the present data result in an underestimate of the enhancement of mutation in males.     

Influence of dominance relationships on the estimation of dominance variance with sire-dam subclass effects

Two data sets from the USDA Livestock and Range Research Laboratory were analyzed to study dominance variance and the influence of dominance relationships. The first consisted of 4,155 birth weight (3,884 weaning weight) records of inbred USDA Line 1 Herefords. The second consisted of 8,065 birth weight (7,380 weaning weight) records from a line-cross experiment with five lines. Two models were used. Both included fixed effects of year-sex of calf and age of dam, and covariates for calving date, inbreeding of animal, and inbreeding of dam. For the second set, additional covariates were line composition and heterozygosity coefficients. Random effects were direct and maternal additive genetic, maternal permanent environment, sire-dam subclass, and residual. Model 1 considered sire-dam subclasses unrelated. Model 2 related sire-dam subclasses with a parental dominance relationship matrix. Variance components were estimated using REML. Differences between estimates with Model 1 and 2 were unimportant except for dominance variance. For the first data set, estimates with Model 2 of relative genetic direct and maternal variances, direct-maternal correlation, permanent environment, and dominance variances for birth weight were .35, .13, -.02, .03, and .25, respectively, and they were .39, .11, .04, .06 and .14 for the second data set. For weaning weight, the first data set estimates were .20, .15, -.37, .19, and .11, respectively, and they were .16, .20, -.07, .18, and .18 for the second data set. Changes, decreases and increases, in estimates of dominance variances may be due to increased information from relationships and family types other than full-sibs. The assumption of unrelated sire-dam subclasses might not be appropriate for estimation of dominance variance in populations with many dominance relationships among sire-dam classes.     

Ocular squamous cell carcinoma in Simmental cattle in Zimbabwe

In Zimbabwe, ocular squamous cell carcinoma (OSCC) was frequently observed in 5 breeding herds of Simmental cattle, a Bos taurus breed originating from Switzerland. In these herds, initial signs of OSCC were already noticeable in cattle about 3 years old. Gradually, OSCC prevalence increased, and 36 to 53% of cattle over 7 years old had 1 or more tumors. More tumors developed in Simmental cattle with periorbital white skin than in cattle with periorbital pigmented skin. Other breeds of cattle (eg, Friesian) also are partly white-faced and live in Zimbabwe in a comparable environment; yet, OSCC prevalence was lower in those breeds.     

Cumulative selection and genetic change for weaning or yearling weight or for yearling weight plus muscle score in Hereford cattle

Selection in three lines of Hereford cattle for 1) weaning weight (WWL), 2) yearling weight (YWL), and 3) an index of yearling weight and muscle score (IXL) was studied. Remnant foundation cows and semen from seven foundation sires were used to establish an unselected control line for the last 11 yr of the experiment. Performance data collected over a 23-yr period on birth weight (BWT), weaning weight (WWT), postweaning gain (PWG), yearling weight (YWT), muscle score (MSC), and an index (IDX) giving equal weight to standard deviations of yearling weight and muscle score were analyzed. Generation interval of midparents was about 4.16 yr in each selected line. Sire and dam selection differentials, in standard deviation units per generation, for primary criteria were, respectively, 1.59 and .33 for WWT in WWL, 1.75 and .25 for YWT in YWL, and 1.42 and .25 for IDX in IXL. Components of direct and maternal genetic variances, direct-maternal covariance, and dam permanent environmental variance were estimated by REML. The average annual response of males and females in actual units for each trait in WWL, YWL, and IXL was, respectively, BWT, .22, .24, and .27 kg; WWT, .98, .63, and 1.26 kg; YWT, 2.43, 2.64, and 3.44 kg; and MSC, .053, .009, and .104 scores. Average selection responses in BWT, WWT, YWT, MSC, and IDX per unit of primary criteria in each selection line (all in standard deviation units) were .22, .20, .31, .10, and .24 for WWT in WWL; .23, .12, .32, .04, and .21 for YWT in YWL; and .27, .22, .40, .20, and .36 for IDX in IXL. Responses in bold type are realized heritability and others are correlated responses. Realized genetic correlations were .78 for WWT and YWT, .87 for WWT and IDX, and .86 for YWT and IDX. Responses for all traits in IXL were greater than in other selected lines.     

Structure of the Drosophila projectin protein: isoforms and implication for projectin filament assembly

The rare alleles model of mutation-selection balance (MSB) hypothesis for the maintenance of genetic variation was evaluated for two quantitative traits, ovariole number and body size. Mutational variances (VM) for these traits, estimated from mutation accumulation lines, were 4.75 and 1.97 x 10(-4) times the environmental variance (VE), respectively. The mutation accumulation lines were studied in three environments to test for genotype x environment interaction (GEI) of new mutations; significant mutational GEI was found for both traits. Mutations for ovariole number have a quadratic relationship with competitive fitness, suggesting stabilizing selection for the trait; there is no significant correlation between mutations for body size and competitive fitness. Under MSB, the ratio of segregating genetic variance, VG, to mutational variance, VM, estimates the inverse of the selection coefficient against a heterozygote for a new mutation. Estimates of VG/VM for ovariole number and body size were both approximately 1.1 x 10(4). Thus, MSB can explain the level of variation, if mutations affecting these traits are under very weak selection, which is inconsistent with the empirical observation of stabilizing selection, or if the estimate of VM is biased downward by two orders of magnitude. GEI is a possible alternative explanation.     

Children's Depression Inventory: Sex and grade norms for normal children.

Collected normative data for a children's depression inventory developed by M. Kovacs (see record 1981-31663-001) on 705 male and 758 female public school children in Grades 2–8. Although significant sex and grade differences were obtained through ANOVA, with females reporting fewer depressive symptoms than males, the absolute magnitude of these differences was small. Scores were consistent with those previously reported. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A model of litter size distribution in cattle

Genetic increases in twinning of cattle could result in increased frequency of triplet or higher-order births. There are no estimates of the incidence of triplets in populations with genetic levels of twinning over 40% because these populations either have not existed or have not been documented. A model of the distribution of litter size in cattle is proposed. Empirical estimates of ovulation rate distribution in sheep were combined with biological hypotheses about the fate of embryos in cattle. Two phases of embryo loss were hypothesized. The first phase is considered to be preimplantation. Losses in this phase occur independently (i.e., the loss of one embryo does not affect the loss of the remaining embryos). The second phase occurs after implantation. The loss of one embryo in this stage results in the loss of all embryos. Fewer than 5% triplet births are predicted when 50% of births are twins and triplets. Above 60% multiple births, increased triplets accounted for most of the increase in litter size. Predictions were compared with data from 5,142 calvings by 14 groups of heifers and cows with average litter sizes ranging from 1.14 to 1.36 calves. The predicted number of triplets was not significantly different (chi2 = 16.85, df = 14) from the observed number. The model also predicted differences in conception rates. A cow ovulating two ova was predicted to have the highest conception rate in a single breeding cycle. As mean ovulation rate increased, predicted conception to one breeding cycle increased. Conception to two or three breeding cycles decreased as mean ovulation increased because late-pregnancy failures increased. An alternative model of the fate of ova in cattle based on embryo and uterine competency predicts very similar proportions of singles, twins, and triplets but different conception rates. The proposed model of litter size distribution in cattle accurately predicts the proportion of triplets found in cattle with genetically high twinning rates. This model can be used in projecting efficiency changes resulting from genetically increasing the twinning rate in cattle.