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R L Quaas

Publications and source records attributed to R L Quaas.

28 records · Page 2Linked to original sources
PubMed1991

Clinical ketosis: phenotypic and genetic correlations between occurrences and with milk yield.

The repeatability and heritability of ketosis were estimated using data from 28,277 Finnish Ayrshire cows. A four-trait linear model including community-year, calving age and month, genetic group, and random sire effects was used to describe first and second lactation milk yields and veterinary diagnoses of ketosis. Variance components were estimated using REML. The disease traits were also analyzed with a categorical model including the same effects except that community and year were separate factors. Variance components were estimated with marginal maximum likelihood. Genetic relationships between 339 sires analyzed were included in models. The phenotypic correlation between the first and second lactation was defined as a repeatability of trait. The lactational incidence risk of ketosis was .05 in both the first and the second lactation. Average milk production was 4956 and 5547 kg in the first and second lactations, respectively. Estimates of heritabilities were .09 and .07 for ketosis and .23 and .19 for milk in the first and second lactations, respectively. Genetic correlations between first and second lactation recordings were .64 for ketosis and .93 for milk. Repeatabilities between subsequent lactations were .36 (.13 in linear analysis) for ketosis and .68 for milk. In the first lactation, genetic relationship between milk yield and ketosis was unfavorable, but in the second lactation ketosis and milk yield were genetically and phenotypically unrelated.

Animals↗
PubMed1989

Variance heterogeneity in direct and maternal weight traits by sex and percent purebred for Simmental-sired calves.

Phenotypic variances for linear and transformed weight traits were partitioned into residual, direct genetic (D) and maternal genetic (M) components using REML techniques with American Simmental Association data from calves born 1969 to 1985. Variance components were estimated separately from subclasses defined by sex (male, female) and percent Simmental (50, greater than or equal to 75). The model included fixed effects of contemporary group and age-of-dam (less than 3, 3 to 5, greater than 5 yr). Additive relationships among sires and maternal grandsires were included. Results follow for a sire-maternal grandsire model for greater than or equal to 75% Simmental untransformed data based on 143,280 male and 281,805 female weaning weights (WW) representing 4,763 and 7,406 sires, respectively. Female results are bracketed. For computational simplification, 47,650 [30,909] postweaning gain (PW) records were included in the analysis only for 114,404 [182,255] calves with birth weight (BW). Phenotypic standard deviations (kg) were: BW, 4.5 [4.1]; WW, 26.9 [23.2]; and PW, 25.9 [19.9]. Heritabilities were: BWD, .40 [.45]; WWD, .32 [.39]; PWD, .26 [.32]; BWM, .13 [.15]; WWM, .20 [.16]; and PWM, .01 [.01]. These heritabilities are higher than previously used for genetic evaluations in this breed. Moderate and positive correlations .26 to .50, existed between direct effects and were similar for both sexes. Direct and maternal effects on the same trait were correlated negatively: BW, -.45 [-.31]; and WW, -.27 [-.34]. Genetic correlation between BWM and WWM was .53 [.49]. First-cross progeny exhibited less genetic and residual variation and had lower heritabilities than Simmental calves of higher percent. Correlations between sire evaluations on the subsets were consistent with those expected given a perfect genetic correlation between traits for each sex and percent Simmental. Logarithmic transformed records were no more homogeneous than untransformed records.

Analysis of Variance↗
PubMed1989

Multiple trait prediction for a type of model with heterogeneous genetic and residual covariance structures.

A restricted set of models is defined that allows for heterogeneous genetic and residual covariance structures. Multiple trait models and models with multiple random factors are included. The restriction on the model is that the correlations among genetic effects in different classes are the same. Equivalently, the genetic covariance matrices are assumed to differ between classes due to scaling. This assumption greatly reduces the number of parameters that must be specified and does not adversely affect the computational burden of a mixed model analysis. An application of the model for genetic evaluation of beef cattle is described and illustrated numerically.

Analysis of Variance↗
PubMed1988

Describing interactions in dystocia scores with a threshold model.

Field data on calving difficulty scores provided by the American Simmental Association were subjected to two methods of analysis: ordinary least-squares analysis and maximum likelihood with an assumed threshold model. In each analysis, the model included the interaction of sex of calf X age of dam. This interaction was readily apparent in the data (observed scale): within the youngest dams 58% of the heifer calves and 37% of the bull calves were born unassisted vs 96% and 92%, respectively, in the oldest dams. The objective was to determine if this interaction would be greatly reduced or would disappear on the underlying scale of a threshold model. The least-squares estimate of the sex difference was greatest within the youngest age-of-dam group (18 to 24 mo) and steadily declined with increasing age of dam, approaching zero for dams 6 yr and older. In contrast, the estimates of the sex difference from the threshold analysis were remarkably similar across ages of dam. It was concluded that observed interactions in calving ease data could be adequately described by a threshold model in which the effects of age of dam and sex of calf act additively on the underlying variable.

Age Factors↗
PubMed1987

Analysis of gestation length in American Simmental cattle.

Records of gestation length (71,461) for Simmental cattle were distributed with mean 284.3 d and standard deviation 5.52 d. Gestation length was found to increase with percent Simmental and was 1.9 d longer for calves born to mature dams than for those born to heifer dams. Bull calves experienced gestation lengths 1.5 d longer than heifer calves. Sire, maternal grandsire, residual and total variances were estimated to be 2.42, .58, 22.78 and 25.78 d2, respectively, by Henderson's Method III. Heritability of gestation length was calculated to be .374 from the sire variance and .09 from the maternal grandsire variance. Direct additive genetic variance was considered to be of greater importance than maternal additive genetic variance. Correlations between the evaluations of sires for gestation length and heifer calving ease, birth weight and weaning weight were .26, .26 and .13, respectively.

Animals↗
PubMed1987

Estimation of variance and covariance components to determine heritabilities and repeatability of weaning weight in American Simmental cattle.

Components of (co)variance for weaning weight were estimated from field data provided by the American Simmental Association. These components were obtained for the observational components of variance corresponding to a sire, maternal grandsire, and dam within maternal grandsire model. From these estimates, direct additive genetic variance (Sigma2A), maternal additive genetic variance (Sigma2M), covariance between direct and maternal additive genetic effects (SigmaAM), variance of permanent environment(Sigma2pe) and temporary environment variance(Sigma2te) were determined. A procedure to approximate restricted maximum likelihood (REML) estimates of the observational components of variance based on the expectation-maximization (EM) algorithm is described. From these results, phenotypic variance ( ) of weaning weight was 667.88 kg2. Values forSigma2A, Sigma2M, Sigma2pe and Sigma2te were 79,30,58,38,49.45, and 469.97 kg2, respectively. Genetic correlation between direct and maternal additive genetic effects was .16.

Animals↗
PubMed1986

Lambing performance of Morlam and Dorset ewes under accelerated lambing systems.

Two accelerated lambing systems, Morlam using Morlam sheep (USDA, Beltsville 1966 to 1975) and Camal using Dorset ewes (Cornell 1978 to 1981), were evaluated for first lambing ages, interlambing intervals and conception probabilities. Morlam ewes were continuously exposed to rams over the year, while Camal Dorset ewes were exposed every other month. Morlam lambs were mated as early as 367 d of age and Camal Dorset lambs as early as 340 d. Early lambing was associated with higher rates of perinatal mortality (P greater than .05) and smaller litter size (P less than .01). Lambing years among Morlam ewes and season of birth of Camal Dorset ewes influenced (P less than .01) their first lambing ages. Lambing intervals averaged 293 and 303 d among Morlam and Camal Dorset ewes, respectively. Age at first lambing and season in which the previous lambing occurred with influential factors (P less than .01) on lambing intervals of Morlam ewes; longer intervals resulted when ewe lambs were mated at early ages (less than 12 mo), and when the previous lambing occurred in winter. Estimates of conditional probabilities of conception by month given the occurrence of estrus, reflected seasonal changes in both systems. The overall probability of conception for the Morlam system (P = .16) was relatively higher than that for the Camal Dorset system (P = .14); numbers of lambings per ewe per yr were 1.28 and 1.21, respectively. Estimates of heritability for age at first lambing, lambing interval and conception probability were .31, .06 and .30, respectively.

Animals↗
PubMed1986

Approximating prediction error variances for multiple trait sire evaluations.

The coefficient matrix for multiple trait (milk, fat, and protein) mixed model equations may be too large to obtain prediction error variances from inverse elements. The commonly used reciprocals of diagonal elements may not be accurate approximations when sire relationships or multiple traits are included since much information is contained in offdiagonal elements. Approximations incorporating increased information from coefficient matrix were compared with actual prediction error variances for multiple trait evaluations for milk, fat, protein, and dollar value (relationships included) of 229 Ayrshire and 248 Brown Swiss bulls. Six approximations were selection index using number of daughter records, inverses of individual sire diagonal blocks, inverses of group and individual sire blocks, and inverses of all diagonal blocks and offdiagonal blocks associated with individual sires. All approximations under-estimated actual prediction error variances, but most, except selection index, were highly correlated (.90 to .99) with actual prediction error variances of sire evaluations for milk yield and product value for contemporary bulls. The approximation incorporating most information from the coefficient matrix is recommended for use on basis of high correlation with and closeness to actual prediction error variances.

Analysis of Variance↗
PubMed1981

Sample size for detection of Y-chromosomes in lymphocytes of possible freemartins.

The number of metaphases that need to be examined to detect a Y-chromosome in a lymphocyte of a possible freemartin with a prescribed degree of certainty depends on the distribution of % XY cells among freemartins. To quantify this, the beta-binomial distribution was fit by maximum likelihood to% XY cells observed in blood samples of 70 freemartins (twin births only). The estimate mean and standard deviation of XY cells frequency in 70 freemartins (12,885 metaphases) was 0.48 and 0.30, respectively. These estimates correspond to a U-shaped distribution of XY cell frequency, i.e., one in which either an XX or an XY cell type predominates in most freemartins. These values indicate that sample sized of 26 and 168 are required to by 95% and 99% confident, respectively, that a female co-twin will not be misclassified.

Animals↗