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Heterogeneity of variance of growth traits over age is a common issue in estimating genetic parameters and is addressed in this study by selecting appropriate variance structure models for additive genetic and environmental variances. Modeling and partitioning those variances connected with analyzing small data sets were demonstrated on Lipizzan horses. The following traits were analyzed: withers height, chest girth, and cannon bone circumference. The measurements were taken at birth, and at approximately 6, 12, 24, and 36 mo of age of 660 Lipizzan horses born in Croatia between 1948 and 2000. The corresponding pedigree file consisted of 1,458 horses. Sex, age of dam, and stud-year-season interaction were considered fixed effects; additive genetic and permanent environment effects were defined as random. Linear adjustments of age at measuring were done within measuring groups. Maternal effects were included only for measurements taken at birth and at 6 mo. Additive genetic variance structures were modeled by using uniform structures or structures based on polynomial random regression. Environmental variance structures were modeled by using one of the following models: unstructured, exponential, Gaussian, or combinations of identity or diagonal with structures based on polynomial random regression. The parameters were estimated by using REML. Comparison and fits of the models were assessed by using Akaike and Bayesian information criteria, and by checking graphically the adequacy of the shape of the overall (phenotypic) and component (additive genetic and environmental) variance functions. The best overall fit was obtained from models with unstructured error variance. Compared with the model with uniform additive genetic variance, models with structures based on random regression only slightly improved overall fit. Exponential and Gaussian models were generally not suitable because they do not accommodate adequately heterogeneity of variance. Using the unstructured error variance model, the heritability estimates ranged from 0.17 to 0.33 for withers height, 0.07 to 0.27 for chest girth, and 0.14 to 0.30 for cannon bone circumference. This study demonstrated the necessity of accounting for heterogeneity of variances and covariances for body shape traits in Lipizzan horses, and possible difficulties in estimating variance and covariance components when applying more complicated structure models on a small data set. The choice of models depends not only on overall fit but also on the fit of genetic and environmental components. Key words: body shape, heritability, heterogeneity of variance, Lipizzan horse, model selection doi: 10.2527/jas.2009-2453

The aim of this study was to estimate genetic parameters for coat color in horses. Besides defining coat color classes (gray, chestnut, bay, and black), the phenotypes were also measured quantitatively according to standardized international procedures (Commission Internationale de l'Eclairage L *, a *, b *), where L * describes lightness, a * describes color saturation from red to green, and b * describes color saturation from yellow to blue. The total color saturation was derived from a * and b * and referred to as Chroma. A total of 294 horses from the breeds Lipizzan, Nonius, Arabian Pure Bred, Shagya Arabian, and Gidran were measured at neck, shoulder, and belly. Heritabilities (within and between breeds or color classes) and repeatabilities were estimated using REML from univariate animal models defined separately for gray and nongray horses. For gray horses, the estimated within-breed heritabilities for L * ranged from 0.45 to 0.49 and for a *, b *, and Chroma from 0.09 to 0.52, indicating moderate polygenic effect. For nongray horses, between-color class heritabilities were high (0.70 to 0.85) and within-color class heritabilities were negligible (except for L * measured on neck and belly, 0.21 and 0.34, respectively). Additionally, the importance of L * was described by the relation with the total melanin content of horse coat hair; for gray and nongray horses, a strong negative linear relationship was detected (P < 0.01). The spectrometric measures and the results of this study demonstrate a possible approach to the estimation of the polygenic component involved in coat color inheritance. Key words: coat color, heritability, horse, melanin, repeatability

Objectives: To evaluate in a prospective multicentre setting the feasibility of transcranial colour coded duplex sonography (TCCS) for examination of the middle cerebral artery (MCA) in patients with acute hemispheric [...]

The objective of this study was to determine the effects of a metallothionein/bovine GH transgene on duration and rate of growth of lean and fat in mice. Mice were produced by mating hemizygous transgenic males to nontransgenic females. Ten weights and six measurements of total body electrical conductivity to estimate body composition were taken on 147 progeny between birth and 84 d of age. Growth traits for fat-free mass (FFM) and body fat mass (FM) were obtained by fitting FFM and FM to a logistic curve y = A/(1 + exp(k(b - t))), where y is FFM or FM, A is asymptotic mass, k and b are curve parameters, and t is time in days. The function and its first, second, and third derivatives for FFM and FM were used to model growth. A mixed model was used with animal and litter as random effects and transgenotype, sex, and transgenotype x sex as fixed effects in analyses of growth traits. Estimates of transgenotype and transgenotype x sex interaction were tested by using their corresponding standard errors. Males had greater response to the transgene than females in final FFM and growth rate during the entire growth period. Transgenic males and females had greater duration of lean growth than nontransgenics. Transgenic males began to accumulate fat later, but they eventually gained more fat than transgenic females. Key Words: Mice, Transgenics, Composition, Somatotropin

Genetic and environmental variances and covariances and associated genetic parameters were estimated for weaning weight, asymptotic mature weight, and repeated mature weights. Data consisted of a set of weight measurements of 3,044 Angus cows born between 1976 and 1990. Mature weight was predicted by individually fitting Brody growth curves (asymptotic weight) and by using weights repeatedly measured after 4 yr of age. Variance and covariance components for mature weight were estimated by REML from a single-trait animal model with asymptotic weight, a two-trait animal model with asymptotic and weaning weight, and a two-trait animal model with repeated weights and weaning weight. Weaning and cow contemporary groups were defined as fixed effects. Random effects for weaning weight included direct genetic, maternal genetic, and permanent environmental effects; and for mature weight, direct genetic and repeated measurements (if in the model). Heritability estimates for weaning weight were similar for both two-trait models (.53 and .59). Estimates of heritability for mature weight were .44, .52, and .53 for the single-trait model with asymptotic weight, two-trait model with asymptotic weight, and two-trait model with repeated measures weights, respectively. The estimate of the genetic correlation between mature and weaning weight was higher for the repeated measures model (.85 vs. .63). A lower heritability estimate for mature weight from the single-trait model was likely due to postweaning culling. Therefore, a genetic evaluation of mature weight from field data should include a trait recorded earlier in life that is less subjected to selective data reporting. Key Words: Beef Cattle, Genetic Parameters, Maturity, Weight

We conducted a two-way selection experiment in a composite rabbit population to investigate the responses to selection for postweaning ADG and feed conversion (FC). Two generations of crossing, followed by four generations of random pair matings, preceded three generations of selection. Selection was practiced within four lines: high-feed conversion (HFC), low-feed conversion (LFC), high gain (HG), and low gain (LG). Data on 1,446 rabbits from the random mating and selection generations were fitted to an animal model to estimate heritabilities of and the genetic correlation between ADG and FC. The two-trait model included rabbit and common litter random effects and line, generation, and sex fixed effects. Estimates of heritability of ADG and FC were .48 and .29, respectively, and the genetic correlation between them was -.82. Common litter environmental effects accounted for a proportion of .11 and .13 of the phenotypic variation of the two traits, respectively. For ADG (in g/d) the regressions of mean breeding values on generation number during the selection period were 1.23 [+ or -] .12 (P < .01) in the HG line and -.86 [+ or -] .12 (P < .01) in the LG line; the regressions for FC (in g feed/g gain) were -.07 [+ or -] .01 (P < .01) in the HFC line and .03 [+ or -] .01 (P < .05) in the LFC line. Selection for ADG was effective in improving ADG and FC. Key Words: Rabbits, Selection, Growth, Feed Conversion, Genetic Parameters