Estimates of genetic parameters for Holstein cows for test-day yield traits with a random regression cubic spline model

Genetic parameters were estimated with restricted maximum likelihood for individual test-day milk, fat and protein yields and somatic cell scores with a random regression cubic spline model. Test-day records of Holstein cows that calved from 1994 through early 1999 were obtained from Dairy Records Management Systems in Raleigh, North Carolina, for the analysis. Estimates of heritability for individual test-days and estimates of genetic and phenotypic correlations between test-days were obtained from estimates of variances and covariances from the cubic spline analysis. Estimates were calculated of genetic parameters for the averages of the test days within each of the ten 30-day test intervals. The model included herd test-day, age at first calving, and bovine somatropin treatment as fixed factors. Cubic splines were fitted for the overall lactation curve and for random additive genetic and permanent environmental effects, with five predetermined knots or four intervals between days 0, 50, 135, 220, and 305. Estimates of heritability for lactation one ranged form 0.10 to 0.15, 0.06 to 0.10, 0.09 to 0.15, and 0.02 to 0.06 for test-day one to test-day 10 for milk, fat and protein yields and somatic cell scores, respectively. Estimates of heritability increased over the course of the lactation. Estimates of genetic and phenotypic correlations were smaller for test-days further apart

Up hill, down dale: quantitative genetics of curvaceous traits

‘Repeated’ measurements for a trait and individual, taken along some continuous scale such as time, can be thought of as representing points on a curve, where both means and covariances along the trajectory can change, gradually and continually. Such traits are commonly referred to as ‘function-valued’ (FV) traits. This review shows that standard quantitative genetic concepts extend readily to FV traits, with individual statistics, such as estimated breeding values and selection response, replaced by corresponding curves, modelled by respective functions. Covariance functions are introduced as the FV equivalent to matrices of covariances. Considering the class of functions represented by a regression on the continuous covariable, FV traits can be analysed within the linear mixed model framework commonly employed in quantitative genetics, giving rise to the so-called random regression model. Estimation of covariance functions, either indirectly from estimated covariances or directly from the data using restricted maximum likelihood or Bayesian analysis, is considered. It is shown that direct estimation of the leading principal components of covariance functions is feasible and advantageous. Extensions to multi-dimensional analyses are discussed

Relação entre características morfológicas e produção de leite em vacas da raça Gir Relationship between morphological traits and milk yield in Gir breed cows

O objetivo deste trabalho foi determinar parâmetros genéticos relacionados a características morfológicas e suas correlações genéticas com a produção de leite, em vacas da raça Gir. Utilizaram-se 3.805 registros provenientes de 2.142 vacas. O modelo utilizado na análise de características morfológicas continha os efeitos fixos de rebanho, ano e estação de classificação, estádio da lactação e idade da vaca à classificação, além da identificação do classificador. Quanto à produção de leite, foram incluídos no modelo os efeitos fixos de rebanho, ano e estação de parição e idade da vaca ao parto. Os parâmetros genéticos foram obtidos por meio do aplicativo REMLF90. As estimativas de herdabilidade variaram de 0,09 a 0,54. A variabilidade genética aditiva da maioria das características é suficiente para que ganhos genéticos anuais significativos possam ser alcançados com o processo de seleção. As correlações genéticas entre as características morfológicas variaram de baixas a altas e, entre elas e a produção de leite, de baixas a moderadas. Altas correlações genéticas entre algumas características morfológicas implicam a possibilidade de exclusão de algumas delas do programa de melhoramento genético da raça Gir, no Brasil. As correlações genéticas entre produção de leite e algumas características morfológicas indicam que estas podem ser utilizadas na formação de índices de seleção.<br>The objective of this work was to determine genetic parameters related to morphological traits and their genetic correlation with milk yield of Gir breed cows. A total of 3,805 records from 2,142 cows was used. For morphological trait analysis, the used model included the herd fixed effects, classification year and season, lactation phase and animal age at evaluation, besides the classifier identification. For milk yield, the fixed herd effects, year and season of calving and cow age at calving were included in the model. The genetic parameters were estimated using the REMLF90 software. The heritability estimates varied from 0.09 to 0.54. The additive genetic variability of the majority of traits is sufficient to achieve significative annual genetic gain by selection practices. The genetic correlations among morphological traits varied from low to high and, between them and milk yield, from low to moderate. High genetic correlations among some morphological traits implies on the possibility of exclusion of some of them from the breeding program, for Gir breed in Brazil. The genetic correlations between milk yield and some morphological traits indicate that they may be used in the formation of selection indexes

Genetic parameters for type traits in Holstein cows in Brazil

Data from 26,558 Holstein cows in 802 herds were used to estimate genetic, residual and phenotypic parameters for 22 type traits. The model included the fixed effects of herd-year, period of classification, classifier, stage of lactation and age of cows at calving (covariate) and random genetic and residual effects. Heritability for type traits ranged from 0.10 to 0.39. The genetic variability in these traits suggested the possibility for moderate genetic gains through selection. The phenotypic correlations were moderated, mainly in the section conformation. Genetic correlations between type traits ranged from -0.44 to 0.85. High genetic correlations indicated that breeding programs could be successful without including all type traits. The selection for the final score at the expense of other traits must be performed with restraint, because in the long term, this may promote undesirable changes in some type traits