Inbreeding depression for global and partial economic indexes, production, type, and functional traits

peer reviewedThe objective of this research was to examine the effects of inbreeding in the population of Holstein cattle in the Walloon region of Belgium. The effects of inbreeding on the global economic index and its components were studied by using data from the genetic evaluations of February 2004 for production, somatic cell score (SCS), computed from somatic cell counts and type. Inbreeding coefficients for 956,516 animals were computed using a method that allows assigning an inbreeding coefficient to individuals without known parents. These coefficients were equal to the mean inbreeding coefficient of contemporary individuals with known parents. The significance of inbreeding effects on the different evaluated traits and on the different indexes were tested using a t-test comparing estimated standard errors and effects. The inbreeding effect was significantly different from zero for the vast majority of evaluated traits and for all of the indexes. Inbreeding had the greatest deleterious effects on production traits. Inbreeding decreased yield of milk, fat, and protein during a lactation by 19.68, 0.96, and 0.69 kg, respectively, per each 1% increase in inbreeding. The regression coefficient of SCS per 1% increase in inbreeding was +0.005 SCS units. The inbreeding depression was thus relatively low for SCS, but inbred animals had higher SCS than non-inbred animals, indicating that inbred animals would be slightly more sensitive to mastitis than non-inbred animals. Estimates of inbreeding effects on evaluated type traits per 1% increase were small. The most strongly affected type traits were chest width, rear leg, and overall development on a standardized scale. For several type traits, particularly traits linked to the udder, the estimates suggested a favorable effect of inbreeding. The global economic index was depressed by around 6.13 Euro of lifetime profit per 1% increase in inbreeding for the Holstein animals in the Walloon region of Belgium

Linear and curvilinear effects of inbreeding on production traits for walloon Holstein cows

The nonlinear effects of inbreeding were studied by comparing linear and curvilinear regression models of phenotypic performances on inbreeding coefficients for production traits (milk, fat, and protein yields) of Holstein cows in their first lactation. Three different regression models (linear, quadratic, and cubic) were introduced separately into a single-trait, single-lactation, random regression test-day model. The significance of the different regression coefficients was studied based on a t-test after estimation of error variances and covariances associated with the different regression coefficients. All of the tested regression coefficients were significantly different from 0. The traditional regression coefficients of milk, fat, and protein yields on inbreeding were, respectively, -22.10, -1.10, and -0.72 kg for Holstein cows in their first lactation. However, the estimates of 305-d production losses for various classes of animals based on inbreeding coefficients showed that the effect of inbreeding was not a linear function of the percentage of inbreeding. The 305-d milk yield loss profiles attributable to inbreeding, obtained by the various regression models, were different. However, for inbreeding coefficients between 0 and 10%, these differences were small

Genetic evaluation for birth traits in dual-purpose Belgian Blue using a mixed inheritance model

In this study a genetic evaluation, based on a mixed inheritance model, was developed for birth traits (calving ease, gestation length and birth weight) in dual-purpose Belgian Blue (dpBB), a separated type inside Belgian Blue Herd-book. About 80% of dpBB animals have a single or a double copy of the muscular hypertrophy gene. This heterogeneity is the reason of a great variability in birth performance traits like calving ease or birth weight. The muscular hypertrophy gene substitution and dominance effects for calf genotype had a significant impact both on birth weight and calving ease, in accordance with partially recessive expression of the muscular hypertrophy gene. Observed high heritability estimates of direct calving ease (0.334) and birth weight (0.260) suggested that a large genetic variability for birth traits was present in dpBB, and that genetic improvement was possible through selection. This variability has allowed dpBB breeders to apply mass selection successfully in the past. However analysis of breeding values showed that a sire selection for calving ease within genotype was progressively applied by breeders, the selection intensity being more important for calving ease in double muscled lines. This study illustrated the possible confusion that can appear by the use of a major gene in selection, and the importance to use appropriated models combining polygenic and monogenic information, like mixed inheritance models

Analysis of longitudinal data for selection and management

Until recently the description of dynamic biological processes was done using static models even if those biological processes such as lactation or growth provided us with longitudinal data. A classical example was the use of lactational milk yields even if individual test-days describing the underlying lactation curves were available. Similarly for growth, weights were corrected phenotypically to fit into categories like weaning or yearling weights. Several recent developments stimulated the research on alternative methods describing the evolution of the mean and the variances of continuos dynamic biological processes. These developments were especially the extension of repeatability models towards random regressions and the development of the (co)variance function approach, but the development of better computers allowing the storage and the processing of a huge quantity of data. Despite this the analysis of certain types of longitudinal data as test-day yields in large populations and/or international settings is still a major challenge. But a very important aspect of the analysis of longitudinal data is often forgotten: they give us other information than the one classically extracted from genetic evaluation systems. In fact, the detailed modeling of dynamic biological processes provides opportunities for the development of advanced management tools. This may have a large influence on the way genetic evaluation systems may evolve in the future, making them integrated systems for the management and selection of animals

Correlations of longevity evaluation with type traits in Walloon Region.

Approximated genetic correlations between direct longevity and type traits were computed for a sire Holstein population. Data were based on results for type traits (77,965 records) and for direct longevity (74,289 records) from the INTERBULL routine run of November 2005. Most of type traits presented a high relationship with direct longevity (from 0.06 up to 0.29). The strongest positive correlation with longevity was for udder depth (0.29) and the strongest negative correlation was for chest depth (-0.21). According the different results, an animal with a good direct longevity seemed to be smaller and less heavy than an animal with a shorter longevity

Estimation of (co)variance components across breeds by a test-day model adapted to New Zealand dairy cattle.

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