The effect of preventive trimming on weight bearing and force balance on the claws of dairy cattle.

Claw disorders and lameness in dairy cattle are an increasing problem of the modern dairy industry. To prevent claw disorders from evolving from the subclinical to the clinical stage, trimming is the management practice most routinely applied. The goal of preventive trimming (Toussaint-Raven method) is to promote natural loading by increasing the weight-bearing contact area of the claws and improving the balance between the medial and lateral claw. The biomechanical effect of preventive claw trimming was investigated with the aid of pressure distribution and ground reaction force recordings of the standing cow sampled simultaneously at 250 Hz. It appeared that preventive trimming of the hind limbs (n = 10) brought the claws slightly more in balance. Before trimming, 80% of the total force is taken up by the lateral claw and 20% by the medial claw. After trimming, this becomes 70 to 30%, respectively. Thereby, a significant increase in the weight-bearing contact area from 27.5 to 40.0 cm2 was achieved, resulting in a significant decrease in average pressure. However, the claws remained subjected to unaltered, high maximum pressures after trimming. The suggestion was made that the main focus of claw trimming should not be force balance; instead, a reduction of local maximum pressures at the contact area should be targeted in such a way that the strongest parts of the claw capsule (i.e., the wall) will be subjected to the highest pressures.

Population parameters to compare dog breeds: differences between five Dutch purebred populations.

Differences in five purebred dog populations born in 1994 in the Netherlands were evaluated using different parameters. Numerically, the Golden Retriever was the largest breed (840 litters of 234 sires) and the Kooiker Dog (101 litters of 41 sires) the smallest. The litter per sire ratio was largest in the Bernese Mountain Dog (4.59) and lowest in the Kooiker Dog (2.46). The mean relatedness and the actual mean level of inbreeding in the studied generations were 0.102 and 0.056 respectively for the Bernese Mountain Dog, 0.041 and 0.046 for the Bouvier des Flandres, 0.087 and 0.061 for the Boxer, 0.020 and 0.018 for the Golden Retriever, and 0.146 and 0.070 for the Kooiker Dog. Quantification and visualization of population parameters for purebred dogs will facilitate the comparison of breeds and the comparison of breeds in different periods or countries. It appears unlikely that the increase in inbreeding is a major determinant of the possible increase in the frequency of genetic diseases.

Genetic evaluation for longevity of Dutch dairy bulls.

Parameters needed for survival analysis of longevity records of cows to predict breeding values of their sires were estimated with data on Dutch Black and White and Red and White cows. The heritabilities of functional productive life were 0.041 and 0.036 on the log scale for Black and White and Red and White cows, respectively. Although the heritabilities and other parameters differed between both breeds, the resulting breeding values were hardly affected: the correlation between breeding values of Red and White bulls using either Red and White parameters or Black and White parameters was 0.992. Genetic correlations between the direct breeding value for functional longevity (based solely on longevity of sires' daughters) and breeding values for conformation, health, and fertility traits were calculated. Several alternative selection indices were investigated using these correlations. Based on the resulting reliabilities, it was concluded that the Dutch breeding value for functional longevity should be based on longevity, rump angle, teat placement, udder depth, feet and legs, and somatic cell count. The index was expressed on a scale with average of 100 and a standard deviation of 4 points (at 80% reliability). The economic value was Dfl. 65 per genetic standard deviation, which was 0.46 times the economic value of INET (Net Milk Revenue Index). For the breeding value for functional longevity that was first published in August 1999, slight modifications in the model were made.

Modeling of energy balance in early lactation and the effect of energy deficits in early lactation on first detected estrus postpartum in dairy cows.

The general pattern of energy balance in early lactation was modeled. For this purpose, several lactation curves were investigated. The best fitting curve was fit in a random regression model that provided predicted energy balance curves for all lactations. By use of these curves, total energy deficit per lactation, postpartum interval of return to positive energy balance, and nadir of energy balance was determined. In predicted energy balances, nadir of energy balance was present, but variation in postpartum interval to nadir was small. First lactation cows had a smaller energy deficit in early lactation than did older cows. Differences among cows in nadir and total energy deficits in early lactation were large. Both were related to the postpartum interval to first detected estrus with a larger energy deficit and a smaller nadir corresponding to a larger postpartum interval to first detected estrus. From this study, it can be concluded that large energy deficits in early lactation delay first detected estrus.

Evaluation of genetic, common-litter, and within-litter effects on preweaning mortality in a birth cohort of puppies.

OBJECTIVE: To determine relative impact of genetic, common-litter, and within-litter factors on puppy mortality. ANIMALS: 2,622 Boxer puppies of 413 litters born during a 14-month period. PROCEDURE: For each puppy, pedigree was determined, and litter in which it was born was registered. Overall mortality and mortality per specific cause of death were analyzed by use of a model that included an additive genetic effect, common-litter effect, within-litter effect, and regression of mortality on inbreeding coefficient. Relative importance of the effects was determined from estimates of the variance in mortality explained by each factor. RESULTS: 22% of the puppies died before reaching 7 weeks old. Stillbirth was the most frequent cause of death, followed by infection. Most observed differences were attributable to within-litter factors, which explained 67% of the variance in death attributable to infection and < or = 96% of the variance in death attributable to asphyxia. Common-litter factors were more important than additive genetic factors. Variance attributed to common-litter factors ranged from 2% for cheiloschisis, palatoschisis, or cheilopalatoschisis to 30% for death attributable to infection, and variance attributed to additive genetic factors ranged from 0% for asphyxia to 14% for euthanatized because of white color. Inbreeding coefficient had a significant effect on death attributable to infection, which increased 0.26% for each percentage increase of inbreeding. CONCLUSIONS AND CLINICAL RELEVANCE: Additive genetic factors have less impact on preweaning mortality than common-litter factors, which in turn have less impact than within-litter factors. Mortality attributable to infection increases significantly with increases in inbreeding.

Microsatellite polymorphism in commercial broiler and layer lines estimated using pooled blood samples.

For 17 microsatellite markers, allele frequencies were determined in nine highly selected commercial broiler and six highly selected commercial layer lines using pooled blood samples from 60 animals. The average number of marker alleles was 5.8 over all lines, 5.2 over broiler lines, and 3.0 over layer lines. The average number of marker alleles within a line was 2.9, 3.6, and 2.0 for all, broiler, and layer lines, respectively. Over all 15 lines, the average percentage of heterozygosity was 42, whereas the heterozygosity in the broiler lines was 53% and in the layer lines only 27%. In broiler lines, 50% of the marker-line combinations showed a heterozygosity above 60%, whereas this was only 5% in layer lines. Estimation of allele frequencies with microsatellite markers was first assessed in pooled and individual samples before usage in the commercial lines. Allele frequencies for 19 microsatellite markers were estimated in chicken pooled blood samples and compared with allele frequencies from individual typed animals. Similar results were obtained when pooled blood samples (heterozygosity of 35.3%) or individual typed animals (heterozygosity of 34.2%) were used. The method to determine allele frequencies using pooled blood samples is faster, cheaper, and as reliable and repeatable as determining allele frequencies using individual typings.

Use of deterministic sampling for exploring likelihoods in linkage analysis for quantitative traits.

Deterministic sampling was used to numerically evaluate the expected log-likelihood surfaces of QTL-marker linkage models in large pedigrees with simple structures. By calculating the expected values of likelihoods, questions of power of experimental designs, bias in parameter estimates, approximate lower-bound standard errors of estimates and correlations among estimates, and suitability of statistical models were addressed. Examples illustrated that bracket markers around the QTL approximately halved the standard error of the recombination fraction between the QTL and the marker, although they did not affect the standard error of the QTL's effect, that overestimation of the distance between the markers caused overestimation of the distance between the QTL and marker, that more parameters in the model did not affect the accuracy of parameter estimates, that there was a moderate positive correlation between the estimates of the QTL effect and its recombination distance from the marker, and that selective genotyping did not introduce bias into the estimates of the parameters. The method is suggested as a useful tool for exploring the power and accuracy of QTL linkage experiments, and the value of alternative statistical models, whenever the likelihood of the model can be written explictly.

Power of two and three-generation QTL mapping experiments in an outbred population containing full-sib or half-sib families.

QTL mapping experiments involve many animals to be genotyped and performance tested. Consequently, experimental designs need to be optimized to minimize the costs of data collection and genotyping. The present study has analyzed the power and efficiency of experiments with two or three-generation family structures containing full-sib families, half-sib families, or both. The focus was on data from one outbred population because the main interest is to locate genes that can be used for within-line selection. For a two generation experiment more animals had to be typed for marker loci to obtain a certain power than for a three generation experiment. Fewer trait values, however, had to be obtained for a two-generation experiment than for a three-generation experiment. A two or three-generation family structure with full-sib offspring was more efficient than a two or three-generation family structure with half-sib offspring. A family structure with full-sib grand-offspring, however, was less efficient than a family structure with half-sib grand-offspring. For the most efficient family structure each pair of parents had full-sib offspring that were genotyped for the marker. For the most-efficient family structure each full-sib offspring had half-sib grand-offspring for which trait values were obtained. For equal power with a heritability of 0.1 and 100 grand-offspring per full-sib offspring, 30-times less marker typings were required for this most efficient family structure than for a two-generation half-sib structure in which marker genotypes and trait values were obtained for half-sib offspring. The effect of heritability and the type of analysis (single marker or interval analysis) on the efficiency of a family structure is described. The results of this study should help to design QTL mapping experiments in an outbred population.

Criteria to optimize designs for detection and estimation of linkage between marker loci from segregating populations containing several families.

Construction of a genome map of highly polymorphic markers has become possible in the past decade. Establishing a complete marker map is an enormous task. Therefore, designs to map molecular markers should be optimal. Designs to detect and estimate linkage between markers from segregating populations were studied. Two measures of design quality were used. The expectation of the maximum lod score indicates the possibility of designs to detect linkage. The accuracy of estimating recombination rate was measured as the probability that the true recombination rate is in a specified internal given the estimate. Accurate approximate methods were developed for rapid evaluation of designs. Seven family types (e.g., double backcross) can be distinguished that describe all families in a segregating population. The family type influences the expected maximum lod score and the accuracy of estimation. The frequency of favorable family types increased with increasing marker polymorphism. At a true recombination rate of 0.20,27 observations on offspring when five alleles were segregating, and 55 observations on offspring when two alleles were segregating, were necessary to obtain an expected maximum lod score of 3. The probability that the true recombination rate was between 0.15 and 0.25, given an estimate of 0.20, was about 0.85 for a design with 40 families with ten offspring and two alleles segregating and for a design with ten families with ten offspring and six alleles segregating. For smaller designs, accuracies were less, approximate evaluation of accuracy was not justified and, on average, true recombination rates were much greater than estimated given a specified value for the estimated recombination rate.

High levels of linkage disequilibria between serologically defined class I bovine lymphocyte antigens (BoLA-A) and class II DQB restriction fragment length polymorphism (RFLP) in Norwegian cows.

Serum defined BoLA-A antigens, together with BoLA-DQB RFLP patterns, were determined in 87 almost unrelated Norwegian cattle. Statistical analysis revealed strong linkage disequilibria between these loci at the population level. A total of 13 haplotypes were found to be present at frequencies significantly greater than those predicted on the basis of their component gene frequencies. Among these, the subgroups 1A and 1B of the DQ1 haplotype were found to be closely associated with the class I antigens A11 and w16, respectively. The association between A11 and DQ1A is of particular interest, as two independent studies, one employing class I serology, and the other RFLP analysis of the class II locus DQ, have previously indicated that A11 and DQ1A confer relative susceptibility to mastitis.