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PubMed2003

Genetic correlations between the maternal genetic effect on chick weight and the direct genetic effects on egg composition traits in a White Leghorn line.

Selection can be a useful way to alter yolk proportion and thereby egg dry matter which, owing to its economic importance, is a trait of substantial importance for the egg-processing industry. However, the egg is primarily the chamber of embryonic development. The main purpose of this study was to estimate genetic correlations between the maternal effect on chick weight at hatching and the direct effect on different egg composition traits, in particular, yolk proportion. Additionally, genetic parameters were estimated for egg composition traits. To create a data set suitable for estimation of genetic parameters, a three-round selection experiment was set up. Birds were selected based on their predicted breeding values for the genetic maternal effect on chick weight and the direct genetic effect on yolk proportion according to the theory of elliptical selection. Genetic parameters were estimated using a multiple trait animal model and restricted maximum likelihood. The maternal heritability for chick weight was 0.5, whereas the direct heritability was dose to 0. The genetic correlations between the maternal effect on chick weight and the direct effect on yolk proportion, yolk weight, albumen weight, albumen dry matter concentration, and egg weight were 0.14, 0.76, 0.93, 0.14, and 0.99, respectively. The heritabilities for yolk proportion, yolk weight, albumen weight, albumen dry matter concentration, and egg weight were 0.33, 0.43, 0.57, 0.38, and 0.60, respectively. We conclude that breeding ought to be a useful way to increase egg dry matter with no expected unfavorable correlated effects on chick weight.

Analysis of Variance↗

PubMed1994

Impact of different strategies and amounts of preferential treatment on various methods of bull-dam selection.

Three records of milk yield, fat yield, and type were simulated for each cow in 20 herds of 200 cows over 13 yr. Preferential treatment or bias was simulated by increasing milk and fat yields by an average of 0, 16, and 32% for separate copies of the simulation. The bias was given to a limited number of cows from the original herds based on four strategies. Five methods of bull-dam selection that used an index with a 2:2:1 ratio of milk to fat to type to select the top 2% of cows were compared: ETA using first lactation, using all lactations, after phenotypic minima were required, after preselection on three-generation pedigree index, and on pedigree index alone. Selection on ETA for first or all lactations gave the highest average of true breeding values at 0 and 16% for all strategies studied. In general, selection on pedigree index alone or after phenotypic minima were required gave poor results and should not be considered to be viable. Preselection of bull-dams on pedigree index proved to be extremely useful for biased and unbiased data. The optimal policy was to preselect the top 12% of the population before reranking and selecting on ETA for all lactations.

Animals↗

PubMed2025

Genomic prediction and genome-wide association study for liver abscesses in crossbred beef cattle.

Liver abscesses are a concern in feedlot cattle, and little is known about the role of genetics in their development. This study aimed to estimate genetic parameters and to identify single-nucleotide polymorphisms (SNPs) associated with liver abscesses. Crossbred cattle representing 18 breeds in the U.S. Meat Animal Research Center Germplasm Evaluation Program were phenotyped for liver abscesses at slaughter (n = 9,044). Seventeen percent of cattle had liver abscesses. These cattle had genotypes that were imputed to sequence variant genotypes. After filtering and quality control, 340,723 SNPs were used in the analysis. Liver abscess prevalence was modeled with a single-step genomic best linear unbiased prediction (ssGBLUP) threshold model using a Bayesian framework. The model included contemporary group (sex, treatment group, and slaughter date), additive genomic, and residual effects. Genomic heritability was 0.039 (95% highest posterior density = 0.005, 0.081), which was very small. To assess prediction quality, a 5-fold random cross-validation structure was used. Method Linear Regression was used to assess accuracy, bias, and dispersion by comparing estimated breeding values (EBV) from full and reduced analyses. Cross-validation metrics showed EBV based on genotypes had 0.05 reliability (SD < 0.01) with no bias relative to EBV based on genotypes and phenotypes. For the genome-wide association study, SNP effects were back calculated from the EBV solutions from ssGBLUP. No SNPs were associated with liver abscesses at a Benjamini-Hochberg adjusted 0.05 significance level. Although a large dataset was used, this result was because of the low genomic heritability and imprecise EBV used to calculate SNP effects. Based on these results, environmental factors contribute to most of the variation in liver abscesses. Genetic selection to reduce liver abscesses would be slow because of the low genomic heritability, measurement late in life, and inability to measure breeding animals. A faster approach would be finding additional environmental interventions that maintain animal performance.

Animals↗

PubMed1990

Alternative methods of selection for litter size in mice: II. Response to thirteen generations of selection.

Selection was conducted on an index of components of litter size (I = 1.21 x ovulation rate + 9.05 x ova success; ovulation rate measured by number of corpora lutea and ova success measured as number of pups born + number of corpora lutea), on uterine capacity (measured as number of pups born to unilaterally ovariectomized dams) and on litter size concurrent with an unselected control for 13 generations. Selection criteria (IX = index, UT = uterine capacity, LS = litter size and LC = control) were applied in each of three replicates. In an evaluation after five generations, IX and LS each exceeded LC by about .5 pups, with no response in UT. After 13 generations, mean ovulation rate, ova success and litter size (measured as number of fetuses at 17 d gestation in intact females) were, for IX, 14.25, .84, 11.95; for LS, 14.15, .82, 11.64; for UT, 12.61, .86, 10.77; and for LC, 12.27, .82, 9.98. The regression of number born (litter size in IX, LS and LC; uterine capacity with only a functional left uterine horn in UT) on cumulative selection differential across 13 generations was .12 +/- .01, .09 +/- .02 and .08 +/- .02 for IX, LS and UT, respectively. The regression of breeding value for litter size on each selection criterion, estimated as response in the generation-13 evaluation divided by cumulative selection differential, was .11 +/- .02, .08 +/- .01 and .05 +/- .03 for IX, LS and UT, respectively. Regression of response in number born on generation number was .17 +/- .01, .15 +/- .04 and .10 +/- .02 for IX, LS and UT, respectively. Selection in IX was promising relative to LS, and selection in UT changed number born.

Animals↗

PubMed2006

Pregnancy rate and first-service conception rate in Angus heifers.

The objective of this project was to determine the genetic control of conception rate, or pregnancy percentage in Angus beef heifers. Producers from 6 herds in 5 states provided 3,144 heifer records that included breeding dates, breeding contemporary groups, service sires, and pregnancy check information. Two hundred fourteen sires of the heifers were represented; with 104 sires having less than 5 progeny, and 14 sires having greater than 50 progeny. These data were combined with performance and pedigree information, including actual and adjusted birth weights, weaning weights, and yearling weights, from the American Angus Association database. Heifer pregnancy rate varied from 75 to 95% between herds, and from 65 to 100% between sires, with an overall pregnancy rate of 93%, measured as the percentage of heifers pregnant at pregnancy check after the breeding season. Pregnancy was analyzed as a threshold trait with an underlying continuous distribution. A generalized linear animal model, using a relationship matrix, was fitted. This model included the fixed effects of contemporary group, age of dam, and first AI service sire, and the covariates of heifer age at the beginning of breeding, adjusted birth weight, adjusted weaning weight, and adjusted yearling weight. The relationship matrix included 4 generations of pedigree. The heritability of pregnancy and first-service conception rates on the underlying scale was 0.13 +/- 0.07 and 0.03 +/- 0.03, respectively. Estimated breeding values for pregnancy rate on the observed scale ranged from -0.02 to 0.05 for sires of heifers. Including growth traits with pregnancy rate as 2-trait analyses did not change the heritability of pregnancy rate. As expected for a reproductive trait, the heritability of pregnancy rate was low. Because of its low heritability, genetic improvement in fertility by selection on heifer pregnancy rate would be expected to be slow.

Animals↗

PubMed2002

Antler size in red deer: heritability and selection but no evolution.

We present estimates of the selection on and the heritability of a male secondary sexual weapon in a wild population: antler size in red deer. Male red deer with large antlers had increased lifetime breeding success, both before and after correcting for body size, generating a standardized selection gradient of 0.44 (+/- 0.18 SE). Despite substantial age- and environment-related variation, antler size was also heritable (heritability of antler mass = 0.33 +/- 0.12). However the observed selection did not generate an evolutionary response in antler size over the study period of nearly 30 years, and there was no evidence of a positive genetic correlation between antler size and fitness nor of a positive association between breeding values for antler size and fitness. Our results are consistent with the hypothesis that a heritable trait under directional selection will not evolve if associations between the measured trait and fitness are determined by environmental covariances: In red deer males, for example, both antler size and success in the fights for mates may be heavily dependent on an individual's nutritional state.

Age Factors↗

PubMed2006

Data depth, data completeness, and their influence on quantitative genetic estimation in two contrasting bird populations.

Evolutionary biologists increasingly use pedigree-based quantitative genetic methods to address questions about the evolutionary dynamics of traits in wild populations. In many cases, phenotypic data may have been collected only for recent parts of the study. How does this influence the performance of the models used to analyse these data? Here we explore how data depth (number of years) and completeness (number of observations) influence estimates of genetic variance and covariance within the context of an existing pedigree. Using long-term data from the great tit Parus major and the mute swan Cygnus olor, species with different life-histories, we examined the effect of manipulating the amount of data included on quantitative genetic parameter estimates. Manipulating data depth and completeness had little influence on estimated genetic variances, heritabilities, or genetic correlations, but (as expected) did influence confidence in these estimates. Estimated breeding values in the great tit were not influenced by data depth but were in the mute swan, probably because of differences in pedigree structure. Our analyses suggest the 'rule of thumb' that data from 3 years and a minimum of 100 individuals per year are needed to estimate genetic parameters with acceptable confidence, and that using pedigree data is worthwhile, even if phenotypes are only available toward the tips of the pedigree.

Animals↗

PubMed2004

Trace of native cattle in Japanese Holstein assessed by mitochondrial DNA sequence polymorphism.

On the basis of sequence variation in the displacement loop region of mtDNA, 588 Japanese and North American Holstein cows were classified into 5 mitochondrial haplotypes, which were found in Japanese Black cattle. One of the haplotypes (named type 1), which was present at the highest frequency in Japanese Black cattle, was not observed in either European or African cattle. This haplotype is characterized by 2 single-nucleotide polymorphisms. One is called the type B polymorphism, and it refers to a base change from T to C at nucleotide 16042 of the mitochondrial genome (T160042C). The other is called the type I polymorphism, and it refers to the base change as G16093A. The proportion of the Japanese Holstein population with both polymorphisms was 18.3%, whereas none of the North American cows had this genotype. Because the mitochondrial types were inherited maternally, it is clear that a considerable number of Japanese Holstein cows are descended from native Japanese cattle. Polymorphisms B and I accounted for no variance in the estimated breeding value for milk production among cows from the Hyogo herd (582 cows) or the Chiba region herd (758 cows). This result suggests that most autosomal genes of native animals have been successively replaced by those of pure Holstein after grading up of over 15 generations, even though resulting animals have native animal-oriented mitochondrial types and may still have some number of the native autosomal genes.

Animals↗

PubMed2004

[Recent findings on the genetics of gastro-intestinal nematode resistance in ruminants].

The control of helminthiases in ruminants raised in open pasture has been mainly undertaken by using prophylactic measures in the environment, but these are often inadequate due to incorrect application. With the appearance of anthelmintics, the strategy for controlling these parasitoses, passed to pharmacological treatments which became effective in reducing their impact. However, the frequent and incorrect utilisation of these molecules resulted in resistance to anthelmintics and the presence of chemical residues in animal products for human consumption. Anthelmintic resistance is widespread throughout the world, heterogeneous and probably underestimated. This has encouraged the introduction of homeopathic agents and products derived from plants whose effectiveness has not been scientifically assessed. It is well known that it is possible to detect differences in resistance to the most important parasites between breeds. In Europe, it has been reported that some ovine autochthonous breeds, Scottish Blackface and Lacaune, showed higher resistance. The implementation of breeding strategies aimed at obtaining animals with naturally low susceptibility to nematode infestations could therefore play an increasingly important role. Standard animal breeding techniques have been largely successful in improving the performance of domestic animals in the last century. Standard quantitative selection requires field data on: i) individual phenotype performance; ii) expected covariance among animals due to blood relationship between them. The whole process of predicting the breeding value of animals in order to select subsequently the genetically superior parents of the next generation is entirely based on sophisticated computations (BLUP-animal model). In sheep, the main objective is always selecting for milk yield and sometimes, in addition, milk composition. However, due to the evolution of the EU agricultural policy and consumer demand in terms of healthy and organic food, more attention is now being given to traits related to health (resistance to EST, mastitis or parasitic diseases). Some studies conducted in New Zealand and Australia showed that nematode resistance is genetically controlled with high heritabilities and quite low genetic correlations with production traits. In this sense, some studies showed that it is possible to decrease the number of parasites in the framework of a traditional breeding programme. However, in most situations, this trait is not extensively recorded due to the high cost of individual recording. Therefore, it would be useful to implement breeding strategies based on the knowledge of the genes involved in this trait expression. Traditionally, two approaches are available to locate a gene: i) genome scan; ii) candidate gene approach. The candidate gene approach attempts to link general resistance to some particular genes. To date, genetic resistance against parasites is considered to be linked with the MHC and IgE genes. Furthermore, several gene detection studies based on the genome scan approach for this trait are currently being carried out on both crossed experimental populations (fat x lean Blackface lines and Sarda x Lacaune) and pure breeds (Churra). The preliminary results seem promising as to the use of marker assisted or genotype assisted selection for this trait, which is difficult and expensive to measure on a population scale.

Animals↗

PubMed2001

International genetic evaluation of dairy sires using a multiple-trait model with individual animal performance records.

The objectives of this study were to estimate variance components and predict sire breeding values for milk, fat, and protein yield by using a multiple-trait model in which lactation yield in each country was considered as a different trait. Data included first lactation records of 16,145,832 Holstein-sired cows that calved between January 1, 1990, and December 31, 1997, in 243,466 herds in Australia, Austria, Belgium, Canada, the Czech Republic, Estonia, Finland, Germany, Hungary, Ireland, Israel, Italy, The Netherlands, New Zealand, South Africa, Switzerland, and the USA. Milk, fat, and protein were analyzed separately by using a 17-trait sire model; in this case, "traits" refer to measurements of the same biological parameter in different production systems. Our genetic model included the systematic effects of herd-year-season of calving, age at calving, milking frequency, and heterosis class (i.e., breed composition). Heritability estimates ranged from 0.24 in Australia (protein) to 0.34 in Israel (milk) and The Netherlands (fat). Genetic correlations between countries ranged from 0.77 for Austria-Czech Republic (protein), Estonia-Finland (fat), Estonia-Ireland (milk), Estonia-Israel (milk), and Hungary-New Zealand (fat), to 0.96 for Australia-Ireland (milk), Australia-New Zealand (milk), Belgium-Netherlands (milk), and Belgium-USA (fat). Correlations differed markedly from parameters used currently in international sire evaluations. In particular, genetic correlations were 0.91 to 0.96 between Australia, Ireland, and New Zealand; all of these countries rely heavily on rotational grazing. Correlations were also 0.91 to 0.96 between Belgium, Canada, Italy, The Netherlands, and the USA; all of these countries use intensive management systems. Correlations between these two groups of countries were 0.80 to 0.90. The percentage of elite bulls (top 1% for milk yield) selected in common by each pair of countries ranged from 0.42 for Germany-Estonia and Germany-Israel to 0.78 for Belgium-Netherlands.

Animals↗

PubMed2005

Heritabilities, genetic correlations, and genetic change for female fertility and protein yield in Norwegian Dairy Cattle.

Data from 1,815,581 first insemination records from daughters of 2697 Norwegian Dairy Cattle (NRF) sires were analyzed. A multitrait model was used to estimate genetic parameters and genetic change for 56-d nonreturn rate in virgin heifers (NR56D0), for 56-d nonreturn rate in first lactation cows (NR56D1L), for interval from calving to first insemination (CFI1L), and for protein yield (PY(305)1L). The heritabilities for NR56D0, NR56D1L, CFI1L, and PY(305)1L were 1.08, 0.99, 3.01, and 20.80%, respectively. Genetic correlation between heifer and cow fertility was high and favorable between NR56D0 and NR56D1L (0.54) and moderate and unfavorable between NR56D0 and CFI1L (0.24). The genetic correlations between NR56D1L and CFI1L and between NR56D0 and PY(305)1L were 0.08 and 0.04, respectively. A small, unfavorable genetic correlation between NR56D1L and PY(305)1L (-0.18) was found, while the genetic correlation between PY(305)1L and CFI1L was strongly unfavorable (0.47). Since 1972, NRF sires have been selected for NR56D0 using breeding values estimated from large progeny groups and with considerable weight in the total merit index. A linear regression analysis of sire PTA on year of first insemination of daughters showed an annual genetic change of 0.14% units for NR56D0. Selection was able to stabilize the genetic change of NR56D1L (0.03%/yr) but an undesirable change for CFI1L (0.11 d/yr) was found. The change of sire PTA for PY(305)1L was 0.63 kg/yr.

Analysis of Variance↗

PubMed1998

Optimizing pure line breeding strategies utilizing reproductive technologies.

The development of new reproductive techniques has had a great effect on schemes for dairy cattle improvement; AI resulted in progeny-testing schemes, and, more recently, multiple ovulation and embryo transfer has resulted in nucleus breeding schemes. In traditional breeding schemes, the use of multiple ovulation and embryo transfer resulted in only small increases of genetic gains because the selection intensity of bull dams was already high, but the selection intensity of cows in nucleus breeding schemes increased considerably. This increase makes nucleus schemes very competitive, especially when in vitro maturation and fertilization is used to increase female reproductive rates further. The increased genetic gain results in the selection of young females (i.e., optimal generation intervals are shortened). The combined effect of multiple ovulation and embryo transfer and shorter generation intervals increases the rate of gain by approximately 15% but also increases the rate of inbreeding and variances of the selection response (i.e., the risk of the breeding scheme) by about 80%. Recently, selection methods have been developed to reduce the rates of inbreeding or the variance of the selection response in breeding schemes. A scheme that maximized the selection differential while constraining the rate of inbreeding yielded about 30 to 60% more selection response than selection for BLUP estimated breeding value at the same rate of inbreeding. For the future, the combination of juvenile predictors of genetic merit (e.g., DNA markers) and techniques that further increase female reproductive rates seem very promising methods to increase the rates of genetic gain. As an example, the genetic gain of an optimized hybrid nucleus scheme could be increased 24% by the combined use of juvenile predictors and in vitro maturation and fertilization. Fertilization of fetal embryos was predicted to increase rates of gain by up to 18%.

Animals↗

PubMed2005

Animal breeding and disease.

Single-locus disorders in domesticated animals were among the first Mendelian traits to be documented after the rediscovery of Mendelism, and to be included in early linkage maps. The use of linkage maps and (increasingly) comparative genomics has been central to the identification of the causative gene for single-locus disorders of considerable practical importance. The 'score-card' in domestic animals is now more than 100 disorders for which the molecular lesion has been identified and hence for which a DNA test is available. Because of the limited lifespan of any such test, a cost-effective and hence popular means of protecting the intellectual property inherent in a DNA test is not to publish the discovery. While understandable, this practice creates a disconcerting precedent. For multifactorial disorders that are scored on an all-or-none basis or into many classes, the effectiveness of control schemes could be greatly enhanced by selection on estimated breeding values for liability. Genetic variation for resistance to pathogens and parasites is ubiquitous. Selection for resistance can therefore be successful. Because of the technical and welfare challenges inherent in the requirement to expose animals to pathogens or parasites in order to be able to select for resistance, there is a very active search for DNA markers for resistance. The first practical fruits of this research were seen in 2002, with the launch of a national scrapie control programme in the UK.

Animal Diseases↗

PubMed1998

Bayesian analysis of Wood's lactation curve for Spanish dairy cows.

A Bayesian procedure is presented to analyze test day performances in the scope of Wood's lactation function: atb (exp (-ct)), where a, b, and c = parameters, and t = time-dependent variable. The procedure has been applied to 148,557 test day controls corresponding to records for 15,349 first lactations of Spanish dairy cows. The procedure uses all available information and reduces the presence of atypical lactations. Moreover, the posterior marginal distribution of (co)variance components, breeding values, and systematic effects for the underlying variables of Wood's function are provided. The posterior means of the heritabilities were 0.43, 0.17, 0.40, and 0.29 for the parameters a (initial milk yield), b (ascent to peak), c (descent from peak), and total milk yield, respectively. Selection for total milk yield implies a great effect on the initial milk yield (a) but only minor effects on ascent to peak (b) and descent from peak (c).

Aging↗

PubMed2006

Association of polymorphisms in the bovine FASN gene with milk-fat content.

Fatty acid synthase (FASN) is a multifunctional protein that carries out the synthesis of fatty acids so it plays a central role in de novo lipogenesis in mammals. Previously, we defined the genetic structure and expression of the bovine FASN gene. Our mapping studies placed FASN on BTA19 (19q22) where several quantitative trait loci (QTL) affecting milk-fat content and related traits have been described. This study was conducted to identify polymorphisms in the bovine FASN gene and to study their association with milk-fat content. The bovine FASN gene was screened for polymorphisms in two cattle breeds. Sequence analysis revealed several single nucleotide polymorphisms (SNPs), and two of them were analysed: a G>C substitution in the untranslated exon 1 (g.763G>C), altering a potential Sp1 transcription factor-binding site, and an A>G substitution in exon 34 (g.16009A>G), which determines a non-conservative substitution of threonine by alanine. Allele-specific amplification of the SNPs in FASN revealed significant frequency differences for both polymorphisms in Holsteins with high and low breeding values for milk-fat content. The intragenic haplotypes comprising exon 1 (alleles G and C) and exon 34 (alleles A and G) polymorphisms were studied, and the existence of linkage disequilibrium between these SNPs was found (D(CG) = 0.048, P < 0.001). Our results suggest that the FASN gene polymorphisms contribute to variation in milk-fat content. We propose that the bovine FASN gene is a candidate gene for a milk-fat content QTL.

Alleles↗

PubMed1985

Effectiveness of genetic selection for prolificacy in pigs.

This paper attempts to summarize and discuss the new evidence on the effectiveness of selection for prolificacy. In recent years selection between lines, and the adoption of formal cross-breeding programmes, have led to considerable improvements at a commercial level. Within-line selection has not been tackled seriously except in a few experiments. The mainly negative results from these should not lead to the conclusion that progress is impossible, but rather that it needs larger resources, applied consistently for several generations, to overcome the inherent problems. There are now many estimates of genetic parameters, based on large data sets, and these have helped to clear up some of the confusion resulting from previous inadequate material. A heritability of around 0.1, repeatability of 0.15, and fairly high genetic correlations between successive records seem justified. The negative environmental effect of being reared in a large litter is frequently present, but there is no good reason why this should seriously affect attempts to improve the trait by selection. Information from a candidate's relatives other than its dam can undoubtedly increase the accuracy with which its breeding value is estimated, but the routine use of such data in practical programmes is not straightforward. Prolificacy is only one group of traits contributing to net economic worth. The need to strike a balance between all relevant traits is explored in the particular context of a scheme based on hyperprolific sows. Finally, selection can only have lasting and cumulative effectiveness if it is applied at the top of a pyramid of improvement. Both culling and selection of replacement gilts within the commercial sector are largely irrelevant.

Animals↗

PubMed1998

Litter, permanent environmental, ram-flock, and genetic effects on early weight gain of lambs.

Twelve models were fitted to early growth data of two Swiss sheep breeds to investigate their suitability for evaluation of breeding values. Models were identical for fixed parity, litter size, sex and lambing season effects, random flock-year, and direct genetic effects but differed for combinations of random litter, permanent environmental, ram-flock, and maternal genetic effects. Records of average daily gain to 30 d of 25,564 lambs of the Black-Brown Mountain Sheep (SBS) and of 26,391 lambs of the White Alpine Sheep (WAS) born 1989 to 1995 and their pedigrees were available. A single-trait animal model was fitted by the restricted maximum likelihood method. The information criterion of a particular model (i.e., the maximum of the likelihood function adjusted for the number of independently estimated parameters) was used to evaluate the models for their fitting power. The litter effect accounted for between 26 and 31% of the phenotypic variance, with little variation within breed. Models containing the ram-flock effect provided a better fit of the data than otherwise identical models. This effect contributed 6 and 4% to the phenotypic variance in the two breeds and strongly influenced estimates of other components. The proportion of phenotypic variance due to the flock-year effect was 23 and 25% without and 19 and 23% including the ram-flock effect in the model in the two breeds. Including permanent environmental effect of the ewe in addition to litter effect led to a better fit of the data. Depending on the model, it then contributed between 3 and 6% to the phenotypic variance. Fitting the ram-flock effect reduced heritability considerably and increased the breed difference of the estimates of this parameter. Estimates ranging from .16 to .10 and from .08 to .14 were obtained for the SBS and WAS breeds, respectively. For models without the ram-flock effect, negative estimates of the direct-maternal correlation of between -.38 and -.45 were observed. Including the ram-flock effect reduced this correlation substantially to between -.08 and -.17. Including the direct-maternal covariance in addition to the ram-flock effect did not improve the fit any further in either breed. Ranking of the models investigated differed between breeds, but the same model provided the best fit. It contained the random litter, permanent environmental, ram-flock, direct, and maternal genetic effects, but not the covariance between the last two.

Aging↗

PubMed2000

Direct and correlated responses to selection for milk yield: results and conclusions of regional project NC-2, "improvement of dairy cattle through breeding, with emphasis on selection". NC-2 Technical Committee.

Measurement of direct and correlated responses to single-trait selection for milk yield was the major objective of regional project NC-2. The NC-2 Technical Committee included representatives from Alaska, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Nebraska, South Dakota, Wisconsin, and the USDA. All representatives, except Illinois, Kansas and Nebraska, maintained a selection line formed by using AI sires selected for high estimated transmitting abilities for milk and a second line that served as some type of a control. Stations varied in criteria for selection of bulls for control lines. Farms were managed similarly, including feeding and management of selection and control lines as one herd, random mating within line, and restricted culling policies. Selection for milk yield effectively increased milk production. All selection lines increased milk and net income per lactation more than control lines. Realized gains matched or exceeded gains expected from estimates of breeding values. Yields of milk components increased, but component percentages decreased appreciably for selection lines. Reproduction of nulliparous animals was not affected, but days open for lactating selection cows increased in some of the individual projects. Selected cows tended to have larger health costs, specifically for mammary treatment. Udder and conformation traits did not deteriorate for selection lines, although control lines with selection of sires on genetic evaluations for type received higher type scores. There should be few reservations about undesirable responses correlated with selection for milk yield.

Animal Feed↗