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Abstract Background Control of the environmental variability by genetic selection offers possibilities for new selection objectives for productive traits. This methodology aims at reducing heterogeneity in productive traits and has been applied to several traits and species for which animal homogeneity is profitable. In horse breeding programmes, rank in competitions is a common selection objective but has been challenging to model. In this study, the parameters of environmental variability for the rank of a horse were computed to analyse the capability of a horse to maintain the best ranking across competitions that consist of long-distance races in which the adapted physical condition of the horse is essential. The genetic component of the environmental variance for the rank in endurance competitions was evaluated, which resulted in proposing a new transformation of horse scores in competitions. Results Homogeneous and heterogeneous variance models were compared by assaying three random effects that affect both the rank and its variability, using endurance ride data consisting of 2863 records. The pedigree relationship matrix contained 5931 animals. The rank trait was transformed into a normalized variable to prevent false estimates of the genetic correlation by inappropriate artificial skewness. The models included the number of participants in the race, sex, and age as systematic effects. The rider, the rider-horse interaction, or an environmental permanent effect were tested as random effects, in addition to additive genetic and residual effects. The models were analysed using the GSEVM program. Estimates of heritability for rank ranged from 0.12 to 0.15. The heterogeneous variance model that fitted the rider was assessed as the best model based on the deviance information criterion. Estimates of genetic variance for rank variability ranged from 0.12 to 0.13. The genetic correlation between the rank and its environmental variability was low and did not differ from 0. Conclusions These results offer an opportunity to select animals for canalization by reducing the variability of race results and achieving the best positions, which could be a new selection objective by weighting estimated breeding values for rank and its variability in a selection index.

The present manuscript provides an overview of a large study, which examined the relation of laterality test results in horses obtained on the ground with laterality during riding, the interaction with human handedness and the heritability of the lateral displacement of the hindquarters. It compared 12 different laterality test methods on the ground and during riding between 5 groups of horses (N = 6.553) and examined rein tension of 110 rides (88 horses, 65 riders). Rein tension was analysed using linear mixed models. The relation of test methods was investigated using cross-tabulations, chi2-tests, phi and Cramer's V, as well as Pearson-correlations. Heritability was estimated using uniand bivariate linear animal models in DMU6. Laterality test results obtained on the ground did not agree with laterality during riding (p > 0.05). Only the rider's assessment of their horse's laterality (p = 0.02) and the lateral displacement of the horses hindquarters (p = 0.003) allowed conclusions. Heritability was high (warmbloods, n = 3.973) and low to moderate (Thoroughbreds, n = 1.822). The magnitude and symmetry of rein tension was mainly influenced by horse's laterality (p = 0.04 and p = 0.003) and rider's handedness (p = 0.0003). [ABSTRACT FROM AUTHOR]

The development of breeding strategies for improved disease resistance and associated improvements in animal welfare is of increasing importance in dairy farming. Endoparasite infections represent a serious problem with high economic losses in pasture-based production systems. The genetic and genomic mechanisms for endoparasite resistance were analysed in four consecutive studies. We identified significant SNP and candidate genes with immunological functions for economic important endoparasite pathogens, being associated with improved resistance. Moreover, significant allele substitutions and dominance effects for endoparasite traits were estimated for loci in close distance or within functional mutations. Estimated quantitative-genetic correlations and SNP effect correlations between endoparasite resistance traits with production and health traits are the basis when developing breeding indices for improved disease resistance and robustness. Association analyses between endoparasite infections with milk production and health traits on a phenotypic scale completed the identification of host resistance mechanisms from genotype to phenotype. The results from phenotypic association analyses provide novel insights into the relationships between endoparasite infections and health indicators from routine milk recording. The enhanced methods and models contributed to a deeper understanding of resistance mechanisms, with impact on genomic selection improvements and further optimisation of farm management strategies in pasture-based production systems. [ABSTRACT FROM AUTHOR]

Breeding on improved heat tolerance in dairy cattle is a topic of increasing importance due to the climatic challenges, even in Germany. Attempts in this regard, i.e., the development of genetic evaluations, are under progress in some states of North America. Consequently, the aim of the present study was to estimating genetic parameters and variance components for novel physiological cow traits in dependency of a continuous temperature-humidity-index (THI). Genetic correlations in same traits across THI were evaluated as indicators for possible genotype by environment (heat stress) interactions. Own trait recording during several years considered 838 cows of the local breed Deutsches Schwarzbuntes Niederungsrind (DSN) and their genetic upgrades with HF, which were kept in eight different herds reflecting a pasture based production system. Repeated trait recording considered more than 7000 observations. The recorded physiological traits included respiration rate (RESPR, in number of breaths per minute), pulse frequency (PULSF, in number of heartbeats per minute), body temperature (KT, in C°), vaginal temperature (VT, in C°) and surface temperature recorded via infrared thermography for different segments of the cow body (free-form polygon covering the whole surface (OTG), rectangle along the spine (OTWI), line along the spine (OTR) circle at withers (OTW)). Barn temperature and humidities from intervals in one minute were used for the calculation of hourly THI, which were merged with the corresponding point in time for cow trait recording. Phenotypically, trait variations were more pronounced under heat stress (THI > 65) in comparison to trait reactions under temperate climatic conditions (THI ≤ 65). The estimation of variance components for physiological traits was conducted with repeatability models considering distinct THI classes (THI > 65 und THI ≤ 65), as well as via random regression methodology on a continuous THI scale. From both modelling approaches, additive genetic variances and heritabilities increased with increasing THI, implying improved genetic differentiations under stress conditions. Genetic correlations in same traits recorded at THI > 65 and THI ≤ 65 were close to 0.80 or even smaller, indicating obvious genotype by environment interactions. Especially for THI in greater distance, genetic correlations substantially declined, e.g. 0.31 for OtG. Genetic (co)variance components indicated environmental sensitivity for a local breed, which should be adapted to heterogeneous climatic impact. The longitudinal physiological trait data allows ongoing studies to enhance genetic evaluations towards improved heat tolerance and robustness. [ABSTRACT FROM AUTHOR]

Since tail-docking is under critical focus in sheep production, breeding for short tails or breeding with short-tailed populations is of increasing importance. For sustainable breeding approaches in short-tailed populations, knowledge of genetic (co)variance components of economically important breeding goal traits, i.e., fattening and slaughtering characteristics, is imperative. The short-tailed Iceland sheep population with recorded data for fattening and slaughter performance traits, accompanied with a deep pedigree structure, is a unique database in this regard. The dataset comprised the traits carcass weight (SG), EUROP conformation (EUROPm) and EUROP fat scores (EUROPf) of slaughtered lambs from a farm with 272 sheeps. The recording period included the birth years 2008 to 2015. Mixed model analyses identified gender, a combined birth-rearing type, the age of the dam and the birth years as significant effects on SG, EUROPm and EUROPf. Genetic models included both components direct genetic and maternal genetic effects. The estimated direct heritability was 0.13 for SG and ranged from 0.31 to 0.40 for EUROPm and between 0.11 and 0.18 for EUROP, depending on whether the covariable carcass weight and maternal effects were included in the model. For SG, the maternal heritability and the common environmental effect were larger than the direct heritability. In contrast, for EUROPm and EUROPf, estimates for the direct heritability were larger than the maternal heritabilities. The genetic correlation between SG and EUROPm was 0.25, and 0.78 between SG and EUROPf. In general, the short-tailed sheep population showed a range of genetic (co-)variance components, as known from studies in other sheep populations. However, on the basis of the deep pedigree structures and systematic recording of performances, further model extensions were possible, e.g., to infer direct genetic and maternal genetic associations. [ABSTRACT FROM AUTHOR]

Besides milk yield and fitness, meat performance is important for life efficiency in German Fleckvieh (FL) and German Brown Swiss (BV). So far, data from young bulls are mainly considered for breeding value estimation. The aim of the present study is to investigate to what extent the breeding value estimation can be improved by adding slaughterhouse data of female animals as well as calf marketing data. In addition to the traits net daily gain and the trading class considered in the routine breeding value estimation, genetic parameters for the traits of daily gain (calf) and marketing price (calf price/kg) were estimated for FL and BV. A breeding value estimation with different density of performance information was performed. The trait daily gain (calf) has a medium (FL) or high (BV) heritability and is suitable as an auxiliary trait, due to a medium genetic correlation with the net daily gain. The heritabilities of the marketing price (calf price/kg) are low and the trait is influenced by many factors not previously recorded. Therefore this trait does not meet the requirements for auxiliary traits. In breeding value estimation, the ranking of the animals has hardly changed due to the inclusion of female slaughter data and/or calf marketing data. With addition of new information sources and traits, the reliability of the breeding value estimation only increases by 1.0%. When simulating optimal data, reliability increases by 9.1%. This shows, how important the performance test is in different traits for the meat complex. Further work is required in regard of the completeness of the performance data, eventually financial support for the trait recording is necessary. [ABSTRACT FROM AUTHOR]

The linear description of conformation traits of dairy goats was included in the breeding programs of German Fawn (BDE) and German White (WDE) goats in Bavaria and Baden- Württemberg in 2014. Besides the description of each dairy goat in her first lactation, data could be used to evaluate buck-proofs for conformation traits. Data based on measurements or linear descriptions of 19 frame, leg and udder traits were available for the evaluations. The largest percentage of data is represented by the population of the BDE, which allowed the estimation of genetic parameters. Heritabilities of the linear conformation traits range from low (rear legs set and udder depth: h² = 0.06) to high level (stature: h² = 0.76) and are comparable to the results of other studies. Heritabilities close to zero were estimated for the traits loin strength and central ligament. So far, these traits are not practicable for breeding. On the basis of the estimated genetic parameters, a breeding value estimation for conformation traits for the BDE and WDE was developed. Breeding values are published since January 2018. In further investigations, the correlations to dairy traits will be examined. It is assumed that linear conformation traits can be used as auxiliary traits for fitness or life performance traits. The aim to develop a breeding value estimation for lifetime performance has come much closer through the establishment of the linear description and the development of a breeding value estimation for conformation traits. [ABSTRACT FROM AUTHOR]

In Germany, the importance of goat cheese and goat-milk products raised continuously during the last years. Therewith increased the number of dairy goat farms and consistent breeding programs for dairy goat production are needed. Less developed breeding structures were a constraint for setting up breeding value estimation for dairy goats so far. In this study, a regional approach is applied to overcome the structural barriers. Bavaria and Baden-Wuerttemberg are planning to cooperate within their breeding programs. They agreed upon a joint breeding objective of high lifetime dairy performance with high milk ingredients and good robustness. For breeding value estimation a total of 54,955 lactations of German Fawn (BDE) and German White (WDE) goats are used. Heritabilities of 0.33 for milk-, 0.39 for fat- and 0.35 for protein-kg as well as 0.48 for fat- und 0.52 for protein-% are within the expected medium to high range. Genetic trend for milk-kg is slightly positive in herdbook animals and slightly negative (BDE) to constant (WDE) in non-herdbook animals. Genetic trends for protein-% are slightly (WDE) to clearly positive (BDE) for all goats. Genetic trends are increasing stronger since 2015 which could be an indicator for selection based on the breeding values. Breeding values are published since 2013. Overall, the regional approach is useful for setting up a breeding value estimation for dairy goats. Nevertheless, a nationwide expansion is still desirable. [ABSTRACT FROM AUTHOR]

Sow longevity is an important trait for both economic as well as ethical reasons. Data from all sows under recording in Bavaria indicated that over the last ten years important figures related to sow longevity were almost constant. This study included approximately 60.000 sows from commercial farms raised in multiplier herdbook farms. Longevity was defined as the ability of a sow to have a second litter after a first litter was recorded (stayability), and it was coded as a binary trait. For single-trait analyses of stayability, binomial models fitting a logit-link function as well as linear models were applied. Estimates of heritability were very low for both models (0,04 and 0,02, respectively). Estimates of genetic correlation between stayability and performance test and station test traits were moderate to considerable and unfavourable. Estimates of genetic correlation between stayability and fertility traits were slightly negative. For certain traits it can be very helpful to combine data from herdbook farms and data from commercial farms for breeding purposes. Because of different selection strategies, data for longevity traits like stayability from commercial farms may be more informative than data from herd-book farms. [ABSTRACT FROM AUTHOR]

Abstract The wide range of genetic parameter estimates for production traits and nematode resistance in sheep obtained from field studies gives rise to much speculation. Using a mathematical model describing host – parasite interactions in a genetically heterogeneous lamb population, we investigated the consequence of: (i) genetic relationships between underlying growth and immunological traits on estimated genetic parameters for performance and nematode resistance, and (ii) alterations in resource allocation on these parameter estimates. Altering genetic correlations between underlying growth and immunological traits had large impacts on estimated genetic parameters for production and resistance traits. Extreme parameter values observed from field studies could only be reproduced by assuming genetic relationships between the underlying input traits. Altering preferences in the resource allocation had less pronounced effects on the genetic parameters for the same traits. Effects were stronger when allocation shifted towards growth, in which case worm burden and faecal egg counts increased and genetic correlations between these resistance traits and body weight became stronger. Our study has implications for the biological interpretation of field data, and for the prediction of selection response from breeding for nematode resistance. It demonstrates the profound impact that moderate levels of pleiotropy and linkage may have on observed genetic parameters, and hence on outcomes of selection for nematode resistance.

Abstract Since feed conversion ratio (FCR) is higher in slow-growing "Label Rouge" chickens than in broiler chickens, it is important to work on its improvement in this breed. However, this involves rearing animals in cages (C), an environment very different from that used for selection (in floor pens, S) and production (outdoor, E). The aim of this study was to evaluate the importance of genotype by environment (G × E) interactions between S, C, and E environments, to find the best way to select for FCR, using 2002 related animals. Growth curve parameters were estimated and body composition measured. Individual feed conversion ratios (FCR) were recorded between 8 and 10 weeks in C. The presence of G × E interactions was assessed by the genetic correlations between the same trait recorded in different environments. Moderate but significant G × E interactions were detected for carcass traits, a significant one was observed between E and S or C for growth curve parameters but none between C and S. If G × E interactions are set aside, i.e. selecting on traits recorded in C, abdominal fatness is the best indirect selection criterion for FCR but if they are taken in account then leg yield or growth curve parameters in S and growth curve parameters in E are better.

In Baden-Württemberg, a voluntary cattle health monitoring system (GMON) is in place since 2010. Aims of the present study were to identify if farm type (organic vs conventional) and breed (Fleckvieh vs Vorderwaelder) have an effect on health traits. Additionally, genetic relationship between health traits and dairy performance traits were analysed. Traits analysed were mastitis (MAST), ovary cysts (CYST), milk fever (MF+) and early reproduction disorders (EREPRO+). Farm type and breed had significant effects: cows on organic farms showed significant less diagnoses for MAST, CYST and EREPRO + than cos on conventional farms. Vorderwaelder cows showed significantly higher diagnosis frequencies than Fleckvieh. Genetic correlations between MAST and persistency were lightly negative and between EREPRO + and 305-day-lactation positive. This points to negative genetic relationships between dairy performance and udder health resp. fertility. Overall, opportunities and constraints of GMON could be shown. For being able to use GMON even more comprehensive as performance testing tool it is important to recruit more farms for the voluntary monitoring. [ABSTRACT FROM AUTHOR]

Abstract Weaning weights from 83 389 Limousin calves born between 1993 and 2002 in France and the Trans-Tasman block (Australia/New Zealand) were analysed to compare different strategies for running an international genetic evaluation for the breed. These records were a subset of the complete data for both countries and comprised a sample of herds that had recorded progeny of sires used across both countries. Genetic and phenotypic parameters for weaning weight were estimated within the countries. The estimates of direct genetic heritabilities were higher in France than in the Trans-Tasman block (0.31 vs. 0.22), while direct-maternal genetic correlations were less negative in the Trans-Tasman block (-0.10) than in France (-0.21). Different strategies for an international evaluation were studied, and the correlations between the estimated breeding values (EBV) of national evaluations and these strategies were derived. The international evaluation strategies were a) an animal model on raw performance data with non unity genetic correlations and heterogeneous residual and genetic variances across countries; b) the same animal model applied to pre-corrected (for fixed effects) performance data; and c) a sire model on de-regressed proofs (MACE). Estimates of the genetic correlations between weaning weight in both countries were 0.86 (0.80) for direct (maternal) genetic effects for the first strategy. Estimation of variance components by MACE appeared to be very sensitive to the sample of bulls and their reliability approximations. Variance component estimates obtained using pre-corrected data were inconsistent with estimates on raw data. However, the EBV predicted using pre-corrected data and parameters estimated from the raw data were similar to those predicted from raw data. Correlations between national and international EBV were always high (> 0.90) for sires, whichever genetic effect (direct or maternal) or international evaluation model was considered. The ranking of the bulls in the top 100 is of primary interest in terms of international genetic evaluation. In this study, some re-ranking of sires was observed for the top 100 bulls between countries and between the three international evaluation models. Thus, the origin of top sires may vary according to the implemented international evaluation strategy.

Abstract Application of test-day models for the genetic evaluation of dairy populations requires the solution of large mixed model equations. The size of the (co)variance matrices required with such models can be reduced through the use of its first eigenvectors. Here, the first two eigenvectors of (co)variance matrices estimated for dairy traits in first lactation were used as covariables to jointly estimate genetic parameters of the first three lactations. These eigenvectors appear to be similar across traits and have a biological interpretation, one being related to the level of production and the other to persistency. Furthermore, they explain more than 95% of the total genetic variation. Variances and heritabilities obtained with this model were consistent with previous studies. High correlations were found among production levels in different lactations. Persistency measures were less correlated. Genetic correlations between second and third lactations were close to one, indicating that these can be considered as the same trait. Genetic correlations within lactation were high except between extreme parts of the lactation. This study shows that the use of eigenvectors can reduce the rank of (co)variance matrices for the test-day model and can provide consistent genetic parameters.

Abstract The effects of selection for growth rate on weights and qualitative carcass and muscle traits were assessed by comparing two lines selected for live body weight at 63 days of age and a cryopreserved control population raised contemporaneously with generation 5 selected rabbits. The animals were divergently selected for five generations for either a high (H line) or a low (L line) body weight, based on their BLUP breeding value. Heritability (h2) was 0.22 for 63-d body weight (N = 4754). Growth performance and quantitative carcass traits in the C group were intermediate between the H and L lines (N = 390). Perirenal fat proportion (h2 = 0.64) and dressing out percentage (h2 = 0.55) ranked in the order L < H = C (from high to low). The weight and cross-sectional area of the Semitendinosus muscle, and the mean diameter of the constitutive myofibres were reduced in the L line only (N = 140). In the Longissimus muscle (N = 180), the ultimate pH (h2 = 0.16) and the maximum shear force reached in the Warner-Braztler test (h2 = 0.57) were slightly modified by selection.

Abstract This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential.

Abstract Genetic parameters for meat quality traits and their relationships with body weight and breast development were estimated for a total of 420 male turkeys using REML. The birds were slaughtered in a commercial plant and the traits measured included pH at 20 min (pH20) and 24 h post-mortem (pHu) and colour of the breast and thigh meat. The heritabilities of the rate and the extent of the pH fall in the breast muscle were estimated at h2 = 0.21 ± 0.04 and h2 = 0.16 ± 0.04, respectively. Heritabilities ranging from 0.10 to 0.32 were obtained for the colour indicators in the breast muscle. A marked negative genetic correlation (rg = -0.80 ± 0.10) was found between pH20 and lightness (L*) of breast meat, both traits corresponding to PSE indicators. The pH20 in the thigh muscle had a moderate heritability (h2 = 0.20 ± 0.07) and was partially genetically related to pH20 in the breast muscle (rg = 0.45 ± 0.17). Body weight and breast yield were positively correlated with both initial and ultimate pH and negatively with the lightness of breast meat.

Abstract An experimental population (1216 lambs from 30 sires) of the Inra401 sheep was created in an Inra flock to allow QTL detection for susceptibility to Salmonella infection, wool and carcass traits. The Inra401 is a sheep composite line developed from two breeds: Berrichon du Cher and Romanov. At 113 days of age on average, the lambs were inoculated intravenously with 108 Salmonella abortusovis Rv6 (vaccinal strain). They were slaughtered 10 days after the inoculation. Several traits were measured at inoculation and/or slaughtering to estimate the genetic resistance of the lambs to Salmonella infection: specific IgM and IgG1 antibody titres, body weight loss, spleen and pre-scapular node weights and counts of viable Salmonella persisting in these organs. This paper presents a quantitative analysis of the genetic variability of the traits related to salmonellosis susceptibility. The heritabilities of the traits varied between 0.10 and 0.64 (significantly different from zero). Thus, in sheep as well as in other species, the determinism of resistance to Salmonella infection is under genetic control. Moreover, the correlations between the traits are in agreement with the known immune mechanisms. The genetic variability observed should help QTL detection.

Abstract The effects of some environmental variation factors and the genetic parameters for total milk traits (fat content, protein content, casein content, serum protein content, lactation mean of individual laboratory cheese yield (LILCY), lactation mean of somatic cell count (LSCC), and milk yield) were estimated from the records of 1 111 Churra ewes. Genetic parameters were estimated by multivariate REML. Heritability for fat content was low (0.10) as is usually found in the Churra breed. Heritabilities for protein content, casein content, serum protein content, LILCY, milk yield and somatic cell count were 0.31, 0.30, 0.22, 0.09, 0.26 and 0.11, respectively. The highest heritability estimates were for protein and casein contents. Casein content is not advisable as an alternative to protein content as a selection criterion for cheese yield improvement; it does not have any compelling advantages and its measurement is costly. Our results for LSCC indicated that efforts should focus on improving the level of management rather than selecting for somatic cells, in the actual conditions of the Churra breed.

Abstract Genetic analysis for mastitis resistance was studied from two data sets. Firstly, risk factors for different mastitis traits, i.e. culling due to clinical or chronic mastitis and subclinical mastitis predicted from somatic cell count (SCC), were explored using data from 957 first lactation Lacaune ewes of an experimental INRA flock composed of two divergent lines for milk yield. Secondly, genetic parameters for SCC were estimated from 5 272 first lactation Lacaune ewes recorded among 38 flocks, using an animal model. In the experimental flock, the frequency of culling due to clinical mastitis (5%) was lower than that of subclinical mastitis (10%) predicted from SCC. Predicted subclinical mastitis was unfavourably associated with the milk yield level. Such an antagonism was not detected for clinical mastitis, which could result, to some extent, from its low frequency or from the limited amount of data. In practice, however, selection for mastitis resistance could be limited in a first approach to selection against subclinical mastitis using SCC. The heritability estimate of SCC was 0.15 for the lactation mean trait and varied from 0.04 to 0.12 from the first to the fifth test-day. The genetic correlation between lactation SCC and milk yield was slightly positive (0.15) but showed a strong evolution during lactation, i.e. from favourable (-0.48) to antagonistic (0.27). On a lactation basis, our results suggest that selection for mastitis resistance based on SCC is feasible. Patterns for genetic parameters within first lactation, however, require further confirmation and investigation.

Abstract Simulations were used to study the influence of model adequacy and data structure on the estimation of genetic parameters for traits governed by direct and maternal effects. To test model adequacy, several data sets were simulated according to different underlying genetic assumptions and analysed by comparing the correct and incorrect models. Results showed that omission of one of the random effects leads to an incorrect decomposition of the other components. If maternal genetic effects exist but are neglected, direct heritability is overestimated, and sometimes more than double. The bias depends on the value of the genetic correlation between direct and maternal effects. To study the influence of data structure on the estimation of genetic parameters, several populations were simulated, with different degrees of known paternity and different levels of genetic connectedness between flocks. Results showed that the lack of connectedness affects estimates when flocks have different genetic means because no distinction can be made between genetic and environmental differences between flocks. In this case, direct and maternal heritabilities are under-estimated, whereas maternal environmental effects are overestimated. The insufficiency of pedigree leads to biased estimates of genetic parameters.

Abstract In an experimental strain of white plumage geese created in 1989, two experiments were carried out from 1993 to 1995 in order to estimate genetic parameters for growth, and carcass composition traits in non-overfed animals, and genetic parameters for growth and fatty liver formation in overfed animals. Four hundred and thirty-one non-overfed animals were bred and slaughtered at 11 weeks of age; they were measured for forearm length, keel bone length, chest circumference and breast depth before and after slaughtering. The carcasses were partly dissected in order weigh breast, breast muscle and skin + fat, and abdominal fat. Four hundred and seventy-seven overfed animals were slaughtered at 20 weeks of age; they were measured for "paletot" (breast meat, bone and meat from wings, bone and meat from thigh and legs) weight and liver weight. In these two experiments, the weights had moderate to high heritability values. Breast depth measured on live animals showed a low heritability value. In overfed animals, liver weight showed a high heritability value. Liver weight could be increased by selection without a great effect on "paletot" weight. Thus, obtaining a white plumage geese strain for fatty liver production by selection would be difficult because only 20% of overfed animals had fatty liver. The results did not allow to conclude on the influence of selection on liver weight on carcass traits such as muscle or fatty tissue weight.

Abstract Genetic parameters of body weight at weaning and of prolificacy were estimated in three commercial lines of pigeons selected by BLUP (Best Linear Unbiased Prediction) on both traits. The model of analysis took into account the direct genetic effects for both traits and the effect of parental permanent environment for body weight. Depending on the line considered, body weight varied from 556.7 g to 647.6 g and prolificacy ranged from 12.5 to 16.8 pigeons weaned per couple of parents per year. Heritability of body weight was high, varying between 0.46 and 0.60, and permanent environment was responsible for 6% to 9% of the total variability. On the contrary, prolificacy was poorly heritable (0.04 to 0.12). They were highly and negatively correlated (-0.77 to -0.82). Body weight showed significant genetic trends in lines B and C. No significant genetic difference could be observed between males and females for both traits.

Abstract Genetic parameters of body weight at 4 (W4 w), 8 (W8 w) and 22 (W22 w) weeks of age, days from 20 to 100 kg (DT), average backfat thickness at 100 kg (ABT), teat number (TEAT), number of good teats (GTEAT), total number of piglets born (TNB), born alive (NBA) and weaned (NW) per litter, and birth to weaning survival rate (SURV) were estimated in the Chinese × European Tiameslan composite line using restricted maximum likelihood methodology applied to a multiple trait animal model. Performance data from a total of 4 881 males and 4 799 females from 1 341 litters were analysed. Different models were fitted to the data in order to estimate the importance of maternal effects on production traits, as well as genetic correlations between male and female performance. The results showed the existence of significant maternal effects on W4w, W8w and ABT and of variance heterogeneity between sexes for W22w, DT, ABT and GTEAT. Genetic correlations between sexes were 0.79, 0.71 and 0.82, respectively, for W22w, DT and ABT and above 0.90 for the other traits. Heritability estimates were larger than (ABT and TEAT) or similar to (other traits) average literature values. Some genetic antagonism was evidenced between production traits, particularly W4w, W8w and ABT, and reproductive traits.