Pedigree analysis in the mhorr gazelle (Nanger dama mhorr): Genetic variability evolution of the captive population.

Breeding programs have an essential role in the recovery of threatened populations through optimal genetic management and mating strategies. The dama gazelle (Nanger dama) is a North African ungulate listed as critically endangered. The mhorr subspecies is extinct in the wild and currently survives thanks to the creation in 1971 of an ex situ breeding program. The aim of the present study was to assess the evolution of genetic variability in this mhorr gazelle captive population, as well as the mating strategy used in two reference populations studied (Almeria and Europe). The entire pedigree, with 2739 animals, was analyzed to measure demographic characters, pedigree completeness level, probability of gene origin, level of relatedness and genetic structure of the population. The population size has been progressively increasing, with up to 264 individuals alive in Europe at the time of the study. The average number of equivalent complete generations was 5.55. The effective number of founders and ancestors was both 3, and the founder genome equivalent was 1.99. The genetic contributions of the four main ancestors were unbalanced. The average values of inbreeding and average relatedness for the whole pedigree were, respectively, 28.34% and 50.14%. The effective population size was 8.7 by individual increase in inbreeding and 9.8 by individual increase in coancestry. F-statistics evidenced a very small level of population subdivision (F ST = 0.033370). The mating strategy used, based on the minimum coancestry of the individuals, has minimized the losses of genetic variability and helped to balance the genetic contributions between ancestors. The strategy also avoided large subdivisions within the population and the appearance of new bottlenecks. This study shows how pedigree analysis can both be used to determine the genetic variability of the population and to assess the influence of the mating strategy used in the breeding program on such variability.

Differential patterns in runs of homozygosity in two mice lines under divergent selection for environmental variability for birth weight.

Runs of homozygosity (ROH) are defined as long continuous homozygous stretches in the genome which are assumed to originate from a common ancestor. It has been demonstrated that divergent selection for variability in mice is possible and that low variability in birth weight is associated with robustness. To analyse ROH patterns and ROH-based genomic inbreeding, two mouse lines that were divergently selected for birth weight variability for 26 generations were used, with: 752 individuals for the high variability line (H-Line), 766 individuals for the low variability line (L-Line) and 74 individuals as a reference population. Individuals were genotyped using the high density Affymetrix Mouse Diversity Genotyping Array. ROH were identified using both the sliding windows (SW) and the consecutive runs (CR) methods. Inbreeding coefficients were calculated based on pedigree (FPED ) information, on ROH identified using the SW method (FROHSW ) and on ROH identified using the CR method (FROHCR ). Differences in genomic inbreeding were not consistent across generations and these parameters did not show clear differences between lines. Correlations between FPED and FROH were high, particularly for FROHSW . Moreover, correlations between FROHSW and FPED were even higher when ROH were identified with no restrictions in the number of heterozygotes per ROH. The comparison of FROH estimates between either of the selected lines were based on significant differences at the chromosome level, mainly in chromosomes 3, 4, 6, 8, 11, 15 and 19. ROH-based inbreeding estimates that were computed using longer homozygous segments had a higher relationship with FPED . Differences in robustness between lines were not attributable to a higher homozygosis in the L-Line, but maybe to the different distribution of ROH at the chromosome level between lines. The analysis identified a set of genomic regions for future research to establish the genomic basis of robustness.

Genomic inbreeding measures applied to a population of mice divergently selected for birth weight environmental variance.

This study aimed to compare different inbreeding measures estimated from pedigree and molecular data from two divergent mouse lines selected for environmental birth weight during 26 generations. Furthermore, the performance of different approaches and both molecular and pedigree data sources for estimating Ne were tested in this population. A total of 1,699 individuals were genotyped using a high-density genotyping array. Genomic relationship matrices were used to calculate molecular inbreeding: Nejati-Javaremi (F NEJ), Li and Horvitz (F L&H), Van Raden method 1 (F VR1) and method 2 (F VR2), and Yang (F YAN). Inbreeding based on runs of homozygosity (F ROH) and pedigree inbreeding (F PED) were also computed. F ROH, F NEJ, and F L&H were also adjusted for their average values in the first generation of selection and named F ROH0, F NEJ0, and F L&H0. ∆F was calculated from pedigrees as the individual inbreeding rate between the individual and his parents (∆F PEDt) and individual increases in inbreeding (∆F PEDi). Moreover, individual ∆F was calculated from the different molecular inbreeding coefficients (∆F NEJ0, ∆F L&H, ∆F L&H0, ∆F VR1, ∆F VR2, ∆F YAN, and ∆F ROH0). The Ne was obtained from different ∆F, such as Ne PEDt, Ne PEDi, Ne NEJ0, Ne L&H, Ne L&H0, Ne VR1, Ne VR2, Ne YAN, and Ne ROH0. Comparing with F PED , F ROH , F NEJ and F VR2 overestimated inbreeding while F NEJ0 , F L&H , F L&H0 , F VR1 and F YAN underestimated inbreeding. Correlations between inbreeding coefficients and ∆F were calculated. F ROH had the highest correlation with F PED (0.89); F YAN had correlations >0.95 with all the other molecular inbreeding coefficients. Ne PEDi was more reliable than Ne PEDt and presented similar behaviour to Ne L&H0 and Ne NEJ0. Stable trends in Ne were not observed until the 10th generation. In the 10th generation Ne PEDi was 42.20, Ne L&H0 was 45.04 and Ne NEJ0 was 45.05 and in the last generation these Ne were 35.65, 35.94 and 35.93, respectively F ROH presented the highest correlation with F PED, which addresses the identity by descent probability (IBD). The evolution of Ne L&H0 and Ne NEJ0 was the most similar to that of Ne PEDi. Data from several generations was necessary to reach a stable trend for Ne, both with pedigree and molecular data. This population was useful to test different approaches to computing inbreeding coefficients and Ne using molecular and pedigree data.

Differential sensitivity of climate conditions on birth weight genetic values in mice divergently selected for birth weight residual variance.

After 32 generations of a divergent selection experiment for residual variance of birth weight in mice, two divergent lines were thus obtained: the heterogeneous line (H-line) and the homogeneous line (L-line). Throughout the generations, differences were observed between the two lines in traits such as litter size, survival at weaning, and birth weight variability caused by unidentified environmental conditions. The L-line exhibited advantages in terms of higher survival rates, larger litter sizes, and less sensitivity to changes in food intake. The study is an examination of the effects of climate as an environmental factor on the performance of these animals. Climate factors including maximum, minimum, and mean temperature (T), humidity (H), and TH index; at three stages (the fecundation, a week before the parturition and the parturition), were linked to a birth weight dataset consisting of 22,614 records distributed as follows: 8,853 corresponding to the H-line, 12,649 to the L-line, and 1,112 to the initial population. Out of the 27 analyzed climatic variables, the maximum temperature 1 wk before parturition (MXTW) was identified as the most influential when comparing heteroscedastic models with the deviance information criterion. The order of Legendre polynomial to apply in the following random regression model was tested by a cross-validation using homoscedastic models. Finally, MXTW was compared on how it affected the two divergent lines by analyzing predicted breeding values (PBV) obtained from a random regression heteroscedastic model. The mean PBV of the H-line in the first generation showed a range of 0.070 g with a negative slope, which was 35 times higher than the range obtained for the L-line, which varied within 0.002 g. In the last generation of selection, the H-line exhibited greater instability of PBV across temperatures, with a difference of 0.101 g between the maximum and minimum mean PBV, compared to 0.017 g for the L-line. The standard deviations of the slopes in the H-line were more dispersed than in the L-line. Unlike the H-line, the L-line had slopes that were not significantly different from 0 throughout the generations of selection, indicating greater stability in response to MXTW variations. The H-line exhibited a higher sensitivity to changes in MXTW, particularly in birth weight, with the L-line being more stable. The selection for uniformity of birth weight could lead to less sensitive animals under environmental changes.

Two mice lines obtained by divergent selection for birth weight residual variance were used to determine whether environmental factors could differently affect the homogeneous and heterogeneous lines. The maximum temperature 1 wk before parturition (MXTW) had the higher impact on the birth weight of the animals. A random regression model showed the individual trajectory of birth weight throughout the changes in MXTW. It was evident that the homogeneous line is less susceptible to changes in climate. This result, therefore, supports the hypothesis that the selection for homogeneity in production animals is more advantageous. More robust animals are obtained that can better cope with changes in climate without compromising their productive traits.

Effect of Recycled Polyvinyl Butyral (rPVB) Addition on the Tribological Performance of Glass-Fiber Reinforced Polyamide (PAGF) during Reciprocating Sliding Wear Conditions.

Plastic recycling in the automotive industry is a priority. In this study, the effect of adding recycled polyvinyl butyral (rPVB) from automotive windshields on the coefficient of friction (CoF) and specific wear rate (k) of a glass-fiber reinforced polyamide (PAGF) is investigated. It was found that, at 15 and 20 wt.% of rPVB, it acts as a solid lubricant, reducing CoF and k up to 27% and 70%, respectively. Microscopical analysis of the wear tracks showed that rPVB spreads over the worn tracks, forming a lubricant layer, which protects the fibers from damage. However, at lower rPVB content, fiber damage cannot be prevented as the protective lubricant layer is not formed.

Embryo survival and fertility differ in lines divergently selected for birth weight homogeneity in mice.

The selection of animals for lower environment sensitivity around the optimum trait value can also provide benefits in productivity and welfare. A divergent selection experiment for birth weight environmental variability in mice was successfully conducted over 17 generations. Animals from low variability selected line (L-line) were more robust by having a higher litter size and survival at weaning in a common breeding environment, than those from high variability line (H-line). The objective of this study was to analyze the differences between those divergently selected lines for embryo and fetal survival and for fertility and prolificacy rate. To study embryo survival and ovulation rate, a total of 98 females (34 H-line and 50 L-line) were studied in four generations of the divergent experiment. To analyze fetal survival and fertility rate, 378 female mice (138 H-line and 240 L-line) in 10 generations or the divergent experiment were studied. Ultrasound scans were performed at day 14 of gestation to establish the number of total fetal and the embryo absorptions. Mortality was addressed as the difference between litter size at birth and the number of fetuses at 14 days of gestation. The number of pregnant females in the first 3 days after mating was used to measure fertility. A linear model was also fitted to analyze embryo mortality, litter size, and the number of embryos at 14 days of gestation. A categorical model was then used to study fertility, including line, generation, and its interaction as effects. Despite the fact that there were no significant differences in the ovulation rate, litter size at birth was significantly higher in the L-line than in the H-line (9.82 vs. 8.36 pups, p < 0.001). Moreover, embryo mortality was significantly lower in the L-line than in the H-line (1.39 vs. 2.87 fetuses, p < 0.001). L-line females were more fertile (53.49% vs. 23.26% for the H-line). According to these results, the line selected for low environmental variance would be preferable for robustness and animal welfare.

Genetic parameters for fleece uniformity in alpacas.

Fiber diameter is the main selection objective and criterion in alpaca breeding programs, but it can vary across anatomic regions of the animal. As fiber diameter is usually registered from a unique sample from the mid side of the body, fiber diameter variability within fleece is never addressed and phenotypic and genetic differences may exist for fleece uniformity in alpaca populations. The objective of this work was to estimate the genetic parameters of fleece uniformity in an alpaca population. Fiber diameters measured in three different locations were used as repeated records of the same animal and studied for fitting a model that considers heterogeneous the residual variance of the model. Also, the logarithm of the standard deviation of the three measures was used as a measure of the fleece variability. Estimate of the additive genetic variance of the environmental variability was 0.43±0.14, enough high to suggest the existence of wide room to select for fleece uniformity. Genetic correlation of the trait with its environmental variability was 0.76±0.13 showing that fleece uniformity will be indirectly selected when aiming to reduce the fiber diameter. In the light of these parameters, and due to the cost of registering and the cost of opportunity, it looks no worthy to include uniformity as a selection criterion in alpaca breeding programs.

The quality of alpaca fiber is mainly assessed by a low fiber diameter. However, the fiber diameter can greatly vary along the different body locations of the animal, the industry demands not only the fineness of the fiber but also the fleece uniformity. This work studied the genetic parameters related to fleece uniformity by analyzing the diameter of three samples from different body locations (mid side, shoulder, and thigh) under two different models of analysis. The results showed variability between sampling locations and the existence of important genetic variability susceptible to being used in alpaca selection. Nevertheless, selection based on a single measurement could be used as the high correlations between locations and between the trait and its variability, saving the cost of sample analyses, being the fleece uniformity indirectly selected.

Fine-tuning genomic and pedigree inbreeding rates in equine population with a deep and reliable stud book: the case of the Pura Raza Española horse.

BACKGROUND: Estimating inbreeding, which is omnipresent and inevitable in livestock populations, is a primary goal for management and animal breeding especially for those interested in mitigating the negative consequences of inbreeding. Inbreeding coefficients have been historically estimated by using pedigree information; however, over the last decade, genome-base inbreeding coefficients have come to the forefront in this field. The Pura Raza Española (PRE) horse is an autochthonous Spanish horse breed which has been recognised since 1912. The total PRE population (344,718 horses) was used to estimate Classical (F), Ballou's ancestral, Kalinowski's ancestral, Kalinowski's new and the ancestral history coefficient values. In addition, genotypic data from a selected population of 805 PRE individuals was used to determine the individual inbreeding coefficient using SNP-by-SNP-based techniques (methods of moments -FHOM-, the diagonal elements of the genomic -FG-, and hybrid matrixes -FH-) and ROH measures (FRZ). The analyse of both pedigree and genomic based inbreeding coefficients in a large and robust population such as the PRE horse, with proven parenteral information for the last 40 years and a high degree of completeness (over 90% for the last 70 years) will allow us to understand PRE genetic variability better and the correlations between the estimations will give the data greater reliability. RESULTS: The mean values of the pedigree-based inbreeding coefficients ranged from 0.01 (F for the last 3 generations -F3-) to 0.44 (ancestral history coefficient) and the mean values of genomic-based inbreeding coefficients varied from 0.05 (FRZ for three generations, FH and FHOM) to 0.11 (FRZ for nine generations). Significant correlations were also found between pedigree and genomic inbreeding values, which ranged between 0.58 (F3 with FHOM) and 0.79 (F with FRZ). In addition, the correlations between FRZ estimated for the last 20 generations and the pedigree-based inbreeding highlight the fact that fewer generations of genomic data are required when comparing total inbreeding values, and the opposite when ancient values are calculated. CONCLUSIONS: Ultimately, our results show that it is still useful to work with a deep and reliable pedigree in pedigree-based genetic studies with very large effective population sizes. Obtaining a satisfactory parameter will always be desirable, but the approximation obtained with a robust pedigree will allow us to work more efficiently and economically than with massive genotyping.

Impact of selection for birth weight variability on reproductive longevity: A mice model.

Uniformity, understood as a similar performance in relevant livestock traits, such as birth weight within the litter, is being included as one of the selection objectives in breeding programmes, especially for polytocous livestock species. A divergent selection experiment for birth weight within-litter variability in mice during 23 generations showed that homogeneous animals were better for litter size, survival and feed efficiency but less heavy than heterogeneous animals. The aim of this study was to compare the reproductive longevity in both divergent lines as time to the end of the reproductive period. Two generations from both lines with an initial number of 43 females and 43 males were mated one to one and stayed together to have consecutive parturitions until the end of the reproductive life. Females were discarded when the time elapsed from the last parturition was longer than 63 days. The time to the end of the reproductive period between both lines was compared by fitting a Cox proportional hazard regression model adjusting for line, generation and its interaction. The rate of parturitions in both lines was also compared using a Prentice-Williams-Peterson model adjusted for the same effects. The low variability line was associated with a higher parturition rate, e.g., adjusted hazard ratio was 2.93 (95% CI 2.17-3.94). The Cox model showed that the low variability females also presented benefits of time to the end of the reproductive period, with an adjusted hazard ratio of 0.26 (95% CI 0.16-0.41). The median of reproductive days was 55.50 in the high variability line whilst the median was 252.50 days for the low variability females. The homogeneous line presented important reproductive advantages suggesting higher robustness and animal welfare. Further research should confirm whether the findings presented here of a better performance in the low variability line could be properly applied to some livestock species.

Impact of the event effect in genetic evaluation for ranking traits in horses.

In genetic evaluation of horses, the genetic trend does not correspond into a phenotypic trend when using ranking as a phenotype due to its uniform distribution, and some other effects might be absorbing that trend. From a founder population, a further four discrete generations of 100 individuals were simulated under random mating. Then, ten additional discrete generations were simulated by selecting the best 10% of the animals. Likewise, an underlying variable with heritability 0.1 or 0.2, affected by an event environmental influence, generation and permanent environment, was simulated to establish the ranking assignment of 10 random participants or according to the competitive level for each event, in 10 or 100 structured or unstructured events. The ranking trait genetic evaluation model was tested to include or exclude the event effect and the permanent environment effect, depending on the scenario. The results showed that the event effect fitted the different competitive level of each event, leading to a 5% to 23% of selection response improvement for structured competitions. Therefore, the event effect should be included in the genetic evaluation models of horses. The permanent environment fitted or simulated did not significantly improve the selection response. The event effect explained the competition genetic level, by compensating the genetic trend obtained by selection.

Breeding Strategies to Optimize Effective Population Size in Low Census Captive Populations: The Case of Gazella cuvieri.

Small-sized animal populations can undergo significant loss of genetic variability that can lead to their extinction. Therefore, studies on animal breeding have focused on mating systems for minimizing the disappearance of genetic variability. The main objective of this study was to compare, using computer simulations, the performance of different breeding schemes to limit the loss of genetic diversity in small-sized populations. This objective was achieved by monitoring the evolution of the effective population size obtained by 23 strategies throughout 20 generations in two populations of Gazella cuvieri. The scenarios were designed with different assumptions, in both reference subpopulations, regarding: the use of parents coancestry or offspring coancestry, the use of their increases or the coefficients themselves, and the number of males and females involved. Computations were performed using an experimental module of Endog v4.9 developed for this purpose. The results of the study showed that strategies for minimizing the coancestry of the parents were better in the short term; however, these strategies were worse in the long term. Minimizing the average coancestry of the offspring was a better approach in the long term. Nevertheless, in both populations, the best results were obtained when both the coancestry of the parents and the coancestry of the offspring were weighted at 5% each and neither males nor females were assumed to contribute to the next generation. In any case, not all strategies had the same evolutionary pattern throughout generations in both populations. The current results show that neither traditional nor new strategies have any general use. Therefore, it is important to carefully test these strategies before applying them to different populations with different breeding needs under different conditions, such as different generation intervals, and different natural breeding systems such as monogamy or polygyny.

Genetic parameters for uniformity of harvest weight in Pacific white shrimp (Litopenaeus vannamei).

BACKGROUND: Uniformity of body weight is a trait of great economic importance in the production of white shrimp (Litopenaeus vannamei). A necessary condition to improve this trait through selective breeding is the existence of genetic variability for the environmental variance of body weight. Although several studies have reported such variability in other aquaculture species, to our knowledge, no estimates are available for shrimp. Our aim in this study was to estimate the genetic variance for weight uniformity in a farmed population of shrimp to determine the potential of including this trait in the selection program. We also estimated the genetic correlation of weight uniformity between two environments (selection nucleus and commercial population). METHODS: The database contained phenotypic records for body weight on 51,346 individuals from the selection nucleus and 38,297 individuals from the commercial population. A double hierarchical generalized linear model was used to analyse weight uniformity in the two environments. Fixed effects included sex and year for the nucleus data and sex and year-pond combination for the commercial data. Environmental and additive genetic effects were included as random effects. RESULTS: The estimated genetic variance for weight uniformity was greater than 0 (0.06 ± 0.01) in both the nucleus and commercial populations and the genetic coefficient of variation for the residual variance was 0.25 ± 0.01. The genetic correlation between weight and weight uniformity was close to zero in both environments. The estimate of the genetic correlation of weight uniformity between the two environments (selection nucleus and commercial population) was 0.64 ± 0.06. CONCLUSIONS: The existence of genetic variance for weight uniformity suggests that genetic improvement of this trait is possible. Selection for weight uniformity should not decrease weight, given the near zero genetic correlation between these two traits. The strong genetic correlation of weight uniformity between the two environments indicates that response to selection for uniformity in the nucleus will be at least partially transmitted to the commercial population if this trait is included in the breeding goal.

Genetic parameters for canalization analysis of morphological traits in the Pura Raza Español horse.

Measurements from 13 different morphological traits of importance in the Pura Raza Español (PRE) horse were used to estimate genetic and environmental parameters following a heteroscedastic model in which data were assigned to stallions. Data sets used ranged from 20,610 (height at withers) to 48,486 measurements (length of shoulder), and the number of animals analysed in the pedigrees varied from 17,662 (height at withers) to 23,962 (dorsal-sternal diameter). Results of heritabilities of the traits varied from 0.09 (width of chest and upper neck line) to 0.30 (muscular development). Further, genetic correlations between traits and their environmental variability were estimated, obtaining values from -0.56 (muscular development) to 0.69 (height at withers). Also, predicted breeding values for the mean and for the environmental variability were obtained for all horses in the pedigrees, providing individual information about not only the expected phenotypic value of their offspring but also the expected heterogeneity among them. Results proved the possibility of improving morphological traits and reducing the heterogeneity of offspring at a time by the selection of animals and levels of systematic effects.

Combining Threshold, Thurstonian and Classical Linear Models in Horse Genetic Evaluations for Endurance Competitions.

The racing time and rank at finish traits are commonly used for endurance horse breeding programs as a measure of their performance. Even so, given the nature of endurance competitions, many horses do not finish the race. However, the exclusion of non placed horses from the dataset could have an influence on the prediction of individual breeding values. The objective of the present paper was to develop a multitrait model including race time (T), rank (R) and placing (P), with different methodologies, to improve the genetic evaluation in endurance competitions in Spain. The database contained 6135 records from 1419 horses, with 35% of the records not placed. Horse pedigree included 10868 animals, with 52% Arab Horses. All models included gender, age and race effect as systematic effects and combined different random effects beside the animal and residual effects: rider, permanent environmental effect, and interaction horse-rider. The kilometers per race was included as a covariate for T. Heritabilities were estimated as moderately low, ranging from 0.06 to 0.14 for T, 0.09 to 0.15 for P, and 0.07 to 0.17 for R, depending on the model. T and R appeared mostly as inverse measures of the same trait due to their high genetic correlation, suggesting that T can be ignored in future genetic evaluations. P was the most independent trait from the genetic correlations. The possibility of simultaneously processing the threshold, Thurstonian and continuous traits has opened new opportunities for genetic evaluation in horse populations, and much more practical genetic evaluations can be done to help a proper genetic selection.

Selection Response in a Divergent Selection Experiment for Birth Weight Variability in Mice Compared with a Control Line.

Birth weight (BW) in animal production is an economically important trait in prolific species. The laboratory mouse (Mus musculus) is used as an experimental animal because it is considered a suitable model for prolific species such as rabbits and pigs. Two mouse lines were divergently selected for birth weight variability with a third line of non-selected control population of the same origin as the animals starting the experiment. The objective of this study was, therefore, to compare and evaluate the differential response of each line. The animals were from the 17th generation of both low and high BW variability lines of the divergent selection experiment, including in addition animals from the control line. The dataset contained 389 records from 48 litters of the high line, 734 records from 73 litters of the low line, and 574 records from 71 litters of the control line. The studied traits were as follows: the BW, the BW variance, the BW standard deviation, the BW coefficient of variation within-litter, the weaning weight (WW), the litter size at birth and at weaning, the weight gain, and the preweaning survival. The model included the line effect jointly with the parturition number and its interaction, the linear and quadratic LS as covariates except for the LS trait itself when analyzing litter traits, as well as the pup sex when analyzing individual traits. The low line had a lower BW and WW, but a higher litter size, and greater robustness owing to a higher survival at weaning. As a model of livestock animals, the findings from this experiment led to a proposal of selection for pig production that would combine an increase in litter size with higher survival and welfare. Compared with the control line, a much higher response was observed in the low variability line than in the high line, making it extremely satisfactory given that homogeneity provides advantages in terms of animal welfare and robustness.

Calving date and its variability as a potential trait in the breeding objective to account for reproductive seasonality in alpacas.

The low fertility and offspring survival indicators in alpacas can be partially due to their particularity seasonal reproduction that reduces the opportunities of the females to become pregnant within a season, with the survival of the offspring concerned by the availability of food and exposure to diseases that depends on the calving date. Optimizing the date of delivery and reducing its variability are shown as eligible criteria that could be used as selection criteria within the genetic improvement programmes in alpacas, the calving date being a much more appropriate trait to measure and optimize fertility unlike of age at first calving and the calving interval, this due to the reproductive seasonality in camelids. For this study, 6,533 birth date records were taken between 2001 and 2018 of Peruvian alpacas, to estimate the genetic parameters. Models assuming heterogeneity in the residuals were fitted besides classical homogeneous models to address, not only the possibility of forwarding or delaying the calving date, but also the trend to have parturitions in similar dates. The heritability and repeatability ranged from 0.07 to 0.20 for a homogeneity model and from 0.08 to 0.23 for a heterogeneity model, and suggest the possibility of advancing or delaying the calving date. It should be taken into account that the gestation length of camelids makes it difficult to adapt many reproductive traits, and trying to centre the calving date could delay it. It was concluded the feasibility to genetically select the calving date, also in the production of camels and dromedaries, which have the same reproductive characteristics as alpacas. This selection can be combined with other traits. The heterogeneity model was shown to provide a better fit.

Challenging the selection for consistency in the rank of endurance competitions.

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 Statistical Scale Effect as a Source of Positive Genetic Correlation Between Mean and Variability: A Simulation Study.

The selection objective for animal production is the highest income with the lowest production cost, while ensuring the highest animal welfare. A selection experiment for environmental variability of birth weight in mice showed a correlated response in the mean after 20 generations starting from a crossed panmictic population. The relationship between the birth weight and its environmental variability explained the correlated response. The scale effect represents a potential cause of this correlation. The relationship between the mean and the variability implies: the higher the mean, the higher the variability. The study was to quantify by simulation the genetic correlation between a trait and its environmental variability. This can be attributable to the scale effect in a range of coefficients of variation and heritabilities between 0.05 and 0.50. The resulting genetic correlation ranged from 0.1335 to 0.7021 being the highest for the highest heritability and the lowest CV. The scale effect for a trait with heritability between 0.25 and 0.35 and CV between 0.15 and 0.25 generated a genetic correlation between 0.43 and 0.57. The genetic coefficient of variation (GCV) affecting residual variability was modulated by the strength reducing the impact of the scale effect. GCV ranged from 0.0050 to 1.4984. The strength of the scale effect might be in the range between 0 and 1. The scale effect would explain many reported genetic correlation and the additive genetic variance for the variability. This is relevant when increasing the mean of a trait jointly with the reduction of its variability.

Effect of feed restriction on the environmental variability of birth weight in divergently selected lines of mice.

BACKGROUND: Selection of mice for decreased environmental variability of birth weight has achieved higher survivability and larger litter size as a correlated response to canalized selection, which suggests higher welfare and robustness, and animals that are more homogeneous. However, in these studies, animals were not exposed to an environmental challenge. To demonstrate the advantages of this mouse line with a low environmental variability of birth weight, animals from two divergent lines (high and low variability of birth weight) were subjected to feed restriction. The objective of this study was to use these divergent lines to compare their response in terms of robustness against an environmental challenge. At weaning, 120 females, i.e. four full-sib females from 10 random litters of three consecutive generations of selection, were chosen from these divergent lines. The total number of females was divided into four groups, which were subjected to a feeding regimen by imposing different levels of feed restriction (i.e. 75, 90 and 85% of full ad libitum feed across three generations, respectively) in different combinations during the growth and reproduction periods. RESULTS: Animals from the "low" line were less sensitive to a change in feed level than those from the "high" line. Regarding reproduction, the "low" line performed better in terms of number of females having parturitions, number of parturitions, and litter size. Imposing a feed restriction on female mice during their growth period did not affect the birth weight of their pups. The "low" line was preferred because of its higher reproductive efficiency and survival under an environmental challenge. CONCLUSIONS: Selection for decreased environmental variability of birth weight produces animals that are less sensitive to environmental conditions, which can be interpreted as having greater robustness.

Feed and reproductive efficiency differences between divergently selected lines for birthweight environmental variability in mice.

Sustainability has come to play an important role in agricultural production. A way to combine efficiency with sustainability might be by searching for robust animals that can be selected for the homogeneity of certain traits. Furthermore, the optimization of feed efficiency is one of the challenges to improve livestock genetics programmes, but this might compromise reproductive efficiency. Animals from two divergent mouse lines, regarding variability of birthweight, were used to check whether homogeneity was also related to both feed and reproductive efficiency. The objective of this study was to use these divergent lines of mice to compare them with their feed efficiency and the reproductive capacity. Animal weight, weight gain, feed intake, relative intake and cumulated transformation index were considered as feed efficiency traits. Animals from the low line had both lower weight and feed intake from 21 to 56 days. They had a worse transforming index in the three last weeks when litter size was fitted as an effect of the model, but the lines become similar if the higher litter size of the low line was not included. Reproductively, the low line performed better considering the number of females having parturitions, the number of parturitions, and with higher litter size and survival in both parturitions. Hence, the low variability line was preferred because of reproductive efficiency without seriously affecting its feed efficiency. Homogeneity seemed to be related to robustness with similar feed efficiency but higher reproductive efficiency.