Estimation of crossbreeding parameters between Large White and Meishan porcine breeds. III. Dominance and epistatic components of heterosis on reproductive traits

A crossbreeding experiment using Large White (LW) and Meishan (MS) pig strains was conducted. Dominance, additive x additive and dominance x dominance epistatic components of direct and maternal heterosis effects were investigated for various litter productivity and sow traits: total number born (TNB), number born alive (NBA), number weaned (NW), litter weight at birth (LWB) and at 21 d (LW21), either adjusted or not for litter size, sow weight loss (SWL), sow total (SFC) and maximum (SFCM) feed consumption, sow feed efficiency - computed as SFC per piglet weaned (SFC/NW) or per unit of litter weight gain (SFC/LWG) - during lactation. Data from 1148 litters farrowed by 250 sows were analysed. Models involving all possible combinations of dominance and epistatic parameters were compared for goodness of fit on the basis of their mean squared error (MSE). The model with the lowest MSE was then used to estimate crossbreeding parameters. Models involving dominance effects only for maternal heterosis had the lowest MSE for all litter productivity traits. Dominance also appeared as the main component of direct heterosis effects on litter productivity traits. Favourable dominance and unfavourable epistatic effects contributed to direct heterosis effects for all sow traits except SFCM. Epistatic effects were additive x additive effects for SFC/NW and dominance x dominance effects for SWL, SFC and SFC/LWG. Estimates of direct, maternal and grand-maternal breed effects are presented. A possible contribution of cytoplasmic effects to between-breed variation is also hypothesized.Une expérience de croisement entre des lignées porcines Large White (LW) et Meishan (MS) a été réalisée. Les composantes de dominance et d’épistasie additive x additive et de dominance x dominance des effets d’hétérosis direct et maternel ont été estimées pour divers caractères de productivité de la portée et de la truie: nombre de porcelets nés totaux (NT), nés vivants (NV), sevrés (NS), poids de la portée à la naissance (PPN) et à 21 j (PP21), ajustés ou non pour la taille de la portée, perte de poids (PPT), consommation totale (CAT) et maximale (CAM), efficacité alimentaire - calculée comme CAT par porcelet sevré (CAT/NS) et CAT par unité de gain de poids de la portée (CAT/GPP) - de la truie en lactation. Les analyses ont porté sur 1148 portées issues de 250 truies. La validité de l’ajustement des modèles incluant l’ensemble des combinaisons possibles des paramètres de dominance et d’épistasie est comparée sur la base du carré moyen de l’erreur (CME). Le modèle ayant le plus faible CME a ensuite été utilisé pour estimer les paramètres du croisement. Les modèles incluant uniquement des effets de dominance pour l’hétérosis maternel avaient le CME le plus faible pour l’ensemble des caractères de productivité de la portée. Les effets de dominance sont également apparus comme la principale composante de l’hétérosis direct pour les caractères de productivité de la portée. Des effets de dominance favorables et d’épistasie défavorables contribuent aux effets d’hétérosis direct pour l’ensemble des caractères de productivité des truies, sauf CAM. Les effets d’épistasie sont de type additif x additif pour CAT/NS et de dominance x dominance pour PPT, CAT et CAT/GPP. Des estimations des différences directes, maternelles et grand-maternelles entre races sont présentées. L’hypothèse d’une contribution possible d’effets cytoplasmiques à la variation entre races est émise

Selection for litter size components: a critical review

The measurement of component variables such as the number of ova shed (OR) and its inclusion in a linear index with litter size (LS) or prenatal survival has been suggested in order to accelerate genetic progress for LS. Despite optimistic theoretical predictions, however, in no selection experiment has the advantage of including OR in an index as compared to direct selection for LS been convincingly demonstrated. A literature survey shows no clear evidence of changes in genetic parameters with selection. By contrast, genetic drift may suffice to explain the less than expected usefulness of measuring OR, although it is not necessarily the sole cause. It is shown that an approximate figure of how much can be gained by measuring OR relative to direct selection for LS is given by (voir formule piece-jointe)1/2 with mass selection, where(voir formule piece-jointe) is the phenotypic variance. Nonetheless, the size of the experiment needed to test this prediction is likely to be very large.Plusieurs auteurs ont proposé de mesurer le taux d’ovulation (TO) et de l’inclure avec la taille de la portée (TP) dans un indice de sélection (IX) afin d’accroître l’efficacité de la sélection pour TP. Malgré des prédictions théoriques optimistes, aucune expérience de sélection n’a pu démontrer de façon convaincante l’avantage d’une sélection sur l’indice IX par rapport à une sélection directe sur TP. Une revue des expériences de sélection disponibles dans la littérature montre que la réponse plus faible qu’attendue à une sélection sur IX ne peut être expliquée par un changement des paramètres sous l’effet de la sélection, mais pourrait l’être par les effets de la dérive génétique. De façon générale, la formule (voir formule piece-jointe) est la variance phénotypique, donne une estimation réaliste de l’avantage relatif de la sélection sur IX par rapport à la sélection directe sur TP. Malheureusement, des expériences sur un grand nombre d’animaux seraient nécessaires pour vérifier cette prédiction

Genetic variability of age and weight at puberty, ovulation rate and embryo survival in gilts and relations with production traits

International audienc

Estimation of crossbreeding parameters between Large White and Meishan porcine breeds. II. Growth before weaning and growth of females during the growing and reproductive periods

A crossbreeding experiment using Large White (LW) and Meishan (MS) pig strains was conducted. Direct, maternal and grand-maternal additive genetic effects together with direct, maternal and paternal heterosis effects were estimated for traits during the preweaning, growing and reproductive periods. Weight at birth (WB) and at 21 d of age (W21) was recorded in 3731 male and female piglets. After weaning at 28 d, 543 females were weighed at 73 (W73) and 154 (W154) d of age. From these, 148 sows were weighed before farrowing from 1st to 5th parity. Average daily gains were computed from birth to 21 days of age (ADG 0-21), 21 to 73 days of age (ADG 21-73) and 73 to 154 days of age (ADG 73-154). The genetic influence on preweaning traits was mainly maternal in origin. Maternal additive differences between breeds significantly increased with parity of the dam. Average values were 0.33 ± 0.05 kg (26%) and 1.24 ± 0.22 kg (26%) in favour of LW for WB and W21 respectively. Maternal heterosis effects were 0.05 ± 0.02 kg (6%) for WB and 0.65 ± 0.09 kg (14%) for W21. Significant grand-maternal additive and direct heterosis effects were also observed on WB. Adjustment of data for litter size slightly increased additive and heterosis maternal values. After weaning, direct effects became important. Additive differences between breeds rapidly increased during the growing period and averaged 4.1 ± 1.0 kg (18%), 22.9 ± 3.3 kg (36%) and 231 ± 33 g/d (47%) in favour of LW for W73, W154 and ADG 73-154 respectively. Direct heterosis effects for these traits were 3.7 ± 0.7 kg (15%), 19.2 ± 2.3 kg (25%) and 187 ± 24 g/d (30%) respectively. Direct additive differences in favour of LW increased from 58 ± 9 kg at the first farrowing to 111 ± 10 kg at the fifth one. Direct heterosis effects were similar throughout reproductive life and averaged 27 ± 3 kg (11%). The other crossbreeding parameters were small and non-significant after weaning, with the exception of maternal heterosis effects, which remained significant until 154 days.Une expérience de croisement entre des lignées Large White (LW) et Meishan (MS) a été réalisée. Les effets génétiques additifs directs, maternels, grand-maternels ainsi que les effets d’hétérosis directs, maternels et paternels ont été estimés pour les caractères de croissance au cours des périodes d’allaitement, de croissance et de reproduction. Les poids à la naissance (PN) et à 21 j (P21) ont été mesurés sur 3731 porcelets mâles et femelles. Après sevrage à 28 j, 543 femelles ont été pesées à 73 (P73) et 154 (P 154) j d’âge. Cent quarante-huit d’entre elles ont ensuite été pesées avant mise bas de la 1er à la 5e portée. Les gains moyens quotidiens ont été calculés entre la naissance et 21 j d’âge (GMQ 0-21), 21 et 73 j d’âge (GMQ 21-73) et de 73 à 154 j d’âge (GMQ 73-154). La variabilité génétique des performances avant sevrage était essentiellement d’origine maternelle. Les différences additives maternelles entre races augmentaient de façon significative avec le numéro de portée. Elles s’élevaient en moyenne à 0,33 ± 0,05 kg (26%) et 1,24 ± 0,22 kg (26%) en faveur de LW pour PN et P21 respectivement. Les effets d’hétérosis maternel s’élevaient à 0,05 ± 0,02 kg (6%) pour PN et 0,65 ± 0,09 kg (14%) pour P21. Des effets grand-maternels et d’hétérosis direct significatifs ont également été observés sur PN. L’ajustement des données pour la taille de la portée a légèrement accru les valeurs des effets additifs et d’hétérosis maternel. Après le sevrage, les effets directs devenaient importants. Les différences additives directes entre races ont augmenté rapidement au cours de la croissance après sevrage et atteignaient 4,1 ± 1,0 kg (18%), 22,9 ± 3,3 kg (36%) et 231 ± 33 g/j (47%) en faveur de LW pour W73, W154 et GMQ 73-154 respectivement. Les effets d’hétérosis directs pour ces caractères s’élevaient à 3,7± 0,7 kg (15%); 19,2 ± 2,3 kg (25%) et 187 ± 24g/j (30%)respectivement. Les différences additives directes en faveur de LW ont augmenté de 58 ± 9 kg à la première mise bas à 111 ± 10 kg à la cinquième mise bas. Les effets d’hétérosis directs sont restés similaires tout au long de la période de reproduction et atteignaient en moyenne 27 ± 3 kg (11 %). Les autres paramètres du croisement étaient faibles et non significatifs après le sevrage, à l’exception des effets d’hétérosis maternels, qui subsistaient jusqu’à 154 j

Selection for litter size in pigs. II. Efficiency of closed and open selection lines*

A selection experiment on litter size in the pig was carried on for seventeen generations in an Inra experimental herd. The founder population was made up of 10 males and 120 females from the Large White breed. Selection was first performed for ten generations in a closed line, compared to a control line derived from the same founder population. Selection was carried on within sire family on the total number of piglets born in the first two litters of the dam (TB1 + TB2). After ten generations, the selection criterion became dam TB1 only. The control line was then discontinued and a panel of frozen semen from the 11th generation boars was created for later comparisons. The selected line was opened to gilt daughters of hyperprolific boars and sows, at a rate of 1/8 per generation, and the same selection procedure was applied irrespective of the origin of the gilt. During the whole experiment, the number of ova shed (OS) and the number of live embryos (LE) at 30 days in the 3rd pregnancy were recorded. These two parts of the experiment were analysed using REML estimation of genetic parameters and a BLUP-Animal Model in order to estimate the responses to selection. Significant heritabilities for TB1, TB2, OS and LE were obtained, i.e. 0.10, 0.05, 0.43 and 0.19, respectively. Significant common environment variances and covariances were estimated for nearly all traits. Significantly positive BLUP responses per generation were observed from G0 to G17 for TB1 (+0.086), TB2 (+0.078), OS (+0.197) and LE (+0.157). However, the responses were 3- to 4-fold higher in the G12–G17 interval compared to G0–G11, and they were also in fair agreement with previous estimates based on standard least-squares procedures, using the control line and the control frozen semen panel. Since G11, the selection intensity was increased by nearly 80 p. cent compared to the previous generations, and the proportion of hyperprolific ancestry increased up to 65 p. cent in the sows of the last generation. The total genetic gain of about 1.4 piglets at birth per litter could be shared between a gain due to immigration, of about 0.8 piglets per litter, and a within-line selection gain of about 0.6 piglets. Thus by combining selection and immigration in the second part of the experiment, advantage could be taken from both the genetic superiority of the immigrants and the higher internal selection intensity made possible by immigration

A further look at quantitative trait loci affecting growth and fatness in a cross between Meishan and Large White pig populations

A detailed quantitative trait locus (QTL) analysis of growth and fatness data from a three generation experimental cross between Large White (LW) and Meishan (MS) pig breeds was carried out to search for sex × QTL interactions, imprinting effects and multiple linked QTLs. A total of 530 F2 males and 573 F2 females issued from 6 F1 boars and 23 F1 sows were typed for a total of 137 markers covering the entire porcine genome. Nine growth traits and three backfat thickness measurements were analysed. All analyses were performed using line cross regression procedures. A QTL with sex-specific expression was revealed in the proximal region of chromosome 8, although some confusion between herd and sex effects could not be discarded. This previously undetected QTL affected male growth during the fattening period, with a favourable additive effect of the LW allele. The analyses also revealed the presence of two linked QTLs segregating on chromosome 1, affecting growth traits during the post-weaning period. The first QTL, previously detected using a single QTL model, was located at the end of the q arm of chromosome 1 and had a favourable MS allele. The second QTL had a favourable LW allele and was located in the proximal extremity of the q arm of chromosome 1. Suggestive genomic imprinting was found in the distal region of chromosome 9 affecting growth during the fattening period

Growth, carcass and meat quality performance of crossbred pigs with graded proportions of Meishan genes

International audienc