Lars-Erik Liljedahl

Effects of inbreeding on growth and reproductive traits in rainbow trout (Oncorhynchus mykiss)

Abstract Rate of inbreeding and inbreeding effects on body weight and reproductive traits were studied in three lines of rainbow trout from a Californian selection experiment, in which Line Y was selected for body weight at 364 days of age, Line E was selected for egg size and Line C was a random mated control. The coefficient of inbreeding, as estimated both from effective population size with the assumption of random mating and from observed pedigree increased from Gen. 0 to Gen. 5 by 7.8% and 7.5% in Line C, by 5.7% and 8.3% in Line E, and by 5.2% and 6.5% in Line Y, respectively. The effects of inbreeding on the various traits were measured by the regression of individual performance on the coefficient of inbreeding calculated from pedigree. The regressions of body weight on coefficient of inbreeding were positive but not significant in the age interval from 168 to 252 days of age, and negative but not significant from 280 to 336 days of age. After that, the regressions were significantly negative. Thus, inbreeding depression for body weight per 10% increase in inbreeding was 2.26% (♂ ♂+♀♀) at 364 days, and 3.92% (♂ ♂) and 5.77% (♀ ♀) at spawning as a percent of the mean. There was a tendency for inbreeding depression for body weight to increase with advancing age. A highly significant inbreeding depression was found for spawning age of females and egg number. Per 10% increase of the inbreeding coefficient, spawning age of females was delayed by 0.53% and egg number decreased by 6.10% of the mean, respectively. In contrast, inbreeding did not significantly affect spawning age of males or egg size. The three kinds of inbreeding originating from male, female and embryo had quite different effects on fertility-hatchability. Inbreeding of male had no deleterious influence on this trait. In contrast, inbreeding of female had a strong and significantly negative effect and inbreeding of embryo itself had a noticeable though not statistically significant negative effect on fertility-hatchability. Per 10% increase of the inbreeding coefficient of female and embryo, fertility-hatchability declined by 11.60% and 8.56% of the mean, respectively. The following rank order of traits with regard to the magnitude of inbreeding depression seems to be in agreement with the rank order of the expected correlations of traits with fitness: (1) fertility-hatchability of females; (2) hatchability of embryo; (3) egg number; (4) body weight of males and females at spawning; (5) body weight (♂ ♂) at 308–364 days of age; and (6) spawning age of females, body weight (♀ ♀) at 280 days of age, and egg size.

Genetic and environmental variation of female reproductive traits in rainbow trout (Oncorhynchus mykiss)

Abstract The variation and covariation of reproductive traits were studied by analyzing data from 2020 females divided into 377 full sib families and covering five generations of three lines—a random mated control line (C), an egg size (+) line (E) and a body weight (+) line (Y), in a selection experiment with rainbow trout conducted at Davis, California. Variance components were estimated from a single trait animal model and covariance components from a two-trait animal model by using a derivative-free restricted maximum likelihood algorithm. Pooled over the three lines, the estimates of heritability were 0.65 for spawning date, 0.14 for spawning body weight, 0.60 for egg size, 0.55 for egg number, 0.52 for egg volume and 0.13 for fertility-hatchability. The estimates in line C were lower for spawning date, spawning body weight and egg number, and higher for egg size and fertility-hatchability than those in line E and line Y. Full-sib family effects caused by factors other than additive genetic effects were considerable for spawning body weight but small for other traits. Genetic correlations were estimated from data pooled over the three lines. Spawning date had significant genetic correlations with spawning body weight, egg size and egg volume (0.51–0.73) as well as with egg number (0.25). Significant genetic correlations were also found for spawning body weight with egg size, egg number and egg volume (0.47–0.67); and for egg size with fertility-hatchability (0.35). As expected, the genetic correlations between egg number and egg volume and between egg size and egg volume (0.81 and 0.48) were strong and significant due to the partial auto-correlations originating from commonality among biological components and methods of measuring these traits. The estimated genetic correlations between spawning body weight and egg production traits (egg size, egg number and egg volume) were positive, so that direct selection for growth rate or egg production traits should result in favorable correlated responses. The low heritability of body weight, the moderately high heritability of egg volume, and the strong genetic correlation between spawning body weight and egg volume, suggest that combined selection for body weight and egg volume could be an effective alternative selection method for improving growth rate and also reproductive capacity in rainbow trout.

Genetic and environmental variation of body weight in rainbow trout (Oncorhynchus mykiss)

Abstract Body weight data covering the period from birth year 1978 to 1986 from a selection experiment with rainbow trout conducted at the University of California at Davis were analyzed with regard to the genetic and environmental variation in three lines (Line C reproduced by random selection; Line E selected for egg size; Line Y selected for body weight at 364 days of age). Variance components for body weight from 168 to 364 days were estimated using a derivative-free restricted maximum likelihood algorithm under a single trait animal model. Heritability estimates were low, ranging from 0.03 to 0.13. The estimates for Line Y were lower than those for Line C and Line E, possibly a result of sampling error when the three lines were formed from a small common base population. The heritability estimates tended to increase with age; averaged over the three lines, the estimates were lowest at 168 days (0.05) and highest at 336 and 364days (0.10). Full-sib family effects caused by factors other than additive genetic effects were relatively large, ranging from 0.01 to 0.17 as a proportion of the phenotypic variance, and also increased with age, being lowest at 196 days (0.03) and highest at 364 days (0.14) averaged over the three lines. Both common environmental and non-additive genetic effects could contribute to this component. Common environmental effect may result from the competition for space between families owing to the particular rearing procedures used for the experiment. In addition, the different inbreeding levels among families may have increased the variation between families by reducing the expression of non-additive genetic effects to different degrees. The age trend of full-sib family effects on body weight may be a reflection of the accumulation of competition effect and the increase of non-additive genetic effect as the fish grew larger.

Genetic correlations between body weight at different ages and with reproductive traits in rainbow trout

Abstract The genetic correlations among body weight (BW) at 28 days interval during the first year, and between reproductive traits and BW, were estimated using a multivariate animal model. The data consisted of BW at 168, 196, 224, 252, 280, 308, 336 and 364 days and egg size, egg number, egg volume and post-spawning weight of females. All the traits were measured individually but fish were identified at full-sib-family level at the first year while identified individually at spawning season. The estimated genetic correlations between eight BW were all significantly greater than zero and ranged from 0.24±0.09 for BW at 168 days to 0.93±0.02 for BW at 336 and 364 days. The estimated correlation between BW at contiguous ages were consistently high, ranging from 0.57±0.08 to 0.93±0.02, but decreased with increasing interval between ages. Also, there was a trend for the genetic correlations between BW at earlier ages to be smaller than those between BW at later ages, independent to age interval. The genetic correlations of reproductive traits with BW at ages prior to 252 days were not significantly different from zero, while those with BW at ages from 252 to 364 days were significantly greater than zero and increased with increasing age. The range of estimated genetic correlations between reproductive traits and BW at ages from 252 to 364 days were: for egg size, from 0.18±0.08 to 0.29±0.06; for egg number, from 0.21±0.08 to 0.32±0.06; for egg volume, from 0.28±0.08 to 0.45±0.06 and for post-spawning weight, 0.25±0.11 to 0.61±0.08. As a whole, the genetic correlations between reproductive traits and BW during the first year were favorable, allowing positive genetic improvement in both BW and reproductive traits.

Major Histocompatibility Genes in Egg‐Laying Hens*

ABSTRACT: A common base population of White Leghorn was “synthesized” for a joint project on the genetics of egglaying, undertaken by animal breeding geneticists in 4 Scandinavian countries. After 6 to 7 generations of line selection for various egg‐laying parameters, MHC typing was undertaken of both the selection lines in Denmark, Norway, and Sweden and the respective control lines representing the common base population. Ten MHC haplotypes were defined which jointly accounted for about 95% of the MHC gene pool of the base population. The 2 haplotypes which were predominant in the base population, B15 and B19, responded very differently to the selection pressures applied.

Estimates of phenotypic and genetic parameters for within-season date and age at spawning of female rainbow trout

The phenotypic and genetic characteristics of female spawning date and age at spawning within season were studied by analysing data from rainbow trout populations in which females spawned completely within the second year. Spawning date was measured as the number of days from December 31 of the year preceding spawning. The estimates of regression of daughter on dam and full-sib intraclass correlation for this trait were positive and large. Based on an animal model, the estimate of heritability was high and full-sib family effect was very low. Age at spawning was calculated as days from birth date to spawning date, using the date the eggs are fertilized (i.e., spawning date of dam) as the birth date of the daughters. The results showed a negative regression of daughter age on dam age but a positive and high full-sib intraclass correlation for age at spawning. Consequently, the estimated additive genetic variance was very low along with a high estimate of full-sib family effects. Further examination on the features of covariance between daughter and dam confirmed that the regression of daughter on dam for observed age at spawning is expected to be negative. The cyclic nature of the spawning season over generations could be the biological basis of this result. The results indicated that age at spawning measured as the days from dam spawning date to daughter spawning date is not an effective measurement to assess the genetic effects, and selection based on such a phenotype is not expected to yield a response. Therefore, selection for late sexual maturity, in order to avoid the unfavorable influence of the sexual maturation process on growth, is not applicable for those stocks in which females spawn completely in a single spawning season. Instead, the approach to breed improvement should be designed to select for high growth rate with culling of early sexual maturing fish, so that fish can reach optimal body weight before sexual maturity.

Genotype—Nutrition Interactions in White Leghorn Strains

(1973). Genotype—Nutrition Interactions in White Leghorn Strains. Acta Agriculturae Scandinavica: Vol. 23, No. 2, pp. 127-139.

Genetic studies of assortative mating—a simulation study. III. Assortative mating in selected populations

Effects of 25 generations of positive assortative mating, random mating and negative assortative mating in simulated selected populations of various effective size (N e = 40, 100, 200) were compared. The trait under consideration was controlled by either 100 or 2500 loci. Positive assortative mating produced the highest cumulative selection response (11.61–13.24 σ P ), followed by random mating (11.00–12.48 σ P ) and negative assortative mating (10.88–11.98 σ P ). The differences between the various mating systems were highly significant (P < 0.001) after the second generation and depended on the covariance due to linkage disequilibrium (C 1) and varying rates of fixation of the favourable alleles, leading to different genic variance (V a). Positive assortative mating first caused C 1 to increase to maximum values equal to 10.8% of the base population genetic variance (V A) when the trait was controlled by 100 loci and then to decline gradually. A faster rate of change in gene frequency caused V ato decre...

Population parameters for birth and ewe fleece weight at different parities in Baluchi sheep.

UNLABELLED ZUSAMMENFASSUNG: Populationsparameter für Geburts- und Vließgewicht von Baluchi Schafen Das Datenmarterial stammt von zwei Herden einer Schafzuchtstation in NO Iran aus den Jahren 1966-1989. Die Tiere waren unselektiert und stammten aus zufällig verteilten Paarungen. Es wurden Geburtsgewicht und Vließgewicht bei verschiedenen Altersstufen erhoben und Varianzkomponenten mittels Restringierter Maximaler Likelihood mit einem bivariaten Tiermodell mit fixen Wirkungen von Jahr, Geschlecht, Geburtstyp und Parität sowie Zufallswirkungen für additiven Genotyp des Lammes (direkt) und des Mutterschafes (maternal), gemeinsamer Umwelt (ausgenommen Vließgewicht) und Resteinfluß geschätzt. Direkte und maternale genetische Korrelationen zwischen Leistungen verschiedener Paritäten wurden berechnet. In Herde 1 scheinen Varianzen und Heritabilitätswerte für Lammgewicht bis Parität 5 zuzunehmen, kaum aber in Herde 2. Die durchschnittlichen Heritabilitätswerte, direkt, maternal und gesamt waren 0.12, 0.11 und 0.26, die genetische Korrelation zwischen direkten und maternalen Wirkungen 0.42. Bei Vließgewicht waren in Herde 1 keine Veränderungen der Varianzen und Heritabilitätswerte mit Alter zu erkennen, aber bei Herde 2 nahmen phänotypische und Umweltvarianz mit Alter leicht zu. Durchschnittliche direkte, maternale und Gesamtheritabilität waren 0.19, 0.04 und 0.22, die genetische Korrelation zwischen direkten und maternalen Wirkungen geringgradig positiv in Herde 1, aber mit Alter zunehmend negativ in Herde 2. Die genetischen Korrelationen für direkte Wirkungen auf Geburtsgewicht waren hoch zwischen Paritäten 1 bis 5, aber niedriger bei Parität 6 und jene zwischen maternal bedingten Wirkungen zeigten ähnliche Trends. In Herde 2 waren Werte mit Parität 6 ähnlich wie die zwischen den übrigen Paritäten. Die die Vließgewichte betreffenden direkt genetischen Korrelationen zwischen Paritäten waren in beiden Herden ähnlich (0.73-0.92), jene, die maternale Wirkungen betreffen, deutlich geringer, besonders soweit sie Paritäten 5 und 6 betroffen haben und zeigten besonders bei Herde 2 starke Schwankungen (-0.54 bis 0.74). SUMMARY Direct and maternal performance of ewes at different parities were examined in Baluchi sheep. The data set was collected during the period 1966-1989 from two flocks at a sheep breeding station in the north-east of Iran. The animals included in the data set were unselected and randomly mated. The traits analysed were birth weight of lamb and fleece weight at different parities of the ewe. Variance components were estimated using Restricted Maximum Likelihood with a bivariate animal model including fixed effects of year, sex, type of birth and parity, and random effects of additive genotype of lamb (direct genetic effect), additive genotype of ewe (maternal genetic effect) and common environment (excluded for ewe fleece weight), and random residual effect. Direct and maternal genetic correlations between different parities were estimated. There was evidence of increasing phenotypic and genetic variances and heritabilities from parity 5 for birth weight of lamb in flock 1, but only evidence of a slightly increasing age trend for the environmental and phenotypic variance in flock 2. The average heritabilities over flocks and parities were 0.12, 0.11 and 0.26 for the direct, maternal and total heritability, respectively, while the average genetic correlation between direct and maternal effects for this trait was 0.42. There were no indications of any age changes in variances or heritabilities for ewe fleece weight in flock 1, but indications of slightly increasing age trends for the environmental and phenotypic variance. The average heritabilities over flocks and parities were 0.19, 0.04 and 0.22 for the direct, maternal and total heritability, respectively, while the average genetic correlation between direct and maternal effects was slightly positive in flock 1 but increasingly negative with age of the ewe in flock 2. Direct genetic correlations between parities 1-5 were very high for birth weight of lambs (on average 0.96) in contrast to the markedly lower correlations of parities 1-5 with parity 6 (on average 0.67) in flock 1 with a similar pattern for the maternal genetic correlations. In flock 2, these correlations were also high but without the marked decrease between parities 1-5 with parity 6 that was found in flock 1. Direct genetic correlations between the various parities for ewe fleece weight were similar for the two flocks, ranging from 0.73 to 0.92 and without any obvious differences between the various combinations of parities. However, the maternal were markedly lower than the direct genetic correlations, especially for the combinations of parity 5 and 6 with the earlier parities, and most pronounced in flock 2 fluctuating from -0.54 to 0.79. To obtain reliable estimates of breeding values for birth weight of lamb, it is recommended that the prediction should include not only earlier but also later parities (ages) of the ewe.

Genetic correlations and heritabilities for frequency of cracked eggs, egg number and egg weight in laying hens

Abstract 1. Data on egg weight and egg number were obtained from two consecutive generations in a White Leghorn line. Each egg was candled and the frequency of cracked eggs was calculated. 2. The estimates of heritability for the frequency of cracked eggs ranged from 0.11 to 0.43, for egg number from 0.12 to 0.29 and for egg weight from 0.58 to 0.65. 3. The estimates of the genetic correlations between the traits were variable but in general showed no evidence of antagonism between a reduction in crack frequency and an increase in the production traits. 4. The efficiency of selection for reduction in the frequency of cracked eggs based on early measurements is briefly discussed.