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Mortality due to feather pecking (FP) has large economic and welfare consequences in the commercial poultry industry, and reduces survival of birds. With FP, the survival time of a hen depends both on her own genetic ability to avoid becoming the victim of FP (direct genetic effect; DGE), and on the genetic tendency of her group mates to perform FP (indirect genetic effect; IGE). Thus, to improve survival time of laying hens, it is important to use a breeding strategy that captures both the DGE and the IGE of selection candidates. Here, we investigate the prospects for solving mortality due to FP in laying hens by genetic selection. First, we review genetic parameters for survival time. Second, we use deterministic simulation to predict response to selection for 2 multi-trait crossbred breeding programs, a traditional recurrent testing scheme (RT) and a genomic selection scheme (GS). Finally, we investigate the prospects for sustained improvement of survival time when mortality becomes low. Results show that survival time has considerable heritable variation; most estimates of the total additive genetic standard deviation are larger than 1 mo. As expected, predicted single generation response to selection in survival time with GS is substantial larger than with RT. Particularly when the correlation between survival time and other breeding goal traits is zero, the GS scheme yields substantial improvement in survival time. For example, when mortality is 35%, the genetic correlation between survival time and other traits is 0, allowing for a 10% reduction of response in other traits, and when selection takes place in both the sire line and dam line, survival time can be improved with ∼23 D in one generation, using GS. Results, however, also show a strong decrease in heritability when mortality decreases, indicating that continued improvement becomes increasingly difficult. In summary, our results show that breeders can considerably reduce mortality due to FP with limited reduction of improvement in other breeding goal traits. [ABSTRACT FROM AUTHOR]

Social interactions among individuals may affect individual productivity and welfare in aquaculture. Since social effects may have a genetic component, known as an indirect genetic effect (IGE), genetic selection may be a promising tool to simultaneously improve welfare and productivity in aquaculture. Here we compare two experimental designs that have been previously proposed for the genetic improvement of socially affected traits. We used stochastic simulations to compare a design where each group consisted of members of two families (2-FAM) with a design where each group consisted of members of three families (3-FAM). The 2-FAM and 3-FAM designs were compared using an equal number of groups (96 groups). The group size, i.e., number of individuals within each group, was either 30 or 60 individuals. Both designs were compared for the precision of estimated direct and social genetic parameters and for response to selection, either with or without a restriction on the rate of inbreeding. Four different schemes with a low variance (heritability for social effects or h S 2 = 0.1), a moderate variance ( h S 2 = 0.3), or a high variance ( h S 2 = 0.5) of the social genetic effects, and a negative correlation between direct and social genetic effects ( r A D , S = − 0.6) were compared. The negative r A D , S indicates competition between group mates. Differences in precision of estimated genetic parameters between both designs were small. At low h S 2 and group size of 30, the 2-FAM design was superior with respect to precision of social additive genetic variance. When the social genetic variance was small, a larger group size, e.g. 60 is recommended. The 2-FAM design resulted in a higher accuracy of selection for social and total genetic effects, but also in a higher rate of inbreeding compared to the 3-FAM design. When the rate of inbreeding was restricted to ~ 2%, the total response to selection was significantly higher for the 3-FAM design. In conclusion, the 2-FAM and 3-FAM designs differ little in accuracy of the direct and social genetic parameter estimates, while the 3-FAM design is superior with respect to the response to selection at a fixed rate of inbreeding. This study is particularly important for making decisions regarding experimental design when breeding for social genetic effects in aquaculture. Statement of relevance Communal or family rearing with a large number of animals in a group is common practice in aquaculture. Large variation in body size, which may inflate competition for feed, is generally observed in the communal rearing tank. In addition, cannibalistic or aggressive behaviour is frequently observed in a large variety of fish species. So far, the issue is addressed by management measures, such as size grading, which may be labour intensive. Sustainable solutions through selective breeding have not been tested. Previous studies compared two experimental designs for social interaction traits; groups composed of two families (2-FAM) and three families (3-FAM) with groups composed at random and found that the 2-FAM and 3-FAM designs were better with respect to genetic parameter estimates than designs with groups composed at random. It is however still unknown whether the 2-FAM or the 3-FAM design is better. Previous studies did not consider the rate of inbreeding when studying the designs. This paper describes the results from a comparison of the two experimental designs for estimating genetic parameters and obtaining response to selection, taking into account the rate of inbreeding. As such, this paper should be of interest to a broad readership including those interested in aquaculture genetics. [ABSTRACT FROM AUTHOR]

Abstract: Pigs may affect each other''s health, welfare and productivity through their behaviour. The effect of a pig on the growth rate of its pen mates is partly heritable and is referred to as its social genetic effect. Social genetic effects, also known as indirect genetic effects, have been found in a number of livestock breeds, in natural and laboratory populations, and in plant breeding and forestry, and have become an important research topic in recent years. In pigs, social genetic effects are hypothesized to be related to behaviour. The mechanism behind social genetic effects for growth, as well as the relationship between behaviours and growth itself, is largely unknown. To gain insight in the mechanism behind social genetic effects, we investigated the relationship between behaviours and growth rate in pigs. On a commercial pig farm, 398 finishing pigs in 50 pens (eight pigs/pen) were observed at 12 weeks of age using 2-min instantaneous scan sampling for 6h during daytime. For 324 observed pigs, growth rate during the finishing period was known. The relationship between behaviours and growth rate during the finishing period was analysed with behaviour as explanatory variable in a mixed model. Results show that time spent giving behaviours, like oral manipulation, social nosing, aggression and belly nosing, was not related to own growth rate. Receiving behaviours, however, did relate to growth. Pigs that received more oral manipulation, observed as tail biting, ear biting and paw biting, grew less well (P <0.05). Growth rate was 43(±17)g/d lower in pigs that received oral manipulation during more than 2% of the observations as compared to pigs that did not receive oral manipulation. Pigs that received social nosing, a gentle touch or sniff at any part of the body, had a higher growth rate (P <0.05): growth rate differed 29(±17)g/d between pigs that received social nosing during more than 2% of observations as compared to not receiving social nosing at all. Receiving aggression and belly nosing, a forceful rubbing of the belly, did not influence growth rate. In conclusion, receiving oral manipulation and social nosing related to growth rate. This suggests that pigs selected for positive social genetic effects for growth may potentially show behavioural changes. Effects of selection for social genetic effects on behaviour and growth will be studied in future research. [Copyright &y& Elsevier]

Reproductive techniques have a major impact on the structure of breeding programmes, the rate of genetic gain and dissemination of genetic gain in populations. This manuscript reviews the impact of reproductive technologies on the underlying components of genetic gain and inbreeding with special reference to the role of female reproductive technology. Evaluation of alternative breeding schemes should be based on genetic gain while constraining inbreeding. Optimum breeding schemes can be characterised by: decreased importance of sib information; increased accuracy at the expense of intensity; and a factorial mating strategy. If large-scale embryo cloning becomes feasible, this will have a small impact on the rate of genetic gain but will have a large impact on the structure of breeding programmes. [Copyright &y& Elsevier]

Competition for resources is common in aquaculture, which inflates the variability of fish body weight. Selective breeding is one of the effective approaches that may enable a reduction of size variability (or increase in uniformity) for body weight by genetic means. The genetic variance of uniformity is commonly known as genetic heterogeneity of environmental variance for particular traits. The data collected from a social interaction experiment were used to investigate the presence of genetic variation in heterogeneity of environmental variance for harvest weight in the GIFT strain. A total of 944 records pooled (by family-group) from 6330 individual harvest weights were used in the analysis. For the estimation of genetic parameters we fitted a bivariate sire–dam model to harvest weight and its standard deviation. To normalize the residuals, individual harvest weight was Box–Cox transformed. The heritability (at the family by group level) and genetic coefficient of variation for standard deviation of Box–Cox transformed harvest weight (0.23 and 0.17, respectively) indicated that uniformity of harvest weight was partly under genetic control. In addition, we found a very low genetic relationship between Box–Cox transformed harvest weight and its standard deviation, r A = 0.095 ± 0.183. Hence, these two traits are unrelated and can be selected in different directions using index selection, namely, aiming to increase growth rate while decreasing size variation. We conclude that there is potential to increase harvest weight and its uniformity by selective breeding in the GIFT strain of farmed tilapia. Statement of relevance Uniformity will help to increase aquaculture production. [ABSTRACT FROM AUTHOR]

Trait values of individuals are affected not only by their genetic makeup, but also by environmental factors and interactions with other individuals. The heritable effect of an individual on the trait values of other individuals it interacts with is known as an indirect genetic effect (IGE). Such IGEs may affect response to selection. Fish selected for high growth rate, for example, have been shown to be more aggressive and competitive, which may reduce the observed response in growth rate. The main objective of this study is to quantify the genetic and non-genetic indirect effects for harvest weight in the GIFT strain of Nile tilapia. A total of 6330 fish with harvest weight information were used to estimate genetic and non-genetic parameters. A bivariate analysis of harvest weight and survival was conducted by fitting different mixed models to investigate the presence of IGEs and other non-genetic effects. The full set of genetic parameters could not be estimated simultaneously with the inclusion of maternal common environmental effects. A confounding between maternal common environmental effects and direct genetic effects resulted from the mating strategy, where one sire was mated to only one or two dams. A 1 male to 2 females mating design is common in aquaculture, but it has limited power to estimate genetic parameters. Models without maternal common environmental effects showed significant IGE on harvest weight, which contributed 48% of total heritable variance. Models with maternal common environmental effects suggested the presence of IGE. The direct–indirect genetic correlation for harvest weight was negative (− 0.38 ± 0.19), indicating that traditional selection, if performed in an environment where the fish have to compete with each other for the resources, will increase competition. A strongly negative genetic correlation between direct effects on survival and indirect effects on harvest weight (− 0.79 ± 0.30) showed that individuals with better genes for survival suppressed growth rate of their social partners. Our results suggest that heritable competitive interactions affect harvest weight in Nile tilapia. Hence, breeding schemes may need to be adapted to avoid an increase in aggressiveness due to selection for growth rate in a competitive environment. Further studies are required to investigate the relevance of IGE and its implications on different systems of commercial aquaculture production. Statement of relevance Sociable fish will help to improve aquaculture production. [ABSTRACT FROM AUTHOR]

Abstract: Three discrete generations of GIFT fish (Nile tilapia strain, Oreochromis niloticus; a total of 10,065 fish with pedigree and phenotypic information) were tested in pond and cage culture environments to determine genotype by production environment interaction between both environments in Malaysia. Live weight (selected trait), standard length, body depth and width were recorded. A bivariate animal model was used to estimate variance and covariance components, whereby the homologous body traits in pond and cage environments were treated as genetically distinct traits. The heritabilities estimated for these body traits ranged from 0.19 to 0.40 in the pond environment, and from 0.23 to 0.34 in the cage environment. Across all traits the maternal common environmental effects ranged from 0.14 to 0.26 and were greater for the pond than for the cage environment. The genetic correlations between the pond and cage environments were 0.73±0.09 for live weight, 0.81±0.09 for standard length, 0.78±0.10 for body depth, and 0.85±0.13 for body width. Coupled with the total selection responses for live weight after two generations of selection, being 35% for the pond environment and 45% for the cage environment, we concluded that genotype by environment interaction for GIFT strain between pond and cage environments was not important. Hence, it would not be necessary to have two separate selective breeding programs for the GIFT strain in Malaysia. [Copyright &y& Elsevier]