Changes in heterosis under within-line selection or reciprocal recurrent selection: an experiment on early egg production in Japanese quail

In much animal production, commercial animals are crossbreds from closed lines or breeds under long-term directional selection. Therefore it is desirable to be able to predict heterosis gains over the generations as it is done for genetic progress under within-line selection. However, heterosis is the phenotypic expression of a complex phenomenon which may involve several types of genetic effects like dominance and epistasis. In animal breeding, basic quantitative genetics theory indicates that heterosis should be proportional to (squared) differences in gene frequency between populations (e.g. F alconer and M ac K ay 1996), and it has been found approximately correct, so it is commonly used for planning crosses. Under that type of heterosis, however, selection towards the same objective in two populations should bring gene frequencies closer, and therefore it should eventually decrease heterosis. On the other hand, reciprocal recurrent selection designed to increase genetic distance between lines should eventually achieve maximum heterosis (O llivier 1982). Some experiments reviewed by brun (1982) have already compared genetic progress under within-line and reciprocal recurrent selection, but they did not focus on comparing the trend of heterosis with generations between the two selection methods. Also, heterosis was monitored periodically in some selection experiments on poultry, and results were reviewed by F airfull (1990). They were somewhat contradictory, but they generally failed to relate genetic progress to loss of heterosis under within-line selection. Moreover, in commercial production, as purebreds and crossbreds are not contemporaries and are generally maintained under very different management systems, estimations of heterosis and of the evolution of crossbred advantage over the generations may be difficult to obtain. Using the Japanese quail as an experimental animal, the present work was initiated specifically to follow the changes in heterosis brought about by selection for a single heterotic trait, early egg production (M invielle et al. 1995). For that purpose, two selection methods expected to have opposite effects on heterosis, directional within-line (or individual) selection and reciprocal recurrent selection, were applied for 13 generations in four quail lines started from two different origins, and trends of heterosis in the selected character and in weight and egg traits were evaluated.     

Inbreeding and heterosis effects on quantitative traits in a White Leghorn population under long-term reciprocal recurrent selection

1. Inbreeding and heterosis effects for quantitative traits were estimated in two White Leghorn lines selected with reciprocal recurrent selection (RRS) since 1950. 2. Pedigreed progeny were produced from full-sib, half-sib and unrelated pure line as well as reciprocal cross line matings to estimate inbreeding and heterosis effects "within sires". 3. Inbreeding effects estimated as linear regressions agreed well with estimates considering inbreeding as fixed effect. The inbreeding depression per 10% inbreeding was highest for hatchability (6-7%), intermediate for production-related traits (3%), and about 1% for shell quality, body weight and egg weight. 4. Heterosis effects were estimated by comparing pure line and cross line progeny of the same sires. 5. Results indicate considerably less heterosis for egg production than found earlier, which is interpreted as a consequence of pure line selection.     

A new explanation for egg production heterosis in grosses between white leghorns and australorps

1. Present population genetics theory treats heterosis as the reversal of inbreeding depression. This theory is not generally applicable to heterosis occurring in crosses between different breeds or between unrelated strains of the same breed.

2. Heterosis occurring in such crosses is explained in terms of different complementary epistatic gene pathways homozygous in the parental breeds.

3. In the absence of linkage, these epistatic gene pathways segregate in the second and subsequent cross‐bred generations leading to the loss of the heterosis observed in the first cross‐bred generation.     

Long-term goose breeding for egg production and crammed liver weight

1. Results of an 8-year (1981 to 1988) period of breeding geese for egg production and crammed liver weight, including phenotypic and/or genetic parameters for various traits (1982 to 1985), as well as line tests (1987 to 1988), are summarised for two lines. 2. The regressed annual genetic gains over years were 2.7 eggs and 30.8 g crammed liver. However, there was a decline in the rate of genetic progress after 4 years of selection. 3. Heritability estimates were found to be relatively high for most traits, whereas phenotypic and genetic correlation coefficients between traits were rather low, as would be expected from lines not previously subjected to an intense selection programme. 4. Phenotypic correlation coefficients between part-period records and full-period egg production, suggest that 3-month (October to December) records may be adequate to identify most of the best first-year layers. However, sexual maturity should be treated as a separate trait. 5. The cross between the 'Grey' (male) line, superior in crammed liver weight, and the 'White' (female) line, excelling in egg production, seems to be superior to the pure lines, in a fully-integrated enterprise.     

Maternal effects and heterosis for growth in reciprocal cross populations of chickens

SUMMARY: Two lines of chickens differing greatly (6- to 8-fold) in 8-week body weight due to divergent selection for this trait were crossed reciprocally from generations 29 through 36. The crosses showed two consistent characteristics: large maternal effects and no positive heterosis. ZUSAMMENFASSUNG: Maternalwirkungen und Heterosis für Wachstum in reziproken Hühnerkreuzungen Zwei im Hinblick auf 8-Wochen-Gewicht sehr stark unterschiedliche (6- bis 8fach) Linien wurden reziprok in den Generationen 29-36 des divergenten Selektionsversuches gekreuzt. Die Kreuzungen zeigen zwei konsistente Ph?nomene: gro?e Maternalwirkungen und keine positive Heterosis.     

Heterosis in body weight related to growth performance of parental lines of Japanese quail and to heterosis in lay

1. Three outbred lines of Japanese quail and their reciprocal crosses were used. The lines differed in mature body weight or in the shape of the growth curve. Growth was described by body weight (BW) at 0, 4, 7, 14, 21, 28, 35, 42, 48, 56, 63 and 70 d of age and expressed by the parameters of Richards' function. Dickerson's model was used to estimate direct genetic, maternal genetic and direct heterotic effects. 2. The magnitude of BW heterosis was not constant during postnatal growth, it showed a different curvilinear age-trend for each hybrid combination. 3. The age-trend of BW heterosis resulted from the change of the shape of the growth curve. 4. The age-trend of BW heterosis and its maximum magnitude were associated with differences in the growth pattern of parental lines. 5. The heterosis at the inflection point was accompanied by heterosis in egg number.     

Divergent selection for shape of growth curve in Japanese quail. 7. Effect of egg storage at high temperature on embryo development and hatchability

1. Hatching time, hatchability of fertile eggs and embryo mortality in relation to (1) physical quality of fresh eggs and (2) embryonic development during storage and incubation periods were analysed after egg storage for 1, 5 or 10 d at 30°C in the meat-type lines of Japanese quail, HG and LG, divergently selected for high and low relative weight gain between 11 and 28 d of age, respectively, and constant body weight at 49 d of age.

2. In both lines, the increase of egg storage temperature from 12°C (standard level) to 30°C increased the egg weight loss during storage, shortened the incubation period and reduced the hatching success.

3. Similar to standard egg storage temperature, LG quail hatched earlier than HG quail after egg storage at 30°C and early and late mortality of both lines increased with a prolonged period of egg storage. In contrast to the standard egg storage conditions, no line differences in hatchability were observed.

4. The results did not identify a relationship between the decrease in hatchability or embryo viability and line differences in external egg parameters as well as any important role of undesirable changes induced by a high storage temperature on albumen viscosity.

5. The pattern of embryonic death, low developmental rate of embryos and a dichotomy between the development of the extra-embryonic vascular system and the embryo itself during egg storage at high temperature implied that an insufficient nutrient supply in consequence of developmental delay could represent a key factor in increasing early and late embryo mortality.     

Influence of stocking density and layer age on production traits and egg quality in Japanese quail

1. Japanese quail hens were housed from 6 to 26 weeks of age in cages providing areas of 150, 180, 210 and 240 cm²/bird.

2. Body weight gain, age at 50% egg production, mortality, hen‐day egg production and food conversion values showed significant improvement with proportionate increase in cage space per layer.

3. Egg weight gradually increased with age but shell thickness was influenced neither by age of the hen nor by stocking density.

4. Yolk index and colour were superior in the lowest stocking density (more cage space) group; other egg quality traits and egg weight were not influenced by stocking density.

5. The albumen index, internal quality unit, yolk index and yolk colour values increased with age.     

Components of heterosis for growth traits and litter size in line crosses of mice after long-term selection

Strains selected for 54 generations for large 8-week weight (N8, S8), for small weight (N6, S6), for high 3–5-week gain and low 8-week weight (N1) as well as unselected randomly mated control strains (N9, S9) were crossed, and F ₁, F ₂ and both back crosses created. N strains are derived from a NMRI base, S strains from a synthetic four-way cross among inbred lines. Heterosis for 8-week weight (8-ww) was some 6%, but 30% for 3–5-week gain and it was on average negative (22%) for 5–8-week gain. When epistatic effects were taken into account, it appeared that heterosis for 8-ww was largely due to beneficial effects of non-parental gene combinations, i.e. additive × additive epistatic effects were negative. These non-parental combinations neutralized the mostly negative dominance effects. The latter were mostly positive for early gain but in all 9 line crosses negative for late gain. The digenic effects of the non-parental origin were not large enough to balance the negative dominance effects for late gain, so that heterosis was negative. It appears therefore that early and late gain are affected by different sets of genes. Maternal additive effects on 8-ww and early gain are smaller than direct additive effects but mostly of similar sign. For late gain there appears to be no connection with direct additive effects. Direct litter heterosis was almost 50% but much of this was due to positively acting recombinational gene combinations, while direct litter dominance was mostly negative. Maternal additive effects on litter size differed depending on whether they were estimated from dams with crossbred or with purebred litter. Heterosis was small in crosses between control strains. Heterosis caused by recombinant gene pairs should be amenable to improvement by selection.     

Genetic study of embryonic mortality in White Leghorn lines selected for egg production traits

The present study compares embryonic mortality between lines selected for different production traits, assesses the effects of inbreeding of the hen and embryo on embryonic mortality, and estimates genetic parameters of embryonic mortality. The experiment covered 10 generations of selection for increased egg number (EN), egg weight (EW), egg mass (EM) and a control line (C). The data included age at 1st egg, egg number and egg weight. Percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent dead chick at hatch (PDH) were also recorded for the selected parents. PDH was higher in the selected lines than in the control line. Among the selected lines, the EW line had the highest embryonic mortality. Inbreeding of the hen and embryo had no significant effect on PDH in any of the lines. Estimates of heritability for PDH were 0.10+/-0.05, 0.02+/-0.02, 0.03+/-0.02 and 0.02+/-0.02 for lines EN, EW, EM and C, respectively. There was a positive genetic correlation between egg weight and PDH in line EW indicating that selection for increased egg weight was associated with high embryonic mortality. A negative genetic correlation between PDH and reproductive traits in line EN was observed, which is favourable.     

Lamb production and its components in pure breeds and composite lines. II. Breed effects and heterosis

Ewe performance was compared for five pure breeds of sheep (Finnsheep, F; Rambouillet, R; Dorset, D; Targhee, T; Suffolk, S) and the crosses in development of two maternal composite lines (C1 = 1/2F1/4R1/4D and C2 = 1/2F1/4T1/4S). The data involved 10,959 breeding season records of 4,219 ewes by 412 sires. Ewe production and the components (fertility, litter size, neonatal and preweaning lamb survival and mean lamb weaning weight) were adjusted for age and standardized across season of lambing and years. The D and F ewes produced more weight of lamb/ewe exposed than R, S and T ewes because of higher D and F fertility, higher D lamb survival and larger F litters. First cross and inter se generations of C1 and C2 ewes averaged 17 to 27% higher fertility than the parental mean. Litter size averaged about one lamb higher for F than for other pure breeds, but only slightly higher for C1 and C2 than for the mean of F and other breeds. Lower neonatal survival for F than for other breeds and crosses was associated with the larger F litters and with 2 to 8% positive heterosis in the crosses. Preweaning survival of suckled and nursery lambs was low for F and S and positive heterosis ranged from 9 to 19% in crosses. Mean lamb weaning weights were highest for S, lowest for F, with little heterosis in crosses. Crossbred ewes reared .3 to .4 more lambs than mean for parental pure breeds. Heterosis in C1 and C2 ranged from 11 to 28% for lambs born, 27 to 43% for lambs weaned and 29 to 44% for weight of lamb weaned/ewe exposed. Decline in heterosis with inter se mating of crosses was no greater than expected from the reduction in predicted heterozygosity.     

Inbreeding and inbreeding depression on reproduction and production traits of White Leghorn lines selected for egg production traits.

1. The rate of inbreeding and its effect on reproduction and egg production traits were studied in White Leghorn lines selected for egg production traits. The experiment was carried out for 10 generations in a control line (C) and in lines selected for increased egg number (EN), egg weight (EW) and egg mass (EM). 2. Data were available on reproduction traits, such as percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent hatched of total eggs set (PHT), and on egg production traits such as age at 1st egg (AFE), egg number and egg weight. 3. The rate of increase in average inbreeding per generation was 1.50, 1.24, 1.14 and 0.18% for the line EN, EW, EM and C, respectively. The effect of inbreeding on reproduction and production traits was estimated by including the inbreeding coefficient of the hen (Fh), embryo (Fe) and mate (Fs) as a partial linear regression in the model. 4. There was a significant effect of inbreeding on reproduction traits in line EW attributable to the inbreeding of the hen, embryo and mate. No such effect was observed in the other lines. 5. In all lines inbreeding tended to reduce egg number and delay sexual maturity. In general, all lines reacted differently to inbreeding.     

鸡群产蛋率下降或长期不升的原因及防治

在养鸡生产中经常可见到以下三种情况：一是鸡群产蛋率上升到９０％以上后，突然下降到６０％以下；二是产蛋率上升到９０％以上后，逐渐下降到８０％左右长期不再上升；三是产蛋率长期低于８０％。上述情况经临床诊断无典型症状。这样的病鸡群在养鸡生产中经常可见，因缺乏典型的临床症状和病理变化，给诊断和治疗带来一些困难，直接影响养鸡的经济效益。１原因分析我们在长期工作实践中发现，这样的病鸡群常由一种非典型疾病慢性感染或由几种非典型疾病混合感染，或由多种因素混合并存而引起，归纳起来有病理学、管理学、营养学等方面的原…     

Association of endogenous viral genes with quantitative traits in chickens selected for high egg production and susceptibility or resistance to Marek's disease

1. The association of endogenous viral ( ev ) genes with quantitative traits in 2 genetically distinct sets of White Leghorn strains were investigated. Strain S had been selected for susceptibility to Marek's disease (MD) whereas strain K had been selected for resistance to MD and high egg production and egg weight. 2. In all, 8 ev genes were typed. Ev 10, ev 19 and ' newB ' occurred exclusively in strain S, ' newA ' occurred only in strain K, and ev1 , ev3 , ev6 and ev8 occurred in both strains. 3. Whereas ev6 and ev8 were associated with reduction in egg production rate in strain S, in strain K, the presence of ev3 was associated with increased group specific antigen. 4. The genetic background of the chicken strain may play a role in the way certain ev genes affect traits. 5. It was thought that the position of ev genes on the chromosome may be important and their association with traits of economic importance make them potential genetic markers for uncovering quantitative trait loci.     

Effects of poppy seed meal on egg production and hatching results in quail (Coturnix coturnix japonica)

This study was carried out to determine the effects of poppy seed meal (PSM) on the egg production and hatching of quail. Two experiments were undertaken. In the first experiment, 240 quail, reared under the same conditions, were divided into four groups of 60 birds each (which were, in turn, subdivided into four subgroups of 15 each for experimental replicates). The first, second, and third experimental groups were fed ratios containing 5%, 15%, and 25% PSM, respectively, over 12 weeks. The control group received no PSM. Feed and water were supplied ad libitum and artificial light was provided for 16 h a day. During the first experiment, egg production, egg weight, and feed conversion ratio (FCR) were measured. In the second experiment, 240 female and 48 male quail were divided into four groups, as in the preceding experiment, and the birds were housed in cages at a ratio of one male to five females. The diets and their presentation to the quails were the same as in the preceding experiment. The results of the two experiments showed that the addition of PSM to the feed ratios increased egg production, feed consumption, and feed conversion per kg of eggs and per dozen eggs. However, PSM addition at all percentages significantly reduced (P<0.001) hatchability, mainly because of increased infertility and embryonic deaths.     

Illuminance,sexual maturation,and early egg production in female broiler breeders

1. Broiler breeders were reared at an initial illuminance of 13, 21 or 44 lux and transferred at 20 weeks and a mean body weight of 2.06 kg to floor pens at 25, 55 or 71 lux, or to individual cages at various intensities between 3 and 138 lux.

2. Rate of sexual maturation was not significantly affected by the light intensity experienced during the rearing period, but was progressively accelerated by the provision of a brighter illuminance after 20 weeks, up to a ceiling of about 14 lux. There was no interaction between the pre- and post-20-week illuminance.

3. Cumulative egg numbers to 39 weeks were unaffected by illuminance in the rearing period, positively correlated with illuminance post 20 weeks up to an asymptote at about 8 lux, and highly correlated with age at sexual maturity. Peak rate of lay was both delayed and depressed at 3 lux.

4. It is concluded that the minimum light intensity required at bird-head height to achieve satisfactory photostimulation and an optimal peak rate of lay in broiler breeders is 10 lux, but that a higher illuminance would be prudent for broiler breeders kept in floor pen facilities to maximise nest-box usage.     

Automated early detection of drops in commercial egg production using neural networks

1. The purpose of this work was to support decision-making in poultry farms by performing automatic early detection of anomalies in egg production.

2. Unprocessed data were collected from a commercial egg farm on a daily basis over 7 years. Records from a total of 24 flocks, each with approximately 20 000 laying hens, were studied.

3. Other similar works have required a prior feature extraction by a poultry expert, and this method is dependent on time and expert knowledge.

4. The present approach reduces the dependency on time and expert knowledge because of the automatic selection of relevant features and the use of artificial neural networks capable of cost-sensitive learning.

5. The optimum configuration of features and parameters in the proposed model was evaluated on unseen test data obtained by a repeated cross-validation technique.

6. The accuracy, sensitivity, specificity and positive predictive value are presented and discussed at 5 forecasting intervals. The accuracy of the proposed model was 0.9896 for the day before a problem occurs.     

Effect of rooibos tea (Aspalathus linearis) on Japanese quail growth, egg production and plasma metabolites

1. Birds have been proposed as a suitable model for studies on ageing because of their long life in comparison with similar-sized mammals. However, some weak fliers, such as Galliformes, are the exception to this rule. The aim of the present study was to determine the effects of the treatment with rooibos tea (Aspalathus linearis), a natural source of flavonoid antioxidants and compounds with phyto-oestrogenic activity, on postnatal development and egg production of aged Japanese quail (Coturnix coturnix japonica). 2. Substitution of drinking water with traditional rooibos tea or diet supplementation with ground rooibos tea affected body weight of Japanese quail up to 100 d of age. The body weight of males drinking rooibos tea or eating rooibos-supplemented food decreased significantly. There was a trend toward increased body weight of tea drinking females and a significant increase in the body weight of hens fed the rooibos-supplemented diet. Although rooibos treatment did not significantly increase egg production in young hens, the decrease in egg production of rooibos-treated aged hens (360 d of age) was significantly reduced, regardless of the egg production levels (high - 80%; low - 20%) before the treatment. 3. The results suggest that treatment with rooibos tea positively affected body weight and egg production in quail hens and prolonged the productive period of aged animals. Further studies would be needed to address the question whether these effects are due to the antioxidant or phyto-oestrogenic activities of rooibos.     

Plasma glucose-insulin relationship in chicken lines selected for high or low fasting glycaemia

1. Selected Fat or Lean chickens differ in their plasma glucose insulin relationship: in the fed or fasted state, Fat chickens have a lower glycaemia associated with normal or higher insulinaemia, depending upon the difference in glycaemia. 2. Conversely, chickens selected for low fasting glycaemia (LG) are fattier than their counterparts selected for high fasting glycaemia (HG), although the divergence in fat content is lower than in the Fat-Lean model. 3. The plasma glucose insulin relationship has been investigated in males of the HG and LG lines in the F4 and F5 generations. 4. A difference in glycaemia is suggested during embryonic development and was present at hatching and later on in the fasted or the fed state; insulinaemia did not differ. 5. During refeeding after an overnight fast, glycaemia differed between lines (except at intermediate times); cumulative food intake and insulinaemia were similar. 6. During a glucose tolerance test, glucose disposal rate and insulinaemia were rather similar. 7. Exogenous insulin exerted a very similar hypoglycaemic effect in both lines. 8. Other variables (body temperature, plasma concentrations of potassium and alpha NH2-non protein nitrogen) did not differ between HG and LG chickens. 9. In conclusion, HG and LG chickens do not exhibit any differences in glucose disposal rate, insulinaemia (in various nutritional conditions) or sensitivity to exogenous insulin, which contrasts with Fat or Lean chickens and may explain why HG and LG chickens have diverged to a lesser extent in fat content.