Heterosis for egg production in white leghorn Australorp crosses

1. Australorp and White Leghorn pullets were compared with their F_l, F₂ and F₃ crossbred offspring for a range of egg production variables.

2. The substantial hybrid vigour for efficiency of food conversion, hen‐housed egg production, hen‐day egg production and total egg mass of the F₁ crossbred populations was lost in the F₂ and F₃ crossbred populations.     

Survey of line crosses in a Brown Leghorn flock. II. Relations of hatched chick weight of egg weight in inbred lines and their crosses

A preliminary study of the hatching weight of chicks of two pairs of pure lines and their reciprocal crosses shows that the relationship of net chick weight, excluding yolk sac, to egg weight, is constant for the lines ; although this is not so for an exceptional line selected for small size, but not examined in detail. Chicks from one pair of reciprocal matings are relatively larger than representatives of their parent lines, but those from the other are not.

Detailed examination of the amount of egg material used to form the chick shows that two lines which produce the same relative size of chick do so because one line uses more of the egg, but utilises it less efficiently, than the other. Further, the different genotypes take different times to hatch, the hybrids being earlier than their corresponding dam line. There are differences between reciprocals in hatching time and in efficiency of egg utilisation, but they tend to be confounded. There is no evidence of an optimal egg size for relative chick weight either within lines or within hybrid groups.     

Defective egg production in a population of dwarf white leghorns 1

1. The incidence of defective eggs during the first 60 weeks of age increased with time due to significant increases in broken and membranous eggs in a population of dwarf White Leghorn hens.

2. The production of double‐yolked eggs/100 hen d, high during the initial weeks of lay, rapidly declined and disappeared by 30 weeks of age.

3. The frequencies of broken, membranous and soft‐shelled eggs were significantly correlated with each other and with the frequency of multiple daily ovulations indicating a common aetiology for these defective egg types.

4. Double‐yolked eggs were produced by the heavier, earlier‐maturing pullets in the population.

5. Normal egg production in dwarf White Leghorns may be enhanced by reducing the incidence of defective eggs.     

Ovum formation and multiple ovulation in lines of white Plymouth Rocks and their crosses

The production of double-yolked eggs and the duration of the rapid growth phase of yolks were measured in parental lines of White Plymouth Rock pullets and their crosses over 30 d, commencing with the day of first egg. Significant differences were found between mating combinations in the incidence of multiple-yolked eggs, but not in the period of rapid yolk growth. Heterosis and recombination effects for multiple ovulation were respectively -9% and -66% of the mean, while the corresponding values for the period required for rapid yolk growth were -1% and -5%. Three double-yolked eggs were observed containing yolks which differed by 3 d in their periods of rapid growth. Hypotheses are were presented for the origin of double-yolked eggs.     

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.     

Heterosis, maternal and direct effects for postweaning growth traits and carcass performance in rabbit crosses

SUMMARY: A crossbreeding experiment was carried out in Egypt using a local breed (Baladi Red, BR) and New Zealand White (NZ) to estimate direct heterosis, maternal additive effects and direct sire effects on some growth and carcass traits in rabbits. Data of body weight (at 5, 6, 8, 10, 12 weeks) and daily gains (at intervals of 5-6, 6-8, 8-10, and 10-12 weeks) on 2153 weaned rabbits were collected. Carcass performance at 12 weeks of age (weight and percentages of carcass, giblets, head, fur, blood and viscera) on 213 male rabbits was evaluated. Estimates of coefficients of variation (CV) for most growth and carcass traits were high and ranged from 10.0 to 40.2%. Sire-breed was of considerable importance in the variation of growth traits and some carcass traits, while dam-breed contributed little. Sire-breed × dam-breed interaction affected (P<0.01 or P<0.001) most body weights and gains studied, while it contributed little to the variation of carcass traits. The purebred NZ resulted in rabbits with heavier weights and carcass and with lighter non-edible carcass (blood and viscera) compared to the BR. Heterosis percentages for most growth traits were significant and ranged from 2.5% to 5.0% for body weights and from 0.7% to 9.5% for daily gains. Insignificant positive direct heterosis was observed for most carcass traits. Crossbred rabbits from NZ sires with BR dams were superior to from the reciprocals. Maternal-breed effects on most weights and gains were insignificant, while sire-breed contrasts for some weights and gains proved significant. Postweaning growth and carcass performances of BR-mothered rabbits generally surpassed the NZ mothered, while NZ-sired rabbits were superior at later ages. High edible carcass was observed for BR-sired rabbits, while more non-edible carcass wastes (blood and viscera) for NZ-sired rabbits. Maternal-breed effects appeared to be less important than paternal-breed effects in influencing most weights, gains and carcass traits studied. ZUSAMMENFASSUNG: Heterosis, maternale und direkte Wirkungen bei Wachstums- und Schlachtk?rpermerkmalen in Kaninchenkreuzungen Der Kreuzungsversuch wurde mit lokalen ?gyptischen Rassen (BR) und Neuseeland Wei?en (NZ) zur Sch?tzung direkter Heterosis, maternaler additiver Wirkungen, direkter Vater-Wirkung auf einige Wachstums- und Schlachtk?rpermerkmale von Kaninchen durchgeführt. Angaben über K?rpergewicht (5, 6, 8, 10, 12 Wochen) und Zuwachs (Intervalle 5 bis 6, 6 bis 8, 8 bis 10, 10 bis 12 Wochen) wurden von 2153 abgesetzten Kaninchen gewonnen. Die Schlachtk?rperleistungen bei 12 Wochen Alter (Gewicht und Anteil von Schlachtk?rper, Kopf, Pelz, Blut und Innereien) stammen von 213 m?nnlichen Kaninchen. Sch?tzungen der Variationskoeffizenten (CV) für meiste Wachstums- und Schlachtk?rpermerkmale waren hoch und bewegten sich zwischen 10 und 40,2%. Vaterrasse hatte erheblichen Einflu? auf Unterschiede in Wachstumsrate und einige Schlachtk?rpermerkmale, w?hrend die Mutterrasse weniger beigetragen hat. Interaktion zwischen beiden beeinflu?te die meisten K?rpergewichts- und Zuwacnsleistungen, w?hrend sie wenig zur Variabilit?t der Schlachtk?rpermerkmale beigetragen hat. Reinrassige NZ waren schwerer und hatten weniger nicht nutzbare Schlachtk?rperteile (Blut und Eingeweide) verglichen mit BR. Heterosis-Prozente für die meisten Wachstumsmerkmale waren signifikant und schwankten zwischen 2,5 und 5% für K?rpergewicht, 0,7 bis 9,5% für Zuwachs. Insignifikante positive direkte Heterosis wurde für die meisten Schlachtk?rpermerkmale beobachtet. Kreuzungskaninchen von NZ V?tern waren den reziproken überlegen. Maternale Wirkungen auf meiste Gewichtsmerkmale waren insignifikant, w?hrend Vaterrassenkontraste hierfür signifikant waren. Zuwachs- und Schlachtk?rperleistung von BR ges?ugten Kaninchen haben im allgemeinen die von NZ ges?ugten übertroffen, w?hrend von NZ B?cken gezeugte in sp?teren Altersabschnitten überlegen waren. Hohe Werte für Schlachtk?rper wurden für BR ges?ugte Kaninchen gefunden, w?hrend mehr nicht verzehrbare Abf?lle (Blut und Eingeweide) bei NZ gezeugten vorhanden war. Maternale Rassenwirkungen schienen weniger wichtig als paternale zu sein.     

不同玉米自交系耐深播性评价及遗传多样性分析

为了筛选玉米耐深播鉴定指标,探讨耐深播综合评价方法并挖掘耐深播种质类群,本研究采用PVC管盆栽试验,在3,15和20cm三种深播处理下,测定各自交系的出苗率、中胚轴长、胚芽鞘长、中胚轴与胚芽鞘之和、苗长、根长,利用隶属函数法综合评价51份玉米自交系的耐深播性,并用70对SSR标记对其遗传多样性进行了分析。结果表明,随着播种深度的增加,各自交系的中胚轴长、胚芽鞘长、中胚轴与胚芽鞘之和大体呈增加趋势,而出苗率降低,苗长及根长先下降后增加。不同播深条件下,玉米自交系幼苗性状的方差分析表明,出苗率、中胚轴长、胚芽鞘长、中胚轴与胚芽鞘之和、苗长、根长与自交系间的差异极显著;同时5个性状(出苗率、中胚轴长、胚芽鞘长、中胚轴与胚芽鞘之和、苗长)与播深以及5个性状与自交系和播深间相互作用的差异极显著;同时根长与播深之间的差异达到显著水平,但是根长与自交系和播深间相互作用的差异不显著。另外,不同播深处理下各性状的相关分析表明,在3cm播深条件下的出苗率与中胚轴、中胚轴和胚芽鞘之和、苗长3个表型性状呈正相关;而在15和20cm播深下,出苗率与中胚轴长、胚芽鞘长、中胚轴与胚芽鞘之和、苗长、根长都极显著正相关。利用隶属函数法筛选出了6份强耐深播系,11份中等耐深播系。同时,利用70对SSR标记共检测出222个等位基因,平均3.17个,多态性信息量平均为0.579,幅度为0.265~0.801,遗传相似系数幅度为0.496~0.946,并将供试自交系划分成两大优势群或6个亚群,其中四平头亚群(SPT)、兰卡斯特亚群(Lan)和旅大红骨亚群(LRC)的耐深播性较强,出苗率、中胚轴长、胚芽鞘长、中胚轴与胚芽鞘之和、苗长、根长表现良好,含有较多的强或中等耐深播系,是重要的耐深播种质类群。     

Food consumption records for the genetic improvement of income over food costs in laying flocks of white leghorns

1. A study of genetic parameters of egg mass based on the weights of all eggs laid, individual food consumption, body weight and age at first egg was made. Data from three populations differing in average egg weight were available over two production periods, from 20 to 40 and from 40 to 60 weeks of age, respectively.

2. Selection indexes designed to maximise income over food costs (IOFC) were used to evaluate the usefulness of food consumption data for the genetic improvement of laying flocks.

3. Given reliable estimates correlating food consumption to egg mass, body weights and age at first egg it is possible to construct highly efficient selection indexes for genetic improvement of IOFC without the direct use of food consumption data.

4. Selection for genetic gains in egg mass appears to be the most important factor for genetic improvement of IOFC. Correlated increases in egg weight were observed for two of the populations.

5. Body weights showed very small and inconsistent genetic responses under index selection suggesting that a reduction in body weight need not be necessary for more efficient egg production.

6. Indexes which showed greatest genetic improvement also resulted in an increase of food consumption. Thus genetic efficiency in egg laying flocks would be achieved by increasing egg mass through earlier sexual maturity, larger eggs and higher production rates with increased food consumption and only slight, if any, reduction in body size.

7. Estimates of heritabilities and genetic correlations indicate that food consumption measurements can be based on partial records; high heritabilities were found for egg mass and food consumption measurements in both early (20 to 40 weeks) as well as late (40 to 60 weeks) production periods.     

Heterosis, direct and maternal genetic effects on semen quality traits of rabbits

A complete diallel cross involving two rabbit sire lines (C and R) was carried out to estimate the crossbreeding genetic parameters of seminal traits. 2140 ejaculates from 153 males were analyzed. The traits studied were: presence of gel plugs (G), urine (U), and calcium carbonate deposits (CC), number of useful ejaculates (UE), pH, volume (V), mass and individual motility (Mm, Mi), useful Mi (UM), concentration (Cn), number of spermatozoa per ejaculate (TSE), percentage of viable spermatozoa (Vi), spermatozoa with normal apical ridge (NAR), normal spermatozoa (Nr), spermatozoa with morphological abnormalities of head (H), neck-midpiece (Nm), and tail (T), presence of proximal and distal cytoplasmic droplet (Dp, Dd).

Estimates of heterosis, direct and maternal genetic effects were obtained from the solutions of the mixed model. There were major differences in direct genetic effects between lines, which were favourable to line C for Cn and TSE, and unfavourable for CC, Nm and Dp. Smaller differences were also observed in Vi and NAR favourable to line R. Differences between lines with respect to the maternal genetic effects were relevant and favourable to line C for V and to line R for U, UM, Cn, TSE, Nm, Mi, and Mm. Individual heterosis was high for Dp and Dd.     

Genetic effects of ageing on fertility and hatchability in the first laying cycle of three white leghorn strains and their two-way crosses

1. Fertility and hatchability of 3 White Leghorn strains and their 2-way crosses were examined in the 1st laying cycle to evaluate the effects of ageing on mean heterosis, reciprocal effects, additive (A), Z-chromosomne (Z) and heterotic effects (H), as well as on their variances. 2. Fertility and hatchability were evaluated at 37, 47 and 70 weeks of age for hens housed 1 per cage in a randomised block design. The mean heterosis was significant over time and increased with advancing age for both traits. Reciprocal effects were not significant across periods and did not show a consistent trend with age. 3. The pattern of age changes in A, Z and H effects varied among strains, indicating genotypic differences in response to ageing. The additive, heterotic, environmental and phenotypic variances increased at the end of the cycle for both traits, except for the additive variance of hatchability, which increased until 47 weeks of age but declined thereafter. 4. Heritability increased with age for fertility but did not show a consistent pattern across the cycle for hatchability. Genetic variance for fertility and hatchability increased at the end of the cycle, stggesting that improvement in performance during the 1st production cycle of layers could be achieved by selecting animals at older ages.     

Heterosis and recombination effects in Hampshire and Landrace swine: I. Maternal traits.

Hampshire and Landrace sows and crossbreds of the two breeds were used to determine heterosis and recombination effects for milk production, milk composition, and litter traits at birth and d 21. Twelve mating types were represented in this study: two purebred, two F1, two F2, two F3, and four backcross. Information was gathered on a total of 358 litters over four farrowing seasons. Milk production was measured at d 10 and 20 of litter age according to the weigh-suckle-weigh procedure. Milk samples were collected at d 10 and 20 of litter age and evaluated for percentages of fat (PCFA), protein (PCPR), lactose (PCLA), and solids-not-fat (PCSN). The model used to evaluate litter traits at birth included main effects of mating type, parity, and farrowing season. The model used for milk production and milk composition traits included these main effects and number of pigs nursed as a covariate. Estimates of maternal genetic effects showed that Landrace females were superior to Hampshire females for number born (NB), number born alive (NBA), litter birth weight (LBW), adjusted 21-d litter weight (ALW), and milk production at d 10 of litter age (WT10). Hampshires were superior to Landrace for PCPR at d 10 of litter age and PCSN at d 10 and 20 of litter age. Heterosis effects were significant (P less than .05) for NBA (.97) and LBW (1.46 kg). Maternal heterosis effects were significant for LBW (3.94 kg; P less than .01). Epistatic recombination losses in the offspring were significant for LBW (6.80 kg; P less than .05). Differences in maternal performance of reciprocal F1 dams were generally not significant. Heterosis and recombination effects were not significant for milk production or milk composition.     

蛋鸡饲料利用率和孵化率的杂种优势

本文报道了蛋鸡饲料利用率及其相关性状和孵化率的杂种优势。材料来源于一个正反反复选择饲料利用率的试验,8个世代共有蛋鸡13408只。试验组(括弧里为对照组)各性状的平均杂种优势分别为:饲料利用率-2.0％ (-0.8％)、饲料消耗量2.9％(3.0％)、产蛋量4.5％(3.6％)、产蛋率2.9％(3.1)、蛋重1.9％(0.8％)、试验期初体重3.7％ (4.5％)、试验期末体重4.3％(5.0％)、受精率2.1％(-0.2％)、受精蛋孵化率15.0％ (4.5％)和入孵蛋孵化率10.2％(7.6％)。正反交组合的杂种优势不同,这可能是由性连锁导致的。     

Heterosis retained in advanced generations of crosses among Angus and Hereford cattle

Data from 1,909 purebred, F1, backcross and F2 and F3 inter se combinations of Angus and Hereford were used to estimate average individual, maternal and grandmaternal genetic effects, individual and maternal heterosis, dominance and epistatic genetic effects. Models for evaluating heterosis and epistatic or recombination effects were discussed. Average individual effects indicate that Angus, compared with Hereford, had calves that were born earlier, had lighter birth weights, lower pre- and postweaning gains and lower pregnancy rates. Angus also produced lighter weight carcasses with more fat cover and marbling. Maternal effects of Angus were in the direction of reduced birth weight, greater calving ease, higher preweaning but lower postweaning growth rate and increased fatness when contrasted with Hereford. There was a tendency for opposite direction of maternal and grandmaternal effects for traits influenced by preweaning maternal environment. When additive X additive effects were ignored, total heterosis was significant for earlier day born, heavier birth weight, preweaning and postweaning gain, and heavier and fatter carcasses. Heterosis retained in F3 inter se vs F1 generation crosses indicated that net epistatic effects were relatively negligible for date of calving, birth weight, weaning gain and fat cover. There was a greater reduction of heterosis effects than expected from dominance alone for survival, pregnancy and marbling score. Loss of heterosis in F3 was less than expected for postweaning gain, carcass weight and rib eye area. Except for survival, pregnancy and marbling, these deviations from dominance expectations, or lack of them, are favorable for F3 composite populations.     

Heterosis effects in a black and white dairy cattle population under different production environments

The effect of the environmental level of production (ENV) on the expression of heterosis for 305-day milk, fat, protein, and fat plus protein (FP) yields, lactation average somatic cell score (LSCS), and age at first calving (AFC) was investigated in first lactation Black and White dairy cows in the Netherlands, and officially enrolled in the Dutch herd-book. Holstein Friesian (HF), Dutch Friesian (DF), and first generation (F₁) crosses obtained from the mating of HF sires and DF dams (HD) were involved in the study, and data from animals with a calving date between 1990 and 2000 were used. A total of 22,930 cows with production and AFC information distributed in 3549 herds and 11,055 cows with LSCS information distributed in 2071 herds, were available. Adjusted lactation yield of milk for each herd was obtained using a model that accounted for fixed effects of herd, year and month of calving, genotype, and AFC. The overall mean of all adjusted data was computed, and 3 ENV were defined on the basis of the overall mean ± 0.5 standard deviations. Once ENV was defined, traits were analysed with a model that included fixed effects of ENV, herd nested within ENV, AFC (only production traits and LSCS), year and month of calving, genotype, and the interaction between ENV and genotype. Least squares means for the interaction effect were used to estimate heterosis and to evaluate its magnitude across ENV. Holstein Friesian achieved higher productions than DF. First generation crosses showed productions close to HF, especially in the low ENV. Estimates of heterosis for yield traits ranged from 2.4% (milk) in the high to 5.3% (fat) in the low ENV, and reduced with increasing ENV. Estimates for LSCS and AFC were low, with the exception of LSCS in the high ENV. Results suggest that the highest non-additive genetic effects for yield traits and LSCS were expressed in the most stressful ENV, i.e., the low one for production and the high one for LSCS.     

Effect of daily feed intake in laying period on laying performance, egg quality and egg composition of genetically fat and lean lines of chickens

1. The objectives of this study were to evaluate the effects of feed intake on laying performance, egg quality and egg composition in a Fat line and a Lean line during the laying period (34 to 54 weeks of age). 2. The experiment was a 2 × 2 factorial design with two dietary intake levels (nutrition recommendation and 75% of recommendation) and two broiler genotypes (Fat line and Lean line). Hens (384 of each line) were randomly divided at 23 weeks of age into 4 treatments, with each treatment represented by 12 replicates of 16 birds each. The experiment started when the rate of lay reached 5% and continued until 54 weeks of age. 3. The results indicated that there was a significant interaction between daily feed intake and genotype on egg production, egg weight, percentage yolk, yolk/albumen ratio and yolk cholesterol content. Fat line hens produced significantly more eggs and had a lower incidence of cracked eggs than the Lean line hens. The reduction in feed intake decreased egg weight and increased egg production, egg-shape index and cholesterol content of yolk significantly.     

Heterosis and recombination effects in Hampshire and Landrace swine: II. Performance and carcass traits.

Twelve different mating types among the Hampshire and Landrace breeds were used to determine direct, maternal, heterosis, and recombination effects for performance and carcass traits. Mating types used were two purebred, two F1, two F2, two F3, and four backcross. Carcass data were collected on 238 barrows and 262 gilts over four replications. Traits measured were length (LENG), 10th rib off midline backfat (BF10), longissimus muscle area (LMA), and dressing percentage (DRS%). Average backfat (AVBF) was calculated as the mean of three midline fat depths measured opposite the first rib, last rib, and last lumbar vertebra. The model used to evaluate the carcass traits included main effects of mating type, farrowing season, and sex and included slaughter weight as a covariate. The performance traits of ADG, feed efficiency (FE), daily feed consumption (DFC), lean gain per day (LNGN), and lean efficiency (LNEF) were measured on a pen basis. Comparisons of reciprocal F1 crosses showed that carcasses from pigs sired by Hampshire boars were leaner and had more LMA than those sired by Landrace boars. Heterosis percentages were significant for AVBF (7.2%; P less than .01), BF10 (8.8%; P less than .01), DRS% (1.5%; P less than .01), ADG (11.5%; P less than .01), DFC (10.2%; P less than .01), LNGN (10.6%; P less than .01), and LNEF (6.0%; P less than .05). Epistatic recombination losses in the offspring were significant for LENG (3.6 cm; P less than .05) and approached significance for BF10 (6.1 mm; P less than .10).