Expression profile of hypothalamic neuropeptides in chicken lines selected for high or low residual feed intake.

The R(+) and R(-) chicken lines have been divergently selected for high (R(+)) or low (R(-)) residual feed intake. For the same body weight and egg production, the R(+) chickens consume 40% more food than their counterparts R(-) lines. In the present study we sought to determine the hypothalamic expression profile of feeding-related neuropeptides in these lines maintained under fed or food-deprived conditions. In the fed condition, the suppressor of cytokine signaling 3 (SOCS3) was 17-fold lower (P<0.05) and the ghrelin receptor was 7-fold higher (P<0.05) in R(+) compared to R(-) chicken lines. The hypothalamic expression of the other studied genes remained unchanged between the two lines. In the fasted state, orexigenic neuropeptide Y and agouti-related peptide were more responsive, with higher significant levels in the R(+) compared to R(-) chickens, while no significant differences were seen for the anorexigenic neuropeptides pro-opiomelanocortin and corticotropin releasing hormone. Interestingly, C-reactive protein, adiponectin receptor 1 and ghrelin receptor gene expression were significantly higher (12-, 2- and 3-folds, respectively), however ghrelin and melanocortin 5 receptor mRNA levels were lower (4- and 2-folds, P=0.05 and P=0.03, respectively) in R(+) compared to R(-) animals. We identified several key feeding-related genes that are differently expressed in the hypothalamus of R(+) and R(-) chickens and that might explain the difference in feed intake observed between the two lines.

Performance comparison of laying hens segregating for the frizzle gene under thermoneutral and high ambient temperatures.

The effect on thermotolerance of the incompletely dominant frizzle (F) gene, which causes feather curling and feather mass reduction, was investigated in 281 laying hens that were homozygous for the frizzle mutation (FF), heterozygous (FN), or normally feathered (NN). One-half of the birds were kept under standard conditions (22°C) and half were exposed to high ambient temperatures (32°C) between 24 and 46 wk of age. Egg production, egg quality, feed efficiency, and dissection traits were recorded and compared. At standard conditions, egg production and quality traits did not differ among the 3 genotypes, whereas feed efficiency was lower for the homozygous birds. Under heat stress conditions, the superiority of the FF hens was evident for all egg quantity and quality traits. No significant difference was measured between heterozygous carriers and normally feathered hens, indicating that the incomplete dominant frizzle mutation behaved as a recessive mutation regarding heat tolerance. From this study, we deduced that the F mutation in its homozygous state has a beneficial effect in decreasing heat stress in poultry production, and it could be particularly advantageous in tropical countries where average temperatures are never too low to negatively affect feed efficiency.

Feed efficiency in the laying duck: appropriate measurements and genetic parameters.

The objective of this study was to characterize residual feed intake (RFI) in common laying ducks by a) adjusting position and duration of the measurement period and b) estimating genetic parameters of RFI. The feed intake (FI), BW, and egg mass laid (EML) were recorded for 64 I444 common ducks at the beginning (-35 wk of age) and the middle (41-48 wk of age) of the laying curve. Much feed wastage was observed at the beginning of the laying curve and led to biased FI data. However, when laying was well-established, weekly and fortnightly FI measurements were well correlated phenotypically (Rp from 0.84 to 0.92 and from 0.91 to 0.94, respectively for weekly and fortnightly FI) with the measurements over the whole 2-mo period. Regarding egg mass laid, phenotypic correlations between the one-week measurements and the measurements over the whole 2-mo period were more variable than those for FI, ranging from 0.74 to 0.94, and similar to whatever was the period of measurement. The RFI was investigated in a second experiment based on 384 common female ducks, for which FI, EML, BW, and BW gain were recorded at 39 wk of age. The RFI was determined by multiple regression of FI on metabolic BW and EML. Heritability values of FI and RFI were 0.34 and 0.24, respectively. In addition, if the heritability values obtained for BW (0.65) and BW gain (0.09) were consistent with studies in chickens, the very low EML estimates (0.06) were unexpected. The RFI was strongly genetically linked to FI (Rg = +0.89) but appeared to be independent from BW. Selection based on RFI should therefore reduce the FI of animals without clearly modifying the other components. Moreover, the correlated responses on reproductive traits seem favorable because lower RFI values increase the number of eggs produced per year as well as the hatchability and fertility rates.

Visfatin gene expression in chickens is sex and tissue dependent.

The present study investigated the expression of visfatin mRNA in various tissues of male and female broiler chickens. We also studied the effect of leptin, cerulenin, and food deprivation, known effectors of energy balance and insulin action, on visfatin gene expression in chickens. Using reverse transcription polymerase chain reaction (RT-PCR) and Northern blot analysis, we detected chicken visfatin mRNA transcript in the kidney, hypothalamus, gizzard, liver, pancreas, proventriculus, breast and leg muscle, ovary, testis, lung, intestine, adipose tissue, and heart. Expression of the visfatin gene in various tissues of male and female chickens was determined by real-time quantitative PCR and found to be tissue and sex dependent. In both sexes, compared to other tissues, the visfatin gene is highly expressed in the muscle. Females exhibited greater (P<0.001) abundance of visfatin mRNA in adipose tissue compared to males, whereas compared to females, males showed greater (P<0.05) visfatin mRNA abundance in the kidney. Also, the regulation of visfatin gene expression by leptin, cerulenin, and food deprivation is tissue specific. Leptin decreased (P<0.05) visfatin mRNA abundance in the liver and hypothalamus, but not in muscle. In contrast, cerulenin increased (P<0.01) visfatin gene expression in the liver and in muscle, but not in the hypothalamus. Interestingly, visfatin mRNA levels increased (P<0.05) in the liver after 24-h food deprivation, but not in muscle or in the hypothalamus of genetically selected fat and lean line chickens. Our results showed that the visfatin gene is ubiquitously expressed in chickens with greater abundance in muscle, and that it is regulated in a tissue-specific manner by energy balance-related factors.

Effect of introducing the naked neck gene in a line selected for low residual feed consumption on performance in temperate or subtropical environments.

The aim of this study was to investigate the possibility of combining the naked neck gene with a genetic background that has been optimized for feed efficiency of laying hens at moderate temperature. In 1997, the naked neck gene was introduced into a line selected for low residual feed intake. In 2003, after 6 generations of introgression, 8 males and 56 females heterozygous for the NA*NA mutation were used to generate all 3 genotypes (NA*N/NA*N, NA*NA/NA*N, NA*NA/NA*NA), in 2 hatches, for rearing in Taiwan and France, respectively, at 3-wk intervals. Growth performance, anatomical traits, laying traits, and feed efficiency were recorded in each country. In addition, comb and rectal temperatures were measured in Taiwan. Performance was generally lower and mortality of laying hens was higher in Taiwan (11%) than in France (1%). Genotype x environment interactions were rare: genotype x environment was observed only for body weight at 10 wk of age and was close to significance for egg weight. The laying performance was significantly decreased in Taiwan by about 25%. The naked neck genotype had a negative effect on body weight and a positive effect of clutch length and egg weight. It also affected heat dissipation traits such as wattle length and rectal and surface temperature measurements. There was a clear additive and negative effect of the NA*NA mutation on rectal temperature. Feed intake and residual feed intake were increased in the homozygous carriers of the NA*NA mutation, which may improve heat tolerance of the low residual feed consumption (R-) line. Feed efficiency tended to be better in NA*NA/NA*NA hens in both environments. Thus, the introduction of the NA*NA mutation in the R- background appeared to be favorable from the viewpoint of feed efficiency, but it did not improve laying performance in a subtropical environment. Other factors than temperature, such as diet composition and lighting regimen, may be involved.

Further investigations on the role of diet-induced thermogenesis in the regulation of feed intake in chickens: comparison of adult cockerels of lines selected for high or low residual feed intake.

The main objective of this study was to investigate the role of diet-induced thermogenesis (DIT) in feed intake regulation in cockerels selected for high (R+) or low (R-) residual feed intake. The selection criterion was defined as the difference between observed feed intake and feed intake predicted by regression between feed intake and BW, BW gain, and egg mass production. Furthermore, the effect of genotype on postprandial oxidation of U-(13)C(6)-glucose, decarboxylation of 1-(13)C(1)-Leu, and key metabolites and hormones was analyzed. Thirty 24-wk-old cockerels of both lines were kept in battery cages under standard conditions on a commercial diet. Three cockerels per genotype were examined twice weekly from wk 30 through 34 in open-circuit respiratory cells. After adaptation, cockerels were feed deprived for 24 h and heat production was measured. During the subsequent 7-h refeeding period, DIT and feed intake, as well as glucose oxidation and Leu decarboxylation were assessed by using breath tests. Blood samples were collected after fasting and refeeding. Finally, 10 animals per genotype were killed to record abdominal fat weight. Body composition of 6 different chickens per genotype was determined by using dual-energy x-ray absorptiometry. During feed deprivation, the R+ cockerels had a significantly higher heat production than their R- counterparts, which was even more pronounced during refeeding. Consequently, the R+ cockerels had a significantly increased DIT and a higher feed intake than the R- cockerels. Thus, no evidence of a feedback effect of DIT on feed intake was observed. The oxidation of U-(13)C(6)-glucose was significantly higher in the R+ cockerels, confirming their higher respiratory quotient values and the augmented fat deposition in the R- chickens, as assessed by abdominal fat weight and dual-energy x-ray absorptiometry measurements. No significant genotype effect on 1-(13)C(1)-Leu decarboxylation was observed, despite increased circulating uric acid levels in the R+ chickens. Genotype did not influence plasma levels of triglycerides, free fatty acids, glucose, triiodothyronine, or thyroxine after refeeding, whereas plasma leptin levels were significantly higher in the R+ cockerels.

Effect of high ambient temperature and naked neck genotype on performance of dwarf brown-egg layers selected for improved clutch length.

1. Two experimental lines of dwarf brown-egg layers selected on clutch length were reciprocally crossed. In total, 288 hens, from three genotypes: L1, purebred normally feathered (121 hens), F1, crossbred and heterozygous for the NA mutation (99 hens) or L2, purebred homozygous for NA (68 hens) were housed in three climatic rooms at 22 degrees C and three climatic rooms at 32 degrees C. 2. Body weight, daily egg production records, feed intake and some anatomical and physiological traits were recorded. Canonical discriminant analysis was used to examine the relationships among all measured traits and to compare the experimental groups as defined by genotype and temperature. 3. Heterosis effects were observed on body weight, feed intake, egg mass and some anatomical traits at 22 degrees C, but were negligible for most of the traits measured at 32 degrees C except for body weight at 34 weeks, clutch length and some anatomical traits. 4. Genotype by temperature interactions were observed for egg production, egg mass and feed intake. The temperature stress was severe, with a marked decrease in egg production. The naked neck gene could limit the negative effect of long-term heat stress. Egg weight was increased by the NA gene, as usually observed in layers. 5. The first three canonical variates explained altogether 97.4% of the variance. The first canonical variate was associated almost exclusively with ambient temperature. The second was associated with genotype. The third was associated with heterozygous genotype for NA mutation and genotype by temperature interaction. Stepwise discriminant analysis indicated that 12 traits out of 20 were effective at detecting the differences among the genotype and temperature combinations.

Effect of the slow (K) or rapid (k+) feathering gene on body and feather growth and fatness according to ambient temperature in a Leghorn x brown egg type cross.

Chicks of both sexes issued from the cross of heterozygous K/k+ cocks for the slow-feathering sex linked K allele with k+ (rapid feathering) hens, were compared from the age of 4 to 10 weeks at two ambient temperatures. In individual cages, 30 male chicks of each genotype (K/k+ and k+/k+) were raised at 21 degrees C, and 60 others, distributed in the same way, were raised at 31 degrees C. 71 K/W females and 69 k+/W females were raised in a floor pen at 31 degrees C till 10 weeks of age. In the males, the body weight, feed consumption and feed efficiency at different ages were influenced only by temperature (lower growth rate and feed intake at 31 degrees C); no significant effects of the genotype at locus K nor genotype x temperature interaction were observed. In females, all at 31 degrees C, the genotype (K/W or k+/W) had no significant effect on growth rate. Plumage weight and weight of abdominal fat (absolute or related to body weight) were measured on half of the males of each group in individual cages, at 10 weeks of age. Moreover, on 36 males and 48 females of the two genotypes, in a group battery at 31 degrees C, the absolute and relative weight of plumage were measured on a sample every two weeks between 4 and 10 weeks. In the first case, no significant effect of genotype appeared. In the second case, an interaction between age and genotype was suggested from plumage weight: its growth, especially in male chicks, appears to be temporarily and unexpectedly faster from 4 to 6 weeks of age for the K/k+ and K/W genotypes.

An uncoupling protein homologue putatively involved in facultative muscle thermogenesis in birds.

The cDNA of an uncoupling protein (UCP) homologue was obtained by screening a chicken skeletal-muscle library. The predicted 307-amino-acid sequence of avian UCP (avUCP) is 55, 70, 70 and 46% identical with mammalian UCP1, UCP2 and UCP3 and plant UCP respectively. avUCP mRNA expression is restricted to skeletal muscle and its abundance was increased 1.3-fold in a chicken line showing diet-induced thermogenesis, and 3.6- and 2.6-fold in cold-acclimated and glucagon-treated ducklings developing muscle non-shivering thermogenesis respectively. The present data support the implication of avUCP in avian energy expenditure.

Hepatic lipogenesis gene expression in two experimental egg-laying lines divergently selected on residual food consumption.

Two Rhode Island Red egg-laying lines have been divergently selected on residual food intake (low intake R- line, high intake R+ line) for 19 generations. In addition to direct response, correlated responses have altered several other traits such as carcass adiposity and lipid contents of several tissues, the R+ animals being leaner than the R- ones. In a search for the biological origin of the differences observed in fat deposit, the hepatic mRNA amounts of genes involved in lipid metabolism were investigated. No difference was found between lines for mRNA levels of ATP citrate-lyase, acetyl-CoA carboxylase, fatty acid synthase, malic enzyme and CCAAT/enhancer binding protein alpha, a transcription factor acting on several lipogenesis genes. The genes coding for stearoyl-CoA desaturase and apolipoprotein A1 displayed significantly lower mRNA levels in the R+ cockerels compared to the R-. All together these mRNA levels explained 40% of the overall variability of abdominal adipose tissue weight, suggesting an important role of both genes in the fatness variability.

Patterns of growth and feed intake in divergent lines of laying domestic fowl selected for residual feed consumption.

At Generations 15 (males) and 18 (females) of a divergent selection experiment on residual feed consumption (RFC) in laying poultry, patterns of growth, feed consumption, and associated traits were monitored between the ages of 4 and 34 wk. This monitoring was done to determine how the well-established RFC and feed intake (FI) divergences between adults of the low intake R- line and of the high intake R+ line took place, in relation to the evolution of correlated traits. In males and females, BW and BW gain were higher in the R- line in the first weeks of test, but patterns of BW were quite similar in both lines afterwards. However, R- hens remained heavier than R+ females to the end of the experiment. Line difference for BW was achieved by 28 wk of age, at 2,974 and 2,094 g, and the R- line was then 135 and 133 g heavier, respectively, for males and females. After a fast initial increase in both sexes, FI diverged quickly around 16 to 18 wk of age (sexual maturity), to attain 13 g/d in males and 28 g/d in females, well before the end of the experiment. At the same time, a divergence was observed for wattle length, which was 21% higher in R+ females. Residual feed consumption gradually diverged in the two lines, and the difference became significant at 14 wk of age. At the same age, shanks were 8% longer in R+ hens. Finally, levels of triiodothyronine decreased faster in the R- line, as FI divergence was increasing. These results indicate that the RFC difference between R- and R+, lines obtained in adult birds by divergent selection lines, starts somewhat early in life. In addition, the RFC difference appears to be associated with specific growth periods, around 14 wk and 18 to 20 wk. It is at this time that large differences appear in morphological traits involved in body heat loss. No significant correlations were found between early (6 wk) measures of FI, feed efficiency, and RFC, with adult values (32 to 34 wk) for RFC and FI.

First Report of Blossom Blight of Strawberry Caused by Xanthomonas fragariae and Cladosporium cladosporioides in California.

In the spring of 1996, severe blossom blight occurred in some strawberry fruit production fields in the Watsonville area. The symptoms, in addition to blighting of entire flowers, were as follows: on the lower surface of the calyx, watersoaked lesions that appeared dark green under reflected light and translucent under transmitted light; necrotic calyces of seemingly healthy green and ripe fruits; watersoaking of the base of the calyx that extended into the pedicel; green-gray sporulation on dead anthers; and presence of flower clusters with small and irregularly shaped fruits. Yellow bacterial colonies were consistently isolated from water-soaked and necrotic lesions on calyces and pedicels. These colonies were entire, circular, raised, glistening, mucoid, and slow growing, characteristics typical of Xanthomonas fragariae on nutrient agar-glucose-yeast extract medium. The bacterial isolate was also identified by rep-polymerase chain reaction as X. fragariae. In addition to the yellow bacteria, a fungus was also frequently isolated from infected anthers, sepals, petals, and pistils, and was identified as Cladosporium cladosporioides. On potato dextrose agar, the fungus had velvetlike colonies colored olivaceous-green to olivaceous-brown, apically and laterally branched conidiophores, and lemon-shaped conidia that were usually smooth but sometimes textured. Blossoms of greenhouse-grown strawberry plants cv. Selva were inoculated with either or both organisms. Blossoms inoculated with X. fragariae developed symptoms distinct from those inoculated with C. cladosporioides. The most prominent visible symptoms caused by X. fragariae were watersoaked lesions on calyces that later became necrotic, watersoaking of the calyx that extended into the pedicel, and blighting of flowers and developing fruits as a result of girdling of the pedicel. Infection by C. cladosporioides was characterized by necrosis of flower parts or the entire flower, presence of green-gray sporulation on dead anthers, and production of small and malformed or misshapen fruits. Inoculation with both organisms produced all the symptoms described above in different flowers of a plant. Infection with both organisms aggravated disease severity, but each organism was capable of inducing blossom blight independently. Both organisms were reisolated from artificially inoculated strawberry flowers, fulfilling Koch's postulate for proof of pathogenicity. This is the first report of the two organisms causing blossom blight of strawberry in California. This is also the first report that C. cladosporioides is a pathogen of strawberry.

Associated effects of divergent selection for residual feed consumption on reproduction, sperm characteristics, and mitochondria of spermatozoa.

Eighteen generations of divergent selection for residual feed intake have been completed in two Rhode Island Red lines of domestic fowl. The high intake R+ line and the low intake R- line cocks used to sire Generation 19 of the selection experiment have been compared for associated responses on fertility, hatching, and sperm quality. Evaluations of sperm samples were based on volume, cell concentration, biochemical parameters (pH, uric acid and protein concentrations), and motility and morphology of spermatozoa. Finally, individual spermatozoa were analyzed by flow-cytometry (FCM) using Rhodamine 123 (Rh123) and nonyl-acrydine-orange (NAO) specific fluorochromes to assess, respectively, overall mitochondrial activity and overall mitochondrial content. Hatchability of incubated eggs was 20 points higher for the R- line, mainly because unfertilized eggs were only 6 vs 30% in the R+ line. Early embryo mortality was also twice as high in the R+ line (21%). The ratio of Rh123 to NAO fluorescence was identical for both lines. This result suggests that there was no difference in the energy producing potential of the individual mitochondria. Therefore, the difference seen for both dyes between the two lines might be attributed to a difference in the quantity of mitochondrial inner membranes present in the cell (with 17% less for the R+ line). In the R+ line, the poor performance at fertilization and during early embryonic development was associated with lower production of motile spermatozoa, possibly in relation to a lower quantity of mitochondria in spermatozoa from R+ cocks. Although the female contribution to the differences between lines was not explored separately, results suggest that selection for residual feed intake may have altered some cellular function related to the production of energy in the R+ line.

Diet-induced thermogenesis in cockerels is modulated by genetic selection for high or low residual feed intake.

Energy balance of adult cockerels genetically selected for high (R+) or low (R-) residual feed consumption was investigated by using indirect calorimetry. Although no between-line difference was found in digestion of ingested energy, the true metabolizable energy (ME) intake was 40% greater in R+ than in R- birds. Basal heat production (HP) did not significantly differ between genotypes. Diet-induced thermogenesis (DIT) was significantly enhanced in R+ compared with R- birds, i.e., +84% when expressed as the difference in kilojoules of heat production determined in feed-deprived and fed cockerels, +31% when calculated as a percentage of ME intake (P < 0.01). The difference in DIT calculated from the regression between HP and physical activity explained 75% of the difference in HP; the remaining 25% could be explained by activity-related HP. The results cannot be explained by differences in the plasma concentration of circulating thyroid hormones: plasma thyroxine concentration did not differ between genotypes, whereas plasma triiodothyronine concentration was lower in feed-deprived R+ than in R- birds and indistinguishable in fed birds of the two lines. Heat production, however, was higher in the R+ line. Propranolol decreased HP only in the R+ line, suggesting a beta-adrenergic control of DIT at least in cockerels of this line. Plasma triglyceride concentration was lower in the R+ than in the R- line in fed cockerels, and plasma nonesterified fatty acid concentration was higher in the R+ than in the R- line in feed-deprived cockerels. These results are consistent with the leanness of the R+ compared with the R- line. The R+ and R- lines constitute an original model of diet-induced thermogenesis (DIT), a process that is under genetic control of appetite and allows R+ birds to balance all of their excessive energy intake without any adipose tissue storage.

Heterosis in egg-laying lines under divergent selection for residual feed consumption.

Two lines selected since 1976 for high (R+) or low (R-) residual feed consumption (RFC) from a common genetic base were compared with one another and with their F1 reciprocal crosses for traits of egg production and quality, for morphological traits, body weights, and feed consumption. Heterosis was 11, -2.5, 8, and 2%, respectively, for egg number, age at first egg, egg laying rate, and egg weight, with marked differences between reciprocal crosses for all those traits but egg number. Heterosis for wattle length and shank length was 3.8 and 1.3%, respectively, essentially because R+ x R- crossbreds, with larger mean values, resembled the R+ line for those traits, which may therefore be associated with the presence of genes linked to the Z chromosomes. On the other hand, heterosis for RFC (-3.6%) originated from similar crossbred advantage in both reciprocal crosses, thereby suggesting that RFC is not determined by sex-linked genes.

Divergent selection for residual food intake in Rhode Island red egg-laying lines: gross carcase composition, carcase adiposity and lipid contents of tissues.

1. A sample of 48 hens and cockerels from generation 17 of a divergent selection experiment on residual food intake was examined to determine whether the large food intake differences between those lines were associated with differences of body composition. 2. Adiposity and lipid contents of various parts of the carcase were higher in the low residual food intake line than in the high residual food intake line, both in males and females, with the cockerels of the high residual food intake line markedly lean. 3. On an equal weight basis obtained by linear correction for body weight differences, males had heavier thigh, drumstick and bones, but less adipose tissue and smaller amounts of lipids in the liver, meat, skin and abdominal adipose tissue than females.

Restricted maximum likelihood estimates of genetic parameters of adult male and female Rhode Island red chickens divergently selected for residual feed consumption.

In adult chickens, feed intake can be predicted by multiple linear regression from body weight, change in body weight during the recording period (for males and females), and egg mass (for females). Residual feed consumption (RFC) is estimated by the deviation of observed from predicted values for feed intake. A divergent selection experiment has been conducted since 1975 in a Rhode Island Red population. Each sex was selected on the basis of its own RFC, Line R+ for high values of RFC and Line R- for low values. In addition to the traits measured to obtain RFC, egg production traits and body measurements (BM) have been recorded, including wattle length, shank length, and rectal temperature. After pooling data from the two lines and the base population, the data set included 1,064 males, each with 7 variables, and 3,780 females, each with 11 variables. Genetic parameters were estimated by a multivariate derivative-free-restricted maximum likelihood procedure, which yields estimates free of bias due to selection and inbreeding. The RFC appeared to be moderately heritable in males (h2 = .33) and in females (h2 = .27) and poorly correlated between sexes, with a genetic correlation of .19 between RFC in males (RFCm) and in females (RFCf). The RFCm and RFCf were weakly correlated with egg production traits. Significant, positive correlations were found between RFCm and the BM traits that were related to heat dissipation. Correlations between feed intake, body weight, and BM traits recorded in males or in females were always < 1, except for shank length.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytogenetic study of early chicken embryos: effect of naked neck gene and high ambient temperature.

High ambient temperature (> 30 C) decreases fertility of breeder hens, but this effect has been shown to be greatly reduced in females carrying the naked neck gene (Na). Sixty-four females each of the three different genotypes, Na/Na (homozygous naked neck), Na/na+ (heterozygous), and na+/na+ (normally feathered), were equally distributed in two climate control rooms with individual cages, at a constant temperature of either 22 C or 31 C. Five hundred and seventy-six embryos were examined after 16 to 18 h of incubation for karyological analyses. Abnormalities consisted of diploid-haploid and diploid-triploid chimeras. The frequency of chimeric embryos was significantly affected by dam genotype. Naked neck females showed a much lower proportion of abnormal embryos than normally feathered females whatever the temperature. The highest proportion of chimeras was observed for the na+/na+ dams maintained at 31 C. However, the effect of temperature was not generally significant.

Heterosis in normal versus dwarf laying hens.

The effect of genotype at the sex-linked dwarf locus on heterosis in crosses between a White Leghorn and a brown egg line for body weight, egg production, and related traits was studied. Heterozygous Dw/dw males were used to produce normal and dwarf pullets in each of the pure lines and their reciprocal crosses (eight genotype-line combinations). There were 54 pullets per combination. Line differences were significant for shank length, body weights at 8, 17, and 52 wk, age at first egg, egg number, clutch length, rate of lay, and egg weight. Heterosis was observed for all of these traits. Body weight as a covariate was not important in analyses of egg number, clutch length, and egg weight. The egg production reduction associated with the dw gene in pure lines was smaller in F1 hens. This discovery may be adequate to warrant use of dwarf crossbred hens for egg production.