Effect of incorporation of thermo-regulatory genes into exotic layers on egg production and quality under tropical environment

A breed development strategy aimed at making exotic layers (Lohmann Brown) more productive under tropical environment using thermo-regulatory genes is underway at Akate Farms in Kumasi, Ghana. The present experiment was carried out to find out the effect of the genes on egg production in hot and humid environments. Three genetic groups comprising naked-neck, frizzle and their normally feathered sibs were obtained after successive generations of crossing between naked-neck and frizzle cocks and Lohmann brown hens. A total of 270 18-week-old pullets, 90 each of the 3 groups, were selected randomly and assigned to a completely randomized design experiment with 3 replicates, with 30 birds in each replicate group and kept up to a period of 72 weeks. The birds were kept in a partitioned open-sided deep-litter house constructed with sandcrete blocks with 30 pullets in each compartment. They were fed ad libitum with layer diets containing 18 % crude protein and 2,800 kcal ME/kg. Results obtained showed that the crossbred naked-neck and frizzle phenotypes produced eggs at a significantly (P?<?0.05) higher rates than their normally feathered sibs and also out-performed their normally feathered sibs in other egg production parameters measured, even though they all segregated from similar parents. This is an indication of the favourable effect of the genes on egg production under hot and humid environments.     

Effect of the frizzle gene (F) on egg production and egg quality of laying hens kept in tropical villages

1. Two experiments were conducted to determine the influence of the frizzle gene (F) on the production and quality of chicken eggs kept on village farms in Ghana.

2. In the first experiment, 144 pullets, 72 each of Ff and ff pullets from F₁ birds, were compared in a randomised complete block design (RCBD), with three villages and 4 batches of hatch as blocks and the two feather genotypes (Ff and ff) as the treatments.

3. The Ff pullets were superior (P < 0.05) to their ff counterparts in terms of the number of eggs per clutch, egg mass and hen-housed and hen-d rates of lay, whereas age at first egg was lower (P < 0.05) in ff layers compared to Ff ones.

4. The eggs of the F₁ heterozygous frizzle (Ff) layers had higher values for albumen height, Haugh unit and yolk height compared with eggs from their normal feathered counterparts.

5. In the second experiment, 144 pullets, 48 each of FF, Ff and ff pullets, were compared in a RCBD, with three villages and 4 batches of hatch as blocks and the two feather genotypes (Ff and ff) as the treatments.

6. The F₂ birds with genotypes Ff and FF were better than their ff counterparts in terms of the number of eggs per clutch, egg mass, and hen-housed and hen-d rates of lay. Age at first egg was significantly lower in ff layers compared to FF and Ff ones.

7. The Haugh unit value was higher in the homozygous and heterozygous frizzles compared to the normal feathered ones.

8. The presence of the frizzle gene (F) in egg type chickens led to an improvement in egg production and egg quality traits in village chickens, and the cross-breeding scheme evaluated in this project could contribute to improved productivity.     

Effects of the naked‐neck gene on traits associated with egg laying in a dwarf stock at two temperatures

1. Naked‐neck (NaNa and Nana⁺ ) and normal hens, all dwarf (dw), were compared for laying performance in two groups at 15 to 20 or 30 °C.

2. Naked‐neck hens, especially homozygotes, weighed less only at the cooler temperature. Body fatness was not different.

3. Normal, but not naked‐neck birds, showed a depression in food intake and egg output at 30 °C. In the hot environment mean egg weight and egg mass output were highest for naked‐neck homozygotes. At the cooler temperature mean egg weight was also higher for this genotype, at fixed body weight.

4. The decline in egg mass with time seemed greater for fully‐feathered layers at high temperature.

5. At moderate temperature residual food intake was slightly increased by the naked‐neck gene, but owing to the reduced body weight, food utilisation was not poorer for the NaNa or Nana ⁺ genotypes. At higher temperature Nana ⁺ and especially NaNa hens utilised food more efficiently.

6. An increase in wattle size and a slight decrease in body temperature were associated with the Na allele.

     

Effect of naked neck gene (NA) and frizzle gene (F) on immunocompetence in chickens

1. A total of 98 birds belonging to 4 genetic groups from two specialised populations--heterozygous naked neck (NA*NA/NA*N) and normally feathered (NA*N/NA*N) from one specialised population and heterozygous frizzle (F*F/F*N) and normally feathered (F*N/F*N) from another specialised population--were evaluated for general immunocompetence by assessing antibody response to SRBC, haemolytic complement level in the serum, in-vivo cell mediated immune (CMI) response to Concanavalin-A (Con-A) and a phagocytic index at 10-12 weeks of age. 2. The naked neck gene did not seem to influence the antibody response to SRBC, CMI to Con-A or the phagocytic index. However, significantly higher haemolytic complement level in serum was observed in birds carrying a copy of the NA mutation as compared to the normally feathered birds. 3. Similar trends were observed for the frizzle gene.     

A note on transgenerational epigenetics affecting egg quality traits in meat-type quail

ABSTRACT

1. The aim of the following experiment was to estimate transgenerational epigenetic variance for egg quality traits using genealogical and phenotypic information in meat-type quail. Measured traits included egg length (EL) and width (EWD), albumen weight (AW), shell weight (SW), yolk weight (YW) and egg weight (EW).

2. A total of 391 birds were evaluated for egg quality by collecting a sample of one egg per bird, during three consecutive days, starting on the 14th d of production. Analyses were performed using mixed models including the random epigenetic effect. Variance components were estimated by the restricted maximum likelihood method. A grid-search for values for the auto-recursive parameter (λ) was used in the variance components estimation. This parameter is directly related to the reset (v) and epigenetic transmissibility (1 ? v) coefficients.

3. The epigenetic effect was not significant for any of the egg quality traits evaluated. Direct heritability estimates for egg quality traits ranged in magnitude from 0.06 to 0.33, whereby the higher estimates were found for AW and SW. Epigenetic heritability estimates were low and close to zero (ranging from 0.00 to 0.07) for all evaluated traits.

4. The current breeding strategies accounting for additive genetic effect seem to be suitable for egg quality traits in meat-type quail.     

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.     

A novel 31-bp indel in the paired box 7 (PAX7) gene is associated with chicken performance traits

1. A novel 31-bp indel polymorphism in intron 3 of the chicken paired box 7 (PAX7) gene was identified and genotyped in an F₂ resource population of Gushi chicken crossed with Anka broiler to analyse its associations with chicken growth, carcass and meat quality traits.

2. Results showed that the 31-bp indel was significantly associated with body weight at 4, 6, 8, 10, 12 weeks of age and body size indices including shank length, shank girth, body slanting length at 8 and 12 weeks of age. Significant associations were found for carcass weight, semi-evisceration weight, evisceration weight, breast muscle fibre diameter, leg muscle fibre diameter, breast muscle fibre density, while no significant association with leg muscle fibre density was observed.

3. It was concluded that the 31-bp indel in intron 3 of the PAX7 gene was associated with chicken growth, carcass and meat quality traits where the 31-bp deletion had a negative effect on chicken growth and carcass traits and positive effect on meat quality traits.     

Identification of potential genomic regions for egg weight by a haplotype-based genome-wide association study using Bayesian methods

ABSTRACT

1. Theoretically, haplotype blocks might be a more suitable alternative to SNP genotypes as they are usually better at capturing multi-allelic QTL effects, compared to individual SNP genotypes in genome-wide association studies. The objectives of this study were to identify genomic regions related to egg weight traits by Bayesian methods (BayesA, BayesB, and BayesN) that fit fixed-length haplotypes using GenSel software.

2. Genotypes at 294,705 SNPs, that were common on a 600K Affymetrix chip, were phased for an egg-laying hen population of 1,063 birds. Recorded traits included first egg weight (FEW) and average egg weight at 28, 36, 56, 66, 72 and 80 weeks of age.

2. Fitting 1Mb haplotypes from BayesB resulted in the highest proportion of genetic variance explained for the egg weight traits. Based on the trait, the genetic variance explained by each marker ranged from 27% to 76%.

3. Different haplotype windows associated with egg weight traits only explained a small percentage of the genetic variance.

4. The top one 1-Mb window on GGA1 explained approximately 4.05% of total genetic variance for the FEW. Candidate genes, including PRKAR2B, HMGA2, LEMD3, GRIP1, EHBP1, MAP3K7, and MYH were identified for egg weight traits.

5. Several genomic regions, potentially associated with egg weight traits, were identified, some of which overlapped with known genes and previously reported QTL regions for egg production traits.     

Polymorphisms in GnRHI and GnRHII genes and their association with egg production and egg quality traits in chicken

1. Two candidate genes, namely, Gonadotropin releasing hormone I (GnRHI) and Gonadotropin releasing hormone II (GnRHII) play pivotal roles in ovulation and egg production in chicken. The objective of this study was to explore polymorphism in these genes and to estimate the effects of polymorphism of these two genes on egg production and egg quality traits in White Leghorn laying hens.

2. Single strand conformation polymorphism followed by sequencing was performed to detect polymorphism in these genes.

3. The coding regions of the GnRHI and GnRHII genes were found to be polymorphic. In the GnRH1 gene, 12 haplotypes were determined, of which the h1 haplotype was predominant and the h5, h9 and h11 haplotypes were the least frequent ones. In the GnRHII gene, eight haplotypes were found, of which the h1 haplotype was the most frequent and the h6 was the least frequent haplotype in the White Leghorn population.

4. The haplogroups of GnRHI had a significant effect on body weight and egg production up to 64 weeks of age, yolk content, Haugh units and egg shell parameters. The h1h2 haplogroup of the GnRHI gene showed the highest egg production, with 211.0 ± 24.3 eggs up to 64 weeks of age, while the highest yolk content and Haugh unit was found in h3h10 haplogrouped birds. The haplogroups of GnRHII had a significant effect on age at sexual maturity (ASM) where the shortest ASM was found in the h1h4 birds (147.3 ± 5.9 d) and the longest ASM was observed in the h1h3 birds (160.6 ± 23.4 d).

5. It was concluded that GnRHI and GnRHII genes are polymorphic and have a significant effect on body weight, egg production and egg quality traits in White Leghorn laying hens.     

Heritabilities and genetic correlations in related dwarf and normal broiler populations 1

1. Heritability estimates were higher for 8‐week body weight in dwarf than in normal broiler populations due to the maternal effects of dwarf dams.

2. The dwarfing gene dw did not induce new genetic variability for egg weight, 30‐week body weight and age at sexual maturation.

3. Genetic correlation estimates showed that the selection for 8‐week body weight will increase egg weight in dwarf pullets more than in normals.

4. Within a dwarf population it should be possible to increase 8‐week body weight without influencing the mature size of pullets.     

矮小型基因(dw)对地方鸡种繁殖性能的影响

矮小型ｄｗ 基因导入地方鸡种清远麻鸡品种中,研究结果表明,含地方鸡种血缘的矮小型鸡（ｄｗ － ） 其开产日龄比同血缘的正常型鸡（ＤＷ－ ） 有提前趋势,３００ 日龄蛋重有降低的趋势,但未达显著水平;６４ 周龄入舍产蛋量和整个饲养期饲料转化率得到极显著提高。分析结果表明,这些都是ｄｗ 基因效应而引起。     

Comparison of sex-linked dwarf genes in chickens from two sources when introgressed into unrelated genetic backgrounds

1. Sex-linked dwarfing genes from 2 broiler stock origins (EU and US) were each introgressed into 2 White Leghorn populations that had been divergently selected for antibody response to sheep erythrocytes. 2. When the resulting backcrossed populations were 87.5% of their respective White Leghorn line, non-dwarf pullets were assessed for body weights, shank lengths, immunoresponsiveness, age and body weight at sexual maturity, egg production, average egg weight, and duration of fertility. For measurements where there were no differences between non-dwarf pullets from the 2 origins of the dwarfing genes, then the dwarf pullets (which were full sisters to the non-dwarfs) were compared. 3. Shank length at 8 weeks of age and mature (24-week) body weights were higher for dwarf pullets from EU than US dwarf origin. Immune response and several egg production traits were higher for dwarf pullets from the high antibody backcross than from those of the low antibody backcross. 4. There were few differences in expression of the dwarfing genes from 2 origins in the unrelated backcross populations used in this study. Also each of the dwarfing genes, when introgressed into different genomic backgrounds, was not discernibly different in its expression in terms of antibody response or egg production characteristics.     

Genetics of changes in economic traits during the laying year

Body weights, egg weights and egg numbers were measured at different ages in two distinct, fully pedigreed, random bred strains of White Leghorns over a period of 3 years. The heritabilities of the separate measurements and the genetic correlations between them were obtained by an analysis of variance and covariance. The principal findings were:

(i) The heritability of weight gain declined sharply with age over consecutive periods after 12 weeks. The genetic correlation of body weight at 12 weeks with gain in subsequent periods was low. There appeared to be sufficient genetic variance in growth rate in these later periods to alter the growth curve substantially by selection. For example, it should be possible to breed strains with a rapid early growth and low mature body size.

(ii) There was evidence of genetic variation in the change of egg weight with time. The genetic variation was, however, so low that in any selection programme to improve 28‐week egg weight without changing 44‐week egg weight the progress would be very slow.

(iii) Body weight at 12 weeks was genetically negatively correlated with sexual maturity. Its correlation with production in the first 44 weeks was positive in both strains, but not significantly different from zero.

(iv) Body weights after 28 weeks were apparently uncorrelated with egg production or sexual maturity.

(v) Egg weight and production traits show considerable heterogeneity of variance between years, probably partly due to their distribution not being normal.

(vi) The pattern of genetic variation appeared to differ significantly between the two strains so that correlated responses would not necessarily be the same.

(vii) There was a suggestion of maternal effects acting upon body weight but the evidence was somewhat contradictory and inconclusive due to the high standard error of the estimates.

(viii) None of the 15 traits measured regressed over the 3 year period of relaxation of selection.     

Effects of dietary red yeast (Sporidiobolus pararoseus) on production performance and egg quality of laying hens

The purpose of this study was to evaluate the effect of dietary red yeast (Sporidiobolus pararoseus) on production performance and egg quality of laying hens. A total of 200 Esa Brown laying hens (23 weeks of age) were allocated equally to negative control group (no yeast supplement); positive control group (2 g/kg of Saccharomyces cerevisiae); 0.5, 1, 2 g/kg red yeast respectively. The experiment was lasted for 12 weeks. Feed intake, hen‐day egg production and egg weight were not different between control and supplemented groups. However, yeast‐supplemented groups were significantly improved feed efficiency (p < .05). Incremental levels of red yeast increased the colour score of egg yolk (p < .05). The cholesterol and triglyceride of serum and yolk were significantly (p < .05) lower in the laying hens fed dietary administration red yeast compared to the control diet; however, no significant (p > .05) differences among yeast‐supplemented groups were observed. The hepatic hydroxymethylglutaryl‐coenzymeA (HMG‐CoA) reductase activity was significantly lower (p < .05) in the 2 g/kg red yeast‐supplemented group compared to the control and other red yeast‐supplemented groups. Concentrations of caecal short‐chain fatty acids was increased (p < .05) in laying hens fed 1 and 2 g/kg red yeast as compared to the control group. Dietary administration of 2 g/kg red yeast (S. pararoceus) significantly improved egg yolk colour, decrease serum and egg yolk cholesterol levels.     

Genome‐wide association study for egg production and quality in layer chickens

Discovery of genes with large effects on economically important traits has for many years been of interest to breeders. The development of SNP panels which cover the whole genome with high density and, more importantly, that can be genotyped on large numbers of individuals at relatively low cost, has opened new opportunities for genome‐wide association studies (GWAS). The objective of this study was to find genomic regions associated with egg production and quality traits in layers using analysis methods developed for the purpose of whole genome prediction. Genotypes on over 4500 birds and phenotypes on over 13 000 hens from eight generations of a brown egg layer line were used. Birds were genotyped with a custom 42K Illumina SNP chip. Recorded traits included two egg production and 11 egg quality traits (puncture score, albumen height, yolk weight and shell colour) at early and late stages of production, as well as body weight and age at first egg. Egg weight was previously analysed by Wolc et al. ( 2012 ). The Bayesian whole genome prediction model – BayesB (Meuwissen et al. 2001 ) was used to locate 1 Mb regions that were most strongly associated with each trait. The posterior probability of a 1 Mb window contributing to genetic variation was used as the criterion for suggesting the presence of a quantitative trait locus (QTL) in that window. Depending upon the trait, from 1 to 7 significant (posterior probability >0.9) 1 Mb regions were found. The largest QTL, a region explaining 32% of genetic variance, was found on chr4 at 78 Mb for body weight but had pleiotropic effects on other traits. For the other traits, the largest effects were much smaller, explaining <7% of genetic variance, with regions on chromosomes 2, 12 and 17 explaining above 5% of genetic variance for albumen height, shell colour and egg production, respectively. In total, 45 of 1043 1 Mb windows were estimated to have a non‐zero effect with posterior probability > 0.9 for one or more traits.     

Dominance genetic and maternal effects for genetic evaluation of egg production traits in dual-purpose chickens

• 1.?A study was conducted to study direct dominance genetic and maternal effects on genetic evaluation of production traits in dual-purpose chickens. The data set consisted of records of body weight and egg production of 49 749 Mazandaran fowls from 19 consecutive generations. Based on combinations of different random effects, including direct additive and dominance genetic and maternal additive genetic and environmental effects, 8 different models were compared.

• 2.?Inclusion of a maternal genetic effect in the models noticeably improved goodness of fit for all traits. Direct dominance genetic effect did not have noticeable effects on goodness of fit but simultaneous inclusion of both direct dominance and maternal additive genetic effects improved fitting criteria and accuracies of genetic parameter estimates for hatching body weight and egg production traits.

• 3.?Estimates of heritability (h²) for body weights at hatch, 8 weeks and 12 weeks of age (BW0, BW8 and BW12, respectively), age at sexual maturity (ASM), average egg weights at 28–32 weeks of laying period (AEW), egg number (EN) and egg production intensity (EI) were 0.08, 0.21, 0.22, 0.22, 0.21, 0.09 and 0.10, respectively. For BW0, BW8, BW12, ASM, AEW, EN and EI, proportion of dominance genetic to total phenotypic variance (d²) were 0.06, 0.08, 0.01, 0.06, 0.06, 0.08 and 0.07 and maternal heritability estimates (m²) were 0.05, 0.04, 0.03, 0.13, 0.21, 0.07 and 0.03, respectively. Negligible coefficients of maternal environmental effect (c²) from 0.01 to 0.08 were estimated for all traits, other than BW0, which had an estimate of 0.30.

• 4.?Breeding values (BVs) estimated for body weights at early ages (BW0 and BW8) were considerably affected by components of the models, but almost similar BVs were estimated by different models for higher age body weight (BW12) and egg production traits (ASM, AEW, EN and EI). Generally, it could be concluded that inclusion of maternal effects (both genetic and environmental) and, to a lesser extent, direct dominance genetic effect would improve the accuracy of genetic evaluation for early age body weights in dual-purpose chickens.

     

Validation of biomarkers for loin meat quality (M. longissimus) of pigs

The aim of this study was to validate previously reported associations between microarray gene expression levels and pork quality traits using real‐time PCR. Meat samples and meat quality data from 100 pigs were collected from a different pig breed to the one tested by microarray (Large White versus Pietrain) and a different country of origin (Denmark versus Germany). Ten genes (CARP, MB, CSRP3, TNNC1, VAPB, TNNI1, HSPB1, TNNT1, TIMP‐1, RAD‐like) were chosen from the original microarray study on the basis of the association between gene expression levels and the meat quality traits meat %, back fat, pH24, drip loss %, colour a*, colour b*, colour L*, WB‐SF, SFA, MUFA, PUFA. Real‐time PCR detection methods were developed for validation of all ten genes, confirming association with drip loss (two of two genes), ultimate pH (three of four genes), a* (redness) (two of six genes) and L*(lightness) (two of four genes). Furthermore, several new correlations for MUFA and PUFA were established due to additional meat quality trait information on fatty acid composition not available for the microarray study. Regression studies showed that the maximum explanation of the phenotypic variance of the meat quality traits was 50% for the ultimate pH trait using these ten genes only. Additional studies showed that the gene expression of several of the genes was correlated with each other. We conclude that the genes initially selected from the microarray study were robust, explaining variances of the genes for the meat quality traits.     

Effect of VRTN gene polymorphisms on Duroc pig production and carcass traits,and their genetic relationships

The thoracic vertebral number is associated with body length and carcass traits, and represents one of the most important traits in the pig industry. Recent studies have shown that vertnin (VRTN) gene is associated with variations in the vertebral number in commercial European pigs. However, the genetic relationships and effect of this VRTN gene in pig production and carcass traits remain uncertain. Therefore, we investigated the genetic relationships among traits such as vertebral numbers, carcass weight and length‐related traits, and meat production traits, and the effect of VRTN gene polymorphisms on these traits in a Duroc purebred population selected for its meat production traits. Highly positive genetic correlations were obtained between the thoracic vertebral numbers and length‐related traits (0.56 to 0.84), whereas low correlations were obtained with production traits and carcass weight (?0.16 to 0.05). VRTN gene polymorphisms indicated that the number of thoracic vertebrae and length‐related traits were significantly associated with the VRTN genotype, but had no significant effect on production traits and carcass weight. The results indicate that VRTN gene may be used as an effective selection marker to obtain pigs with high thoracic vertebral numbers and length‐related traits, without adversely affecting meat production traits.     

Farmers’ breeding practices and traits of economic importance for indigenous chicken in RWANDA

Data on breeding practices and traits of economic importance for the indigenous chicken (IC) were collected through personal interviews using structured questionnaires and direct observations of chicken management practices. The study was conducted from November 2015 to January 2016 in Rwamagana, Rulindo, Ruhango, Kicukiro and Muhanga districts of Rwanda. Data were collected and analysed through computation of indices, which represented a weighted average of all rankings of a specific trait. Spearman’s non-parametric rank correlation was calculated for ranking of traits of economic importance to indicate the directional effects. The results on chicken ecotypes and their attributes showed that prolificacy, mature weight, disease tolerance, egg number and heat tolerance were highly preferred. The dwarf ecotype was most abundantly reared (38.84%) and considered to be significantly smaller and to have poorer growth rate, but to have better prolificacy than other indigenous chicken ecotypes. Selection of breeding cock and hen was based on disease tolerance, body weight at sexual maturity, body size and growth rate. In addition, for hen, mothering ability and egg fertility (Fer) were considered. Indices for the traits perceived by farmers as of primary economic importance were egg yield (0.093), disease tolerance (0.091), high growth rate (0.089), prolificacy (0.088), high body weight (0.087) and egg fertility (0.083). The most important traits considered by the marketers were body weight (BW), disease tolerance (Dtol), plumage colour (Pcol), egg yolk colour (EYC), meat quality (MQ), growth rate (GR) and egg yield (EY) whereas for consumers, meat quality, egg yolk colour, egg yield, body weight and growth rate were considered. Among traits perceived as important by farmers, a positive and significant correlation was found between BW and GR and Fer. Correlation was moderate for BW and prolificacy, drought tolerance (Drtol), Dtol and EYC. BW was negatively correlated with temperament (Temp), heat tolerance, Pcol and egg shell colour (ESC). Regarding marketers and consumers’ preference rank correlation, positive and significant correlation was between BW and GR and MQ. As such, appropriate ecotypes (indigenous chicken) which have these characteristics need to be identified and utilised more based on their performance and adaption to the environment conditions to ensure efficient IC production.     

Influence of the sex-linked dwarfing gene (dw) on the contribution of dietary lipid to yolk lipid synthesis

1. The efficiency and time course of dietary fatty acid incorporation into lipids of egg yolk and abdominal adipose tissue was compared in "White Leghorn", normal (Dw) and dwarf (dw) laying hens at 56 weeks of age, using 14C labelled linoleic acid. 2. The sex-linked dwarfing gene, dw, was shown to reduce not only body weight and abdominal fat pad deposition, but also yolk production and the average clutch size. 3. Higher peak incorporation and total recovery of the linoleic acid radioactivity into yolk lipids, but lower label recovery into adipose tissue triglycerides were found in dwarf hens. 4. The higher esterification of the dietary linoleic acid in its native form into dwarf yolk triglycerides indicates that dwarf hens use more dietary lipids to synthesise yolk lipids but these results also suggest that the dw allele might reduce the lipogenic capacities of the liver and adipose tissue in laying hens.