Dwarf Hens Research Articles

Variation of egg proteins between bird varieties by using SDS-PAGE

Proteins are essential constituents of all organisms; both egg white proteins and egg yolk are source of protein. The aim of this study was conducted to perform preliminary studies to analyses and compare egg white proteins and yolk proteins from different avian species (guineafowl, dwarf hens, local hen, Shami, turkey, duck, geese, partridge and quail) via or with SDS-PAGE (Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis ). 18 Fresh eggs of different poultry species (guineafowl, dwarf hens, local hen, Shami, turkey, duck, geese, partridge and quail) were collected from various farms in the Sulaimani province. Data on egg proteins were analyzed using Statistical Xlstate used for dendrogram construction and PCA. The main egg white proteins were Ovomicin, Ovotransferrin, Ovalbumin, Flavoprotein, α- chymotrypsinogen, and Trypsin inhibitor. The main lipoproteins were Apovitellenin VI, Apovitellenin Vb, Apovitellenin V, Apovitellenin IIIa, Apovitellenin III, Apovitellin 7, B-Livetin, Apovitellenin IIa, Apovitellenin II, and Apovitellenin I. All these lipoproteins were observed in the nine birds species. The egg white proteins and yolk lipoproteins for nine species were examined. It can be concluded the large differences were found in a mount of egg white proteins and yolk lipoproteins of the nine species of birds.

In-Depth Duodenal Transcriptome Survey in Chickens with Divergent Feed Efficiency Using RNA-Seq.

Since the feed cost is a major determinant of profitability in poultry industry, how to improve feed efficiency through genetic selection is an intriguing subject for breeders and producers. As a more suitable indicator assessing feed efficiency, residual feed intake (RFI) is defined as the difference between observed and expected feed intake based on maintenance and growth. However, the genetic mechanisms responsible for RFI in chickens are still less well appreciated. In this study, we investigated the duodenal transcriptome architecture of extreme RFI phenotypes in the six brown-egg dwarf hens (three per group) using RNA sequencing technology. Among all mapped reads, an average of 75.62% fell into annotated exons, 5.50% were located in introns, and the remaining 18.88% were assigned to intergenic regions. In total, we identified 41 promising candidate genes by differential expression analysis between the low and high RFI groups. Furthermore, qRT-PCR assays were designed for 10 randomly chosen genes, and nine (90.00%) were successfully validated. Functional annotation analyses revealed that these significant genes belong to several specific biological functions related to digestibility, metabolism and biosynthesis processes as well as energy homeostasis. We also predicted 253 intergenic coding transcripts, and these transcripts were mainly involved in fundamental biological regulation and metabolism processes. Our findings provided a pioneering exploration of biological basis underlying divergent RFI using RNA-Seq, which pinpoints promising candidate genes of functional relevance, is helpful to guide future breeding strategies to optimize feed efficiency and assists in improving the current gene annotation in chickens.

Effect of sex-linked dwarf gene on exterior appearance, productive performance and egg characteristics in a colored broiler dam line

The effect of sex-linked dwarf gene was investigated through comparison of dwarf hens with their full-sib normal sisters obtained by mating heterozygous males (DW/dw) to normal females (DW/_) from line F (used as maternal form for production of slow-growing colored chickens) with respect to the following traits: body weight, shank and keel length at 40 weeks of age, age of sexual maturity (at 50 % production), egg production, egg weight, feed intake, feed utilization, livability, fertility, hatchability and egg quality characteristics. The results demonstrated that the dw gene caused statistically significant reduction of body weight by 29.15 %, shank length by 20.17 %, keel length by 7 % and egg weight by 5.72 % (p<0.001). The hens with normal genotype attained sexual maturity 7 days earlier (p<0.001), but nevertheless, rate of lay was similar to that of mini forms. There were no considerable differences between both genetic groups with respect to livability percentage over the production cycle. Dwarf hens consumed by 23.38 % less feed (p<0.01) than normal sized hens and converted nutrients more efficiently by 12.69 % (p<0.05). The presence of dw gene in hen genotype increased the eggshell percentage, reduced egg yolk and albumen weights and had no effect on their quality. The positive effect of the sex-linked dwarf gene on economically important traits - feed intake and feed conversion, hatchability of eggs set, is a prerequisite for the development of more efficient broiler breeder hens for production of slow-growing chickens.

Genetic analysis for dynamic changes of egg weight in 2 chicken lines

One of the main concerns for poultry producers is how to maintain egg uniformity and stability in size and weight following the rapid growth during the early laying period. In this study, we aimed to investigate the increase in egg weight with advancing hen age, and to estimate genetic parameters of these increment traits in 2 pure lines of chickens (i.e., 2,010 White Leghorn and 1,200 brown-egg dwarf hens), using the restricted maximum likelihood method with the DMU procedure. We collected age at first egg (AFE), first egg weight (FEW) and kept records of egg weight per 10 wk from 30 to 60 wk of age. Meanwhile, the increments of egg weight were calculated for the evaluation of age-dependent dynamic changes. The increment of egg weight gained dramatically before 30 wk of age and became slower with the advance of age. Heritability estimates of AFE were larger than 0.32, and the low to moderate genetic correlations between AFE and FEW were observed in the 2 lines. The FEW showed high variation level compared with egg weights at later ages in the 2 lines, and had moderate heritability estimates in White Leghorns (0.20) and dwarf hens (0.33). Egg weights at different ages were highly heritable in the 2 lines (h2 ≥ 0.35), and had strong genetic and phenotypic correlations among different ages. The estimates of heritability for most increment traits were low to moderate, especially those increments for 10-wk intervals ranging from 0.00 to 0.14. The genetic correlations among 3 consecutive egg weight increments for 10-wk intervals were low to moderate. Our results in the 2 lines should provide important insights into the genetic architecture of increment traits and offer some suggestions for producing uniform and stable eggs in response to advancing age.

Low-density lipoprotein receptor-related protein 2 gene is associated with egg-quality traits in dwarf layers

Some members of the low-density lipoprotein receptor (LDLR) family play important roles in the regulation of lipoprotein metabolism and egg quality traits. Low-density lipoprotein receptor-related protein 2 (LRP2) gene belongs to the LDLR super family, and widely expresses in many tissues. This work identified and genotyped 1 single-nucleotide polymorphism (SNP), T14347C, at 3'-UTR of the LRP2 using matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS), and analyzed the effects of the SNP (T14347C) on egg-quality traits in 544 dwarf hens from 44 sire families. Frequencies of this SNP in the studied population did not agree with the Hardy-Weinberg equilibrium (P < 0.0001). Egg weight, albumen weight, albumen height, and albumen ratio of the TT genotype were significantly higher than those of the CC genotype (P < 0.05), whereas eggshell ratio of the TT genotype was significantly lower than that of the CC genotype (P < 0.05). The relative expression level of the LRP2 gene in the magnum was determined by real-time quantitative PCR. The gene expression of genotype CC individuals was significantly higher than that of TT and CT birds (P < 0.05). By combining both genetic effects and expression analyses results, we propose that the LRP2 gene is a good candidate gene, exhibiting a key role in albumen formation processes.

The effect of frizzle gene and dwarf gene on reproductive performance of broiler breeder dams under high and normal ambient temperatures

In 3 experimental runs, the influence of genotype × temperature interactions on the reproductive traits (sexual maturity, egg production, fertility, hatchability, and chick production) of hens of a broiler breeder dam line carrying major genes for dwarfism (dw-) and frizzle (F) was investigated. In experiments 1 and 2, the hens were caged individually under hot (30°C) and temperate (19°C) temperatures, from wk 18 to 72 of age, whereas in experiment 3, hens were kept under moderate temperature (24°C). Hens in experiment 1 were heterozygous for the frizzle gene, and those in experiments 2 and 3 were homozygous, both with and without the dwarf gene. Hens without the above-mentioned major genes (ffDw-) served as control lines. In experiment 1, the frizzle gene (Ff) had no significant effect on sexual maturity, egg production, fertility, hatchability, and chick number under the 2 environmental conditions. In experiment 2, there was a significant interaction between feathering genotype (FF) and environmental temperature for all traits except sexual maturity. Under heat stress, there was a distinct reduction in all reproductive traits except sexual maturity for normally feathered hens compared with frizzle-feathered hens, whereas under temperate conditions, egg production and number of chicks of the FF genotype were reduced and sexual maturity was delayed. In experiments 1 and 2, the dw- gene showed a depressive effect on the growth of hens. In experiment 1, the interaction between dwarf genotype and environmental temperature for egg production was significant. Under temperate conditions, the egg production of dwarf hens was inferior to that of normally sized birds, whereas under hot temperatures, the egg production of the 2 body sizes did not differ. In experiment 2, for sexual maturity, egg production and fertility locus × locus interactions could be determined. The genotype combining the 2 major genes (FFdw-) proved to be inferior to the normally feathered dwarf type (ffdw-) for laying performance but superior in fertility. Under the conditions in experiment 3, the egg production of dwarf birds was significant reduced.

The Broiler Breeder Paradox: ethical, genetic and physiological perspectives, and suggestions for solutions

1. Due to intensive selection, broiler chickens became the most efficient meat-producing animals because of their fast growth, supported by a virtually unlimited voluntary feed intake. These characteristics cause many problems in the management of broiler breeder hens because of the negative correlation between muscle growth and reproduction effectiveness. 2. This problem, namely the fast muscle growth versus reproduction health paradox, induces a second paradox, acceptable reproduction and health versus hunger stress and impaired welfare, because broiler breeder hens require dedicated programmes of feed restriction (1) to maximise egg and chick production and (2) to avoid metabolic disorders and mortality in broiler breeders. 3. Given that poultry selection is a global large-scale business and chickens are a prolific species, improvement in profit can only be obtained by selecting on feed conversion and/or for higher breast meat percentage, which will intensify the broiler–breeder paradox. 4. New feeding strategies are being studied, but it is questionable if the paradox can be solved by management tools alone. Because breeding and selection are long-term processes, involving animals, farmers, consumers, industry, environment etc., a more sustainable breeding goal needs to be determined by a multidisciplinary approach and an open debate between several actors in the discussion. 5. Using dwarf broiler breeder hens could be one alternative, because dwarf hens combine relatively good reproductive fitness with ad libitum feeding. Another possibility is to accept lower broiler productivity by assigning economic values to welfare and including integrity traits in an extended breeding goal.

Effect of soybean meal substitution by different concentrations of sunflower meal on egg quality traits of white and coloured dwarf dam lines

1. The effect of soybean meal substitution by different concentrations of sunflower meal on egg quality traits of white and coloured dwarf dam lines was investigated. 2. A total of 144 dwarf hens (38 weeks of age) from the same hatch were randomly divided into 12 groups of 12 birds (4 dietary treatments × 3 replicates). 3. A 2 × 4 factorial design was used to study the effect of 2 lines (Factor A) and substitution of soybean meal (SBM) with 4 concentrations (0, 10, 15 and 20%) of sunflower meal (SFM) [Factor B] on egg quality traits of dwarf dam line hens. 4. All the diets were designed to be isocaloric (11⋅3 MJ ME/kg) and isonitrogenous (180 g/kg crude protein) The duration of the experiment was 12 weeks. 5. Analysis of variance indicated a highly significant line effect. There were non-significant effects of substitution of soybean meal with different concentrations of sunflower meal on egg quality traits except for Haugh unit. 6. White plumaged dwarf broiler breeder dam line produced significantly fewer, but larger, eggs than coloured dwarf dam line hens.

Effects of Dietary Conjugated Linoleic Acid on the Fatty Acid Profile and Cholesterol Content of Egg Yolks from Different Breeds of Layers

Brown Dwarf hens and White Leghorn hens were fed corn- and soybean meal-based diets containing 0, 2.5, or 5.0% conjugated linoleic acid (CLA) for 56 d to explore the effects of dietary CLA on the fatty acid profile and cholesterol content of egg yolks from laying hens of different breeds. Four hens were placed in 1 cage, and 3 cages were grouped as 1 replicate, resulting in 6 replicates per treatment. After feeding the experimental diets for 11 d, eggs were collected to determine the fatty acid composition of the egg yolks. From d 54 to 56, eggs were collected to measure the cholesterol content of yolks, and on d 56, a hen was selected randomly from each replicate and bled to determine the cholesterol content in plasma. There was a significant effect of layer breed on layer performance and egg composition. Concentrations of stearic, arachidonic, and docosahexaenoic acids were higher in the yolks of Brown Dwarf hens than in those of White Leghorn hens. Enrichment of cis-11, trans-13 was higher in the yolks of White Leghorns, but cis-10, cis-12 was higher in those of Brown Dwarf hens. In contrast, feed intake and egg weight, as well as yolk weight and its ratio to egg, were decreased by the 5% dietary CLA treatment. Egg production and feed efficiency were not affected by dietary CLA. Concentrations of total CLA and CLA isomers in the yolk lipids increased (P < 0.01) with increasing dietary CLA. Furthermore, yolk cholesterol was increased with increasing dietary CLA (P < 0.01), but this was significantly decreased in Brown Dwarf hens (P < 0.01) by feeding 2.5% CLA. There was no apparent correlation between yolk cholesterol content and serum cholesterol content. In conclusion, Brown Dwarf layers had the breed-specific characteristics of enrichment of CLA isomers and fatty acids in yolk lipids in response to dietary CLA.

Sex-linked Dwarf Gene for Broiler Production in Hot-humid Climates

This review has been done to examine sex-linked dwarf gene in broiler production in hot-humid climates. Introduction of sex-linked dwarf gene especially in hot harsh tropical environments brings a great advantage for broiler production. The heavy broiler parent suffers due to the stress of these adverse climates. Sex-linked dwarf genes reduce body weight, egg weight, but are superior for adaptability under harsh tropical environments, with a lower requirement for housing and feed, better survivability and reproductive fitness giving fewer defective eggs, more hatching eggs, better fertility, hatchability, feed conversion efficiency and resistance to disease. Overall the cost of chick production from dwarf hens is lower than from their normal siblings. Market weights of broilers from sex-linked dwarf dams is almost similar to those of broilers from normal dams with normal sires. But the net benefit of broiler production from sex-linked dwarf dams is found to be greater than that of broilers from normal dams. This will be the most important to the rural communities in Bangladesh and in other countries where the similar environment and socio-economic conditions exist. Therefore, sex-linked dwarf hens might be used in broiler breeding plan as well as broiler production in the tropics.

Effect of Dwarfism on Reproductive and Meat Yield Parameters of Crossbred Chicken

Twenty four indigenous autosomal dwarf hens were selected and divided equally into 3 groups. Rhode Island Red, White Leghorn and Fayoumi Cocks, 2 for each were placed to each group respectively for breeding. Sixty eggs were selected from each group and hatched in a forced draft incubator. Among those, 36 healthy day-old chicks from each group were selected and reared up to 20 weeks of age. The chicks were identified as normal and dwarf genetic groups at 8 weeks of age. The aim of this study was to observe the reproductive parameters of crosses and parameters related to the meat yield of normal and dwarf genetic group of crossbred chicken under farm condition. Fertility, hatchability on total eggs and hatchability on fertile eggs of cross B (95.57; 68.71; 72.41) were higher (p<0.01) than cross A (93.44;63.44;67.62) and cross C (90.92;60.89;67.19). Dead-in-germ and dead-in-shell were statistically higher (p<0.01) in cross C than cross A&B. Reduced adult body size, improved feed conversion and higher livability were found in all genetic groups of dwarf crossbred. Among those, White Leghorn was found as the best one also considering its different dressing yields. Advantages of adw gene in terms of a good scavenger could better be exploited by introgressing in exotic smaller breeds like White Leghorn from indigenous dwarf chicken.

Effects of Dietary Conjugated Linoleic Acid on the Productivity of Laying Hens and Egg Quality During Refrigerated Storage

Five hundred and four 40-wk-old Brown Dwarf hens (1.51 ± 0.08 kg BW) were fed corn-soybean meal diets containing 0, 1, 2, 3, 4, 5, or 6% conjugated linoleic acid (CLA) for 56 d to measure the effects of dietary CLA on laying hen productivity and egg quality during refrigerated storage. Four hens were placed in 1 cage, and 3 cages were grouped as 1 replicate resulting in 6 replicates per treatment. After feeding the experimental diets for 11 d, eggs were collected to determine the fatty acid composition of egg yolks. From d 12 to 18, eggs from hens fed diets containing 0, 2, 4, and 6% CLA diets were stored at 4°C for up to 28 d. At designated times (1, 14, or 28 d), eggs were taken, broken, and shelled to evaluate water content, pH, and ion concentration. Firmness of hard-cooked egg yolk was also determined. With increased dietary CLA, feed intake, BW gain, rate of egg production, egg weight, and feed efficiency all decreased linearly (P < 0.01). The weight of the yolk, albumen, and shell decreased linearly (P < 0.01) with increasing dietary CLA. Concentration of CLA in the yolk lipids increased quadratically (P < 0.01), with increasing dietary CLA. Concurrent increases (P < 0.01) in the concentration of myristic, palmitic, and stearic acids and decreases (P < 0.01) in oleic, linoleic, linolenic, and archidonic acids in egg yolk lipids were observed. Days of storage and CLA (P < 0.01) increased yolk firmness. Egg yolk water content and pH increased with storage and CLA content (P < 0.01). Corresponding decreases were observed in albumen pH. Regardless of dietary treatment, the concentrations of Na, K, and Mg in egg yolks increased with longer storage time. At 28 d of storage, there was a linear (P < 0.01) increase in Na, K, and Mg content in egg yolks as dietary CLA increased. In contrast to the egg yolk, the concentrations of Na, K, and Mg in egg albumen decreased with storage time. On d 28, there was a linear decrease (P < 0.01) in the Na content of albumen with increasing CLA. This study suggests that the greater firmness of CLA-fed eggs might be related to the change of pH, water content, and ion concentrations during refrigerated storage.

Comparative Physical Features, Egg Production and Egg Quality Characteristics of Normal and Dwarf Indigenous (Deshi) Hens of Bangladesh

Yeasmin, T. and Howlider, M.A.R. 1998. Comparative physical features, egg production and egg quality characteristics of normal and dwarf indigenous (Deshi) hens of Bangladesh. J. Appl. Anim. Res., 13: 191–196. The physical features, egg production and egg quality characteristics of normal and dwarf deshi hens were compared for a period of 36 weeks between 32 and 68 weeks of age. In a test cross one known normal RIR cock was mated to 7 dwarf deshi hens and 14 offsprings were produced to determine the nature of dwarf gene in deshi chicken population. Shank length, maximum wing feather length and body weight were higher in normal than in dwarf hens. The dwarf hens had significantly (P<0.01) higher hen day egg production, egg mass production and feed utilization than their normal sized counterparts. However, the dwarf hens gave lighter eggs and consumed significantly less feed than the normal sized hens, showing better efficiency of feed utilization. All the egg quality characteristics measured were similar in both genotypes, except fresh yolk weight, which was higher in eggs of dwarf hens than that of normal sized birds. The test cross results revealed that the dwarf gene in deshi chicken is autosomal recessive in nature.

Increase of egg weight with age in normal and dwarf, purebred and crossbred laying hens

Summary - An exponential curve, W = P - Q exp (-Rt) was fitted to egg weights (W) of individual hens from 8 genetic groups tested for egg production from 18-51 weeks of age (t). The groups were constituted of the combination of genotype at the sex-linked dwarfism locus (normal or dwarf) and line (White Leghorn, Brown Egg and both reciprocal crosses). The least-squares mean of the residual standard deviation about the curve was between 1.27 and 1.74 g in the 8 groups and estimated values of the initial P-Q and mature egg P weights were between 26.9 and 33.9 g and 56.9 and 65.8 g, respectively. Effects of genotype and line as well as heterosis were estimated for both egg weights and for rate of growth relative to the remaining expected growth (R). R was smaller for dwarf hens which thus reached mature egg weight later than normal females. Significant heterosis was found for both egg weights of dwarf hens (12.6 and 9.5%) and for the initial egg weight of normal ones (12.8%). Negative heterosis for R obtained for dwarf hens (-17.4%) corresponded to a flatter egg weight curve of these crossbreds.

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.

Influence of the Sex-Linked Dwarfing Gene (dw) on the Lipid Composition of Plasma, Egg Yolk and Abdominal Fat Pad in White Leghorn Laying Hens: Effect of Dietary Fat

The levels and fatty acid composition of lipids were determined in very low density lipoproteins (VLDL, d less than 1.006), yolk and abdominal adipose tissue of normal (Dw) and sex-linked dwarf (dw) White Leghorn laying hens. Effects of adding 4% tallow to the diet were also examined. In 40-wk-old hens, neither plasma lipids (triglycerides, phospholipids and cholesterol), VLDL levels, nor the chemical composition of VLDL was altered by the dw gene or dietary fat. Dwarfism reduced egg and yolk weights. Though the yolk lipid content was similar in normal and dwarf hens, yolk from dwarfs had slightly more phospholipids and less triglycerides than yolk from normal hens. Higher linoleic acid [18:2(n-6)] and lower oleic acid [18:1(n-9)] levels were observed in triglycerides of VLDL, yolk and adipose tissue from dwarf hens. In addition, the dietary fatty acid pattern had a greater influence on the fatty acid composition of the yolk lipid major precursors (VLDL triglycerides) in dwarf laying hens than in normal hens. These results suggest that the dwarfing gene might reduce the hepatic de novo fatty acid synthesis and/or dwarf hens might incorporate more dietary lipids into yolk than do normal hens.

A decreased capacity of hepatic growth hormone (GH) receptors and failure of thyrotrophin-releasing hormone to stimulate the peripheral conversion of thyroxine into triiodothyronine in sex-linked dwarf broiler hens

The effect of two different doses of thyrotrophic releasing hormone (TRH) upon the plasma levels of growth (GH) and thyroid hormones in both sex-linked dwarf (dw) and normal (Dw) broiler hens was determined. In normal hens, 1.5 and 24 microg TRH/kg increased the GH plasma concentrations after 15 min. Plasma concentrations of T3 increased significantly 1 h after TRH injection, whereas T4 concentration decreased after 2 following injection of 24 microg/kg TRH. In dwarf hens both doses of TRH increased the plasma concentrations of GH and the GH response lasted longer. However, TRH was ineffective in raising T3 and T4 levels. Saline-injected dwarf birds showed no differences in plasma T4 and T3 levels in comparison with normal hens. A smaller number of hepatic cGH receptors was found in dwarf hens, whereas the affinity of the hepatic GH receptor was not influenced by the genotype. It is concluded that the sex-linked dwarf broiler hen is unable to respond to a TRH-induced GH stimulus probably because of a deficiency in hepatic GH receptors resulting in a failure to stimulate the T4 to T3 converting activity.

Parental Effects on Performance of Broiler Chicken Progenies

Mortality among broiler progeny from a meat-type parent population, consisting of four maternal genotypes (two normal and two dwarf) mated with two normal paternal genotypes (White and Gold) and fed three different breeder diets was not significantly (P>.05) affected by genotypes or parental dietary treatments. Body weights of male and female progenies from matings with White males were significantly (P<.05) heavier at both 21 and 42 days than those sired by Gold males but progeny sired by Gold males exhibited the best feed conversion. The progeny from normal hens were heavier, had a better feed conversion up to 21 days, and yielded higher monetary returns than those from dwarf hens. Parental diets had no significant effect on progeny weights, feed conversion, or monetary returns. A low magnitude first-order interaction, involving paternal and maternal genotypes, occurred for feed conversion and monetary returns.

Determination of Body Fat and Moisture in Dwarf Hens with Near-Infrared Reflectance Spectroscopy

The accuracy of near-infrared (NIR) reflectance (R) spectroscopy for predicting whole-carcass percent fat and moisture in mature dwarf hens was established. Fat and moisture contents of ground samples from 99 hens were determined by standard fat extraction and oven-drying procedures. Homogenized samples from the same birds were also scanned in a NIR spectrophotometer (1.445 to 2.310 μm), and the log 1/R was recorded. Calibration equations were generated with 49 randomly selected samples, and the coefficients of determination between chemical values for fat and moisture and reflectance readings were .92 and .94, respectively. The caliration equations were then used to predict fat and moisture values in the remaining 50 samples. Coefficients of determination between the predicted fat and moisture values and actual chemical values were .96 and .95, respectively. Near-infrared reflectance spectroscopy was found to be a rapid and effective method for determining percent body fat and moisture.

Body Composition and Other Physical Parameters as Determinants of Age at Sexual Maturity and Performance Efficiency in Dwarf Hens Divergently Selected for Body Weight

Hens in this study were produced from random breeding within lines (high, low, and control) of dwarf White Leghorns that had been divergently selected for four generations for 20-week body weight. Birds were weighed at 10 weeks of age and placed in individual cages at 18 weeks of age. Body weights, shank lengths, and egg weights were obtained at sexual maturity (day of first egg) and at 4, 8, 12, and 16 weeks after sexual maturity. Egg production was recorded during 28-day periods. Thirty hens/line were sampled at sexual maturity and at the above times after sexual maturity for body composition (percent fat, protein, moisture, and ash). High line hens showed increased percent body fat and reduced percent protein and moisture compared to low and control hens. Coefficients of determination (R2) for age at sexual maturity and body weight were small (R2 <.20) for high and control hens. There were no meaningful relationships between body weight or other physical measurements and sexual maturity in low hens. There were no significant relationships between body composition and age at sexual maturity in high and control hens. There was a strong cubic association (R2=.73; P<.001) between percent ash and age at sexual maturity in low hens, although the biological importance of this relationship was uncertain. Coefficients of determination between body weight and performance efficiency (egg mass per body weight) were small to moderate (R2 = .04 to .46) for high and control hens. The relationship of body weight to efficiency was nonsignificant for low hens, even though these birds were most efficient. The effects of body composition on performance efficiency were related to composition changes associated with selection for body weight.