Asymmetries in chickens from lines selected and relaxed for high or low antibody titers to sheep red blood cells.

Wattle length, width, and area were measured to classify bilateral asymmetries in four lines of chickens. The lines were the S26 generation of White Leghorns selected for high (HAS) or low (LAS) response to sheep red blood cells and sublines in which selection had been relaxed for three generations (high antibody relaxed [HAR] and low antibody relaxed [LAR]). Antibody titers (AB) were greater for HAS than for HAR with both greater than for LAS and LAR which while different for males did not differ for females. The low antibody lines were heavier and reached sexual maturity at younger age than the high antibody lines. In general, wattle length, width, and area were greater in the low than high antibody lines. In 24 comparisons for bilaterality 18 exhibited fluctuating asymmetry and 6 exhibited directional asymmetry with 5 of the 6 being for wattle length. There was not a clear pattern for changes in degree of asymmetry when selection was relaxed for 3 generations. For females, the relative asymmetry (RA) of wattle area was larger (p≤0.05) for HAR than for LAR and not different from the selected lines and relaxed lines. There were no differences among lines for RA of wattle length and width of females and wattle length, width, and area of males.

Chickens from lines selected for high and low body weight show differences in fatty acid oxidation efficiency and metabolic flexibility in skeletal muscle and white adipose tissue.

OBJECTIVE: The Virginia lines of chickens have resulted from more than 55 generations of artificial selection for low (LWS) or high (HWS) juvenile body weight. We hypothesized that the relative hyperphagia and greater body weight in juvenile HWS chickens are associated with altered fatty acid oxidation efficiency and metabolic flexibility in tissues associated with energy sensing and storage, and relative cellular hypertrophy in white adipose tissue. METHODS: Hypothalamus, liver, pectoralis major, gastrocnemius, abdominal fat, clavicular fat and subcutaneous fat were collected from the juvenile (56-65 days old) LWS and HWS chickens for metabolic, gene expression and histological assays. RESULTS: The HWS chickens had reduced fatty acid oxidation efficiency in abdominal fat (P<0.0001) and reduced rates of oxidation in abdominal fat and gastrocnemius (P<0.0001) as compared with the LWS. There was reduced citrate synthase activity in white adipose tissue (P<0.0001) and greater metabolic inflexibility in skeletal muscle (P=0.006) of the HWS compared with the LWS. Greater pyruvate dehydrogenase kinase 4 (PDK4) and forkhead box O1A (FoxO1) mRNA were found in skeletal muscle and white adipose tissue of 56-day-old HWS than LWS. Expression of peroxisome proliferator-activated receptor γ (PPARγ) in all adipose tissue depots was greater (P<0.05) in LWS than in HWS chickens. The HWS chickens had larger (P<0.0001) and fewer (P<0.0001) adipocytes per unit area than the LWS. CONCLUSION: Compared with the LWS, the HWS chickens have impaired metabolic flexibility and fatty acid oxidation efficiency due to greater pyruvate dehydrogenase activity to accommodate the influx of acetyl-CoA from fatty acid oxidation in skeletal muscle and adipose tissue. These metabolic adaptations can be linked to differences in gene expression regulation, adipocyte cellularity and body composition between the lines, which may provide valuable insight into metabolic disorders in other species.

Chickens from lines artificially selected for juvenile low and high body weight differ in glucose homeostasis and pancreas physiology.

Artificial selection of White Plymouth Rock chickens for juvenile (day 56) body weight resulted in two divergent genetic lines: hypophagic low weight (LWS) chickens and hyperphagic obese high weight (HWS) chickens, with the latter more than 10-fold heavier than the former at selection age. A study was designed to investigate glucose regulation and pancreas physiology at selection age in LWS chickens and HWS chickens. Oral glucose tolerance and insulin sensitivity tests revealed differences in threshold sensitivity to insulin and glucose clearance rate between the lines. Results from real-time PCR showed greater pancreatic mRNA expression of four glucose regulatory genes (preproinsulin, PPI; preproglucagon, PPG; glucose transporter 2, GLUT2; and pancreatic duodenal homeobox 1, Pdx1) in LWS chickens, than HWS chickens. Histological analysis of the pancreas revealed that HWS chickens have larger pancreatic islets, less pancreatic islet mass, and more pancreatic inflammation than LWS chickens, all of which presumably contribute to impaired glucose metabolism.

Exposure of embryos to cyclically cold incubation temperatures durably affects energy metabolism and antioxidant pathways in broiler chickens.

Cyclically cold incubation temperatures have been suggested as a means to improve resistance of broiler chickens to ascites; however, the underlying mechanisms are not known. Nine hundred eggs obtained from 48 wk Ross broiler breeders were randomly assigned to 2 incubation treatments: control I eggs were incubated at 37.6°C throughout, whereas for cold I eggs the incubation temperature was reduced by 1°C for 6 h daily from 10 to 18 d of incubation. Thereafter, chickens were reared at standard temperatures or under cold exposure that was associated or not with a postnatal cold acclimation at d 5 posthatch. At hatch, hepatic catalase activity and malondialdehyde content were measured. Serum thyroid hormone and triglyceride concentrations, and muscle expression of several genes involved in the regulation of energy metabolism and oxidative stress were also measured at hatch and 5 and 25 d posthatch. Cold incubation induced modifications in antioxidant pathways with higher catalase activity, but lower expression of avian uncoupling protein 3 at hatch. However, long-term enhancement in the expression of avian uncoupling protein 3 was observed, probably caused by an increase in the expression of the transcription factor peroxisome proliferator activated receptor-γ coactivator-1α. These effects were not systematically associated with an increase in serum triiodothyronine concentrations that were observed only in chickens exposed to both cold incubation and later acclimation at 5 d with cold rearing. Our results suggest that these conditions of cyclically cold incubation resulted in the long-term in changes in antioxidant pathways and energy metabolism, which could enhance the health of chickens reared under cold conditions.

Expression profiles of muscle genes in postnatal skeletal muscle in lines of chickens divergently selected for high and low body weight.

Long-term genetic selection for BW has generated high weight select (HWS) and low weight select (LWS) lines of chickens. These lines show an approximate 10-fold difference in BW at selection age (d 56). The objective of this study was to profile the expression of master regulators of early lineage specification (Pax3, Pax7) and myogenic regulatory factors (Myf5, MyoD1, MyoG, and Mrf4) on day of hatch and d 7, 28, and 56 in pectoralis major and gastrocnemius muscles. There was a line × age interaction for expression of all 6 genes in both muscles. In pectoralis major muscle, Pax3, MyoD1, and Mrf4 showed greater expression in LWS than HWS at day of hatch, whereas all 6 genes showed greater expression in HWS than LWS at d 28. In gastrocnemius muscle, Pax3, Myf5, MyoD1, and MyoG showed greater expression in LWS than HWS at day of hatch, whereas Pax7, Myf5, MyoD1, and Mrf4 showed greater expression in HWS than LWS at d 28. At day of hatch there was no difference in fiber number in gastrocnemius muscle between HWS and LWS; however, HWS had greater fiber diameter than LWS. These results indicate that in LWS there is enhanced expression of genes that are necessary for proliferation of progenitor muscle cells and muscle cell differentiation at day of hatch compared with HWS, but by d 28 these genes are expressed greater in HWS than LWS. Thus, long-term selection for growth has altered the pattern of muscle gene expression.

Research Note: Phenotypic trends for the multigenerational advanced intercross of the Virginia body weight lines of chickens.

Random samples from generation S41 of the Virginia high and low 8-week body weight lines formed the base population for producing a multigenerational reciprocal intercross population. Although genetic mapping from this intercross has been reported, lacking are phenotypic trends across multiple generations. Here, we provide phenotypic information for the parental base population, the F1 reciprocal cross, and subsequent segregating recombinant generations F2 to F17. Heterosis for the selected trait in the F1 was negative for both reciprocal crosses. Phenotypic correlations for the selected trait in the recombinant generations were essentially nil for both males and females as was percent sexual dimorphism and coefficients of variation.

Phenotypic responses of chickens to long-term, bidirectional selection for juvenile body weight--historical perspective.

A long-term selection experiment for high (HWS) and low (LWS) BW at 8 wk of age (BW8) was conducted in White Plymouth Rock chickens. Over 54 generations of selection, responses to bidirectional selection were profound. Increase in BW8 in line HWS was linear, and there was a significant quadratic response in line LWS for BW at both 4 and 8 wk of age. Although there is no indication that line HWS has come close to approaching a selection limit in more than 50 generations, selection limits occurred in line LWS chickens at generation 48 for females and generation 50 for males. Evidence also exists that one or more beneficial mutations have occurred in line HWS, aiding in progressive increases in BW8 over generations. Analyses of ratios of BW at 4 wk of age with those at 8 wk of age (ratio 4/8) revealed that LWS females grew proportionately faster through 4 wk of age than LWS males or HWS chickens. Comparisons of the selected lines with contemporary lines in which selection had been relaxed (discontinued) indicated that, in line HWS, the relaxed lines generally regressed toward original (preselection) values, suggesting that the linear response to single-trait selection was at least partially due to continued genetic variance. In LWS chickens, a series of plateaus in selection response occurred, but relaxed contemporary lines still regressed toward preselection values for BW8. In spite of the length of this selection experiment (54 generations), genetic variance and beneficial mutations have allowed continued, linear response to selection for increased BW8. Response to selection for decreased BW8 has been tempered by physiological barriers that have decreased survival of young chicks or the ability of females to reproduce. These findings are discussed in a historical perspective.

Low-coverage sequencing in a deep intercross of the Virginia body weight lines provides insight to the polygenic genetic architecture of growth: novel loci revealed by increased power and improved genome-coverage.

Genetic dissection of highly polygenic traits is a challenge, in part due to the power necessary to confidently identify loci with minor effects. Experimental crosses are valuable resources for mapping such traits. Traditionally, genome-wide analyses of experimental crosses have targeted major loci using data from a single generation (often the F2) with individuals from later generations being generated for replication and fine-mapping. Here, we aim to confidently identify minor-effect loci contributing to the highly polygenic basis of the long-term, bi-directional selection responses for 56-d body weight in the Virginia body weight chicken lines. To achieve this, a strategy was developed to make use of data from all generations (F2-F18) of the advanced intercross line, developed by crossing the low and high selected lines after 40 generations of selection. A cost-efficient low-coverage sequencing based approach was used to obtain high-confidence genotypes in 1Mb bins across 99.3% of the chicken genome for >3,300 intercross individuals. In total, 12 genome-wide significant, and 30 additional suggestive QTL reaching a 10% FDR threshold, were mapped for 56-d body weight. Only 2 of these QTL reached genome-wide significance in earlier analyses of the F2 generation. The minor-effect QTL mapped here were generally due to an overall increase in power by integrating data across generations, with contributions from increased genome-coverage and improved marker information content. The 12 significant QTL explain >37% of the difference between the parental lines, three times more than 2 previously reported significant QTL. The 42 significant and suggestive QTL together explain >80%. Making integrated use of all available samples from multiple generations in experimental crosses are economically feasible using the low-cost, sequencing-based genotyping strategies outlined here. Our empirical results illustrate the value of this strategy for mapping novel minor-effect loci contributing to complex traits to provide a more confident, comprehensive view of the individual loci that form the genetic basis of the highly polygenic, long-term selection responses for 56-d body weight in the Virginia body weight chicken lines.

Population dynamics of a long-term selection experiment in White Plymouth Rock chickens selected for low or high body weight.

The population dynamics of 2 lines of chickens from a long-term (59 generations) selection experiment were assessed based on pedigree data. These lines were propagated from phenotypic selection for low and high 8-wk BW in White Plymouth Rock chickens. Our objective was to determine whether the 2 lines maintained similar population structures over the selection horizon to allow meaningful comparisons of their performance data. A complete pedigree of 31,909 individuals, consisting of 102 founders, 1,064 from the parental generation, and 16,245 low weight (LWS) and 14,498 high weight (HWS) select chickens, was available. Inbreeding (F) and average relatedness (AR) coefficients were computed. Average F per generation and AR coefficients were 1.3 (SD 0.8) % and 0.53 (SD 0.001) for LWS, and 1.5 (SD 1.1) % and 0.66 (SD 0.001) for HWS. Mean F for the entire pedigree was 0.26 (0.16) and 0.33 (0.19), and maximum F was 0.64 and 0.63, in LWS and HWS, respectively. Based on Wright's fixation index, at generation 59, substantial genetic differences were established between lines. The effective population size was 39 in LWS and 33 in HWS. The effective number of founders was 17 and 15, effective number of ancestors were 12 and 8, and genome equivalents were 2.5 and 1.9 in LWS and HWS, respectively. About 30 founders explained the marginal contribution to both lines. By generation 59, only 7 male and 6 female founders contributed to both lines. Moderately high levels of inbreeding and low effective population sizes were inevitable, as this was a closed population. However, effects on the fitness of the population were expected to be less substantial because founders were a combination of 7 lines. The effective numbers of founders and ancestors were relatively low compared to the actual number of founders, as few ancestors contributed to descendants. Based on these evaluations, it can be inferred that LWS and HWS had similar population structures. Comparisons of selection responses in the 2 lines therefore should be reliable.

Phenotypic responses of chickens to long-term selection for high or low antibody titers to sheep red blood cells.

A long-term bidirectional selection experiment was conducted to study antibody response to SRBC. Lines, high antibody selection (HAS) and low antibody selection (LAS), originating from the same White Leghorn base population had undergone 37 generations of selection for either high or low antibody response 5 d after a single intravenous injection of 0.1 mL of a 0.25% suspension of SRBC antigen. Subpopulations, where selection was relaxed, were maintained as contemporaries with the selected lines from generations 16 to 24 [high antibody relaxed (HAR) and low antibody relaxed (LAR)] and 24 to 37. Body weights were obtained at 4, 24, and 38 wk of age and at the onset of lay (BW at first egg). Also measured were age in days to first egg, percentages of hen-day ovulations and normal egg production, and percentages of normal and defective eggs from total ovulation (PNE and PDE). Selection lead to a large divergence in antibody titers between the selected lines, with a plateau reached in line LAS. Line HAS and HAR females displayed higher antibody titers, lower BW4, and matured at older ages than those from LAS and LAR (P < 0.05). Correlations between BW at 4 wk and antibody titers were different between the selected lines, being positive in line LAS and negative in line HAS. Quadratic regression models fit well with antibody titers, BW4, and PNE, with limiting values for these traits calculated based on regression curves. For line HAS, plots showed that an increased tendency of antibody titers was followed by decreased BW4 and increased PNE. For line LAS, however, antibody titers and BW4 decreased in parallel while PNE increased. It appears that at the phenotypic level there was a resource balance between immune response, growth, and reproductive traits, which during long-term selection, individuals altered their dynamic of resource allocations to satisfy certain needs.

Egg quality traits differ in hens selected for high as compared with low antibody response to sheep red blood cells.

White Leghorn chickens were selected for 36 generations for high (HAS) or low (LAS) antibody response to SRBC 5 d after an intravenous challenge. Our objective was to determine differences in egg quality resulting from that selection. In total, eggs from 45 hens from each line were assessed for shape index (SI), weight (WT, g), albumen height (AH, mm), Haugh units (HU), yolk color (YC), and eggshell weight (ESW, g) and thickness (EST, mm). Three cycles representing early, middle, and late stages of production were examined. Eggs from HAS hens had higher SI scores (4.12 ± 0.55; P < 0.001) and greater AH (0.27 ± 0.12; P < 0.001) and HU (1.89 ± 0.91; P = 0.04) than LAS hens; conversely, eggs from LAS hens had greater EST (0.03 ± 0.01 g; P < 0.001) and heavier ESW (0.66 ± 0.09 g; P < 0.001) than HAS hens. Lines were similar for WT and YC (P > 0.52). Albumen height and HU decreased (P < 0.001), whereas WT, ESW, and EST increased (P < 0.001) over cycles for both lines. However, SI decreased in LAS hens, yet increased in HAS hens, across cycles (P < 0.001). An interaction between line and cycle was observed in WT, SI, ESW, and EST (P < 0.001), but only for WT did the interaction cause re-ranking across cycles. Egg quality was, generally, superior in HAS compared with LAS hens, suggesting that higher antibody response may maintain overall fitness.

Effect of manipulation of incubation temperature on fatty acid profiles and antioxidant enzyme activities in meat-type chicken embryos.

Eggs (n = 1,800) obtained from Ross broiler breeders at 32 and 48 wk of age were incubated at either a constant temperature of 37.6°C throughout (T1), or the temperature was reduced for 6 h to 36.6°C each day during embryonic age (EA) 10 to 18 (T2). Yolk sac, liver, and brain fatty acid profiles and oxidant and antioxidant status of liver and brain were measured at EA 14, 19, and day of hatch (DOH). Fatty acid profiles of yolk sac, liver, and brain were influenced by age of breeder with significant breeder hen age × incubation temperature interactions. At EA 14, higher levels of 20:4n-6 and 22:6n-3 had been transferred from the yolk sac to T2 embryos from younger than older breeders, whereas for T1 and T2 embryos, yolk sac 20:4n-6 and 22.6n-3 values were similar for older breeders. Accumulation of 20:4n-6 and 22:6n-3 fatty acids in the liver of T1 and T2 embryos from younger breeders was similar; however, T2 embryos from older breeders had higher liver levels of 20:4n-6 and 22:6n-3 than T1 embryos. At EA 19, liver nitric oxide levels were higher for T2 embryos from younger breeders than those from breeders incubated at T1. Brain catalase levels of T2 embryos from younger breeders were higher than those from older breeders at DOH. Thus, changes in fatty acid profiles and catalase and nitric oxide production of brain and liver tissues resulting from 1°C lower incubation temperature from EA 10 to 18 reflect adaptive changes.

Liver enzymes in White Leghorns selected for the sheep red blood cell immune response.

Liver enzymes are essential to xenobiotic metabolism. Expression of these enzymes is dependent upon factors such as age and sex. The objective of this study was to determine basal liver enzyme levels in male and female White Leghorn chickens to provide reference values for future studies. Chickens from 2 lines divergently selected for 35 generations for high antibody and low antibody immune response to SRBC were used. Six male and 6 female chickens from each line were killed at each of 4, 8, 12, and 20 wk of age. Livers were collected and used for enzyme analyses. Liver tissue was analyzed for quinone reductase, glutathione-S-transferase, and cytochrome P450 3A4 activity. All data were analyzed using ANOVA. There were no consistent differences in enzyme activity between high- and low-antibody lines at any age. Cytochrome P450 3A4 activity was substantially greater in 4- and 8-wk than in 12- and 20-wk-old chickens (P < 0.001). This study provides insights into enzyme activities of liver enzymes; however, except for cytochrome P450 3A4, no clear trends across ages were observed.

Reproductive soundness is higher in chickens selected for low as compared with high antibody response.

White Leghorn chickens were selected for 36 generations for high (HAS) or low (LAS) antibody response to SRBC 5 d after an intravenous challenge. The aim of this study was to investigate possible changes in reproductive soundness resulting from that selection. Age and BW at onset of lay (first egg), along with weight of the first egg, were recorded on 45 hens from each line. Intensity of lay was measured as the number of ovulations within a 15-d period over 15 sequential intervals (total 225 d). Three cycles of fertility also were assessed, coinciding with early, middle, and late production stages. For fertility of males and females within a line to be independently evaluated, roosters and hens were mated by artificial insemination to an unrelated control line of White Plymouth Rocks. Twenty roosters from each antibody line were considered, as well as the 45 hens. Pooled semen from the control line was used for mating the hens from the antibody lines. Hens from the LAS line commenced lay at a younger age (11.67±3.53 d; P<0.001), lighter BW (-169.46±40.20 g; P<0.001), and with greater intensity (2.68±0.25%; P=0.001) than those from the HAS line. Any differences in intensity thereafter were trivial between lines (P=0.42), with intensity decreasing sharply toward the end of the 7-mo production period in both lines. Length of fertility differed between hens of the antibody lines during the first cycle (3.35±0.85 d; P=0.002) and between roosters during the first (3.58±1.06 d; P=0.02) and second (3.38±1.07 d; P=0.03) cycles, with chickens from the LAS line having the longer length of fertility in both sexes. A correlated response in reproductive soundness to divergent selection for antibody response was observed. This may in part be due to differences in resource allocations, with particular impact on duration of fertility.

Housing system affects broiler characteristics of local Chinese breed reciprocal crosses.

Artificial selection in closed populations can fix or differentiate alternative alleles of loci associated with selected traits. Two closed chicken populations, A and B, originating from Jiuwu, a Chinese native breed, were bred for more than 10 generations. We compared progeny from reciprocal crosses (AB and BA) under free range (trial 1) and cage and pen (trial 2) systems. Traits measured included feed conversion, live BW, subcutaneous fat thickness, percentages of carcass, semi-eviscerated carcass, eviscerated carcass, breast muscle (pectoralis major and minor), leg muscle (boneless drum and thigh), heart, gizzard, proventriculus, liver, comb, and abdominal fat, plus moisture and fat content in breast muscle at 91 d. In trial 1, there were no significant differences between crosses for any trait except percentage proventriculus (AB > BA). Males were significantly heavier with greater proportions of semi-eviscerated carcass, leg muscle, heart, and comb than females, whereas females had thicker subcutaneous fat and higher percentage abdominal fat, breast muscle, gizzard, and proventriculus than males. In trial 2, chickens raised in cages were significantly heavier, had superior feed efficiency, thicker subcutaneous fat, higher fat content and percentage abdominal fat, carcass, semi-eviscerated carcass, liver, and comb than those reared in pens. Those reared in pens exhibited significantly greater proportions of breast muscle, gizzard, and proventriculus than those raised in cages. The only significant 2-way interaction was cross × sex for percentage semi-eviscerated and eviscerated carcass, because BA males were greater than other combinations. Interactions of cross × sex × housing system for percentage liver and abdominal fat were significant; cage-reared AB females displayed higher percentages than pen-reared BA males. Results implied that subpopulations should be considered rather than a single larger population as a way to reduce loss of genetic variation in local and heritage stocks. Although performance of reciprocal crosses was similar across housing systems, caging during the finishing stage of a slow-growing breed enhanced feed efficiency, BW, and meat composition.

Immunological responses to Clostridium perfringens alpha-toxin in two genetically divergent lines of chickens as influenced by major histocompatibility complex genotype.

Chickens genetically selected for low (LA) or high (HA) antibody response to SRBC displayed a correlated change in MHC, so that LA chickens were 96% B13 and HA chickens were 96% B21. The LA line appears to be less susceptible to invasion by extracellular pathogens, whereas HA chickens are more resistant to infection by intracellular organisms. Resistance to Clostridium perfringens is one instance in which the lines do not follow their established trend of pathogen susceptibility, where during a clinical outbreak of necrotic enteritis, B21B21 genotypes experienced significantly less mortality than B13B13 genotypes. A study was carried out to assess immunological differences between LA and HA lines during exposure to C. perfringens α-toxin. Peripheral blood mononuclear cells were isolated from each genetic line, cultured with or without lipopolysaccharide (4 h), and exposed to varying concentrations of α-toxin (1; 10; 100; and 1,000 U/L) for 2 and 4 h. Evaluation of cellular proliferation, percentage of cytotoxicity, and immunological gene expression was carried out in a series of experiments. Cells isolated from HA chickens had significantly increased proliferation than those from LA chickens at low toxin levels (1 and 10 U/L) and significantly decreased proliferation at high toxin levels (100 and 1,000 U/L). Following exposure to lipopolysaccharide, the percentage of cytotoxicity was higher for LA than HA cells. In both assays, HA cells displayed superior performance following lipopolysaccharide-stimulation. Gene expression analysis of immune transcripts by quantitative real-time PCR revealed significantly upregulated expression of interferon (IFN)-γ, interleukin (IL)-8, IL-13 (2 h), IL-15, and CXCLi1 (4 h) in HA than LA chickens. Cells isolated from the LA line displayed significantly elevated expression of IL-2, IL-10, IL-13 (4 h), IL-16, IL-18, inducible nitric oxide synthase (iNOS), CXCLi1 (2 h), and lipopolysaccharide-induced tumor necrosis factor-α factor (LITAF) compared with the HA line. Clearly, these 2 genetic lines display highly divergent immune responses in regards to C. perfringens toxin exposure.

Epigenetic modifiers identified as regulators of food intake in a unique hypophagic chicken model.

DNA methylation is an epigenetic modification that influences gene transcription; however, the effects of methylation-influencing chemicals on appetite are unknown. We evaluated the effects of single administration of a methyl donor, S-Adenosylmethionine (SAM), or methylation inhibitor, 5-Azacytidine (AZA), on immediate and later-age food intake in an anorexic chick model. The doses of intracerebroventricularly-injected SAM were 0 (vehicle), 0.1, 1, and 10 µg, and of AZA were 0 (vehicle), 1, 5, and 25 µg. When injected on day 5 posthatch, there was no effect of SAM on food intake in either fed or fasted chicks, whereas AZA increased food consumption in the fasted state but decreased it in fed chicks. We then performed a single injection (same doses) at hatch and measured food intake on day 5 in response to neuropeptide Y (NPY; 0.2 µg) injection. Irrespective of NPY, chicks injected with 1 µg of SAM ate more than others on day 5. In contrast, chicks injected with AZA (5 and 25 µg doses) consumed less on day 5. In conclusion, we identified DNA methylation-regulating chemicals as regulators of food intake. AZA but not SAM affected food intake in the short-term, feeding state dependently. Later, both chemicals injected on the day of hatch were associated with food intake changes at a later age, suggesting that feeding pathways might be altered through changes in methylation.

Genomic regions associated with antibody response to sheep red blood cells in the chicken.

F(1) and F(2) populations were generated by crossing two lines of chickens divergently selected from a common founder population for 32 generations for either high or low antibody response 5 days post-injection of a non-pathogenic antigen, sheep red blood cells (SRBCs). The number of loci with major effects on day 5 SRBC titers was estimated to be more than 7 in this population. There was a significant association between MHC haplotype and day 5 antibody titers as well as body weight at sexual maturity. A significant difference between reciprocal F(2) crosses for both 5- and 12-day antibody titers suggests that sex chromosome and/or parent of origin effects on autosomal loci have an important role in immune response. A single marker-trait association analysis on 1024 genetic markers and 128 F(2) individuals detected 11 genomic regions associated with antibody response traits and 17 regions associated with body weight gain. Several of the genomic regions identified as being associated with antibody response have been described previously, while novel regions associated with antibody response were identified on chromosomes 11 and 24. Based on the lack of overlap of the regions associated with body weight and antibody response, we conclude that while these phenotypes are inversely correlated in the selected lines, they are controlled by distinct genetic loci and may be reflective of intense selection pressure on loci affecting the partitioning of nutrients between the immune system and growth pathways.

Genetic diversity and population structure in lines of chickens divergently selected for high and low 8-week body weight.

A long-term selection experiment for high or low 8-wk BW in White Plymouth Rock chickens was conducted to study effects of selection on BW and correlated characters. Two lines [high (HWS), low (LWS) weight] were established and have undergone 48 generations of selection. The lines were managed to curtail inbreeding and to maintain similar population structures; such is necessary for equitable comparison of selection response between lines. Our objective was to test the success of that breeding strategy by characterizing genetic diversity and inbreeding in these lines. A pedigree of 5,998 individuals was assembled, with 68 founders, 2,962 HWS chickens, and 2,968 LWS chickens. Inbreeding coefficients (F) were calculated for each line. Maximum F was 0.53 and 0.61, mean F was 0.26 (SD 0.15) and 0.30 (SD 0.17), and change in F was 1.3 and 1.6% per generation in LWS and HWS lines, respectively. The effective population size was 38.3 in LWS and 32.1 in HWS lines. The effective number of founders was 15.7 in both lines, and the effective number of ancestors was 17.5 and 15.5 in LWS and HWS lines, respectively. Thirty ancestors accounted for 90% of the genetic makeup of both lines. Seven male and eight female founders still contributed to both lines at generation 48, although some contributed more to one line than the other. Family sizes were similar for males and females of each line, with males having larger family sizes with greater variance. Accumulated inbreeding was high and effective population size was low, as expected in closed lines. Effective number of founders was relatively low compared with actual number of founders, indicating some contributed more than others to the last generation. Family size statistics indicated that fewer males than females were used, leading to the observed levels of inbreeding. Given their similarity in genetic diversity and family size, it can be concluded that breeding decisions throughout the project resulted in similar population structures in the lines.

Effects of silymarin on gossypol toxicosis in divergent lines of chickens.

Gossypol, a pigment of cotton, is a hepatic toxin for chickens. Thus, despite its high protein content, inclusion of cottonseed meal in poultry diets is problematic. Silymarin, an extract from milk thistle, has hepatoprotective qualities and could potentially serve as a feed additive to offset the toxicity of gossypol. The objective of this study was to determine if silymarin could counteract gossypol toxicosis. Cockerels (n = 144) from lines divergently selected for humoral immunity were used. Three individuals from each line were randomly assigned to a cage and fed a corn-soybean meal (control) diet for 14 d. Six cages per line were then randomly assigned 1 of 4 dietary treatments (1,000 mg/kg of gossypol, 1,000 mg/kg of silymarin, 1,000 mg/kg of both gossypol and silymarin, or a control diet). Body weight and feed intake data were collected for 21 d, with chickens bled weekly to collect plasma and determine hematocrits. Chickens were then killed, and livers were collected for subsequent histology and enzymatic activity analyses. Endpoints measured weekly were analyzed with repeated measures and regression methodologies. Plasma and liver enzyme activities, and histological measures, were analyzed using ANOVA. No significant interactions between diets and lines were observed. Chickens assigned to the gossypol and gossypol-silymarin diets stopped gaining weight at d 14 (P < 0.001) and lost weight by d 21 (P < 0.001). Gamma glutamyltransferase was also elevated in these chickens at d 14; activities increased further by d 21 (P < 0.001). Histological examination of liver slices indicated substantial lipidosis (P < 0.001). Furthermore, quinone reductase activity was higher in gossypol- and gossypol-silymarin-treated chickens than in control and silymarin-treated chickens (P < 0.001). Silymarin did not alleviate any clinical effects of gossypol toxicosis.