Catherine Beaumont

Genetic analysis of a selection experiment on increased body weight and breast muscle weight as well as on limited abdominal fat weight

1. Genetic parameters of body weight (BW), breast meat weight or yield (BRW, BRY) and abdominal fat weight or yield (FTW, FTY) were estimated in males and females originated from an experimental line selected for improving broiler carcase quality and its control line. 2. Mean heritabilities over both sexes of BW, FTW and FTY were 0.43, 0.56 and 0.63 respectively. Those of BRW and BRY were 0.53 and 0.65 respectively. 3. BW was unfavourably correlated with FTW (rg of 0.40) and to a lesser extent with FTY (rg of 0.12). BW was, as expected, highly correlated with BRW (rg 0.77), but a poor correlation was obtained with BRY (rg of 0.15). Selection for more breast yield should not reduce the leanness of the birds, with a genetic correlation between BRY and FTY of -0.15. 4. The variance explained by the maternal effects accounted for a rather small part of the total phenotypic variance (from 3% to 8% according to the trait), but ignoring these effects led to a significant overestimation of the heritabilities (by 11% to 19%). 5. Except for BRY, the heritability estimates differed between sexes, only moderately for BW but more for BRW, FTW and FTY. However, estimated genetic correlations between sexes were high (between 0.94 and 0.99) and in turn heritabilities of sexual dimorphism of the various traits very low (between 0.02 and 0.07). 6. A significant improvement of the genetic level for growth and carcase composition had been obtained in the selected line, with a mean genetic gain per generation of 0.12 sigma g, 0.13 sigma g and -0.30 sigma g for BW, BRY and FTY respectively.

Chicken meat quality: genetic variability and relationship with growth and muscle characteristics

BackgroundThe qualitative properties of the meat are of major importance for poultry breeding, since meat is now widely consumed as cuts or as processed products. The aim of this study was to evaluate the genetic parameters of several breast meat quality traits and their genetic relationships with muscle characteristics in a heavy commercial line of broilers.ResultsSignificant levels of heritability (averaging 0.3) were obtained for breast meat quality traits such as pH at 15 min post-slaughter, ultimate pH (pHu), color assessed by lightness L*, redness a* and yellowness b*, drip loss, thawing-cooking loss and shear-force. The rate of decrease in pH early post-mortem and the final pH of the meat were shown to be key factors of chicken meat quality. In particular, a decrease in the final pH led to paler, more exudative and tougher breast meat. The level of glycogen stored in breast muscle estimated by the Glycolytic Potential (GP) at slaughter time was shown to be highly heritable (h2 0.43). There was a very strong negative genetic correlation (rg) with ultimate meat pH (rg -0.97), suggesting a common genetic control for GP and pHu. While breast muscle weight was genetically positively correlated with fiber size (rg 0.76), it was negatively correlated with the level of glycogen stored in the muscle (rg -0.58), and as a consequence it was positively correlated with the final pH of the meat (rg 0.84).ConclusionThis genetic study confirmed that selection should be useful to improve meat characteristics of meat-type chickens without impairing profitability because no genetic conflict was detected between meat quality and meat quantity. Moreover, the results suggested relevant selection criteria such as ultimate pH, which is strongly related to color, water-holding capacity and texture of the meat in this heavy chicken line.

Behavioural and physiological responses of three chicken breeds to pre-slaughter shackling and acute heat stress.

1. The aim of this study was to compare the behavioural and physiological responses to hanging and acute heat stress in three different chicken breeds. Chicks were obtained from a slow-growing French ‘Label Rouge’ line (SGL), a fast-growing standard line (FGL) and a heavy line (HL). The SGL, FGL and HL birds were slaughtered at their respective market ages of 12, 6 and 6 weeks, in an attempt to achieve similar body weights. Before stunning, birds were either shackled by their legs on the moving line for 2 min (shackling stress: SH) or placed in a room at 35°C and 60% of humidity for 3·5 h and then shackled for 2 min (acute heat stress plus shackling: H + SH) or subjected to minimal stress by shackling for 10 s before stunning (control group: C). 2. Bird physiological responses to the three pre-slaughter treatments were estimated by measuring blood corticosterone, glycaemia, creatine kinase activity, acid–base status and electrolyte concentration as well as lactate content and glycolytic potential in the breast (Pectoralis major) and thigh (Ilio tibialis) muscles. Behavioural responses to shackling stress were evaluated by measuring wing flapping duration, straightening up attempts and vocalisations. 3. Blood corticosterone was higher in SH and H + SH groups than in the C group, regardless of genotype. The struggling activity on the shackle line differed among chicken breeds. It was more intense and occurred more rapidly after hanging in the SGL birds than in both other breeds. Furthermore, SGL struggling activity was not affected by hanging duration while it increased with hanging duration in FGL and HL birds. 4. Wing flapping duration was negatively correlated with blood pH, bicarbonate concentration and positively correlated with breast muscle lactate content, indicating that struggling stimulated ante-mortem glycolysis activity in breast muscle. Acute heat stress affected blood Ca2+ and Na+ concentration and increased glycaemia and glycolytic potential of thigh muscle. 5. Both acute heat stress and shackling before slaughter were experienced as stressful events by all types of birds.

Integrated maps in quail (Coturnix japonica) confirm the high degree of synteny conservation with chicken (Gallus gallus) despite 35 million years of divergence

BackgroundBy comparing the quail genome with that of chicken, chromosome rearrangements that have occurred in these two galliform species over 35 million years of evolution can be detected. From a more practical point of view, the definition of conserved syntenies helps to predict the position of genes in quail, based on information taken from the chicken sequence, thus enhancing the utility of this species in biological studies through a better knowledge of its genome structure. A microsatellite and an Amplified Fragment Length Polymorphism (AFLP) genetic map were previously published for quail, as well as comparative cytogenetic data with chicken for macrochromosomes. Quail genomics will benefit from the extension and the integration of these maps.ResultsThe integrated linkage map presented here is based on segregation analysis of both anonymous markers and functional gene loci in 1,050 quail from three independent F2 populations. Ninety-two loci are resolved into 14 autosomal linkage groups and a Z chromosome-specific linkage group, aligned with the quail AFLP map. The size of linkage groups ranges from 7.8 cM to 274.8 cM. The total map distance covers 904.3 cM with an average spacing of 9.7 cM between loci. The coverage is not complete, as macrochromosome CJA08, the gonosome CJAW and 23 microchromosomes have no marker assigned yet. Significant sequence identities of quail markers with chicken enabled the alignment of the quail linkage groups on the chicken genome sequence assembly. This, together with interspecific Fluorescence In Situ Hybridization (FISH), revealed very high similarities in marker order between the two species for the eight macrochromosomes and the 14 microchromosomes studied.ConclusionIntegrating the two microsatellite and the AFLP quail genetic maps greatly enhances the quality of the resulting information and will thus facilitate the identification of Quantitative Trait Loci (QTL). The alignment with the chicken chromosomes confirms the high conservation of gene order that was expected between the two species for macrochromosomes. By extending the comparative study to the microchromosomes, we suggest that a wealth of information can be mined in chicken, to be used for genome analyses in quail.

Differences in Frequency, Level, and Duration of Cecal Carriage Between Four Outbred Chicken Lines Infected Orally with Salmonella enteritidis

Four chicken lines, L2, B13, PA12 (egg-type), and Y11 (meat-type), were tested for experimental carrier state of Salmonella enteritidis (SE) in two identical trials. After oral inoculation of SE at 1 wk of age with 5 x 10(4) SE colony-forming units (CFU), 10 chickens per line were necropsied weekly for 6 wk and then every 8 or 15 days until the 12th week postinoculation (PI). Liver, spleen, ovary, and ceca were examined for level of SE colonization. Numbers of positive livers and spleens and levels of the challenge strain in these organs differed little between the four chicken lines. Only three positive ovaries were detected. According to the chicken line, ceca exhibited generally significant (P < 0.05) differences in the number of positive organs during weeks 5-11 PI, in the SE CFU levels (P < 0.05) in the first 5 wk PI and during weeks 8 and 10 PI, and in the duration of colonization. L2 and B13 chickens generally carried SE in their ceca at higher levels, in more animals, and for a longer time than PA12 and Y11 chickens. Y11 chickens were the most resistant to SE cecal colonization.

Genetic control of resistance to salmonellosis and to Salmonella carrier-state in fowl: a review

Salmonellosis is a frequent disease in poultry stocks, caused by several serotypes of the bacterial species Salmonella enterica and sometimes transmitted to humans through the consumption of contaminated meat or eggs. Symptom-free carriers of the bacteria contribute greatly to the propagation of the disease in poultry stocks. So far, several candidate genes and quantitative trait loci (QTL) for resistance to carrier state or to acute disease have been identified using artificial infection of S. enterica serovar Enteritidis or S. enterica serovar Typhimurium strains in diverse genetic backgrounds, with several different infection procedures and phenotypic assessment protocols. This diversity in experimental conditions has led to a complex sum of results, but allows a more complete description of the disease. Comparisons among studies show that genes controlling resistance to Salmonella differ according to the chicken line studied, the trait assessed and the chickens age. The loci identified are located on 25 of the 38 chicken autosomal chromosomes. Some of these loci are clustered in several genomic regions, indicating the possibility of a common genetic control for different models. In particular, the genomic regions carrying the candidate genes TLR4 and SLC11A1, the Major Histocompatibility Complex (MHC) and the QTL SAL1 are interesting for more in-depth studies. This article reviews the main Salmonella infection models and chicken lines studied under a historical perspective and then the candidate genes and QTL identified so far.

Genetic resistance to mortality of day-old chicks and carrier-state of hens after inoculation with Salmonella enteritidis

The heritability of resistance of poultry to Salmonella enteritidis (SE) was investigated. Three measurements of resistance were made: survival after intramuscular inoculation of 419 day-old chicks, absence versus presence of Salmonella in spleens and caeca 4 weeks after oral inoculation of 304 hens at peak of laying, and antibody response of 228 hens following two inoculations of an aroA mutant of this serotype. In the first two models of infection, resistance appeared to be heritable. The heritability was estimated from the sire and dam components, respectively, at 0.14 ± 0.10 and 0.62 ± 0.16 for chick mortality, 0.47 ± 0.21 and 0.13 ± 0.26 for resistance to spleen contamination, and 0.24 ± 0.15 and 0.53 ± 0.26 for resistance to caecal contamination in laying hens. By contrast the estimated heritability of antibody response was very low (0.03 ± 0.08 and 0.10 ± 0.08 when estimated from the sire and dam components, respectively). These results suggest that a selection for increased resistance to SE may be efficient.

A genome scan for quantitative trait loci affecting the Salmonella carrier-state in the chicken

Selection for increased resistance to Salmonella colonisation and excretion could reduce the risk of foodborne Salmonella infection. In order to identify potential loci affecting resistance, differences in resistance were identified between the N and 61 inbred lines and two QTL research performed. In an F2 cross, the animals were inoculated at one week of age with Salmonella enteritidis and cloacal swabs were carried out 4 and 5 wk post inoculation (thereafter called CSW4F2 and CSW4F2) and caecal contamination (CAECF2) was assessed 1 week later. The animals from the (N × 61) × N backcross were inoculated at six weeks of age with Salmonella typhimurium and cloacal swabs were studied from wk 1 to 4 (thereafter called CSW1BC to CSW4BC). A total of 33 F2 and 46 backcross progeny were selectively genotyped for 103 and 135 microsatellite markers respectively. The analysis used least-squares-based and non-parametric interval mapping. Two genome-wise significant QTL were observed on Chromosome 1 for CSW2BC and on Chromosome 2 for CSW4F2, and four suggestive QTL for CSW5F2 on Chromosome 2, for CSW5F2 and CSW2BC on chromosome 5 and for CAECF2 on chromosome 16. These results suggest new regions of interest and the putative role of SAL1.

Line differences in resistance to salmonella enteritidis pt4 infection

1. Four groups of hens, each of a different line, were inoculated at peak of lay, per os in the crop with 1 ml of a suspension containing 10(9) cfu/ml Salmonella enteritidis PT4 (SE). The kinetics of SE contamination in the environment, egg shell and yolk were studied during the first 28 d post inoculation. On the day of slaughter, intestines, caeca, spleen, liver, ovary, oviduct and content were investigated for SE contamination. 2. The commercial egg-type line L2 was found to be the most susceptible to SE. It laid many SE-positive yolks (13.8%) and internal and faecal organs were frequently infected. 3. Certain lines are found to exhibit a degree of resistance to SE; the cause of which is unknown and might be attributed to major genes.

Genetic parameters of meat technological quality traits in a grand-parental commercial line of turkey

Genetic parameters for meat quality traits and their relationships with body weight and breast development were estimated for a total of 420 male turkeys using REML. The birds were slaughtered in a commercial plant and the traits measured included pH at 20 min (pH20) and 24 h post-mortem (pHu) and colour of the breast and thigh meat. The heritabilities of the rate and the extent of the pH fall in the breast muscle were estimated at h2 = 0.21 ± 0.04 and h2 = 0.16 ± 0.04, respectively. Heritabilities ranging from 0.10 to 0.32 were obtained for the colour indicators in the breast muscle. A marked negative genetic correlation (rg= -0.80 ± 0.10) was found between pH20 and lightness (L*) of breast meat, both traits corresponding to PSE indicators. The pH20 in the thigh muscle had a moderate heritability (h2 = 0.20 ± 0.07) and was partially genetically related to pH20 in the breast muscle (rg= 0.45 ± 0.17). Body weight and breast yield were positively correlated with both initial and ultimate pH and negatively with the lightness of breast meat.