Biomedical subjects

A Cahaner

Publications and source records attributed to A Cahaner.

At least 19 recordsLinked to original sources

PubMed2006

Marker-assisted selection based on a multi-trait economic index in chicken: Experimental results and simulation.

A method proposed herein allows simultaneous selection for several production traits, taking into consideration their marginal economic values (i.e. the economic value of a trait's additional unit). This economic index-marker assisted selection (EI-MAS) method is based on the calculation of the predicted economic breeding value (BV), using information on DNA markers that have previously been found to be associated with relevant quantitative trait loci. Based on the proposed method, results with real birds showed that sire progeny performance was significantly correlated with expected performance (r = 0.61-0.76; P = 0.03-0.01). Simulation analysis using a computer program written specifically for this purpose suggested that the relative advantage of EI-MAS would be large for traits with low heritability values. As expected, the response to EI-MAS was higher when the map distance between the marker and the quantitative trait gene was small, and vice versa. A large number of distantly located markers, spread 10 cM apart, yielded higher response to selection than a small number of closely located markers spread 3 cM apart. Additionally, the response to EI-MAS was higher when a large number (ca.150) of progeny was used for the prediction equation.

Animal Husbandry↗

PubMed2005

Genetic variation in major histocompatibility complex class I alpha2 gene among broilers divergently selected for high or low early antibody response to Escherichia coli.

The MHC genes have a profound effect on animal abilities to respond to specific antigens because they play a role in presenting foreign antigens to T cells during the course of the humoral or cellular immune response. In the current study, polymorphism in the MHC class I alpha2 domain was compared in 2 lines divergently selected for high (HH) or low (LL) antibody response to Escherichia coli vaccine. These lines also differ markedly in their antibody response to natural E. coli exposure and to vaccination with Newcastle disease virus, infectious bronchitis virus, and infectious bursa disease virus. Recent trials have shown that the LL chicks exhibit a significantly higher percentage of CD8+ T lymphocytes in their peripheral blood lymphocytes and spleen than HH chicks. Despite symmetrical selection intensity in both lines, polymorphism of the alpha2-domain gene was higher in the LL line than in the HH line. Among 29 single-nucleotide polymorphism positions found, 3 were unique to the HH line, 15 were unique to the LL line, and 11 were polymorphic in both lines. These single nucleotide polymorphism positions were not 100% line specific and were in agreement with the genetic variation in antibody level or cellular response still found within the selection lines. Five amino acid positions showed significant differences in polymorphism between the selection lines. These were located within the antigen-binding cleft, suggesting that these positions might influence the ability of MHC class I to bind foreign antigens and leading to differences in immunocompetence between the lines.

Amino Acid Sequence↗

PubMed2002

DNA markers and crossbreeding scheme as means to select sires for heterosis in egg production of chickens.

Genotypes for 24 microsatellite markers, dispersed across the chicken genome, were used to predict progeny performance and heterosis for egg production (number and mass) in 'layers' (egg-type chickens). These markers were used to evaluate genetic distance between each of 39 sires sampled from two-layer male-lines; Rhode Island Red (RIR) and White egg Leghorn (Leghorn), and a DNA pool of 30 randomly sampled females from a Brown-egg female line (Silver). Each sire was analysed for egg production across months in the laying period and cumulatively in each of three subperiods; onset (2 month), mid (9 month) and late (1 month). The average Reynolds' genetic distance between Leghorn sires and the Silver female line (theta;=0.6) was significantly higher than that between RIR sires and the Silver female line (theta;=0.5). Neither performance nor heterosis values in the RIR sire's daughters were associated with genetic distance values between sires and the Silver female line. On the other hand, performance as well as heterosis values of Leghorn's daughters were positively associated with genetic distance. This association was particularly evident in the mid-subperiod. If 25% of the most genetically distant Leghorn sires from the Silver female line had been selected in a single generation on the basis of DNA markers information only, average egg production of the crossbred daughters would have been improved by about nine eggs (3%). In principle, further improvement is possible if selection to increase genetic distance between the parental lines is carried on.

Animals↗

PubMed2002

Microsatellite markers associated with quantitative trait loci controlling antibody response to Escherichia coli and Salmonella enteritidis in young broilers.

A unique resource population was produced to facilitate detection of microsatellite markers associated with quantitative trait loci controlling antibody (Ab) response in broiler chickens. Three F1 males were produced by mating two lines divergently selected on Ab response to Escherichia coli vaccination. Each F1 male was mated with females from four genetic backgrounds: F1, high-Ab line (HH), low-Ab line and commercial line, producing three resource families, each with four progeny types. About 1700 chicks were immunized with E. coli and Salmonella enteritidis vaccines. Selective genotyping was conducted on the individuals with highest or lowest average Ab to E. coli and S. enteritidis within each progeny type in each sire family. Twelve markers were significantly associated with Ab to E. coli and six of them were also associated with Ab to S. enteritidis, mostly exhibiting a similar low effect (approximately 0.35 phenotypic SD) in all progeny types. Four markers exhibited a highly significant and much larger effect (approximately 1.7 SD), but only in progeny of females from the HH, suggesting that a backcross to the high parental line should be preferred over the commonly used F2 population. Results from two markers suggested a quantitative trait locus on chromosome 2 around 400 cM. The marker MCW0083, significant in two sire families, is closely linked to the bone morphogenetic protein 2 (BMP2) gene, known to be associated with the control of T-cell transformation in humans.

Animals↗

PubMed2002

Genotype-by-environment interaction with broiler genotypes differing in growth rate. 4. Association between responses to heat stress and to cold-induced ascites.

Males and females, selected from a commercial line to represent its phenotypic variation for BW, were mated with similarly ranked mates to produce sire families representing a wide genetic variation in potential growth rate (GR). Following 5 wk of rearing at normal ambient temperatures, birds representing all sire families were exposed to cold (Days 37 to 47, Trial 1) or hot (Days 43 to 48, Trial 2) environments. Birds exhibiting ascites syndrome (AS) in the cold environment (Trial 1) were counted, and the incidence of AS (%AS) per family was calculated. Sire families' least-square means of BW at 37 d of age in Trial 1 and BW at 43 d of age in Trial 2 represented the families' potential GR (i.e., GR under normal conditions). A significant positive correlation was found between potential GR and %AS (r = 0.479, Trial 1), indicating that families with higher potential GR under normal conditions are more likely to suffer from AS under cold stress, compared to families with lower GR. Heat stress markedly reduced weight gain in all families (Trial 2); however, the genetic potential GR was negatively correlated with actual GR under heat stress (r = -0.411, Trial 2). Since offspring of the same sire families were exposed to the two stressful environmental conditions, correlations between sire families' means under the two environments could be calculated. A negative correlation was found between growth under heat stress (Trial 2) and %AS (Trial 1) (r = -0.439), indicating that families whose GR is more depressed under heat stress are more likely to suffer from AS under cold stress. These results suggest that the two stress responses may share similar control of the genetic variation in each trait and their negative genetic correlation with potential GR.

Animals↗

PubMed2002

Antibody responses and morbidity following infection with infectious bronchitis virus and challenge with Escherichia coli, in lines divergently selected on antibody response.

We evaluated the association between antibody (Ab) production and disease resistance. A controlled-challenge protocol was developed to mimic natural infection and to yield a higher rate of mortality following Escherichia coli (EC) challenge. Chicks were first infected with infectious bronchitis virus (IBV) by injecting a high dose of vaccine (attenuated virus) into their air sacs and then were infected with pathogenic EC introduced intratracheally. The experimental population consisted of lines divergently selected for high (HH) or low (LL) Ab response to EC vaccination, an HH x LL cross (HL), and commercial broilers (CC). When chicks were vaccinated with EC vaccine, mean Ab titer 15 d post-EC challenge was threefold higher in HH than LL lines, but both lines exhibited very low mortality (approximately 2%). When chicks were not vaccinated prior to EC challenge, high mortality (8 to 20%) occurred in the slow-growing HH, LL, and HL lines, and much higher mortality (approximately 40%) occurred among the CC broilers that were 38% heavier than the HH, LL, and HL lines. Mean level of Ab to EC, 7 d after EC challenge, was about twofold higher in HH vs. LL chicks and intermediate in HL and CC chicks. Within each line, Ab levels were higher in chicks exhibiting colibacillosis than in healthy ones, suggesting that these Ab were produced as a result of ongoing infection but were too late to fully prevent morbidity and mortality. These results indicate that rapid growth rate substantially reduces broiler viability, whereas Ab levels produced in response to acute pathogenic challenge without prior vaccination do not contribute to disease resistance. Among the relatively slow-growing lines, mortality was about twofold higher in HH than in LL lines. This finding may confirm previous reports that without prior vaccination, high Ab response to acute challenge increases consequent mortality; alternatively, the LL line may be superior in nonspecific defense mechanisms.

Animals↗

PubMed2002

Genotype-by-environment interaction with broiler genotypes differing in growth rate. 3. Growth rate and water consumption of broiler progeny from weight-selected versus nonselected parents under normal and high ambient temperatures.

One cycle of high-intensity selection on BW was conducted to study correlated effects on performance under high ambient temperature (AT). From a large flock of a commercial sire-line, 3 males and 15 females with the highest BW at 35 d of age were mated and produced a group of 120 BW-selected chicks. Three average-BW males and 15 average-BW females from the same flock were mated to produce a control group of 120 chicks. On Day 17, the two groups were equally divided between two temperature-controlled chambers and housed in individual cages. One chamber was set to a normal AT (NAT; constant 22 C) and the second chamber to high AT (HAT; constant 32 C). Under NAT, the relative advantage of the selected broilers over the controls did not change from 17 to 42 d of age, averaging about 15% for BW gain and 9.7% for feed consumption. These differences were halved under HAT from Days 17 to 28 and were reversed from 28 to 42 d of age, when the selected broilers consumed significantly less feed and gained less BW than the controls. Water-to-feed ratio was measured in each AT treatment. From 28 to 42 d of age, averaged over the two groups, birds under HAT consumed 2.5 g water/g of feed compared to only 1.5 g water/g feed under NAT. The diminished superiority of the selected broilers under HAT led to a substantial genotype-by-environment interaction involving high AT and within-stock genetic differences in growth rate. It appears that broilers selected for rapid growth under optimal conditions do not achieve their genetic potential under high AT. Thus, specific indicators of adaptation to heat, possibly water consumption or body temperature, should be added to commercial selection for rapid growth to improve broiler performance in hot climates.

Aging↗

PubMed2002

Genetic and phenotypic correlations between antibody responses to Escherichia coli, infectious bursa disease virus (IBDV), and Newcastle disease virus (NDV), in broiler lines selected on antibody response to Escherichia coli.

The genetic control of antibody (Ab) response to Escherichia coli (EC), infectious bursa disease virus, and Newcastle disease virus and the genetic and phenotypic correlation between these Ab responses, were evaluated under farm conditions in which chicks were simultaneously exposed to these antigens. The experimental population comprised five groups: two lines divergently selected for high (HH) or low (LL) Ab response to EC vaccination; a commercial broiler dam-line (CC), from which HH and LL had been derived; and the HH x CC and LL x CC hybrid groups (HC and LC, respectively). Lines LL and HH expressed similar symmetric divergence to all three antigens. The ranking of the LL, LC, CC, HC, and HH genetic groups according to their mean Ab responses and their very high linear correlation with the LL vs. HH genomic scale clearly indicate the additive nature of the genetic divergence between these lines. Several estimates of correlation were calculated between Ab responses of each pair of antigens and between BW and Ab to each antigen. The high correlation between group means, the near-zero within-group correlation, and the low phenotypic correlation indicate the strongly positive genetic correlation between Ab responses and no correlation with BW. The results of this study suggest that overall immunocompetence of commercial broilers can be improved by selection for high Ab response of young chicks to controlled immunization with a single antigen, without counteracting further selection for high BW.

Animals↗

PubMed2001

DNA microsatellites linked to quantitative trait loci affecting antibody response and survival rate in meat-type chickens.

Selection for immune response parameters may lead to improved general disease resistance. Because disease resistance and immune response are hard-to-measure quantitative traits with low to moderate heritability, they may respond more efficiently to marker-assisted selection (MAS) than to phenotypic selection. To detect DNA markers linked to quantitative trait loci (QTL) associated with immune response, a resource half-sib family of 160 backcross (BC1) and intercross (F2) birds was derived from a cross between two meat-type lines divergently selected for high or low antibody (Ab) response to Escherichia coli. By using 25 microsatellite DNA markers covering approximately 25% of the chicken genome, initial genotyping of 40% of the resource family was followed by complete genotyping of the entire family with four suggestive markers. Three of these markers exhibited significant association with immune response: (1) ADL0146 on Chromosome 2 associated with Ab to SRBC and Newcastle disease virus (NDV), (2) ADL0290 on linkage group 31 affecting Ab to NDV, and (3) ADL0298 on linkage group 34 associated with Ab to E. coli and survival. The family was also genotyped with five linked markers from two of the suggested regions, and interval mapping was applied. The results confirmed the significant effects, suggested the location of the QTL, and confirmed the genetic association between immune responses and disease resistance. These findings support the idea of improving poultry immunocompetence by MAS.

Animals↗

PubMed2001

Minimal number of chicken daily growth velocities for artificial neural network detection of pulmonary hypertension syndrome (PHS).

Previously, evaluation of the first 2 wk of daily growth velocity with an artificial neural network (ANN) provided an effective noninvasive approach for predicting the susceptibility of broilers to pulmonary hypertension syndrome (PHS). This study was conducted to define the minimum number of days of growth data and the type of ANN required for the best prediction of PHS susceptibility. Four experiments were conducted in which broilers were weighed daily at 0800 h. In Experiment 1, Hubbard male broilers were reared to 50 d of age, with 13 developing PHS and 33 remaining normal (N), for a PHS:N ratio of 13:33. In Experiment 2, ANAK broilers were exposed to cool temperatures (16 to 17 C) from 17 to 42 d of age, resulting in a PHS:N ratio of 16:46 for males. In Experiments 3 and 4, Hubbard male and female chicks from a base population and a PHS-resistant line were exposed to cool temperatures from 17 to 42 d (Experiment 3) or 49 d of age (Experiment 4). The PHS:N ratios were 40:68 for males and 6:96 for females in Experiment 3 and 26:91 for males and 10:58 for females in Experiment 4. Four ANN, back propagation (BP3), Ward back propagation (WardBP), probabilistic (PNN), and general regression (GRNN), were evaluated for their ability to predict PHS in the shortest number of days based on daily growth velocities (BWd+1-BWd). A 100% prediction of PHS and N birds was considered the criterion of success. Starting with 14 d of data, each ANN was trained on daily growth velocity, and the number of predictive days was reduced with each run of the ANN. The best ANN was a GRNN, which correctly diagnosed PHS and N male broilers on 4 and 6 d of growth velocity data for Experiments 1 and 2, respectively. The results were poorer with the BP3, WardBP, and PNN. The diagnostic ability of the neural network was not consistent over all four experiments. In Experiment 2, a minimum of 6 d was required for 100% PHS detection for males. In Experiment 3, the best diagnostic value for males was 93% PHS detection and 100% N detection at 15 d. For females, the 100% PHS detection occurred at a minimum of 8 d. In Experiment 4, males had 100% PHS and N detection at a minimum of 11 d. Females had a 100% PHS and N detection at a minimum of 10 d. An attempt to build a single neural network that would detect PHS susceptibility in Hubbard (Experiment 1) and ANAK (Experiment 2) broilers was unsuccessful. The application (validation) of neural networks between experiments also was not successful (data not presented). However, these studies demonstrate that within a breed or line reared under similar selection pressures for ascites, a GRNN based on the first 14 d of growth velocity can detect, with at least 93% accuracy, broilers susceptible to PHS.

Age Factors↗

PubMed2001

Genotype-by-environment interaction with broiler genotypes differing in growth rate: 2. The effects of high ambient temperature on dwarf versus normal broilers.

High ambient temperatures (AT) reduce feed consumption (FC) and BW in broilers, thereby leading to lower efficiency and profitability of poultry meat production in hot climates. These negative effects have been found to be more pronounced in chicken lines with high BW. The effects of high AT were investigated in a broiler population segregating for the Dw gene and, thus, consisting of normal-sized and dwarf broilers, which differed markedly in BW but had the same genetic background. All chicks were reared under normal AT (constant 22 C) up to Day 44, when AT was gradually raised, over 24 h, to 32 C and then held constant to Day 49. The dwarf chicks had 23% lower BW and BW gain (WG) at all ages until Day 44. During the first 24 h at 32 C, FC of the dwarf broilers was reduced by 35% and their average WG was 7.6 g/d, whereas FC of their normal-sized counterparts was reduced by 46% and they lost BW (average WG: -42.1 g/d). Thereafter, however, the dwarf and normal broilers adapted similarly to the chronic heat stress, with FC and WG of both phenotypes averaging 72 and 35%, respectively, of the corresponding means at normal AT. The two phenotypes had similar body temperatures at normal AT, but following its increase, body temperature in the normal-sized broilers rose by 1.14 C, whereas in the dwarf ones it rose by only 0.47 C. This finding suggested better thermoregulation during acute heat stress, apparently due to the latter's smaller body size. Under chronic heat stress, however, FC and WG were similarly reduced in the dwarf and normal broilers. We concluded that the dwarf gene has no value with regards to broiler tolerance to chronic heat stress, either for production or as a model.

Adaptation, Physiological↗

PubMed2001

Genotype-by-environment interaction with broiler genotypes differing in growth rate. 1. The effects of high ambient temperature and naked-neck genotype on lines differing in genetic background.

High ambient temperature (AT) significantly depresses growth rate and meat yield of commercial broilers, thus making it a major factor hindering poultry meat production, especially in hot climates. The effects of high AT were variably moderated when feather coverage was reduced by the naked-neck gene (Na). In this study, the effects of high AT and Na were investigated in broiler progeny of hens from a sire line and two dam lines, differing in growth rate and meat yield due to different breeding histories. Heterozygous naked-neck (Na/na) males were mated with normally feathered (na/na) hens from the three lines. The 500 progeny were segregated for Na/na and na/na genotypes. After brooding, chicks of each maternal background, Na genotype, and sex were equally divided to two similar chambers and were reared on litter to 53 d of age. One chamber was set to normal AT, averaging 25 C; the second chamber was set to high AT, averaging 30 C. The high AT treatment reduced growth and meat yield in the progeny of all three groups. This reduction increased with age and was highest in the broilers produced by hens from a sire line bred for high growth rate and breast meat yield. The two other groups, produced by hens from selected and relaxed dam lines, differed in growth rate but were similarly affected by the high AT. It is suggested that the magnitude of the high AT effect depends not only on differences in potential growth rate but also on differences in overall genetic background. It was also shown that broiler performance in the final weeks could be improved by introducing the Na gene into commercial flocks. The advantage of the Na/na genotype was much more pronounced at high AT and in broilers with genetically higher growth rate and breast meat yield.

Animals↗

PubMed2001

Immune response and resistance to infectious bursal disease virus of chicken lines selected for high or low antibody response to Escherichia coli.

Two experimental broiler lines were developed by divergent selection for high (HH) and low (LL) antibody response to Escherichia coli. Antibody response of these lines to immunization with a commercial vaccine (whole inactivated virus, WIV) against infectious bursal disease virus (IBDV) or with proteins VP2 and VP3 of that virus, and their resistance to challenge with a virulent IBDV, were tested. The study was performed with 213 male and female chicks from the tenth generation of the HH and LL lines. At 15 d of age, after disappearance of maternal antibodies, chicks from each line were randomly divided into four groups and injected with WIV, VP2, VP3, or adjuvant alone as a negative control. Chicks were bled 18 d postinjection, and antibody titers were determined by ELISA. Ten days later, the chicks were challenged with a virulent strain of the virus and killed after 10 d; the ratio of bursa of Fabricius to 100 g BW was determined for each bird. Significant differences in antibody titers were found among immunized and control chicks. Chicks from the HH line exhibited significantly higher antibody titers than LL chicks in response to WIV and VP2 vaccines but not to VP3 vaccine. Following challenge, bursa weight (relative to BW) of HH and LL chicks vaccinated with WIV and VP2 was significantly higher (P < 0.01) than that of chicks vaccinated with VP3 or the challenged unvaccinated control. No difference was found in this parameter between the latter two groups. Possible explanations for the differences in the line response to VP2 and VP3 are discussed.

Animals↗

PubMed2000

The dynamics of antibody response to Escherichia coli vaccination in meat-type chicks.

The dynamics of serum antibody (Ab) response in young broilers were studied in lines divergently selected for high (HC) or low (LC) Ab response to Escherichia coli vaccination at an early age, and their cross (HL). Chicks were divided into three vaccination-age (VA) groups: 8, 10, and 12 d of age (VA8, VA10, and VA12, respectively). Antibody response was determined five times for each chick, at 6, 8, 10, 12, and 14 d postvaccination (dPV). The effects of line, VA, and dPV on Ab titers were highly significant. The HC and LC chicks exhibited the highest and lowest mean titers, respectively, in all VA groups. The HL chicks exhibited midparent Ab values for all VA and dPV combinations, indicating additive inheritance of early Ab production. In LC, the highest mean Ab titer was obtained on Day 26 (14 dPV of the VA12 group), whereas in HC, the same titer had already been obtained on Day 18 (VA8-10 dPV and VA10-8 dPV combinations). The VA8 and VA12 chicks differed markedly in their Ab titer dynamics curves, and the VA10 chicks exhibited an intermediate curve. The three VA groups exhibited a similar change in Ab level from 6 to 10 dPV, but they differed in Ab change from 10 to 14 dPV. This significant dPV x VA interaction suggests that the VA12 and VA10, but not VA8, chicks maintained the capability to produce persisting Ab.

Aging↗

PubMed2000

Microsatellite polymorphism between and within broiler populations.

Two independent broiler chicken populations were genotyped with microsatellite markers to determine genetic polymorphisms within and among broiler populations. Birds were genotyped with primers from the US Poultry Genome Mapping Kits 1 and 2. The 59 primer sets selected for this study provided wide genomic coverage. All 59 primer sets amplified a polymerase chain reaction product in Population L, whereas 57 primer sets produced a product in Population C. The average allele number per line per microsatellite was 2.8 and 2.9 for Populations L and C, respectively. Considering the 57 primer pairs generating product in both lines, 72.3% of the total alleles were unique to one or the other population. This study illustrates the high polymorphism level in broiler populations of microsatellites amplified from primers developed from Red Jungle Fowl or White Leghorn sequences.

Alleles↗

PubMed2000

Immunocompetence and viability under commercial conditions of broiler groups differing in growth rate and in antibody response to Escherichia coil vaccine.

Mortality and morbidity due to infectious diseases are an increasing source of losses to the broiler industry. Breeding chickens for improved disease resistance may reduce these losses. A study was designed to evaluate the contribution of selection for immune response to viability of broilers under farm conditions. The experimental populations consisted of six groups: two lines divergently selected for high (HH) or low (LL) antibody (Ab) response to Escherichia coli vaccination; commercial broilers (CC); and the HH x CC, LL x CC, and HH x LL crosses. Chicks were tested under standard vaccination program and management on commercial farms in two years (1997 and 1998). Mortality was recorded in the whole groups, each consisting of several hundred or thousand of chicks, whereas BW and Ab to natural exposure to E. coli and to vaccination with Newcastle disease virus (NDV) were determined in samples of 50 to 120 chicks/group per yr. Groups were clustered into three levels of BW: CC representing contemporary fast-growing broilers; HH, LL, and HL representing broilers 10 yr earlier; and HC and LC with intermediate BW. The HH and LL groups exhibited the highest and lowest E. coli Ab titers, respectively. Mean Ab of the CC group equaled the average of the selected lines, and all crosses exhibited mid-parent Ab titers, indicating additive genetic control. Group means for Ab to NDV were highly correlated with those of E. coli, suggesting a common genetic control for the immune response to these two antigens. In both years, the highest mortality was found in the fast-growing group (CC), and the lowest mortality was in the slow-growing HH, LL, and HL groups. In the crosses, despite their similar mean BW, mortality was one-third higher among LC vs. HC birds. These results suggest that Ab response and potential growth rate interact in their effect on mortality due to infectious diseases.

Animals↗

PubMed1999

Major histocompatibility complex (MHC) related cDNA probes associated with antibody response in meat-type chickens.

The major histocompatibility complex (MHC) region was examined as a set of candidate genes for association between DNA markers and antibody response. Intercross F2 families of chickens were generated from a cross between high (HC) and low (LC) Escherichia coli(i) antibody lines. Restriction fragment length polymorphism (RFLP) analysis was conducted by using three MHC-related cDNA probes: chicken MHC class IV (B-G), chicken MHC class I (B-F), and human MHC-linked Tap2. Association between RFLP bands and three antibody response traits (E. coli, sheep red blood cells and Newcastle disease virus) were determined by two methods: by statistically analyzing each band separately and also by analyzing all bands obtained from the three probes by using multiple regression analysis to account for the multiple comparisons. The MHC class IV probe was the highest in polymorphisms but had the lowest number of bands associated with antibody response. The MHC class I probe yielded 15 polymorphic bands of which four exhibited association with antibody response traits. The Tap2 probe yielded 20 different RFLP bands of which five were associated with antibody production. Some Tap2 bands were associated with multiple antibody response traits. The multiband analysis of the three probes' bands revealed more significant effects than the analysis of each band separately. This study illustrates the efficacy of using multiple MHC region probes as candidate markers for quantitative trait loci (QTLs) controlling antibody response in chickens.

Animals↗

PubMed1999

The effects of naked neck genotypes, ambient temperature, and feeding status and their interactions on body temperature and performance of broilers.

The effect of ambient temperature (AT) and feeding status on body temperature (BT) were investigated in broilers of the three naked neck genotypes (Na/Na, Na, na, and na/na). From 29 to 49 d of age, chicks were reared in a temperature-controlled chamber, where AT alternated daily between 24 and 32 C. At Day 47, all birds were deprived of feed for 12 h at 32 C, followed by 12 h of ad libitum intake at 24 C, then 12 h of ad libitum intake at 32 C, and finally feed deprivation for 12 h at 24 C. Body temperature was measured at the end of each of these 12-h periods. Body weight, feed consumption, feather coverage, and breast yield were determined. The Na/na and Na/Na birds had 20 and 40% less feather mass than the na/na birds. The three genotypes had similar BW at Day 49, but the naked neck birds had a higher breast yield. At high AT, BT was positively associated with feather mass of the three naked neck genotypes. The highest BT was exhibited by the fully feathered birds, and the lowest by the homozygous naked neck birds. The feeding status also affected BT of all birds, but to a larger extent in the normally feathered than in the naked neck birds. It appears that the lower negative effects of high AT on growth rate and meat yield in naked neck broilers can be attributed to their lower BT. Thus, it is suggested that measuring BT of broilers can be used as an indicator of the level of stress imposed on them by high AT.

Animal Feed↗