The viability and performance under hot conditions of featherless broilers versus fully feathered broilers.

Hot conditions decrease the difference between ambient temperature (AT) and the average temperature of the body surface. A smaller difference reduces the rate of sensible heat loss of excessive internal heat, elevates the body temperature (BT), and may lead to mortality during heat waves. Under conditions of chronic heat, broilers avoid lethal BT elevation by reducing their feed intake; consequently, growth rate and meat yield are lower. Practices to avoid hot conditions are costly, whereas breeding for heat tolerance offers a sustainable approach. Being featherless was shown to provide heat tolerance; this was reevaluated in experimental broilers with a growth rate similar to that of contemporary commercial broilers. In experiment 1, 26 featherless birds and 49 feathered siblings (sibs) were reared at warm AT and exposed to moderate and acute heat waves. The featherless birds maintained normal BT under a moderate heat wave, with a slight elevation under an acute heat wave, and only 1 bird died. In contrast, the heat waves led to a significant elevation in BT of the feathered sibs, and 34% of them died. In experiment 2, featherless broilers were compared with feathered sibs and commercial broilers at 2 AT treatments: a constant temperature of 25°C (control AT) or a constant temperature of 35°C (hot AT). The birds were reared to 46 or 53 d at the control and hot AT, respectively, and the measured traits included BT, growth, and weight of the whole body and carcass parts (breast meat, legs, wings, and skin). At the hot AT, only the featherless broilers maintained a normal BT; their mean d 46 BW (2,031g) was significantly higher than that of birds maintained at the control AT, and it increased to 2,400 g on d 53, much higher than the corresponding means of all feathered broilers (approximately 1,700 g only). Featherless broilers had significantly higher breast meat yield (approximately 20% in both AT), lower skin weight, and supposedly better wing quality. These results confirmed that being featherless improved the livability and performance of fast-growing broilers in hot conditions and suggests that introduction of the featherless phenotype into commercial broiler stocks would facilitate highly efficient yet low-cost production of broiler meat under hot conditions.

Yolk sac nutrient composition and fat uptake in late-term embryos in eggs from young and old broiler breeder hens.

In the present study, we examined the composition, amount, and uptake of yolk nutrients [fat, protein, water, and carbohydrates (COH)] during incubation of eggs from 30- and 50-wk-old broiler breeder hens. Eggs were sampled at embryonic d 0 (fresh eggs), 13, 15, 17, 19, and 21 (hatch). Egg, embryo, yolk content, and yolk sac membrane were weighed, and the yolk sac (YS; i.e., yolk content + yolk sac membrane) composition was analyzed. From 30 to 50 wk of age, the albumen weight increased by 13.3%, whereas the yolk increased by more than 40%. The proportion of fat in the fresh yolk of the 30-wk-old group was 23.8% compared with 27.4% in the 50-wk-old group, whereas the proportion of protein was 17.9% compared with 15.6%, respectively. During incubation, results indicated that water and protein infiltrated from other egg compartments to the YS. Accordingly, the calculated change in the content of water and protein between fresh yolk and sampled YS does not represent the true uptake of these components from the YS to the embryo, and only fat uptake from the YS can be accurately estimated. By embryonic d 15, fat uptake relative to embryo weight was lower in the 30-wk-old group than in the 50-wk-old group. However, by embryonic d 21, embryos of both groups reached similar relative fat uptake, suggesting that to hatch, embryos must attain a certain amount of fat as a source of energy for the hatching process. The amount of COH in the YS increased similarly during incubation in eggs from hens of both ages, reaching a peak at embryonic d 19, suggesting COH synthesis in the YS. At hatch, the amount of protein, water, and COH in the residual YS, relative to the weight of the yolk-free chick, was similar in eggs from young and old hens. However, chicks from the younger hens had less fat in the YS for their immediate posthatch nutrition compared with those from the older hens.

The effects of feed restriction and ambient temperature on growth and ascites mortality of broilers reared at high altitude.

The development of ascites was investigated in broilers at low versus high altitudes, cold versus normal ambient temperatures (AT), and 3 feeding regimens. One-day-old chicks obtained at sea level were reared at high altitude (highA; 1,720 m; n = 576) with 2 AT treatments, low AT from 3 wk onward at highA (highA/cold) and normal AT from 3 wk onward at highA (highA/norm), or at sea level (normal AT from 3 wk onward at low altitude, lowA/norm; n = 540). Under highA/cold, AT ranged between 16 to 17 degrees C in the fourth week, 17 to 19 degrees C in the fifth week, and 19 to 21 degrees C thereafter. Under highA/norm and lowA/norm, AT was 24 degrees C in the fourth week and ranged between 22 to 24 degrees C thereafter. Broilers in each condition were divided into 3 groups: feed restriction (FR) from 7 to 14 d, FR from 7 to 21 d, and ad libitum (AL). Ascites mortality and related parameters were recorded. Low mortality (0.4%) occurred under lowA/norm conditions. Under highA/norm, mortality was lower in females (8.6%) than in males (13.8%) and was not affected by the feeding regimen. The highA/cold treatment resulted in higher mortality but only in males; it was 44.2% among highA/cold AL-fed males and only about 26% under the FR regimens, suggesting that FR helped some males to better acclimatize to the highA/cold environment and avoid ascites. However, mortality was only 13.3% in AL-fed males at highA/norm and FR did not further reduce the incidence of ascites under these conditions. Thus, avoiding low AT in the poultry house by slight heating was more effective than FR in reducing ascites mortality at highA. Compared with FR from 7 to 14 d, FR from 7 to 21 d did not further reduce mortality and reduced growth. At 47 d, the majority of surviving broilers at highA had high levels of hematocrit and right ventricle:total ventricle weight ratio (>0.29), but they were healthy and reached approximately the same BW as their counterparts at low altitude. This finding may suggest that in broilers reared at highA from day of hatch, the elevation in hematocrit and in right ventricle:total ventricle weight ratio happens gradually and therefore is not necessarily indicative of ascites development.

Physiological parameters in broiler lines divergently selected for the incidence of ascites.

Ascites syndrome (AS) is manifested in flocks of contemporary broilers that are allowed to fully manifest their genetic potential for rapid growth. After successful selection, a pair of divergent lines was established, AS-susceptible (AS-S) and AS-resistant (AS-R). These lines facilitate comparisons between genetically resistant and susceptible healthy young broilers when reared under standard brooding conditions (SBC). The aim of the present study was to look for predictive indicators for AS susceptibility by comparing relevant physiological parameters in the AS-S and AS-R lines under SBC and after exposure to extreme ascites-inducing conditions (AIC). In this design, a trait differing significantly between the 2 lines under SBC is expected to be a reliable indicator for selection against AS susceptibility in breeding stocks when reared under noninducing conditions. Males from the AS-S and AS-R lines were reared together under SBC to 19 d of age, then under the AIC protocol. Cumulative incidence of AS mortality was 93.2% in the AS-S line and only 9% in the AS-R line, confirming the genetic divergence between the lines. Exposure to AIC enhanced the imbalance between oxygen demands and supply in the AS-S birds and induced differences in blood parameter level between the 2 lines. The AS-S birds exhibited elevated hematocrit and red blood cell counts and a decline in oxygen saturation in the arterial blood. No difference in hemoglobin concentration was found, but calculation of hemoglobin content per 1,000 red blood cells revealed a significant reduction in hemoglobin content in the AS-S birds. Under SBC, there were no significant differences between the lines for hematocrit, red blood cell count, hemoglobin concentration, hemoglobin count per 1,000 red cells, and blood oxygen saturation. However, heart rate during the first week of life was significantly higher in the AS-S birds than in the AS-R birds on d 1 and 7, suggesting that high heart rate may potentially serve as an early criterion for selection against AS susceptibility.

Unique co-expression of immune cell-related genes in IBDV resistant chickens indicates the activation of specific cellular host-response mechanisms.

Infectious bursal disease virus (IBDV) causes highly contagious, immunosuppressive disease that leads to high mortality in young chickens. The purpose of this study was to look for the genetic regulation of the immune acute immune response to IBDV in our selected lines. Chicks of a F2 generation of two lines divergently selected for early high (HH) or low (LL) antibody (Ab) response to Escherichia coLi vaccination were challenged with virulent IBDV. Viral load in infected bursae was used to determine resistant (R) and susceptible (S) birds. By using a 13K chicken cDNA microarray, and pooled spleen mRNA of R, S and non-challenged, control (C) chicks, several genes were identified with differential expression associated with host resistance to IBDV. These genes were also subjected to RT-PCR on individual samples to verify the results obtained from microarrays. The major finding was the co-upregulation of seven genes--ETS2, H963, RGS1, ABIN-2, CREM/ICER, DUSP1 and CXCR4- in several R, but not S or C individuals, and characterized by a high correlation of expression levels. Resistance also generally coincided with reduced transcript levels of acute-phase serum amyloid A (A-SAA) and increased levels of IL-8. Based on reported functions of these genes, these findings suggest that resistance was mediated by the activation of specific cellular mechanisms, indicated by increased activity of splenic macrophages and T-lymphocytes 3 days post-challenge.

Growth rate of ascites-resistant versus ascites-susceptible broilers in commercial and experimental lines.

The high growth rate (GR) of contemporary broilers is driven by high rate of feed intake and metabolism. Because of the consequent high oxygen demand, especially when coupled with exposure to high altitude or low temperatures, some broilers fail to regulate oxygen supply and develop the ascites syndrome (AS), which leads to mortality and economic losses. Because of the association between high GR, oxygen demand, and AS, it has been suggested that AS is induced by high GR. If true, further GR enhancement should be avoided because it will increase the proportion of AS-susceptible individuals in contemporary stocks. An alternative hypothesis claims that AS is associated with high actual GR only because the latter increases oxygen demand and that there are genetically AS-resistant broilers that do not develop AS, even when exhibiting high GR. These hypotheses were tested in trials in the years 2002 and 2006, with broilers differing in potential GR: contemporary fast-growing commercial lines and an experimental line derived from commercial broilers in 1986, and (in 2002 only) divergently selected AS-susceptible and AS-resistant lines. A protocol of high-challenge ascites-inducing conditions (AIC) from d 19 was used to distinguish between AS-susceptible and AS-resistant individuals and to determine their GR up to this age. The difference in AS incidence between the divergent lines (93.9 vs. 9.5%) was not explained by the 5% difference in their GR, thus indicating a lack of genetic correlation. In the broiler lines, AS incidence was 31 and 47% in 2002 and 2006, respectively, and 32% in the 1986 slow-growing line. Most broilers that remained healthy under the high-challenge AIC exhibited the same early GR and BW as those that later developed AS. These results, and the relatively high incidence of AS in the slow-growing line, indicate that there is very little, if any, direct genetic association between AS and genetic differences in potential GR, and suggest that AS-resistant broilers can be selected for higher GR and remain healthy even under AIC.

Effects of the genetically reduced feather coverage in naked neck and featherless broilers on their performance under hot conditions.

Under hot conditions, contemporary commercial broilers do not reach their full genetic potential for growth rate, body weight (BW), or breast meat yield because dissipation of their excessively produced internal (metabolic) heat is hindered by the feathers. Therefore, it was hypothesized that heat stress can be alleviated by using the naked-neck gene (Na) or the featherless gene (sc). The study consisted of 4 experimental genetic groups (fully feathered, heterozygous naked neck, homozygous naked neck, featherless), progeny of the same double-heterozygous parents (Na/na +/sc), and commercial broilers. Birds from all 5 groups were brooded together until d 21 when one-half of the birds from each group were moved to hot conditions (constant 35 degrees C), and the others remained under comfortable conditions (constant 25 degrees C). Individual BW was recorded from hatch to slaughter at d 45 and 52 at 25 and 35 degrees C, respectively, when breast meat, rear part, heart, and spleen weights were recorded. Body temperature was recorded weekly from d 14 to 42. Feather coverage significantly affected the thermoregulatory capacity of the broilers under hot conditions. With reduced feather coverage (naked-neck), and more so without any feathers (featherless), the birds at 35 degrees C were able to minimize the elevation in body temperature. Consequently, only the featherless birds exhibited similar growth and BW under the 2 temperature treatments. The naked-neck birds at 35 degrees C showed only a marginal advantage over their fully feathered counterparts, indicating that 20 to 40% reduction in feather coverage provided only limited tolerance to the heat stress imposed by hot conditions. Breast meat yield of the featherless birds was much greater (3.5% of BW, approximately 25% advantage) than that of their partly feathered and fully feathered counterparts and the commercial birds under hot conditions. The high breast meat yield (at both 25 and 35 degrees C) of the featherless broilers suggests that the saved feather-building nutrients and greater oxygen-carrying capacity contribute to their greater breast meat yield. Because of these results, further research on genetically heat-tolerant broilers should focus on the featherless phenotype.

Segregation among test-cross progeny suggests that two complementary dominant genes explain the difference between ascites-resistant and ascites-susceptible broiler lines.

Ascites syndrome (AS) is a major cause of economic losses to the broiler industry. The tendency of broilers to develop AS was found to be heritable, suggesting that selective breeding could provide a solution to this problem. To further elucidate the genetic control of AS, AS-susceptible (AS-S) and AS-resistant (AS-R) lines were established by 3 cycles of divergent selection on pedigree data of AS mortality under AS-inducing conditions. The rapid divergence between the lines suggested the involvement of a major gene with dominance for AS resistance. It was hypothesized that the difference between the lines is controlled by a single dominant gene, denoted A, with AA (and some Aa) individuals in the AS-R line, and aa individuals in the AS-S line. The current study was designed to test this hypothesis by test-crossing heterozygous (Aa) sires from the AS-R line and F(1) from the AS-R x AS-S cross, with recessive homozygous (aa) dams from the AS-S line. A ratio of 1:1 was expected between progeny with AS vs. healthy progeny when reared under AS-inducing conditions. Test-cross progeny of 5 sires from the AS-R line segregated 1:1, indicating that these sires were heterozygous (Aa) in the suggested major gene and thus supporting the hypothesis of a single major gene with dominance of AS resistance. There was segregation among test-cross progeny of 8 F(1) sires, but with a 3:1 ratio of AS progeny to healthy progeny. The 3:1 ratio is expected if the F(1) sires are heterozygous (AaBb) with complementary interaction between the dominant alleles in 2 unlinked major genes. The segregation among test-cross progeny of the 9 heterozygous AS-R sires could also be explained by the same model. These results suggested that 2 major genes are responsible for the difference between the AS-R and AS-S lines. Resource populations derived from these lines will facilitate an efficient genomic search for these 2 genes. Once the alleles of these genes are identified and genotyping tests are developed, breeders will easily be able to select against AS susceptibility.

The expression patterns of hypoxia-inducing factor subunit alpha-1, heme oxygenase, hypoxia upregulated protein 1, and cardiac troponin T during development of the chicken heart.

Oxygen is one of the critical determinants of appropriate embryonic and fetal development, including cardiogenesis. When the demand of tissues for oxygen exceeds oxygen supply, hypoxic conditions develop. In the developing embryo, hypoxia is associated with increased fetal mortality, cerebrovascular anomalies, cardiovascular dysfunction, and altered angiogenesis. Tissue hypoxia may elicit a broad range of responses, many of which are dependent upon hypoxia-inducible transcription factors. Three genes that are stimulated by hypoxia-hypoxia-inducing factor subunit alpha-1, heme oxygenase, hypoxia upregulated protein 1, and cardiac troponin T, which is responsible for binding tropomyosin to regulate calcium binding and contractility of heart muscle-were examined in the embryonic heart of the chicken to determine if expression patterns were altered throughout development. On embryonic day (E) 7, all 3 hypoxic-induced genes were expressed at their highest levels, followed by a decrease from E7 to E19 followed by an increase between internal (E19) and external pipping (E20). The cardiac troponin T exhibited a similar expression level for E7 and E15 with a similar significant increase at E19 and E20. During these periods of development, significant changes in the primary gas exchange organs occur. Based on our observation of upregulation of these hypoxia response genes, it appears that tissue hypoxia is likely a normal component of embryonic development in the chicken based on the upregulation of hypoxia response genes.

Development of ascites-resistant and ascites-susceptible broiler lines.

The rapid growth of modern broilers is associated with enhanced appetite and high metabolic rate and, consequently, high O(2) demand. Ascites syndrome (AS) develops in individuals that fail to fully supply the increasing demand for O(2) in their bodies under ascites-inducing conditions (AIC) such as high altitude or low temperatures. The tendency of broilers to develop AS is heritable, but efficacious selection against AS susceptibility (without affecting the normal expression of other important traits) requires identification of indirect selection criteria. In the present study, divergent AS-susceptible (AS-S) and AS-resistant (AS-R) lines were developed to confirm the heritability of AS and to facilitate future detection of criteria for indirect selection against AS susceptibility. The base population consisted of 85 sire families with a mean of 73 progeny per sire, reared in a commercial broiler house under low-challenge AIC (cold environment and pelleted feed). Chicks dying with AS manifestations were designated AS-susceptible, whereas the surviving birds were designated AS-resistant. By the end of the trial (d 48), AS mortality had accumulated to 17.2%, but AS incidence per family (%ASF) ranged from 0 to 49%, with a high heritability (0.57). Parents of 7 families with very high %ASF produced the first generation (S(1)) of the AS-S line, and parents of 7 families with very low %ASF produced the S(1) of the AS-R line. The S(1) males and females reproduced generation S(2) of the selected lines, whereas additional S(1) males were tested under high-challenge AIC (individual cages, cool wind, and pelleted feed). Progeny testing under this high-challenge AIC, followed by sib selection, was repeated in generations S(2) and S(3), resulting in a divergence of 86.6% in the incidence of AS between the AS-S (91.3%) and AS-R (4.7%) lines. The rapid genetic divergence, and family analysis of %ASF suggested that a single or few major genes are responsible for the difference between the 2 selected lines. These lines may facilitate more sensitive and effective genomic research aimed at detecting these genes or identifying the primary physiological cause of AS.

Evaluation of growth rate, body weight, heart rate, and blood parameters as potential indicators for selection against susceptibility to the ascites syndrome in young broilers.

The continuous selection for rapid growth has been accompanied by an increasing occurrence of ascites syndrome (AS), which develops in broilers failing to supply the increasing demand for O(2) in their bodies. Moderate heritability has been reported for AS in broiler populations, suggesting that selection against AS is feasible. However, direct selection based on AS mortality requires exposure of candidate birds to AS-inducing conditions (AIC), which hinder selection for performance traits. Noninvasive indicators of AS, expressed under standard husbandry, may facilitate the integration of selection against AS into breeding programs. This study was designed to look for differences in heart rate, hematocrit, O(2) saturation of hemoglobin in arterial blood (SaO(2)), BW, and weight gain, all measured at early ages under standard brooding conditions, between birds that later developed AS and those that remained healthy under AIC, and to estimate the heritability of these AS-related parameters and their genetic correlation with the tendency of broilers to develop AS. The experimental population was derived from a broiler dam line. Male progeny of 34 half-sib sire families were reared under standard brooding conditions to 19 d of age, then under an AIC protocol consisting of housing in individual cages, cool air high-speed ventilation, and growth enhancement using high-energy pelleted feed and 23 h/d of light. Birds were necropsied upon mortality or at the end of the trials and were recorded as being susceptible, with manifestations of AS (SUS), or resistant and healthy (RES). About 44% developed AS, confirming the efficacy of the novel AIC protocol. The SUS and RES chicks did not differ in BW and weight gain up to 19 d of age, suggesting that there was no association between AS susceptibility and rapid early growth. The SUS chicks exhibited lower SaO(2) and heart rate than the RES chicks. Moderate heritability was estimated for all traits, but only SaO(2) exhibited consistently significant genetic correlation (-0.5) with AS, suggesting that it may serve as an early indicator for selection against AS, albeit with a limited efficacy.

Maternal and genetic effects on broiler bone properties during incubation period.

In order to examine the differences in bone properties between fast-growing and slow-growing broiler embryos and to understand the effects of genotype and egg size on these differences, fast- and slow-growing hens and males were reciprocally crossed to create 4 egg groups: FST (laid by fast-growing hens, inseminated by fast-growing males), H-FST (fast-growing hens and slow-growing males), H-SLW (slow-growing hens and fast-growing males), and SLW (slow-growing hens and slow-growing males). Embryos (n = 8) from these 4 groups were sacrificed and weighed, and both tibiae were harvested on embryonic d (E) 17, 19, and 21. Left tibiae were tested for their whole-bone mechanical properties using a micromechanical device. Cortical bone structure and bone mineral density (BMD) were examined by micro-computed tomography of the left tibiae. Bone mineralization was evaluated by measuring BMD and ash content, while the rate and location of mineralization were evaluated by fluorochrome labeling. Osteoclastic activity and osteocyte density were evaluated by histological stains [TRAP (Tartrate resistant acid phosphatase) and H&E (Hematoxylin and Eosin), respectively]. Groups with larger eggs (FST and H-FST) had higher BW and tibia weight than groups with smaller eggs (SLW and H-SLW); however, they had a lower ratio of tibia weight to BW. Between groups with similar egg weight, stiffness, maximal load, and yield load of the bones were higher in the SLW than the H-SLW, while no differences were found between the FST and H-FST. Additionally, the tibiae of the SLW were stiffer and their osteocyte density higher than in the FST on E21 and their periosteal mineralization rate was higher between E19 and E21. No differences were found between the groups in cortical bone structure. This study demonstrates that faster growing hatchlings, especially those that hatch from relatively small eggs, have inferior bone mechanical properties in comparison to slower growing hatchlings, and suggests that fast-growing chicks hatching from small eggs are at a higher risk for developing bone pathologies. Accordingly, selection for increased egg size may lead to improved mechanical performance of the skeleton of fast-growing broilers.

DNA fingerprints applied to gene introgression in breeding programs.

An application of DNA fingerprints (DFP) for gene introgression in breeding programs of both farm animals and plants is proposed. DFP loci, detectable by minisatellite probes, are extremely polymorphic. Individuals have unique patterns of DFP and thus can be selected for maximal genomic similarity to the recipient line, and minimal similarity to the donor line, using their DFP patterns as the criterion for similarity. This genomic selection (GS) can be performed at generations BC1, BC2 or both, and thus significantly reduce the required number of backcross generations in introgression breeding programs. The association between genomic and DFP similarity is demonstrated. Theoretical distributions and variances of the relative percentages of the donor and recipient genomes as the basis for the GS approach are presented.

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.

Genetic factors accountable for line-specific DNA fingerprint bands in quail.

DNA fingerprints, prepared from mixes of DNA of individuals sampled from lines of Japanese quail selected for high or low 4-week body weight, were used to evaluate the relative contribution of several evolutionary forces to genetic diversity among populations. Comparisons between lines--two replicates of each selection direction and a control unselected line--were used to determine the frequency of line-specific DNA fingerprint bands produced by each of three major evolutionary forces: 1) mutation; 2) genetic drift; 3) selection. The latter force is expected to generate line-specific bands only if there is linkage disequilibrium between DNA fingerprint loci and quantitative loci (QTLs) controlling body weight. Using probes 33.6 and R18.1, an average of 48.4 DNA fingerprint bands in each line were analyzed. On average, 27.8 bands were found to be line-specific among the 96.8 (2 x 48.4) bands analyzed in an average comparison between pairs of lines. Based on the frequencies of line-specific bands in each particular comparison, it was calculated that 21% of the line-specific bands were due to mutation, 11% due to a single genetic drift event, 11% due to selection, 21% due to the combined effects of genetic drift and selection, 22% due to double independent events of genetic drift, and 14% due to undefined factors. Although evidence was found for a high frequency of genetic changes attributable to genetic drift, and a higher than expected frequency of linkage disequilibrium, the emphasis of this report is on the methodology suggested rather than on the particular results.

Immunological parameters in meat-type chicken lines divergently selected by antibody response to Escherichia coli vaccination.

Our group has established two lines of meat-type chickens divergently selected for early (HC line) and late (LC line) antibody responsiveness at 10 days of age to immunization with inactivated pathogenic Escherichia coli bacteria. The question addressed in the study presented here is whether this selection has changed other immunological responses, increasing the overall 'early' immunocompetence. Broilers of the third and fourth generations (S3 and S4) of the selected lines (HC and LC) and a control, unselected line (CT) were vaccinated at 10 days of age with E. coli vaccine, Newcastle virus vaccine (NDV), sheep erythrocytes (SRBC) or bovine serum albumin (BSA). Line-HC chicks exhibited higher antibody titers to E. coli, NDV and SRBC than CT or LC chicks. At 20 days of age HC chicks demonstrated a higher total protein and a higher beta- and gamma-globulin levels in their serum. At 21 days of age, HC chicks cleared carbon particles faster than LC chicks. Peripheral blood lymphocytes (PBL) from HC chicks vaccinated with E. coli vaccine, proliferated in vitro more actively in the presence of the stimulating antigen than the PBL of LC chicks. Peripheral blood lymphocytes (PBL) obtained from HC-line chicks exhibited a higher proliferative response to concanavalin A (Con A)-, phytohemagglutinin (PHA)- or pokeweed mitogen (PWM)-stimulation than LC PBL. These results demonstrate that the selection for high or low antibody response to E. coli at a young age resulted also in a significant change in the response of other parameters of the immune system. The high response to E. coli was found to be associated with a high antibody response to other antigens (NDV and SRBC), increased phagocytic activity and increased proliferative response to antigen or mitogens. The selection most probably affected early immunocompetence.

Relationship between broiler chicken haematocrit-selected parents and their progeny, with regard to haematocrit, mortality from ascites and bodyweight.

A previous work of this group demonstrated that the relative haematocrit value of broilers is inherited and may serve as an indicator to susceptibility to the ascites syndrome in cold-stressed broilers. In this study, a full-pedigreed population was produced from male and female grandparent breeding stock that was selected by haematocrit and by normal selection parameters. Matings were made between low (L), medium (M) and high (H) haematocrit parents: L x L, M x M, and H x H. In their progeny, both before and after cold exposure, there was a statistically linear relationship between actual haematocrit and their H, M and L grouping (P<0.0001); heritability of the haematocrit was high (0.46-0.81). Both the low haematocrit parent and progeny groups showed an increased bodyweight. Exposure of the progeny from all the parental groups to an ascites-predisposing cold environment caused similar losses from ascites in the progeny of all three groups. Although this finding was not the same as in the previous trial where the H haematocrit group was associated with high ascites mortality, it is hypothesized that other factors, such as arterial blood saturation with oxygen, interacted in these birds at genetic or environmental levels.

Effects of high temperature on growth and efficiency of male and female broilers from lines selected for high weight gain, favorable feed conversion, and high or low fat content.

Male and female broiler chicks from five different broiler crosses (WI, LF, and HF = Israeli chicks selected for high body weight gain, and low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for favorable feed conversion and high body weight gain, respectively) were raised at a high ambient temperature (32 to 33 C). Weight gain, protein and fat content in the carcass and feed, and protein efficiency were determined at 4, 6, and 8 wk of age. The effect of the high temperature was evaluated by comparing these data with those of similar chicks raised at a normal temperature (20 to 33 C) up to 6 wk of age. The reductions in body weight, protein gain, and feed and protein efficiency due to the high temperature increased with age and were much larger in males than in females. This trend was more pronounced in WI and WN chicks than in LF, HF, and FC chicks. Females of WI and WN crosses were as heavy as males at 6 wk and heavier at 8 wk. In LF, HF, and FC crosses, both sexes had similar weights at 8 wk. Growth reduction due to the high temperature was largest in the groups with the highest growth rate at the normal temperature (WI and WN males). Chicks with a lower growth rate and a higher capacity for energy storage in fat depots (all females, HF chicks), or a higher capacity for heat loss (FC chicks), were less affected by the high temperature. The results suggest that females should be preferred over males for broiler production in hot facilities or locations. Broiler genotypes selected for feed efficiency at the expense of fast growth may allow for a more profitable broiler production in high-temperature regions.

Genotype by environment interactions using fast-growing, lean or fat broiler chickens, originating from The Netherlands and Israel, raised at normal or low temperature.

Male and female broiler chicks from five different broiler crosses (WI = Israeli chicks selected for body weight; LF and HF = Israeli chicks selected for low and high abdominal fat, respectively; FC = Dutch chicks selected for feed conversion; and WN = Dutch chicks selected for body weight) were raised under normal and subnormal temperatures. Weight gain, protein and fat content in the carcass, and feed and protein efficiency were determined at 4 and 6 wk of age, and at equal body weight. In addition to an overall effect of genotype, contrasts between Dutch (WN and FC) and Israeli (WI and LF) chicks and between chicks selected for body weight (WN and WI) or leanness (LF and FC) were examined. Temperature, genetic background, sex, and age affected all traits examined. Significant interactions were observed for weight gain, protein deposition, and feed and protein efficiency but were less evident for fat deposition. At low temperature, the broilers derived from Dutch strains had higher weight gain and protein deposition than those derived from Israeli strains; at the normal temperature the Israeli chicks performed better. The relations between body composition, weight gain, and efficiency are discussed to explain the interactions found.

Effects of low, normal, and high temperatures on slaughter yield of broilers from lines selected for high weight gain, favorable feed conversion, and high or low fat content.

Male and female broiler chicks from five different broiler crosses (WI = Israeli chicks selected for increased body weight; LF and HF = Israeli chicks selected for low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for improved feed conversion and increased body weight, respectively) were raised at low, normal, or high temperature. Slaughter yield, amount of breast meat, and abdominal fat were determined at 6 wk of age in all groups and at a body weight of 2,360 g for males and 1,965 g for females in the low- and normal-temperature groups, and at 8 wk in the high-temperature groups. Temperature, genotype, and sex influenced both absolute and relative weights of carcass, breast meat, and abdominal fat. Temperature had a negative effect on breast meat yield. Males were affected more by high temperature than females. A significant interaction between temperature and sex for breast meat yield was caused by a low yield for males at the high temperature. A similar interaction for proportion of abdominal fat was caused by a high fat content in males reared at the high temperature. Slaughter yield and especially yield of breast meat were highest in FC chickens in all comparisons.