The objective was to study the effect of dry period length in dairy cows on immunoglobulin content and natural antibodies (NAb) titers in colostrum, growth, and plasma natural and specific antibody titers in plasma of calves. Holstein-Friesian dairy cows (n=167) were randomly assigned to 3 dry period lengths (0, 30, or 60 d). Colostrum production, concentration of colostrum IgG and IgM, and titers of NAb (isotypes IgG and IgM) binding keyhole limpet hemocyanin (KLH) and human serum albumin (HuSA) in colostrum were measured. Female calves were immunized with both KLH and HuSA at wk 6 and 10 of life. Titers of NAb and specific antibody (SpAb) for isotypes IgG, IgM, and total immunoglobulin (IgT) binding KLH or HuSA were determined in plasma of female calves. Primary and secondary antibody responses to KLH or HuSA from wk 6 and 10 were expressed as the increase in antibody titers to wk 10 and 11 of life after primary and secondary challenges, respectively. Pregnancy length for cows with a 0-d dry period was 3d shorter compared with cows with a 30- or 60-d dry period. Birth weight of calves from cows with a 0-d dry period was lower compared with calves from cows with a 30-d dry period. Growth of calves until 12 wk of life was not affected by dry period length. Colostrum production and IgG and IgM concentration in colostrum were lower for cows with a 0-d dry period than a 60-d dry period. Natural IgG and IgM titers binding KLH or HuSA were lower in colostrum from cows with a 0-d dry period compared with cows with a 60-d dry period. Natural antibody titers (IgG, IgM, and IgT) binding KLH or HuSA in plasma were lower during the first 2 wk of life for calves from cows with a 0-d dry period compared with calves from cows with a 30- or 60-d dry period. After primary and secondary immunization of calves with KLH and HuSA, SpAb titers of calves were not affected by dry period length. After secondary immunization, the response of IgG and IgT binding KLH was higher in plasma of calves from cows with a 0-d dry period. The results of this study demonstrate that, although omission of the dry period of dairy cows leads to lower plasma NAb titers in calves during the first 2 wk of life, SpAb titers in calves were not affected and even the secondary antibody responses were enhanced compared with calves from cows with a 30- or 60-d dry period.

Osteochondrosis (OC) develops at a young age and has been associated with lameness and reduced longevity of sows. Early detection of OC is therefore beneficial for selection against OC. Possibly, immunological components within the blood may serve as an indicator for OC development and could therefore be used as a biomarker. Levels of naturally occurring (auto-) antibodies (N[A]Ab) have been associated with homeostatic imbalance and various forms of inflammation, and may have an association with OC. The aim of this study was to investigate possible associations between the presence and levels of N(A)Ab of the IgM and IgG isotypes at an early age with OC in growing gilts at slaughter (24 weeks of age). Plasma samples were obtained from 212 Topigs 20 (Dutch Large White x Dutch Landrace) gilts at 6, 10, and 24 weeks of age and analyzed for N(A)Ab titers against 11 (auto-) antigens using ELISA. After slaughter, the elbow, hock, and knee joints were macroscopically examined for OC status. Due to low prevalence of OC in the elbow joint (5.4%), the elbow joint was not taken into account in analyses. Significant (P≤0.05) associations with OC in both the hock joint and at the animal level (all joints combined) were found for IgM titers against chondroitin sulfate A at 6 weeks of age (OR 1.4 and 1.5), actin at 6 weeks of age (OR 1.4 and 1.3), thyroglobulin at 24 weeks of age (OR 1.5 and 1.3), and IgG titers against insulin at 6 weeks of age (OR 1.7 and 1.4). Additionally, significant (P≤0.05) associations with OC were found at the knee joint for IgM titers against albumin at 6 weeks of age (OR 2.3), at the hock joint for IgM titers against keyhole limpet hemocyanin at 6 weeks of age (OR 1.4), and at the animal level for IgM titers against actin at 24 weeks of age (OR 1.3). This study indicated for the first time associations between the presence and levels of N(A)Ab at a young age and OC at 24 weeks of age in breeding gilts.

Levels of natural antibodies (NAb) binding keyhole limpet hemocyanin (KLH) in layers were shown to be heritable and to be potential indicative parameters for survival. A proportion of NAb are directed to self-molecules, or slightly changed self-molecules (neo-epitopes), labeled as natural autoantibodies (NAAb). It is unknown whether the levels of NAAb are heritable and genetically correlated. In this paper, we estimated genetic parameters in plasma of healthy layers for IgM and IgG antibodies binding ovalbumin (OVA), myosin (MYO), cardiolipin (CAR), lysozyme (LYS), and the model antigen keyhole limpet hemocyanin (KLH). A linear animal model was used to estimate (co)variance components, heritabilities, and correlations. The estimates of heritabilities ranged from 0.10 to 0.17 for IgM, and 0.02 to 0.11 for IgG, respectively. For both IgM and IgG, high genetic correlations were observed between levels of NAAb binding autoantigens and NAb binding KLH, except for IgG binding KLH and LYS, for which a low genetic correlation was found. Low to moderate phenotypic correlations were found between NAAb and NAb. In addition, significant maternal environmental effects of 0.03, 0.07, and 0.04 were observed for IgM binding OVA, LYS, and KLH, respectively. Results from this study indicated that NAAb or NAb levels in plasma were heritable and could provide tools to identify the health status of birds.

Environmental particles enter the chicken via several routes. Entry via the respiratory and cloacal routes likely activates immune responses. We studied the localization of simultaneous intratracheally and cloacally applied beads of 2 sizes in the chicken body in time, and when possible, semiquantified the amount of beads. Ten broiler hens, 3.5 wk of age, received 1.25 × 109 1.0-µm beads and 1.05 × 107 10-µm fluorescein isothiocyanate (green) labeled cloacally, and simultaneously the same number and same sizes of tetramethylrhodamine isothiocyanate (red) labeled beads intratracheally. The bursa of Fabricius, lung, liver, kidney, gallbladder, spleen, thymus, small intestine (upper ileum), cecum, intestinal luminal contents, aerated bones, feces, and blood, from 2 chickens per moment were sampled at 1 h, 6 h, 24 h, 48 h, and 1 wk after challenge and studied for the presence of beads using fluorescence microscopy. The highest amount of beads was found in organs closest to the application site after 1 h (i.e., the lungs for red beads, and the bursa for green beads). All tissue samples showed all 4 types of beads at all time moments, most of them within 1 h. Lower levels of beads were found in lungs and bursa after 6 h and in all other organs after 24 h, except for the kidneys where levels declined after 48 h. Surprisingly, beads were found in thymus tissue and only relatively few beads were found in the spleen. At 1 h, 1-µm intratracheally applied red beads were also found in the cecal luminal content and cecal tissue, but not in the small intestinal luminal content, suggesting that ceca are capable of excreting small particles entering the body via the respiratory route. The presence of nondegradable and nonimmunogenic beads of different sizes in all sampled organs throughout the whole chicken body for 7 d suggested potentially negative chronic health and welfare risks for the chicken of environmental particles.

We studied the effects of a concurrent challenge on slow-growing broilers with 1) airborne particles of 2 sizes: fine dust (smaller than 2.5 microns) and coarse dust (between 2.5 and 10 microns) that were directly collected from a broiler house and 2) lipopolysaccharide on intratracheal immunizations with the specific antigen human serum albumin (HuSA) and measured primary and secondary systemic (total) antibody responses and (isotype-specific) IgM, IgG, and IgA responses at 3 and 7 wk of age. All treatments affected immune responses at several ages, heart morphology, and BW gain, albeit the latter only temporarily. Dust particles significantly decreased primary antibody (IgT and IgG) responses to HuSA at 3 wk of age but enhanced IgM responses to HuSA at 7 wk of age. Dust particles decreased secondary antibody responses to HuSA, albeit not significantly. All of the birds that were challenged with dust particles showed decreased BW gain after the primary but not after the secondary challenge. Relative heart weight was significantly decreased in birds challenged with coarse dust, fine dust, lipopolysaccharide, and HuSA at 3 wk of age, but not in birds challenged at 7 wk of age. Morphology (weight, width, and length) of hearts were also affected by the dust challenge at 3 wk of age. The present results indicate that airborne dust particles obtained from a broiler house when intratracheally administered at an early age affect specific humoral immune responsiveness and BW gain of broilers to simultaneously administered antigens differently than when administered at a later age. The hygienic status of broiler houses at a young age may be of importance for growth and immune responsiveness, and consequently, for vaccine efficacy and disease resistance in broilers. The consequences of our findings are discussed.

The effect of differences in the composition of nutrients of two nutritionally complete layer diets on parameters from innate and adaptive immunity of chickens were examined. The diets were based on ingredients grown either organically or conventionally. As individual differences in nutrient sensitivity have been reported and as the immune system was used as a sensory organ to detect possible effects, layer hens divergently selected for high and low specific antibody (Ab) responses to SRBC, i.e. low line hens and high line hens, reflecting a genetically based differential immune competence were used. The parental line of these hens was randomly bred as the control line, and was used as well. To examine maternal and/or epigenetic effects on nutrient sensitivity, two subsequent generations were studied. In addition, the second generation was challenged with keyhole limpet haemocyanin (KLH). The most pronounced dietary effects were found in the low line birds of the first generation: specific Ab titres to NCD vaccine were significantly elevated in one of the two diets. In the second generation, significant differences were found in Ab and complement responses to the KLH inoculation. Immune competence of the selection lines was not affected. In the second generation control line hens showed the most pronounced effects of dietary treatment in immune responsiveness, with significant effects on specific Ab vaccine titres as well as in innate parameters. The results suggest that small nutritional differences due to the use of different sources of raw ingredients have immunomodulatory effects on innate and adaptive humoral immune parameters. The data indicate the importance of dietary components displaying the capacity to modulate the immune system.

Earlier, we reported that pathogen-associated molecular patterns such as lipopolysaccharide (LPS), when administered intratracheally (i.t.), affected primary and secondary specific antibody responses to antigens administered concurrently, either i.t. or systemically, and also affected BW gain (BWG) of layers and broilers. In the present study, we evaluated the effects of repeated i.t. challenge with LPS concurrently with or before i.t. immunizations with the specific antigens human serum albumin (HuSA) and rabbit gamma globulin (RGG) on primary (HuSA, RGG) and secondary (HuSA) systemic antibody responses and (isotype) IgM and IgG responses at 2 different ages. Broilers were challenged via the trachea at 3 and 7 wk of age with various combinations of LPS, HuSA, and RGG. All treatments affected immune responses at several time points and also affected BWG, albeit temporarily for the latter. Lipopolysaccharide enhanced primary antibody responses to HuSA and to RGG, when challenged concurrently, but birds challenged solely with LPS at 3 wk of age also showed enhanced primary antibody responses to HuSA and RGG given at 7 wk of age. This was true for IgM as well as IgG isotype responses. Lipopolysaccharide challenge negatively affected BWG at 3 wk of age, whereas the negative effects of LPS after a secondary LPS challenge at 7 wk of age were most pronounced in the birds challenged with LPS at 3 wk of age. The present results indicated that LPS, when administered i.t. at a young age, may affect specific humoral immune responsiveness to antigens administered simultaneously and to BWG of broilers, but also when challenged 4 wk later with specific antigens, suggesting an enhanced status of immune reactivity or sensitivity. The hygienic status of broiler houses at a young age may thus influence BWG, immune responsiveness, and, consequently, the vaccine efficacy and disease resistance in broilers at later ages. The consequences of our findings are discussed.

A QTL involved in the primary antibody response toward keyhole limpet hemocyanin (KLH) was detected on chicken chromosome 14 in the experimental population, which was created by crossing commercial White Leghorn and a Polish native chicken breed (green-legged partridgelike). The current QTL location is a validation of previous experiments pointing to the same genomic location for the QTL linked to a primary antibody response to KLH. An experimental population was typed with microsatellite markers distributed over the chicken chromosome 14. Titers of antibodies binding KLH were measured for all individuals by ELISA. Statistical models applied in the Grid QTL Web-based software were used to analyze the data: a half-sib model, a line-cross model, and combined analysis in a linkage disequilibrium and linkage analysis model. Candidate genes that have been proposed were genotyped with SNP located in genes exons. Statistical analyses of single SNP associations were performed pointing out 2 SNP of an axis inhibitor protein (AXIN1) gene as significantly associated with the trait of an interest.

Natural antibodies (NAb) have been divided in 2 classes: overt and cryptic. Overt NAb can be detected in unfractionated normal sera of nonimmunized mammals and chickens. Cryptic NAb as described in mammals need an in vitro physical or biochemical treatment to be detected, which may reflect their biochemical modification in situ during inflammation or infection. We studied the effect of concurrent primary, secondary, and tertiary intratracheal (i.t.) challenges with lipopolysaccharide (LPS) and human serum albumin on levels of 2 cryptic NAb [i.e., NAb binding actin (ACT), or thyroglobulin (THYRO)] and levels of an overt NAb binding keyhole limpet hemocyanin (KLH). In addition, effect of aging of the birds on levels of NAb was taken into account. Presence and changes on the level of the cryptic antibodies directed to ACT and THYRO were expected after the i.t. challenges with LPS (and human serum albumin). However, levels of NAb binding ACT were only significantly enhanced by LPS after primary challenge, whereas levels of NAb binding THYRO were not affected by primary nor secondary challenges but were significantly decreased by LPS after the third immunization. On the other hand, no changes in the levels of overt NAb binding KLH were expected, but levels of NAb binding KLH were significantly enhanced after the primary and secondary challenges with LPS. Levels of all three NAb increased with aging, but the different challenges performed at 3 moments during aging did not significantly or consistently affect levels of the overt nor cryptic NAb. Our results suggest that chickens might react by overt NAb as well as cryptic NAb to an infection or inflammation rather than by cryptic NAb only. The relation between various types of NAb and i.t. immunization with antigen and LPS and aging is discussed.

Pathogen-associated molecular patterns (PAMP) such as lipopolysaccharide (LPS), lipoteichoic acid, beta-glucans (BGL), and possibly many others are important parts of (fine) dust in animal houses. When intratracheally (i.t.) administered, PAMP affected specific primary and secondary humoral immune responses to concurrently i.t. or systemically administered antigens and BW gain (BWG) of layer chickens. In the present study, we evaluated the effects of i.t. challenge with various PAMP known to be present in dust: LPS, lipoteichoic acid, zymosan-A (containing 1,3 BGL), next to heat-inactivated dust particles as a representative of mechanical stress, a combination of the former components, and NH3 as a chemical component of dust on primary and secondary (total) systemic antibody (Ab) responses and (isotype) IgM and IgG responses to concurrently i.t.-administered human serum albumin (HuSA) in broilers. Birds were challenged via the trachea for 2 consecutive days at 3 and 7 wk of age, respectively. All treatments affected immune responses at several moments, BWG, and heart morphology. beta-Glucans and LPS affected the birds most pronounced and for a prolonged period. Intratracheally administered LPS and BGL significantly enhanced primary and secondary total Ab, IgM Ab, and IgG Ab responses to HuSA. All birds that were challenged with dust, PAMP, or NH3 concurrently with HuSA showed a decreased BWG especially after primary, but also after secondary challenge. Weight, width, and length of hearts were enhanced in dust and PAMP-treated birds as well when these birds were challenged with HuSA. The present results indicated that components of dust such as PAMP when i.t. administered affect humoral immune responsiveness of broilers, which may lead to an enhanced status of immune reactivity. Furthermore, our results suggest that the hygienic status of the environment influences BWG and may affect heart morphology, and as a consequence physiology in broilers. The consequences of our findings with respect to dust, (airborne) PAMP, hygienic conditions in the barn, and immune responsiveness of broilers are discussed.

Effects of early life experience with climatic (heat) and hygienic [lipopolysaccharide (LPS)] stress on adaptability to the same stressors in later life were studied in laying hens. Chicks were exposed to 37 degrees C for 24 h at d 5 of age (n = 12) or were i.v.-administered once with 1 mg/kg of BW of LPS at 6 wk of age (n = 12), whereas a control group was reared under standard conditions receiving a placebo treatment of PBS (n = 36). At 24 wk of age, hens treated in early life were reexposed to the same stressor. Early life control hens were exposed to heat stress (n = 12), i.v.-administered with LPS (n = 12), or not exposed (n = 12). To evaluate improvement of adaptability, effects of climatic and hygienic stress on performance, humoral immune competence, and endocrine responsiveness were investigated in hens with early life experience to the stressors and hens only exposed to the stressors in later life. Early life heat exposure did not affect performance, immune, and endocrine parameters. Treatment x time interactions were found for level of antibody (Ab) binding to LPS and keyhole limpet hemocyanin (KLH) after LPS administration, indicating that hens with early life LPS experience differed in response level (Ab binding to LPS) and response pattern (Ab binding to LPS and KLH) compared with hens administered with LPS only at adult age. Our data suggest that early life heat stress exposure did not affect adaptability of laying hens to heat stress in later life. However, early life LPS exposure affected kinetics and magnitude of Ab levels binding to LPS and KLH, indicating that early life LPS exposure can enhance the status of immune reactivity or induce a higher sensitivity to LPS.

The present study estimated the heritability of natural antibody (NAb) levels binding rabbit red blood cells at the day of immunization with SRBC (NAb0) and 5 d postimmunization (NAb5) in 2 chicken lines divergently selected for specific antibody levels (SpAb) against SRBC and a randombred control line. In addition, genetic correlations between the levels of NAb binding rabbit red blood cells and levels of SpAb binding SRBC were estimated. The heritability of the SpAb level against SRBC was estimated based on data from 23 generations of selection and in total 21,842 chickens. The heritability of NAb levels against rabbit red blood cells was estimated on 1,764 chickens in generations 22 and 23 using a bivariate analysis including the trait under selection (i.e., SpAb responses to SRBC). Maternal environmental effects were accounted for in the analyses. The heritability for SpAb was 0.17, the heritability for NAb0 levels was 0.23, and the heritability for NAb5 was 0.09. The genetic correlation between SpAb and NAb0 was 0.15 and the genetic correlation between SpAb and NAb5 was 0.50. The weak, though positive, genetic correlation between SpAb responses and the NAb0 levels in nonimmunized chickens, as well as the moderate genetic correlation between SpAb responses and the NAb levels 5 d postimmunization with SRBC, suggest that selection for enhanced adaptive immune system results in a positive correlated response of the innate immunity of chickens.

Individual differences in nutrient sensitivity have been suggested to be related with differences in stress sensitivity. Here we used layer hens divergently selected for high and low specific antibody responses to SRBC (i.e., low line hens and high line hens), reflecting a genetically based differential immune competence. The parental line of these hens was randomly bred as the control line and was used as well. Recently, we showed that these selection lines differ in their stress reactivity; the low line birds show a higher hypothalamic-pituitary-adrenal (HPA) axis reactivity. To examine maternal effects and neonatal nutritional exposure on nutrient sensitivity, we studied 2 subsequent generations. This also created the opportunity to examine egg production in these birds. The 3 lines were fed 2 different nutritionally complete layer feeds for a period of 22 wk in the first generation. The second generation was fed from hatch with the experimental diets. At several time intervals, parameters reflecting humoral immunity were determined such as specific antibody to Newcastle disease and infectious bursal disease vaccines; levels of natural antibodies binding lipopolysaccharide, lipoteichoic acid, and keyhole limpet hemocyanin; and classical and alternative complement activity. The most pronounced dietary-induced effects were found in the low line birds of the first generation: specific antibody titers to Newcastle disease vaccine were significantly elevated by 1 of the 2 diets. In the second generation, significant differences were found in lipoteichoic acid natural antibodies of the control and low line hens. At the end of the observation period of egg parameters, a significant difference in egg weight was found in birds of the high line. Our results suggest that nutritional differences have immunomodulatory effects on innate and adaptive humoral immune parameters in birds with high HPA axis reactivity and affect egg production in birds with low HPA axis reactivity.

Various potential immune-modulating microbially derived pathogen-associated molecular patterns (PAMP), or so called homotopes, are present in high concentrations in the environment of food animals. In previous studies, intravenously administered PAMP had variable effects on specific primary and secondary immune responses of poultry to systemically administered antigens. In the present study, we evaluated the effects of intratracheal (i.t.) challenge with the PAMP lipopolysaccharide, lipoteichoic acid (LTA), and Zymosan-A (containing 1,3 beta-glucan) on primary and secondary (total) antibody (Ab) responses and (isotype) IgM, IgG, and IgA responses to systemically administered human serum albumin (HuSA), and Ab titers to infectious bursal disease (Gumboro virus) and infectious bronchitis vaccines in layer hens at 9 and 22 wk of age. Birds were challenged via the trachea with PAMP for 5 consecutive days prior to primary and secondary immunization with HuSA. Intratracheally administered LTA and, to a minor extent, lipopolysaccharide significantly enhanced secondary total and IgG Ab responses to HuSA. 1,3 beta-Glucan did not significantly affect Ab responses to HuSA. All birds challenged with PAMP showed a decreased BW. Higher total Ab titers to infectious bursal disease and infectious bronchitis were found in birds challenged with LTA. The present results indicate that i.t. administered PAMP affect the humoral immune responsiveness of poultry, which may lead to an enhanced status of immune reactivity. Furthermore, our results suggest that the hygienic status of the environment influences BW (gain). The consequences of immune modulation by airborne PAMP or hygienic conditions in chicken husbandry for vaccine delivery and immune responsiveness of poultry are discussed.

Planned crosses were designed to produce an F2 and 2 backcross populations from 2 lines of White Leghorn chickens previously selected over 10 generations for 2 different in vivo immune responses. The selection criteria applied on the 2 grandparental lines were as follows: high antibody response to Newcastle disease virus vaccine 3 wk after vaccination (ND3) and high cell-mediated immune response [response to phytohemagglutinin]. Furthermore a control line was kept by random breeding. The objective of the study was to estimate if the 2 selection criteria applied on the pure lines had changed the level of and type of immune (humoral) response to a new antigen, keyhole limpet hemocyanin (KLH), in the various second-generation progeny groups. In addition, correlations between parameters of acquired and innate immunity were tested. Primary total (IgT) and isotype-specific (IgG and IgM) antibody response to KLH 1 wk after immunization and levels of natural antibodies (NAB) binding to Salmonella enteriditis-derived lipopolysaccharide (LPS) were measured. Although no differences were present between IgM and IgG antibodies to KLH and the phytohemagglutinin skin-swelling response, significant differences were present between all the progeny groups for IgT to KLH and ND3 and NAB binding to LPS. The mean values for IgT to ND3 and KLH were significantly different between the crosses using the selected lines compared with the control line, indicating a contribution of the previous selection. In addition, a sex effect was found for IgM to KLH and NAB to LPS, for which females had a higher response than males in both cases. No interaction between progeny type and sex was found. Furthermore, significant positive correlations were found between NAB to LPS and specific antibody titers to KLH. Finally, the results of the present study demonstrated an interaction between innate and acquired immunity under this strategy of selection and crossbreeding and confirmed the effect of selection on general immune response to a new antigen in second-generation crosses.

The relation between survival and levels of humoral components of innate (and specific) immune competence of laying hens was investigated in a population of 1,063 laying hens from 12 purebred layer lines. Natural immune competence of the chickens was studied by measuring levels of natural antibodies (NAb) binding to keyhole limpet hemocyanin (KLH) or lipopolysaccharide (LPS), respectively, and hemolytic (classical and alternative) complement activity at 20, 40, and 65 wk of age. In addition, levels of antibodies binding a Newcastle disease vaccine strain as a measure of specific immunity were investigated at 20 wk of age. A distinction could be made between lines showing high or low immune competence with respect to NAb, complement activity, and specific antibodies. Within lines, significant correlations were found for each of the innate parameters among the 3 ages. The innate and specific parameters were, however, not correlated with each other. Based on the limited data set, it was not possible to draw conclusions on line differences for innate or specific immune competence in relation to survival. However, regardless of line, low levels of NAb binding to KLH or high levels of NAb binding to LPS were detected in chickens that did not survive the laying period. The major difference between the responses of NAb binding to KLH or LPS was that the chickens probably did not encounter KLH, which suggests a reflection of the capacity to respond, whereas the chickens most probably did encounter LPS, which suggests a reflection of the active status of the innate humoral immune system. In conclusion, we propose that levels (KLH) and activation (LPS) of components of natural antibodies are indicative for the probability that chickens survive a laying period.

Quantitative trait loci involved in the primary antibody response to keyhole lympet hemocyanin (KLH) and Mycobacterium butyricum were detected in two independent populations of laying hens. The first population was an F2 cross (H/L) of lines divergently selected for either high or low primary antibody responses to SRBC, and the second population was an F2 cross between 2 commercial layer lines displaying differences in feather pecking behavior (FP). Both populations were typed with microsatellite markers widely distributed over the genome with similar intervals between markers. Titers of antibodies binding KLH and M. butyricum were measured for all individuals by ELISA. Two genetic models were applied to detect QTL involved in the humoral immune response: a half-sib model and a line-cross model, both using the regression interval method. In the half-sib analysis, 2 QTL (on GGA14 and GGA27) were detected for the antibody response to KLH for the H/L population, and 2 QTL (on GGA14 and GGA18) were detected for the FP population. Only 1 QTL was detected for M. butyricum on GGA14 in the FP population using the half-sib analysis model. Two QTL were detected for the FP population on GGA2 and GGA3 using the line-cross analysis model. A QTL for the primary antibody response to KLH detected on GGA14 was validated in both populations under the half-sib analysis model. The present data suggest differences in the genetic regulation of antibody responses to two different T-cell dependent antigens.

Quantitative trait loci for BW at 4, 6, 8, 12, and 18 wk of age were detected in an experimental F2 cross of layers divergently selected for primary antibody response to SRBC. A negative phenotypic correlation between levels of antibody titers and BW, was reported earlier within founder lines. The entire experimental population was genotyped with 174 microsatellite markers equally distributed over the genome. Two genetic models were applied in the QTL analysis: a half-sib model and a line-cross model, both using the regression interval method. In the half-sib model, 3 QTL for BW at 4 wk of age on chromosomes GGA2, GGA3, and GGA9 were detected. For BW at 6 wk of age, 3 QTL were detected on GGA2, GGA3, and GGA6. For BW at 8 wk of age, a QTL was detected on GGA7, and for BW at 12 and 18 wk of age, a QTL was detected on GGAZ. With the line-cross analysis model, one QTL on GGA7 for BW at 4 wk of age was detected. Two QTL were detected on GGA3 and GGA7 for BW at 6 wk of age, and one on GGA3 was detected for BW for 8 and 12 wk of age. For BW at 18 wk of age, there were no QTL under the line-cross analysis model. The present data suggest that 1) a different set of genes affects the early and the late growth, and 2) genes selected to humoral immune responsiveness are different from genes underlying growth.