Genetics of growth and reproduction in the Turkey. 17. Changes in genetic parameters over forty generations of selection for increased sixteen-week body weight.

A line (F) of turkeys was selected over 40 generations for increased 16-wk BW. The base population for the F line was a randombred control population that was maintained without conscious selection and used to remove yearly environmental variation in the F line. Selection was effective in increasing 16-wk BW in the F line. Selection differentials based on the mean of the selected parents minus the mean of the entire population (intended) and intended selection differentials weighted for number of offspring produced (actual) did not differ consistently, indicating that natural selection was not opposing artificial selection during the reproduction of the F line. The realized heritability of 16-wk BW in the F line, based on the linear regression of the selection response on accumulated actual selection differential, declined with selection. For both sexes combined, the realized heritability was 0.309 +/- 0.022 (SE), 0.268 +/- 0.033, 0.268 +/- 0.026, 0.166 +/- 0.016, and 0.242 +/- 0.004, respectively, for generations 1 to 10, 11 to 20, 21 to 30, 31 to 40, and 1 to 40. Genetic increases in 16-wk BW in the F line over 40 generations of selection were positively associated with BW at other ages (8 and 20 wk of age and at 50% production), shank length and width at 16 wk of age, days from stimulatory lighting to production of the first egg, and egg weight but were negatively associated with egg production, intensity of lay (maximum and average clutch length and rate of lay), and walking ability. Over the 40 generations of selection, genetic increases in BW in the F line were not associated with changes in broodiness or mortality to 8 wk of age. During generations 31 to 40, BW at 8 and 20 wk of age continued to increase in the F line, but there was no significant change in adult BW, and the only significant change in reproduction traits was for average clutch length (-0.030). Because the genetic changes in some correlated traits were not consistent in all generation intervals studied, the genetic correlation between the selected trait (16-wk BW) and the correlated trait apparently changed with selection.

Genetics of growth and reproduction in the turkey. 16. Effect of repeated backcrossing of an egg line to a commercial sire line.

The turkey industry's view of the relative economic importance of growth and egg production has changed rapidly, and genetic changes by selection within lines may not be rapid enough to meet the changing needs. The objective of the present study was to determine the feasibility of rapidly increasing the BW of dam lines by repeated backcrossing of a dam line (E) to a commercial sire line (B). The experimental E line was selected long-term for increased egg production and was used as the model for a turkey dam line. The B line was larger (more than 3-fold) in BW at 8, 16, and 20 wk of age, had wider breasts (approximately 1.8-fold) at 16 wk of age, and had lower egg production for 180 d (about 3-fold) than the E line. Based on additive genetic variation, males in the F1 generation of the B x E cross did not differ from expected in BW at any age, but females of this cross had BW less than expected at 16 and 20 wk of age. In the F1 generation, breast width of the cross did not differ from the expected value, but egg production for 180 d was greater than expected (126.6 vs.102.3 eggs/hen). After 3 generations of backcrossing, the backcrosses exhibited a gain in 20-wk BW of 12.5 and 8.8 kg, respectively, for males and females; a gain of 5.9 and 5.3 cm in breast width at 16 wk of age for males and females, respectively; and a loss of 74.1 eggs per hen over a 180-d production period. Based on the results of the current and a previous study, limited backcrossing of a dam line to a sire line may be an economically feasible method to greatly increase the BW of dam lines without unduly sacrificing egg production. For maximum gains per generation, backcrossing probably should be used for a maximum of 2 or 3 generations.

Measurement of copper-binding sites on low density lipoprotein.

Copper is often used to oxidize low density lipoprotein (LDL) in experiments in vitro and is a candidate for oxidizing LDL in atherosclerotic lesions. The binding of copper ions to LDL is usually thought to be a prerequisite for LDL oxidation by copper, although estimates of LDL copper binding vary widely. We have developed and validated an equilibrium dialysis assay in a MOPS-buffered system to measure copper binding to LDL and have found 38.6+/-0.7 (mean+/-SEM, n=25) copper binding sites on LDL. The binding was saturated at a copper concentration of 10 micromol/L at LDL concentrations of up to 1 mg protein/mL. Copper-binding capacity increased progressively and markedly when LDL was oxidized to increasing extents. Chemical modification of histidyl and lysyl residues on apolipoprotein B-100 reduced the number of binding sites by 56% and 23%, respectively. As an example of the potential of this method to assess the effects of antioxidants on copper binding to LDL, we have shown that the flavonoids myricetin, quercetin, and catechin (but not epicatechin, kaempferol, or morin), at concentrations equimolar to the copper present (10 micromol/L), significantly decreased copper binding to LDL by 82%, 56%, and 20%, respectively.

Human serum, cysteine and histidine inhibit the oxidation of low density lipoprotein less at acidic pH.

Low concentrations of serum or interstitial fluid have been shown to inhibit the oxidation of low density lipoprotein (LDL) catalysed by copper or iron, and may therefore protect against the development of atherosclerosis. As atherosclerotic lesions may have an acidic extracellular pH, we have investigated the effect of pH on the inhibition of LDL oxidation by serum and certain components of serum. Human serum (0.5%, v/v), lipoprotein-deficient human serum at an equivalent concentration and the amino acids L-cysteine (25 microM) and L-histidine (25 microM), but not L-alanine (25 microM), inhibited effectively the oxidation of LDL by copper at pH 7.4, as measured by the formation of conjugated dienes. The antioxidant protection was reduced considerably at pH 6.5, and was decreased further at pH 6.0. These observations may help to explain why LDL becomes oxidised locally in atherosclerotic lesions in the presence of the strong antioxidant protection offered by extracellular fluid.

Collagen characteristics and organization during the progression of cholesterol-induced atherosclerosis in Japanese quail.

This study reports the concentration of collagen and its hydroxypyridinoline crosslinks, collagen fibril organization in the dorsal aortas, and systolic blood pressure during the progression of atherosclerosis in Japanese quail selected for cholesterol-induced atherosclerosis. The quail were placed on either a control or 0.5% cholesterol-added diet at approximately 16 weeks of age. The concentration of total collagen did not change in the control arteries during the course of the study, whereas at 5 and 10 weeks of cholesterol feeding, collagen levels decreased in the cholesterol-fed birds. Hydroxypyridinoline concentration increased during the duration of the study in the cholesterol-fed birds and by 15 and 20 weeks of cholesterol feeding, levels were significantly increased over those observed in the control arteries. Transmission electron microscopy showed changes in the organization of collagen fibrils. Increased systolic blood pressure was noted beginning at 10 weeks of cholesterol feeding, which is suggestive of other systemic changes induced by hypercholesterolemia. These results demonstrated remodeling of the collagen component of the dorsal aorta extracellular matrix during the progression of atherosclerosis and are suggestive of other systemic cardiovascular system changes.

Effect of genetic selection for increased body weight and sex of poult on antibody response of turkeys to Newcastle disease virus and Pasteurella multocida vaccines.

Primary and secondary antibody responses of 671 turkeys of two genetic lines to Newcastle disease virus (NDV) and Pasteurella multocida vaccines were examined. The randombred control line (RBC2) and a subline (F) of RBC2 had been selected for increased 16-week body weight. Poults were vaccinated at 6 and 12 weeks of age, and serum samples were collected 3 weeks after each vaccination. Antibody titers were determined using an enzyme-linked immunosorbent assay. Line F turkeys had significantly higher 9-week and 15-week serum antibody titers to NDV than line RBC2. However, line RBC2 had significantly higher serum antibody titers to P. multocida at 15 weeks of age than line F. The 9-week and 15-week serum antibody titers to NDV were significantly higher in females than males, but males had significantly higher 15-week serum antibody titers to P. multocida than females. Sex of poults did not contribute significantly to variation in serum antibody response to P. multocida at 9 weeks of age.

Genetic variation in resistance of turkeys to experimental infection with Newcastle disease virus.

Seven hundred eighty male and female turkeys representing four genetic lines were challenged in four experiments with the Texas GB strain of Newcastle disease virus (NDV). The lines of turkeys included two randombred control lines (RBC1 and RBC2), a subline (E) of RBC1 selected for increased egg production, and a subline (F) of RBC2 selected for increased 16-week body weight. Mortality in turkeys of subline F (32.5%) was significantly higher than that in turkeys of line RBC2 (15.8%), subline E (17.5%), and line RBC1 (18.4%). At the end of each experiment, surviving birds were tested for antibody to NDV using the enzyme-linked immunosorbent assay (ELISA) and hemagglutination-inhibition (HI) test. Turkeys of subline E and line RBC1 had significantly lower ELISA antibody titers than those of subline F and line RBC2. Subline F had the highest HI antibody titers, followed in decreasing order by lines RBC2 and RBC1 and subline E. No apparent correlation was found between antibody response and mortality after NDV challenge.

Identification of decorin and chondroitin sulfate proteoglycans in turkey skeletal muscle.

Turkey pectoral muscles were examined at 15 through 25 d of embryonic age in order to delineate the developmental pattern of proteoglycan expression during skeletal muscle development. Glycosaminoglycan concentration, decorin, and muscle chondroitin sulfate proteoglycan (M-CSPG) levels were measured at each developmental age. Glycosaminoglycan levels rose during the developmental period studied, whereas decorin and M-CSPG levels were initially high at Day 15 and then decreased. The results from this study demonstrate the presence of both decorin and M-CSPG during turkey skeletal muscle development.

Genetics of growth and reproduction in the turkey. 14. Changes in genetic parameters over thirty generations of selection for increased body weight.

A line (F) of turkeys was selected over 30 generations for increased 16-wk BW. The base population for the F line was a randombred control population (RBC2) that was maintained without conscious selection and used to remove yearly environmental variation in the F line. Selection was effective in increasing 16-wk BW in the F line. Selection differentials based on the mean of selected parents minus mean of entire population (intended) and intended selection differentials weighted for number of offspring produced (actual) did not consistently differ, indicating that natural selection was not significantly opposing artificial selection. The realized heritability (h2) of 16-wk BW in the F line, based on the linear regression of the selection response on accumulated actual selection differentials, declined with selection; the decline appeared to be slightly different for males than females. For both sexes combined, the realized h2 was 0.309+/-0.022 (SE), 0.268+/-0.033, 0.242+/-0.026, and 0.254+/-0.007, respectively, for Generations 1 to 10, 11 to 20, 21 to 30, and 1 to 30. Genetic increases in 16-wk BW in the F line were positively associated with BW at other ages (8, 20, and 24 wk of age and at 50% production), days from stimulatory lighting to production of the first egg, and egg weight. Genetic increases were negatively associated with egg production, intensity of lay (maximum and average clutch length and rate of lay), and hatch of fertile eggs. There was no significant relationship between 16-wk BW and total days lost from broodiness or fertility. The genetic changes in some correlated traits were not consistent in all generation intervals studied, indicating that the genetic correlation between the selected trait (16 wk BW) and the correlated trait changed with selection.

Effects of selection for increased body weight, egg production, and shank width on developmental stability in turkeys.

Bilateral asymmetry was measured at 20 wk of age for shank length, shank width (width laterally at the dew claw), shank depth (width perpendicular to the dew claw), and face length (between auditory canal opening and the posterior junction of the upper and lower mandible) in three randombred control lines and three selected lines of turkeys. The data were based on 50 or 51 individuals per line and sex subgroup from a single hatch. The lines were grown intermingled with the sexes being grown in different houses. The selected lines had been selected for increased egg production (38 generations), increased 16-wk BW (32 generations), or increased shank width (19 generations) and had a higher level of inbreeding (average = 36.9%) than the randombred controls (RBC; average = 11.6%). The bilateral differences (right minus left) were analyzed for the presence of fluctuating asymmetry (FA; zero signed mean with normal variation), directional asymmetry (DA; signed mean not zero with normal variation), and antisymmetry (AS; zero mean with non-normal distribution). In order to adjust for possible scaling effects, relative asymmetry (RA), in which the mean of the absolute differences between sides was divided by the mean of the two sides and the resulting value was multiplied by 100, was used as a measure of bilateral asymmetry. The randombred control and selected lines were contrasted to study the effect of homozygosity on RA. Likewise, the large-bodied lines (F, FL, and RBC3) were contrasted to the small-bodied lines (RBC1, E, and RBC2) to study the effect of BW on RA. Only two types (FA and DA) of asymmetry were observed in the present study. The level of asymmetry for the traits was ranked as follows: face length > shank width = shank depth > shank length. The individual lines differed in RA for shank length and shank width for both sexes and for shank depth and face length in females. In general, the influence of BW, as measured in the contrast of large-bodied and small-bodied lines, on RA was larger than that of homozygosity, as measured by the contrast of the selected and randombred control lines.

Serum immunoglobulin G and M concentrations did not appear to be associated with resistance to Pasteurella multocida in a large-bodied turkey line and a randombred control population.

Serum IgG and IgM concentrations in a randombred control line (RBC2) of turkeys and its subline (F), selected long term for increased 16-wk BW were compared. Six-week-old poults were challenged with virulent Pasteurella multocida (1.2 x 10(7) bacteria per bird of serogroup A and serotype 3,4). Sera were collected prior to challenge, and concentrations of IgG and IgM in turkey sera were quantitatively estimated with a Sandwich ELISA using the cross-reactive polyclonal antibodies specific for the chicken Ig isotypes. The F-line turkeys had a higher serum IgM concentration than turkeys from the RBC2 line. There was no significant line difference in IgG concentration. The F line had higher mortality and a shorter number of days to death following challenge with P. multocida than did the RBC2 line. No significant correlation coefficient was found between immunoglobulin isotype concentration in serum and days to death following challenge with P. multocida. The present results suggested that prechallenge IgG and IgM concentrations in serum did not appear to be associated with resistance to P. multocida in a large-bodied turkey line and a randombred control population.

Effect of selection for increased body weight and increased plasma yolk precursor on developmental stability in Japanese quail.

Developmental stability of several Japanese quail lines was measured by bilateral asymmetry. Lines included in the study were as follows: a randombred control (R1), sublines of R1 selected for increased (HW line) and decreased (LW line) 4-wk BW, and sublines of R1 selected for increased (HP line) or decreased (LP line) total plasma phosphorus (TPP; a measure of yolk precursor in the blood) at the beginning of lay. In sublines of the HW line, the males were selected for increased 4-wk BW and the females for increased (HW-HP line) or decreased (HW-LP line) TPP. The HW, LW, HP, and LP lines were in their 41st generation of selection and the HW-HP and HW-LP lines in their 31st generation of selection. The number of birds in each line and sex subgroup was 30. The adult breeders (28 to 32 wk of age) were weighed and killed, and bilateral measurements were made of shank length, width (laterally at the dew claw), and depth (perpendicular to the dew claw), face length, and pectoralis major and p. minor weights. Data on asymmetry was expressed for the right side minus the left side as signed and absolute differences. In order to correct for the correlation between trait size and asymmetry, relative asymmetry (RA) was obtained by dividing the absolute differences between sides by the average value of both sides and multiplying by 100. All lines differed in BW at 4 wk of age with the ranking HW > HW-LP > HW-HP > LP > R1 > HP > LW. Line rankings of adult breeders were similar, except the HP and LP lines did not differ from the R1 line and the order of ranking of the HW-HP and HW-LP lines was opposite that at 4 wk of age. Line differences in signed and absolute differences were significant for most bilateral traits. However, after adjustment for trait size, line differences in RA were less frequent. In general, there were few significant differences in RA for the R1 line versus the selected lines, even though inbreeding of the R1 line (19%) was less than half that of the selected lines (44 to 57%), suggesting that homozygosity did not influence developmental stability. Selection for increased or decreased BW had little influence on RA. Developmental stability tended to be higher in the lines (LP and HW-LP) selected for decreased TPP. The data indicated that bilateral asymmetry was not a good measure of developmental stability in the current study.

Effect of selection for growth rate on embryonic breast muscle development in turkeys.

Muscle development at 20 and 25 d of incubation was studied in a randombred control line (RBC2), a subline (F) of RBC2 selected only for increased 16-wk BW, a commercial sire line (B), and reciprocal crosses of the F and B lines. Muscle samples from three males and three females of each genetic group were collected in such a manner to avoid contraction. After fixing, the muscles were stained with hematoxylin and eosin, measurements of muscle fiber width, muscle fiber bundle length and width, number of fibers within a 15.6 microm2 area, and extracellular matrix perimysial (PW) and endomysial (EW) width were taken with an Olympus XI 70 microscope equipped with an Olympus Magna Fire digital camera linked to Image Pro software. From each slide, 20 measurements were taken for each characteristic analyzed. In most of the muscle traits measured, additive genetic variation, as indicated by line differences, occurred when the RBC2 line was included in the comparison of pure lines. However, when only the B and F lines were compared, line differences were less frequent. In comparisons of the B and F lines and their reciprocal crosses, heterosis, as measured by contrasts of the average of the pure lines and the average of the reciprocal crosses, was an important source of variation for individual fiber measurements (negative) and extracellular space (positive) at 20 d of incubation but was less important at 25 d of incubation. No significant interactions between genetic group and sex were noted at 20 d of incubation, but such interactions were frequent at 25 d of incubation. These results suggest that muscle organizational differences between the two sexes begin to occur between these two ages and are not the same for different genetic groups.

Effect of selection for growth rate and inheritance on posthatch muscle development in turkeys.

The inheritance of, and effect of selection for increased BW on, measurements of muscle fibers and extracellular space in turkeys were studied using a randombred control line (RBC2), a subline (F) of RBC2 selected long-term only for increased 16 wk BW, a commercial sire line (B), and reciprocal crosses of the F and B lines. Measures of additive genetic variation were obtained by comparing all of the pure lines or just the large-bodied F and B lines. Estimates of nonadditive genetic variation were obtained by contrasting the average of the reciprocal crosses with the average of the parental lines. A contrast of the reciprocal crosses provided estimates of sex linkage or maternal effects. Samples of pectoralis major muscle were obtained from three males and three females of each genetic group at 1, 4, 8, and 16 wk of age in a manner to avoid muscle contraction. After fixing and cross sectioning, the muscle samples were stained with hematoxylin and eosin to view muscle morphology. The stained sections were analyzed for muscle fiber width, muscle fiber bundle width (except at 16 wk of age), number of fibers within a 136-microm2 area, and extracellular matrix perimysial (PW) and endomysial (EW) width. Additive genetic variation, as measured by line differences, of measures of muscle fibers and extracellular matrix was a more important source of variation when the RBC2 line was included in the comparison. When all of the pure lines were compared, line differences were significant for fiber bundle width at 4 wk of age; individual fiber width and number of fibers in a given area at 4, 8, and 16 wk of age; PW at all ages; and EW at 1, 8, and 16 wk of age. With the possible exception of PW, nonadditive genetic variation was not an important source of variation for muscle measurements. For PW, the estimates of heterosis were -14.6, 26.4, 14.5, and 17.3% at 1, 4, 8, and 16 wk of age, respectively, but none of the values was significant (P > 0.05). Genetic increases in BW were associated with an increase in muscle fiber width, a smaller number of fibers in a given area, and less extracellular space at older ages. Apparent differences in growth patterns among the genetic groups may have been responsible for the different patterns of change in muscle measurements in the various genetic groups over ages.

Genetic variation in body weight and egg production in an experimental line selected long term for increased egg production, a commercial dam line, and reciprocal crosses between lines.

A line (E) of turkeys selected long term (40 generations) for increased egg production was reciprocally crossed with a commercial dam line (BD). The BD line was larger and had better conformation than the E line, but the E line laid more eggs than the BD line. Heterosis was negative and significant for BW at 8, 16, and 20 wk of age (both sexes) and at 50% production (females only). Values for heterosis ranged from -3.1 to -5.5%. Negative heterosis was observed for breast width at 16 wk of age (10.8 and 3.0% for males and females, respectively). Positive heterosis values of 9.2, 10.2, and 11.3% were observed for egg production when based on 84, 120, and 180 d, respectively. Heterosis (-8.2%) was significant for rate of response to stimulatory lighting of 14 h light per day (days from stimulatory lighting to production of first egg). Based on data for a 180-d production period, heterosis was observed in average clutch length (12.6%) and rate of lay [number of eggs laid: (180 - total days broody)] (8.2%) but not in total days lost from broodiness or the effective length of the laying period (180 minus days lost in periods of 5 or more consecutive days at the end of the laying period). The present results along with those in the literature suggest that more heterosis in egg production traits might be expected in crosses of lines exhibiting extreme differences in BW and body conformation. The negative heterosis in BW in the BD and E reciprocal crosses reduces the commercial importance of such a cross to improve egg production.

The influence of major histocompatibility complex genotypes on resistance to Pasteurella multocida and Newcastle disease virus in turkeys.

Sublines homozygous for each of four MHC haplotypes were developed from randombred control populations of turkeys and challenged with Pasteurella multocida (capsular serogroup a, somatic serotype 3, 4) at 6 wk of age or Newcastle disease virus (NDV; Texas GB strain) at 4 wk of age. In addition, individuals from a randombred control line (RBC2) and a subline (F) of RBC2 long-term selected for increased 16-wk BW were included in most of the challenge trials. The duration of the challenge trials was 2 wk for both organisms. Mortality following challenge with P. multocida or NDV was higher in the F line than in its randombred control. The MHC genotypes differed in mortality following exposure to both organisms but the rankings of the genotypes were not the same for P. multocida and NDV. The increased susceptibility of the F line to both organisms could not be explained by known changes in the frequency of the MHC haplotypes.

Measurement of genetic parameters within and between turkey lines using DNA fingerprinting.

An experiment was conducted to estimate genetic parameters in six experimental and five commercial primary breeding turkey lines using DNA fingerprinting. Eighteen individual DNA samples per line were digested with an HaeIII restriction enzyme and hybridized with Jeffreys' 33.6 probe. The DNA fingerprints were analyzed with computer programs to measure band sharing (BS) and band frequencies. Within lines, BS ranged from 0.39 to 0.62 and reflected the history of the experimental lines. Among lines, BS ranged from 0.21 to 0.33 with an average of 0.26. The BS among the experimental lines reflected known relationships. All lines were subdivided based on indices of population subdivision. About 26 hypervariable loci were estimated from band frequencies. Average heterozygosity and genetic variability estimated from band frequencies were significantly different among lines and displayed a result very similar to the BS among lines. Genetic distance indices among lines were also significantly different and reflected known relationships between the experimental lines. The experimental selected lines displayed lower genetic diversity than did the other lines. The parameters measuring genetic diversity within lines had higher correlation coefficients among them than did the parameters between lines. The computer program used in this study made DNA fingerprinting easier to use in population analysis.

Variation in resistance to Pasteurella multocida among turkey lines.

Previous research has shown that a line (F) of turkeys selected long-term for increased 16-wk body weight was more susceptible to challenge with washed Pasteurella multocida than a randombred control line (RBC2), the base population of F. A previous study also indicated that the mortality of the F line following challenge with P. multocida was similar to that of sire lines from two of the three major primary breeders. The purpose of the present study was to compare the resistance of the sire line from the third major primary turkey breeder (C) not previously studied with that of the F and RBC2 lines to determine whether there is variation in resistance among the sire lines from three major primary breeders. The sire lines from all three primary breeders were used in the production of commercial turkeys. Body weights of the F line were greater than those of the C line at the time of challenge with P. multocida. Both the C and F lines were heavier than the RBC2 line. The birds were challenged at 6 wk of age with a field isolate of washed P. multocida (1.2 x 10(7) organism per bird of capsular serogroup A and somatic serotype 3,4). Mortality was recorded daily for 14 d. Mortality following challenge with P. multocida was higher in the F line than in the C line, and both large-bodied lines had higher mortality than the RBC2 line. Based on the present results and those published in the literature, there may be variation in resistance among commercial sire lines from the three major primary breeders.

Effect of selection for increased body weight in turkeys on lymphoid organ weights, phagocytosis, and antibody responses to fowl cholera and Newcastle disease-inactivated vaccines.

The influence of selection was studied for increased 16-wk BW in turkeys on in vivo phagocytic activity, antibody responses to vaccines, and weight of the spleen and bursa of Fabricius. A line (F) of turkeys selected long term for increased 16-wk BW and its corresponding randombred control (RBC2) were compared. Phagocytic activity was evaluated by the carbon clearance assay. Antibody responses to inactivated Newcastle disease virus and Pasteurella multocida vaccines were examined by ELISA. Body weight and relative weights of spleen and bursa of Fabricius of the two lines were also compared. The F line had lower phagocytic activity than the RBC2 line (P < 0.05). In addition, the F line had greater BW, relative weight of spleen, and ratio of spleen to bursa of Fabricius weight (P < 0.01) but had a lower relative weight of bursa of Fabricius at 9 wk of age. However, there were no line differences in the antibody responses to Newcastle disease virus or P. multocida vaccines at 1, 2, 3, 4, 5, or 12 wk after vaccination. Based on the present results, it is suggested that long-term selection for increased 16-wk BW might have resulted in changes in the immune system, as indicated by changes in the relative weights of the spleen and bursa of Fabricius and phagocytic activity. The decreased phagocytic activity in the F line may be partially responsible for increased susceptibility to specific diseases in this line.

Genetic analysis of antibody responses of turkeys to Newcastle disease virus and Pasteurella multocida vaccines.

Heritability (h2) of 16-wk BW and primary and secondary antibody responses and genetic and phenotypic correlations among these traits were estimated for 931 male and female turkeys vaccinated with Newcastle disease virus (NDV) and Pasteurella multocida. Turkeys from a line selected for 22 or 23 generations for increased 16-wk BW were vaccinated at 6 and 12 wk of age with blood samples collected 3 wk postvaccination. Antibody titers were determined using an ELISA method and transformed to log(e) for analysis. Heritability estimates for primary and secondary antibody responses to NDV were .380 +/- .070 (SE) and .296 +/- .063, respectively. For primary and secondary antibody responses to P. multocida, h2 estimates were .458 +/- .075 and .333 +/- .066, respectively. Heritability estimate for 16-wk BW was .404 +/- .071. The genetic correlation between primary and secondary antibody responses to NDV was .491 +/- .150. There was no genetic correlation between primary and secondary antibody responses to P. multocida. Although the genetic correlation between primary antibody responses to NDV and P. multocida was .292 +/- .159, the genetic correlation between secondary responses to the two antigens did not differ from zero. There were no genetic correlations between antibody responses and 16-wk BW. Similar results were observed for phenotypic correlations. Based on heritability and genetic correlation estimates, it would be possible to improve antibody responses to either NDV or P. multocida singularly; however, to improve antibody responses to both antigens, selection would have to be applied for each antigen.