Replicated Divergent Selection of Broiler Chickens for High or Low Early Antibody Response to Escherichia coli Vaccination1

Replicated Divergent Selection of Broiler Chickens for High or Low Early Antibody Response to Escherichia coii Vaccination1 GABRIEL LEITNER,2'3 ZAHAVA UNI, 2 AVIGDOR CAHANER, 4 MICHAL GUTMAN, 4 and E. DAN HELLER 2 ' 5 Department of Animal Science and Department of Genetics, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O.B. 12, Rehovot 76100, Israel (Received for publication June 17, 1991)

1992 Poultry Science 7127-37

INTRODUCTION

conducted with Leghorn layers possessing a fully matured immune system. The Several approaches have been taken to application of this type of selection in study selection for resistance to diseases in broilers may be limited because of the poultry (Pevzner et al, 1981). In some, short time period required to reach market experimental selection was based on the weight. Heller et al (1981) found evidence immune response to a single antigen, such for the heritability of the rate of developas SRBC, a nonpathogenic, multideter- ment of the immune response in chickens. minant antigen (Siegel and Gross, 1980; In broilers, emphasis should probably be Van der Zijpp, 1983), or to an inactivated placed on selecting chicks whose immune virus such as Newcastle disease virus system matures earlier rather than on antigen (Takahashi et al, 1984). Another those that show a high response after their selection strategy was based on the response to several antigens and mitogens immune system has fully matured. This (Cheng and Lamont, 1988), in order to reasoning is consistent with the thesis that increase general, nonspecific immunocom- selection in broiler chickens should therepetence. All of these experiments were fore be based on immunological testing of chicks whose immune response has not yet fully matured (Pitcovski et al, 1987). Choice of antigens and tests used to This work was supported by the Israel-U.S. Bina- determine immunological responses are of tional Agricultural Research and Development Fund. considerable importance. In developing a Department of Animal Science. strategy for selection the authors chose the 3 This work was performed by G. Leitner as a partial Escherichia coli bacterium, which has the fulfillment of the requirements for a Ph.D. degree. advantage of being a complex and pathoDepartment of Genetics. T o whom correspondence should be addressed. genic antigen. This choice not only al-

27

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

ABSTRACT Four sublines of broiler chickens were selected from a base population for three generations for high or low antibody response to vaccination with Escherichia coli at 10 days of age. Two sublines were selected for a high response (HC) and two for a low response (LC). Realized heritability estimates over three generations of selection for each pair of replicated lines averaged .23 in HC lines and .32 in LC lines. No correlated response in the important production trait, body weight at marketing age, was observed. The ability to survive pathogenic E. coli challenge with or without prevaccination showed no differences between the lines in the unvaccinated chicks, although following vaccination there was higher mortality and morbidity in the LC lines. These data suggest that the use of antibody response in young chicks to E. coli vaccine may be a useful genetic indication of more general disease resistance. {Key words: selection, broilers, vaccine, antibody response, heritability)

28

LEITNER ET AL.

MATERIALS AND METHODS Chickens Twenty males and 80 females from a commercial White Rock dam line (ANAK 80), which has been under intense mass selection for rapid early growth by the Israeli Poultry Breeders Union since 1970, were randomly mated to produce the base population for preliminary trials and the selection experiment. Pedigreed chicks were produced in all generations by artificial insemination. Chicks were wingbanded at hatch and placed in a single Utter pen. Hatches were not intermingled and feeding programs followed that for commercial broilers. At 6 wk of age chicks selected for reproduction were transferred to individual cages in an open shade house, where they were raised to sexual maturity and maintained for reproduction under feeding program for replacement breeders. Body weights at 6 wk of age and at first egg were recorded. Age at first egg and laying rate and number of eggs produced to 300 days of age were recorded for selected

breeders. Hatchability of all eggs set was based on eggs laid to 300 days of age.

Antigens Used for Immunization and Challenge Tests Escherichia coli Serotypes O78:K80 and 02:K1 were used for the immunizations, challenge tests, and ELISA, as described in Leitner et al. (1989). Antibody production and survival rate after challenge with pathogenic E. coli, with or without prevaccination, was tested after the first and second selection cycles. In both generations, approximately equal numbers of chicks from each dam family were taken for the challenge test. Half of the chicks from each line were vaccinated at 10 days of age with the E. coli vaccine. At 20 days of age all the chicks were challenged with the homologous, pathogenic bacteria (median lethal dose). Mortality and morbidity were recorded daily for 8 days. All survivors were then killed by cervical dislocation, and inspected for signs of pericarditis and perihepatitis.

Immunological Assay Immune response to the E. coli vaccine was determined by measuring antibody production in each chick by ELISA (Leitner et al, 1990). The natural log of the antibody titer (Yi) in each serum for O78:K80 was calculated by the following linear regression equation: Yi = 4.90 + 1.35 (Pi 4- N) - 6.25 where Pj is the optical density of the serum taken from the i t h chick; N is the optical density of the negative serum, i.e., a control with no antibody; and 6.25 is the optical density of a serum that equals that of the negative serum, i.e., when Pi + N = 1. By subtracting 6.25, positive Yi values for chicks with no antibody were avoided. For 02:K1 the regression equation was: Yi = 5.96 + .45 (Pi + N) - 6.41

Selection Procedure The base population (Generation So), consisted of 725 chicks (346 males and 379

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

lowed measurement of the specific immune response of one component of the immune system but also examination of the overall immune response through challenge. This approach is important because the major components of the immune system (phagocytosis, cell-mediated immunity, complement activity, and humoral immune response) may be under independent genetic control (Biozzi et ah, 1982; Cheng and Lamont, 1988). The applicability of the method of selection reported in the present study, which is based on the specific immune response, would be reinforced by a positive association between the response and rate of survival after challenge. The present work examines selection for early or late maturation of the immune system based on individual and family antibody responsiveness to immunization with inactivated pathogenic E. coli bacteria at an early age. The heritability of this selected trait, along with its association to survival after challenge with the pathogenic bacteria and to performance traits, are reported.

29

ANTIBODY RESPONSE IN BROILERS

Statistical Analysis Differences between the divergently selected lines were determined in each generation by a four-way ANOVA (direction of selection, replicated lines, hatch, and sex), using .the General Linear Model procedure (SAS Institute, 1987). Chi-square analysis was used to test for differences in mortality and morbidity. Individual antibody titer values were corrected for hatch and year effects. "Narrow sense" heritability (h^) estimates were obtained from nested ANOVA of sire and dam families within lines over generations. Realized heritability (hp estimates were calculated from the actual responses to selection. For h£, the individual value of

each parent was weighted with the number of its offspring. The actual selection differential (S) was the difference between the mean of these weighted values and the mean of the entire fine in a given generation. Responses to selection (R) were obtained in Generation Si from the differences between a selected line mean and the mean of all the lines including the CT. In the S2 and S3 generations, R was obtained from the increase in this difference between a given generation and the previous one. The realized heritability was estimated using h , = R + S for each line in each generation, and by regressing cumulative R over cumulative S.

Experimental Design Experiment 1. To determine the ability of the chicks' immune system to respond to the E. coli vaccine through antibody production, 100 day-old chicks from the base population were divided into 10 groups, each consisting of five males and five females. At hatching, two chicks from each group were bled on the day of hatch to test for maternal antibodies. None were found. Each day from hatch to Day 10, a different group was immunized with the E. coli vaccine. Ten days PV the chicks were bled and their antibody levels were determined by ELISA. Experiment 2. The kinetics of antibody production PV was examined in individual chicks. Seven chicks were vaccinated with the E. coli vaccine at 10 days of age. On Days 3,4,5,6,8,10,13, and 15 PV, each chick was bled and its antibody titer determined by ELISA. Experiment 3. The association between the individual antibody titer 10 days PV and the ability to survive challenge was determined in the base population. Sixty chicks were vaccinated and 25 were used as the unvaccinated control group. Ten days PV, each chick was bled to determine its antibody titer by ELISA, and then the chick was challenged with E. coli.

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

females) from two hatches 10 days apart. At 10 days posthatch, all chicks were injected subcutaneously with the E. coli vaccine. Ten days postvaccination (PV), each chick was bled and its serum antibody titer determined by ELISA. Males and females were ranked according to an index combining their individual titer with mean titers of their full- and half-sib families (Falconer, 1989). To establish two low-coft lines (LCI and LC2), 40 males and 60 females with the lowest antibody titers were randomly divided into two equal groups per sex. Similarly, the same number of males and females with the highest titers were selected to establish two high-coJi lines ( H O and HC2). Prior to selection, 60 males and 90 females, equally representing all families, were randomly chosen to establish a control line (CT). At sexual maturity, 7 of the 20 males from each selected line, and 20 of the 60 males from the CT, were used to produce the next generation (Si). Fertile females from each line were divided into seven equal groups (20 groups in the CT), and each group was inseminated by one male from the same line, avoiding sib matings. The same procedure and numbers of males and females were used within each selected line to produce Generations S2 and S3. The lowest-ranked males and females were selected from LCI and LC2, and the highest-ranked ones were selected from HC1 and HC2. In the CT line, males and females, equally representing all families, were randomly chosen for reproduction.

RESULTS Preliminary Experiments Experiment 1. Effect of Immunization Age on Antibody Production. The mean antibody titer of males and females i n each

30

LEITNER ET AL. I MALE M

antibody titers (Figure 2) show that antibody was first detected between 3 and 6 days PV and increased in all chicks until Day 8. Thereafter, antibody titers continued to increase in some chicks but in others they began to decrease. It was therefore decided that bleeding for antibody determination in future studies would take place on the 10th day PV.

FEMALE

Experiment 3. Association Between Antibody Titer and Disease Resistance.

0

1

2

3

4

5

6

7

8

9

10

1 1

12

13

14

15

16

Time postvaccination (days) FIGURE 2. Individual antibody response of chicks to Escherichia coli vaccinated at 10 days of age.

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

The association between the individual FIGURE 1. Mean antibody titer of male and female antibody titer 10 days PV and the ability to survive challenge was determined in the broiler chicks vaccinated at different ages. base population. The 60 vaccinated chicks were ranked according to their antibody titers and divided into three equal subgroup is presented in Figure 1. No antibody titer was detected in either males or females groups. The subgroup with the highest of the group vaccinated at 1 day of age. The antibody titers (>1.7) exhibited neither antibody level increased with immuniza- mortality nor morbidity. The intermediate tion age from 2 to 8 days, then leveled off. In group (1.2 to 1.7) had 15% mortality and all groups, antibody titers were higher in 10% morbidity. Chicks producing the lowest antibody titer (<1.2) had 25% mortalfemales than in males. Experiment 2. Kinetics of Antibody ity and 15% morbidity, and the unvacciProduction in Chicks Vaccinated at 10nated controls had 48% mortality and 8% Days Of Age. The kinetics of the i n d i v i d u a l morbidity.

ANTIBODY RESPONSE IN BROILERS

31

TABLE 1. Mean Escherichia colt antibody titer of males (M) and females (F) selected from the base population (SQ) to establish each of the low-colt (LC) and high-co/i (HC) lines, The Base Population (S0 Generation).control line (CT), and their deviation (Dev) Mean antibody titers of males and females from the entire base population mean

The Selection Experiment— The Selected Trait

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

used to establish each selected or control line, and their deviation from the entire So E. coli titer generation mean, are given in Table 1. Dev Sex Number X Although 40 males were selected at 6 wk of 7 M -1.70 .77 age to reproduce each direction of the -1.20 1.10 19 F selected lines, only 14 were actually used. -1.47 .94 M + F 26 The deviations in Table 1 were calculated -1.72 7 .75 M for these males and therefore they are -1.28 1.02 19 F -152 M + F 26 "actual" selection differentials (S). The .89 "actual" S were very similar to the "intend257 5.04 7 M 1.95 21 F 4.25 ed" ones, calculated for all selected males 4.64 M + F 26 2.23 (not presented). Similarity between in7 2.63 M 5.10 tended and actual S values was also found 1.20 350 20 F in Generations Si and S2, for females and for M + F 27 1.89 4.30 males. These comparisons indicate that the -.18 20 2.29 M actual parents represented a random samp65 F -.05 2.25 ling of the selected ones, and that natural -.14 237 M + F 85 selection was not a factor in mortality or (1.41)1 2.47 346 M infertility among the individuals selected at (1.29) 379 F 2.30 (1.35) 2.41 M + F725 6 wk of age. The proportion of selected 1 males in So was about 11% (40 out of 346) Phenotypic standard deviation (
LEITNER ET AL.

32 40

Control line High coli

—. 30

Low coli

£

10 H ""•*-="-—i--».=r_-: 1 •—

3

7

5

1 1

FIGURE 3. Distributions of individual antibody titers to Escherichia coli of the control and the selected lines in S3 generation.

though the base population (So) consisted of about 350 chicks from each sex, there were, on the average, only 50 males or females in each selected line in later generations. Therefore, selection intensities were 11 and 16% for males and females, respectively, in Generation So, and only 40 and 60% in later generations (20 of 50 and 30 of 50 for males and females, respectively). The difference in selection intensity accounted for the larger response in Generation Si than in S2 and S3. The response to selection for high and low E. coli antibody titers appears to be symmetrical in the Si and S3 generations. In Generation S2, Line LC2 responded in the direction opposite to selection, for unknown reasons, having a higher titer (2.17) than in Si (1.86), but in S3 it responded as expected, with its mean decreasing to 1.76. An unexpected response was also found in HC1 in Generation S2, but it was much smaller and therefore a temporary asymmetry was observed in this generation. The distribution of individual antibody titers within each line in Generation S3

demonstrated an asymmetry within lines and the effect of selection (Figure 3). When compared with the control, which represents the base population, selection for HC reduced the proportion of chicks with low titers and increased the proportion of high-titer chicks. Some of these were higher than the highest control ones. In the LC lines, selection eliminated the high-titer individuals, but titers of most chicks approached a zero antibody response. Figure 3 indicates that the mean antibody titer of the control line was equal to the mean of the generation pool. Heritability Estimates. The h^ were calculated for each selected line and also averaged over replicates of each direction (Table 4). Values for the three methods based on response to selection yielded similar estimates, which were lower in HC than in LC lines (about .23 and .32, respectively). The estimate of "narrowsense" heritability (h s ), obtained by sirefamily ANOVA, was similar to h^ in HC lines (.27), and lower in LC lines (.15).

TABLE 2. Difference and ratio between uncorrected means of Escherichia coli antibody titers of low-coil (LC) and high-colt (HC) lines, by hatch and generation Generation

Hatch

HC mean

LC mean

HC-LC

HC+LC

Si

1 2 1 2 1 2

1.96 2.76 556 3.12 3.40 2.10

1.31 1.60 2.98 2.02 1.50 .97

.65 1.16 2.28 1.10 1.90 1.13

1.50 1.73 1.77 154 227 2.16

S2

%

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

Ln titer of antibody to E. coli

33

ANTIBODY RESPONSE IN BROILERS

TABLE 3. Mean Escherichia coli antibody titer of males (M) and females (F) of the low-colt (LC) and high-colt (HC) replicated selected lines and the control line (CT), and their deviation (Dev) from the generation's overall mean, after each of three selection cycles1

Sex

n

X

Dev

LCI

M F M + F

LC2

M F M + F

51 50 101 39 56 95

M F M + F M F M + F

55 64 119 72 53 125

1.74 1.87 1.81 1.87 1.85 1.86 1.84 2.87 3.17 3.02

-.62 -.58 -.60 -.49 -.60 -.55 -.57 .51 .72 .61 .44 .47 .45 .53 -.05 -.06 -.06

LC grand means HC1

HC2

HC grand means CT

Generation means

SEM

174 M 135 F M + F 309 391 M 358 F M + F 749 M F

2.80 2.92 2.86 2.94 2.31 2.39 2.35 2.36 2.45 2.41 .164 .154

n 50 48 98 43 25 68 52 65 117 59 56 115 188 175 363 392 369 761

X

Dev

1.63 1.75 1.69 1.89 2.45 2.17 1.93 2.82 3.10 2.96 3.05 3.75 3.40 3.18 2.08 2.27 2.18 2.24 2.58 2.41 .177 .178

-.61 -.83 -.72 -.35 -.13 -.24 -.48 .58 .52 53

i

n 34 35 69 31 37 68 34 43 77

.81 1.17 .99 .77

38 37 75

-.16 -.31 -.23

184 210 394 321 362 683

X

Dev

1.32 1.20 1.26 1.80 1.71 1.76 1.51 3.48 2.83 3.16 3.09 3.83 3.46 3.31 2.44 2.38 2.41 2.41 2.36 2.39 .220 .262

-1.09 -1.16 -1.13 -.61 -.65 -.63 -.88 1.07 .47 .77 .68 1.47 1.07 .92 .03 .02 .02

1

Differences between LC and HC lines were significant (P<.0001) in both sexes in all three generations.

The Selection ExperimentCorrelated Responses

effect of immunization age on antibody production in the first prelirrunary Experiment 1. Antibody titers of males and Survival Following Challenge. Effects females in each group, separated by line, of selection on antibody production and the are summarized in Figure 4. There was no rate of survival after challenge with pathoresponse in either HC or LC lines in the genic E. coli, with or without prevaccinagroup vaccinated at 1 day of age. The HC tion, were tested in Generations Si and S2. male and female chicks began responding The results are presented in Table 5. There when vaccinated at 2 days of age, and the were no differences in the percentage mortality and morbidity 7 days post- level of antibody increased with age of challenge between the LC and HC lines in vaccination u p to 9 days of age, when it the unvaccinated chicks (68 versus 61%). stabilized. In the LC lines, the earliest However, when challenged following vac- response was noted in females vaccinated at cination, there was a higher percentage 4 days of age, and in males vaccinated at 5 mortality and morbidity in the LC than the days of age. Although antibody titers of LC HC lines (60 versus 29% in Si and 39 versus chicks increased with age of vaccination, 23% in So). These differences were due to they were still lower than those of the significant higher mortality in the LC line lowest HC line titers. There was sexual but differences in morbidity were not dimorphism in antibody titers with females having higher values than males in both significant. Maturation of the Immune Response. lines, at all ages. Body Weight and Reproductive PerThe effect of selection on the developmental rate of antibody response to the E. coli formance. Body weight at marketing age is vaccine was evaluated in Generation S3. the most important production trait in The procedure followed that used to study broiler chickens. Chicks from all four gener-

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

Line

S3 generation

Sj generation

Si generation

34

LEITNER ET AL. 1

TABLE 4. Heritability estimates of Escherichia coli antibody titer, calculated from selection differentials (S) and responses (R), and from variance components, for each of the lovf-coli (LC) and high-colt (HC) replicated selected lines Method of heritability estimation Line

Mean R+S

ZR+ZS

b(ZR+ZS)

LCI LC2

.43 .27

LC x HC1 HC2 HC x

.35 .15 .27 .21

.43 .21 .32 .18 .27

.41 .20 .31 .19 29 .24

.23

15

27

ations were weighed at about 6 wk of age. Data for Generation S3 (Table 6) show similar body weights for all lines within a sex, indicating a lack of correlated response in this trait. The correlations between individual body weight and antibody titers were very low and not significant in all line by sex by hatch by generation combinations. Five reproductive traits were mea-

sured for each of the Si, S2, and S3 females used to produce Generations S2, S3, and S4, respectively. Means are given in Table 7. The LC hens of Generation Sj started laying eggs 8 days earlier, but their laying rate was slightly lower than that of HC hens, hence total egg production at 300 days of age was similar in LC and H C lines. In the S2 Generation no such tendency was observed

TABLE 5. Mortality and morbidity 1 of 20-day-old chicks from the low-colt (LC) and high-colt (HC) replicated selected lines in Generations S-y and S2, challenged with 1 x 10 9 cfu of 02:K1 Escherichia coli, with or without vaccination 10 days earlier Lines Treatments Nonvaccinated Mortality, % Morbidity, % Mortality plus morbidity, Number of chicks Vaccinated Ln antibody titer ± SE

%

Generation

LC

HC

Si Si Si Si

15 54 68

23 39 61 44

41

Significance level 2 .4 .3 .5

1.18 ± .05 1.96 + .06 Si 1.77 ± .04 1.39 ± .07 &2 Mortality, % 34 .025 14 Si 7 .08 20 S2 Morbidity, % 15 .5 26 Si .7 20 16 S2 Mortality plus morbidity, % 29 60 .005 Si 23 .1 39 S2 Number of chicks 47 49 Si 41 44 S2 Morbidity = chicks showing pericarditis or perihepatitis or both 7 days after challenge, ^hi-square test for proportions of mortality and morbidity, and F test for Ln antibody titers.

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

Method of heritability estimation: Mean R+S = averaging Ri+S; ratio over the three selection cycles (i = 1,2,3); ZR+ZS = the ratio of cumulative R over cumulative S (ZRi+ZS, for i = 3); b(ZR+ZS) = regression ZRj on 5S; over the three selection cycle (i = 1,2,3); h s = using the sire variance component from the nested ANOVA,h s =4a s +(o s +Od + Oe) = VA + Vp; where h 8 is the heritability estimate; a s is the variance component for sires, Oj is the variance component for dams; and o e is the variance component within full-sib families; V A is the additive genetic variance; and Vp is the phenotypic variance.

35

ANTIBODY RESPONSE IN BROILERS

J 3 -

I 5

"i

0 1 2 3 4 5 6 7 8 9

10

1

1

r

.

.

.

.

0 1 2 3 4 5 6 7 8 9

MALE

10

FEMALE Age (days)

FIGURE 4. Mean antibody titers of male and female broiler chicks of the high-co/i (HC) and low-co/i (LC) lines vaccinated at different ages.

but in the S3 LC hens started laying only 3 days before HC hens. Percentage hatchability of HC eggs was significantly higher than that of LC eggs in all three generations. Combining egg production and hatchability, the estimated overall reproductive ability of the HC lines was higher than that of the LC lines (39.9 and 34.8 chicks per 300-day-old hen, respectively).

DISCUSSION Four lines of chickens were developed over three generations of selection. The immune systems of two lines (HC1 and HC2) responded to E. coli vaccine with high antibody production and two lines (LCI and LC2) responded with low antibody titers. Moreover, the chicks from the HC lines responded by 2 days of age, but those from the LC lines responded 2 days later, on Day 4 or 5. These results confirm those of Heller et d. (1981), who found that antibody responses to E. coli were earlier in chicks from the Sinai breed than in Leghorns. Also in several cases, anti-

body titers of females were higher than those of males, confirming previous observations (Leitner et al., 1989). The differences in the immune system's maturation in lines selected for only three generations indicate genetic variation for the development of the immune response to E. coli, in both, the rate of response and in magnitude of the titers. The hj. estimates over three cycles of selection for the two replicated lines averaged .23 in HC lines. The heritability estimated from sire families (h s ) in these lines was similar to hj., indicating that continuous response (i.e., increased titers) in H C lines can be reliably predicted, at least for few more generations of selection. The higher h£ (.32) in LC than in HC lines does not necessarily reflect greater genetic variation, because it resulted from smaller selection differentials rather than larger responses to selection. The h s was lower than hj. in these lines indicating decreased genetic variation, therefore, further reduc-

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

§

LEITNBR ET AL.

36

TABLE 6. Mean body weight of 6-wk-old males (M) and females (F) of the low-colt (LC) and high-colt (HC) replicated selected lines in Generation S3 and their deviation (Dev) from S3 overall mean Body weight

Line

Sex

Number

LCI

M F M F M + F M F M F

34 36 32 39 141 34 43 38 37

M + F M F

152

Mean

Dev

(g) LC2 Grand mean HC1

Grand mean SEM1

-40 -47 27 66 2 36 -48 -16 5 -5

Probabilities2

Source of variation LC versus HC

M F M F M + F M F M + F

Control line All lines

.672 .332 37 45 82 175 200 375

1,525 1,305 1/414 1,568 1,310 1,439

-43 -5 -25

SEM of HC and LC grand means. Significance level of the difference between HC and LC grand means (the selection's effect).

TABLE 7. Reproductive performance1 of low-coK (LC) and high-coK (HC) hens selected in each generation and reproduced the next one Generation Si

% S3 Grand means SEM2 Probability: LC versus H C 3 1

Line LC HC LC HC LC HC LC HC

n 42 48 42 34 35 29 119 111

BWE1

AE1

LR

TEG

(g)

(days) 202 214 216 213 200 203 206 210 1.7

(%)

(no.) 61 58 51 55 63 59 58 57

3,756 3,769 3,675 3,700 3,549 3,549 3,660 3,659 32.7 .977

.121

62 68 60 62 63 60 62 63 1.3 .492

1.6 .654

PHC

(%) 54 67 65 71 62 70 60 70 2.6 .012

BWE1 = body weight at first egg; AE1 = age at first egg; LR = laying rate; TEG = egg number to 300 days of age; and PHC = percentage hatchability. SEM of HC and LC grand means. Significance level of the difference between HC and LC grand means (the selection's effect).

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

HC2

1,528 1,263 1,595 1,376 1,441 1,604 1,262 1,552 1,315 1/134 39.2 31.6

ANTIBODY RESPONSE IN BROILERS

tion found between the individual antibody titer and survival after challenge, support previous findings (Pitcovski et ah, 1987) that the use of E. coli as an antigen for selection can produce heritable disease resistance. The results indicate that the simple method of selection used here may be used by breeders to improve their broilers viability by selection for earlier maturation of their immune responsiveness. REFERENCES Biozzi, G., D. Houton, A. W. Hermann, and Y. Bouthiller, 1982. Genetic regulation of immunoresponsiveness in relation to resistance against infectious disease. Pages 150-163 in: Proceedings of the 2nd World Congress on Genetics Applied to Livestock Production. Vol. 1. Madrid, Spain. Cheng, S., and S. J. Lamont, 1988. Genetic analysis of immunocompetence measures in a White Leghorn Chicken line. Poultry Sci. 67589-995. Falconer, D. S., 1989. Introduction to Quantitative Genetics. Longman Group, Harlow, England. Heller, E. D., M. Soller, B. A. Peleg, Ron-Kuper, and K. Hornstein, 1981. Immune response to Newcastle disease virus, fowl pox vaccine and Escherichia coli vaccine in Bedouin and White Leghorn. Poultry Sci. 60:34-37. Leitner, G., E. D. Heller, and A. Friedman, 1989. Sexrelated differences in immune response and survival rate of broiler chickens. Vet. Immunol. Immunopathol. 21:249-260. Leitner, G., D. Melamed, N. Drabkin, and E. D. Heller, 1990. An enzyme-linked immunoabsorbent assay for detection of antibodies against Escherichia coli: Association between indirect hemagglutination test and survival. Avian Dis. 34:58-62. Pevzner, I. Y., I. Kujduch, and A. W. Nordskog, 1981. Immune response and disease resistance in chickens. 2. Marek's disease and immune in GAT. Poultry Sci. 60527-932. Pitcovski, J., E. D. Heller, A. Cahaner, and B. A. Peleg, 1987. Selection for early responsiveness of chicks to Escherichia coli and Newcastle Disease Virus. Poultry Sci. 66:1276-1282. SAS Institute, 1987. SAS/STAT® Guide for Personal Computers. Version 6th Edition. SAS Institute Inc., Cary, NC. SiegeL P. B., and E. B. Gross, 1980. Production and persistence of antibodies in chickens to sheep erythrocytes. 1. Directional selection. Poultry Sci. 59:1^5. Takahashi, S., S. Inooka, and Y. Mizuma, 1984. Selective breeding for high and low antibody responses to inactivated Newcastle disease virus in Japanese quail. Poultry Sci. 63:595-599. Van der 2Sjpp, A. J., 1983. Breeding for immune responsiveness and disease resistance. World's Poult. Sci. J. 39:118-131.

Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on June 7, 2015

tion of mean titers in the LC lines should be slower, with a selection limit being approached as more individuals have no antibody titers. The hj. values obtained in the present study were quite similar to the estimates reported by Siegel and Gross (1980) for individual selection, of high or low antibody titers to SRBC (.17 to .44). Higher r£ (.72) calculated from four cycles of divergent family selection on early response to E. coli reported in a previous work by Pitcovski et al. (1987) with family selection. In the latter case, the nongenetic component in the selection differentials is reduced as family size increases, and h£ estimates are expected to be higher than in individual selection. Moreover, although HC:LC ratio after four selection cycles in the previous work was only 1.5, this ratio was 2.2 (3.31:1.51) after three cycles in the present study. N o correlated response in the important production trait, body weight at marketing age, was observed in the present experiment. This lack of genetic relationship between market weight and E. coli immunization was not consistent with those of Pitcovski et al. (1987), who found a greater juvenile growth in their hightiter line. It is important, however, that neither study indicated that selection for high titers would hamper selection for growth rate. The difference in ability of vaccinated and unvaccinated chicks from Lines HC and LC to survive challenge may be explained by the dynamics of the immune response to the antigen. Because of earlier maturation of their immune systems, Line HC chicks, when vaccinated at a young age prior to challenge, have a more rapid and greater response to the vaccine than those from LC line, thus enhancing their ability to survive the challenge. In contrast, when challenged without prior exposure to the antigen, there was not enough time for the specific immune system to respond, resulting in similar survival rates in both lines. The evidence for genetic control of immune system's maturation rate and the estimates of h", together with the associa-

37