RESEARCH NOTE Variation in Resistance to Pasteurella multocida Among Turkey Lines1 K. E. NESTOR,*,2 Y. M. SAIF,† J. W. ANDERSON,* R. A. PATTERSON,* and Z. LI* *Department of Animal Sciences and †Food Animal Health Research Program, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio 44691 ABSTRACT 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 the 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 × 107 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.
(Key words: turkey, body weight, Pasteurella multocida, resistance, genetic lines) 1999 Poultry Science 78:1377–1379
INTRODUCTION Genetic increases in body weight are reportedly associated with a decrease in disease resistance in chickens (Han and Smyth, 1972, 1973; Mauldin et al., 1978; Qureshi and Havenstein, 1994) and turkeys (Saif et al., 1984; Sacco et al., 1991; Nestor et al., 1996a,b). Saif et al. (1984) reported that turkeys from a subline (F) selected for increased 16wk body weight had significantly higher mortality than its randombred control line (RBC2) during natural outbreaks of erysipelas and fowl cholera. Poults of the F line also had higher mortality than poults of the RBC2 line under experimental challenges with Pasteurella multocida (Sacco et al., 1991; Nestor et al., 1996b), the causative agent for fowl cholera and Newcastle disease virus (Tsai et al., 1992). There are three major commercial turkey primary breeders in the world. Each of these breeders uses one or two primary breeding sire and dam lines in crosses to produce the commercial bird. Nestor et al. (1996b) com-
Received for publication December 14, 1998. Accepted for publication July 1, 1999. 1 Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. 2 To whom correspondence should be addressed:
[email protected]
pared the resistance of a sire line used in the production of commercial turkeys from two of the three major primary turkey breeders, the F line, and the RBC2 line, to experimental challenge with P. multocida. The commercial sire lines and the F line had similar mortality following challenge with P. multocida, and all three large-bodied lines had higher mortality than the RBC2 line. The purpose of the present study was to compare the resistance of the F, RBC2, and a primary breeding sire line from the major primary breeder not included in the study of Nestor et al. (1996b; C) to determine whether there is genetic variation in resistance to P. multocida among sire lines used in commercial production from the three largest commercial turkey breeders.
MATERIALS AND METHODS Lines of Turkey The three lines of turkeys used included an unselected RBC2 and two sire lines (F and C). The RBC2 line was initiated in 1966 from the reciprocal cross of two commercial turkey lines (Nestor et al., 1969). Line F, a subline of
Abbreviation Key: C = commercial sire line; F = subline of RBC2 selected long-term for increased 16-wk body weight; and RBC2 = randombred control line.
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Line RBC2, was selected over 31 generations for increased 16-wk body weight (Nestor, 1977, 1984; Nestor et al., 1996a). A sample of Line C, used in commercial turkey production, was obtained from a commercial primary breeder. The selection criteria in Line C were unknown, but a major emphasis had been placed on selection for increased growth rate.
Management of Birds Two challenge trials were conducted involving 168 birds (28/line per trial). Eggs from the C line were obtained from the commercial breeder and hatched simultaneously with Lines F and RBC2 in each of two hatches. The poults in each hatch were wing-banded at hatching according to line and brooded in floor pens with the lines and sexes intermingled. Birds were provided ad libitum access to the first two rations in a five-ration feeding system with declining protein (Naber and Touchburn, 1970) based on the schedule for males. During the 5th wk of age, each bird was weighed and bled via the brachial vein before being moved to isolation facilities. The prechallenge serological status of each poult was determined using ELISA3. Control birds for each line and challenge trial were kept in conventional housing to preclude the possibility that an infection with P. multocida existed at the start of the challenge trial but was not detected serologically. Poults to be inoculated were housed, lines intermingled, in wire cages in isolation rooms for 3 d prior to inoculation so that the birds could become adapted to the cages.
Preparation of Inoculum A field isolate of P. multocida, capsular serogroup A, somatic serotype 3,4, was used to prepare the inoculum. Bacteria were grown in veal infusion broth4 for 24 h at 37 C. The inoculum was washed three times with sterile PBS (pH 7.3), divided into aliquots, and stored at –70 C. The inoculum contained 1.2 × 107 bacteria per milliliter. Growth characteristics of the P. multocida isolate used were given by Sacco et al. (1991).
Challenge Procedures Poults were challenged at 6 wk of age by subcutaneous injection of 1 mL inoculum in the back of the neck. The duration of each trial was 14 d. Mortality was recorded daily. Poults exhibiting severe clinical symptoms of fowl cholera were euthanatized and recorded as deaths.
Statistical Analysis Mortality was analyzed by chi-square analysis. Repeated chi-squares were used to separate line means.
3
Flock Chek: Anti-Pm [T], IDEXX Laboratories, Westbrook, ME 04092. Difco Laboratories, Detroit, MI 48233.
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TABLE 1. Effect of challenge with Pasteurella multocida1 at 6 wk of age on mortality of the RBC2, F, and C lines2 Body weight Line
Males
RBC2 F C
1.138c 2.125a 1.760b
Females (kg) 0.872c 1.744a 1.311b
Response to challenge with P. multocida Birds
Mortality
Days to death
(no.) 56 56 56
(%) 20.4c 64.9a 42.9b
6.73 6.70 6.71
a–c Means in a column with no common superscript are different (P ≤ 0.05). 1 Birds were challenged with P. multocida (capsular serogroup A, somatic serotype 3,4; 1.2 × 107 organisms per bird) at 6 wk of age, and birds were observed daily for 14 d. 2 RBC2 = Randombred control population started in 1966; F = subline of RBC2 selected for increased 16-wk body weight; and C = commercial sire line.
Body weights and days to death were analyzed by an ANOVA for the effect of line and hatch. Means were separated by Duncan’s multiple range test.
RESULTS AND DISCUSSION The F line was larger than the C line at the time of housing in the challenge facilities (Table 1). By 16 wk of age, the C line was heavier than the F line (K. E. Nestor, unpublished data). The F and C lines were both larger than the RBC2 line. The three lines did not differ in days to death following challenge with P. multocida, but mortality was higher in the two large-bodied lines than in the RBC2 line (Table 1). The F line had higher mortality than the C line. There were no deaths caused by P. multocida in the noninjected control birds. Titers to P. multocida were negligible prior to the challenge trials. Days to death following challenge did not appear to be a sensitive indicator of resistance to P. multocida in the present study or in the study of Nestor et al. (1996b). Tsai et al. (1992) reported that days to death was not a sensitive indicator of resistance to challenge with Newcastle disease virus. However, Sacco et al. (1991) found that days to death was associated negatively with mortality in several lines of turkeys following challenge with P. multocida. Nestor et al. (1996b) found that mortality following two challenge trials with P. multocida did not differ among the F line and sire lines from two major turkey primary breeders. The observation in the present study that the C line used had lower mortality following challenge with P. multocida suggests that genetic variation may exist among the sire lines from the three major primary breeders. If it exists, variation among the commercial sire lines in resistance to P. multocida is likely not due to variation in the Class II MHC haplotypes, because Zhu et al. (1996) found that the same commercial sire lines from the three primary breeders had one predominant MHC haplotype that varied from 63 to 83% of all MHC haplotypes and the frequency of other MHC haplotypes did not vary greatly. The MHC haplotype observed most frequently in
RESEARCH NOTE
the commercial sire lines confers resistance to P. multocida (Nestor et al., 1996c). The possible variation in resistance to P. multocida among commercial sire lines may be due to variation in growth rate or growth curves among the lines. In the present study, the C line was smaller than the F line at the time of the challenge but was larger at 16 wk of age (K. E. Nestor, unpublished data). The body weight at the time of challenge was not given in the study of Nestor et al. (1996b) involving the comparison of two commercial sire lines and the F and RBC2 lines. However, unpublished data at the authors’ institution indicated that the F line was heavier at 8 and 16 wk of age but smaller at 20 wk of age than one of the commercial sire lines and similar in BW at 8 wk of age but smaller at 16 and 20 wk of age than the other commercial sire line. Nestor et al. (1999) reported that restricting the body weight of the F line to that of the RBC2 line increased resistance to experimental challenge with P. multocida in males but not in females.
ACKNOWLEDGMENTS The authors thank British United Turkeys of America, Lewisberg, WV 14901, and Hybrid Turkeys Inc., Kitchner, Ontario, Canada N2K 3S2, for providing financial support.
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