Genotype, Feeding Regimen, and Diet Interactions in Meat Chickens.

Genotype, Feeding Regimen, and Diet Interactions in Meat Chickens. 3. General Fitness K. BOA-AMPONSEM,1 N. P. O'SUIXTVAN, W. B. GROSS, E. A. DUNNINGTON, and P. B. SIEGEL2 Poultry Science Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication June 4, 1990) ABSTRACT Several fitness traits were measured in males from two meat lines fed diets differing in nutrient density ad libitum daily or on alternate days. Criteria of evaluation were antibody response to SRBC, blood heterophil:lymphocyte ratios, incidence of leg deformities, and resistance to Escherichia coli inoculation. Males from the heavier line had lower antibody titers to SRBC inoculation than those of the lighter line. Diets, feeding regimens, and interactions among them did not influence response to SRBC. Lines, diets, feeding regimens, and interactions among them were not significant for heterophil:lymphocyte ratios. Chicks fed daily had a higher incidence of leg deformities than those fed on alternate days. There were no differences between lines or diets, nor were interactions significant. Interactions were present between main variables for response to E. coli inoculation whether the measure was initial weight loss, recovery, or lesion scores, demonstrating the complexity of genotype-environmental relationships in resistance to this infectious agent (Key words: chickens, Escherichia coli, immunoresponsiveness, feed restriction, leg disorders) 1991 Poultry Science 70:697-701 INTRODUCTION

Intense selection for juvenile BW under ad libitum feeding has resulted in meat chickens that consume a volume of feed approaching gastrointestinal tract capacity (Nir et al., 1978; McCarthy and Siegel, 1983; Barbato et al., 1984). This condition is possibly due to alterations in hypothalamic satiety mechanisms (Burkhart et al., 1983). Obesity that results from excessive feed consumption impairs reproductive function in broiler breeders (Fuller et al., 1969; Katanbaf et al, 1989). Several feed restriction programs have been used in an attempt to control feed intake, thereby improving reproduction of broiler breeders. Scott et al. (1982) concluded that some regimens, particularly feeding of unbalanced protein or low energy high fiber diets, impaired immunocompetence and disease resistance. Katanbaf et al. (1988) observed that chicks released from alternate-day to ad libitum daily feeding preferentially allocated greater amounts of resources to growth and were, therefore, more susceptible to Escherichia coli infection.

Resent address: Animal Research Institute, Achimoto, Ghana. *To whom reprint requests and correspondence should be addressed.

The present study reports on the effect of nutrient density and feeding regimens on fitness traits in two lines of meat chickens. Criteria of evaluation were resistance to an E. coli inoculation, antibody response to SRBC, incidence of leg abnormalities, and blood heterophil:lymphocyte ratio. Companion papers (Boa-Amponsem et al., 1991a,b) include data on growth, organ size, feed utilization, and behaviors. MATERIALS AND METHODS

Stocks, Diets, and Feeding Regimens Because the genetic stocks, diets, and feeding regimens involved in the present experiment were presented by Boa-Amponsem et al. (1991a), only brief descriptions are presented here. Day-old males from two lines of meat-type chickens (A and B) were vaccinated for Marek's disease, wing-banded, weighed, and randomly assigned to pens in electrically heated battery brooders. Chicks were fed one of two mash diets (H or L). Diets were fed for ad libitum consumption either daily (D) or on alternate days (R). Diet H provided 24% crude protein and 3,146 kcal ME/kg and Diet L contained 20% crude protein and 2,685 kcal ME/kg. Treatments were assigned in a 2 by 2 by 2 factorial

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arrangement of treatments with six replicate pens per line by diet by feeding regimen subclass. Treatments There were 10 chicks in each pen through 21 days of age (DOA) at which time six chicks were randomly selected and transferred to developer batteries. Of the 3 remaining chicks, 1 was inoculated via the posterior thoracic air sac with .1 mL broth culture of E. coli containing 106 organisms (serotype of 01:K1 incubated 24 h in tryptose broth). The second was inoculated similarly with a dosage of 10 4 E. coli. The third chick was not inoculated. Feed was continuously available to both R and D chicks during the 92 h postinoculation. Chicks were individually weighed 24, 44, and 92 h postinoculation. Four hours after the last weighing, survivors were killed by cervical dislocation and scored by die same individual for pericarditis and airsacculitis. Scoring was as follows: 1, none; 2, mild air sac; 3, moderate air sac; 4, mild to moderate heart damage; 5, extensive, severe heart damage; and 6, death during the 92-h postinoculation period. At 28 DOA, 2 males from each pen for a total of 12 per line by diet by feeding regimen subclass were randomly selected and .1 mL of .25% suspension of SRBC was injected into the brachial vein. Five days later blood was collected from the brachial vein and antibody titers were measured by a microtiter hemagglutination procedure (Wegmann and Smithies, 1966). Antibody was expressed as die log2 of the reciprocal of the highest dilution given in which there was hemagglutination. Blood samples used to determine heterophil and lymphocyte counts were collected just before delivery of SRBC antigen. Blood smears were stained witfi May-Grunwald-Giesma stains (Gross and Siegel, 1983). Sixty cells from each slide were classified as heterophils or lymphocytes and the ratio of heterophils and lymphocytes was calculated for each individual. At 33 DOA, leg deformities, defined as any disorder that caused an alteration from the normal pattern of motor activity, were determined for each male. Classifications were deformed or not deformed wim deformed including abnormalities as described by Pierson and Hester (1982).

Statistical Analyses Data were analyzed by analysis of variance with lines, diets, and feeding regimens as main effects. Dosage was added as a main variable for die E. coli inoculation. Body weights were transformed to common logarithms and ratios to arc sine square roots prior to analysis. Body weight changes due to E. coli inoculation were converted to percentages of preinoculation BW before transformation and analysis. For leg weakness, pens witii no deformities (0/n, where n = number of individuals in pen) were replaced with l/4n (Zar, 1984) before transformation and analysis. RESULTS AND DISCUSSION

Livability over the experimental period was 98.5%. There was no definable pattern in livability among treatments. Response to Escherichia coli Inoculation There was no horizontal transmission of E. coli, as none of me uninjected chickens lost weight or exhibited lesions. Uninjected chickens were omitted from statistical analyses. Response to E. coli inoculation, as measured by postinoculation changes in BW, is shown in Table 1. Growui depression was considerable during the first 24 h after inoculation witii recovery exhibited by 44 h postinoculation. First-order and higher order interactions between the main effects for BW changes were not significant. Depression in growui during die first 24 h postinoculation was more severe in Line A than in Line B. Thereafter, recoveries, as measured by BW changes at 44 h and at 92 h, were similar for bom lines. Changes in BW during 24 and 44 h postinoculation were similar for bom diets (Table 1). By 92 h postinoculation, however, die relative increase in BW was greater for Diet L man for Diet H. Even tiiough males fed R prior to E. coli inoculation exhibited more severe growui depression at 24 h postinoculation, tiieir recovery was faster than was mat of meir D counterparts. Growth depression was greater at the higher than the lower E. coli dosage at 24 h postinoculation, a pattern that persisted at 44 h and disappeared by 92 h. There were no interactions between diet and die otiier main variables for lesion score to E. coli inoculation. Scores were similar for both diets, being 3.3 and 3.2 for Diets H and L, respectively. There were significant feeding

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TABLE 1. Means (± SEM) of body weights at time of inoculation and of relative body weight changes (percentage and cumulative over time) from an Escherichia coli inoculation by line, diet, feeding regimen, and dosage

Variable

Initial weight (g)

Line A B

489* 420 b

Diet H L Regimen D R Dosage2 10 6 10 4

Hours postinoculation 24

44

92

.1 ± 1.2b 2.9 ± .7 b

11.2 ± 1.4* 13.6 ± .8*

28.8 ± 2.6* 32.6 ± 2.0*

507* 402 b

1.5 ± .8* 1.5 ± 1.2*

11.9 ± .8* 13.0 ± 1.4*

27.4 ± 1.7b 34.0 ± 2.7*

574* 335 b

4.5 ± .9* -1.5 ± .9 b

11.5 ± 1.1* 13.3 ± 1.1*

24.0 ± 1.9b 37.2 ± 2.3*

450* 459*

-.2 ± l . l b 3.2 ± .9*

10.8 ± 1.3b 14.0 ± .8*

29.8 ± 2.7* 31.6 ± 2.0*

"•"Two adjacent means in a column with no common superscripts are significantly different (P<05). % = high nutrient density diet; L = low nutrient density diet; D = daily feeding; R = alternate day feeding. Corresponding mean changes (± SEM) for controls were 24 h = 7.0 ± .9; 44 h = 18.0 ± .4; 92 h = 41.5 ± 1.2.

regimen by line and feeding regimen by dosage interactions for lesion scores (Table 2). The feeding regimen by line interaction occurred because with daily feeding throughout, resistance to E. coli was greater in Line B than Line A. Li contrast, scores were similar for both lines when feed was offered on alternate days prior to inoculation with E. coli. At the higher E. coli dosage, chicks reared on Regimen D were less resistant than those reared on Regimen R, but there was no difference between feeding regimens at the lower dosage of E. coli. The present results corroborate those of Katanbaf et al. (1988), which showed differences among feeding regimens in BW changes and mortality rates in response to inoculation of broilers with E. coli. They observed that at 24 h postinoculation, chicks fed on alternate days exhibited greater depression in growth than ad libitum-fed chicks, but that within 72 h postinoculation, their recovery was greater. Such responses under ad libitum daily feeding suggest a disproportionate amount of resources are diverted toward growth at the expense of fitness. Sheep Erythrocyte Antibodies No interactions were observed between lines, diets, and feeding regimens for antibody to SRBC 5 days postinoculation. The SRBC titers were lower for Line A than for Line B (1.9 ± .2 versus 2.5 ± .2), but there was no significant difference between Diets H and L (2.2 ± .2

versus 2.2 ± .2) nor between Regimens D and R (2.3 ± .2 versus 2.1 ± .2). Genetic differences in the ability of chickens to mount an antibody response to SRBC have been observed in functionally diverse as well as similar stocks (van der Zijpp, 1983; Siegel et al., 1984). Such genetic differences in immunocompetence may be related to growth (Siegel et al., 1982; Gross and Siegel, 1988). In the present experiment, Line A males were heavier than those of Line B (Boa-Amponsem et al., 1991a), suggesting variation in allocation of resources to growth and immunoresponsiveness between the two lines. Lack of significant diet and feeding regimen effects on antibody response corroborates the results of Glick et al. (1981). These results demonstrated that severe energy restrictions (one-third of normal ME) over a 5-wk period depressed hemagglutination responses at higher but not at lower antigen levels. The low antibody titers obtained in the present experiment are consistent widi those observed in other highly selected meat chickens (Siegel et al, 1984; Cahaner and Siegel, 1986; Dunnington et al., 1987; Dunnington, 1990). Heterophil to Lymphocyte Ratios There were no differences between lines, diets, or feeding regimens for heterophihlymphocyte ratios; means ± SEM were .27 ± .01 for

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TABLE 2. Means ± SEM of lesion scores of males 92 h postinoculation with Escherichia coU where interactions of feeding regimen by line and feeding regimen by dosage were significant Feeding regimen2 D R

Line A 4.0 ± .3 ** 2.6 ± .3

* NS

Dosage 104

B

106

3.1 ± .4 NS 3.0 ± .3

4.6 ± .2 ** 2.8 ± .3

** NS

2.5 ± .3 NS 2.9 ± .4

Scoring of lesions was as follows: 1 = none; 2 = mild air sac; 3=moderate air sac; 4=mild to moderate heart damage; 5 = extensive, severe heart damage; 6 = death. 2 Daily feeding; R = alternate-day feeding. *P£.05. "K.01.

Line A, .30 ± .02 for Line B, .29 ± .01 for Diet H, .28 ± .02 for Diet L, .29 ± .02 for Regimen D and .29 ± .02 for Regimen R. Further, first- and second-order interactions among those variables were not significant. The magnitude of ratios obtained here suggests that under the husbandry conditions of this experiment stressors were minor. When meat-type chicks were fed on alternate days, H:L ratios were elevated at 12 DOA, but by 26 DOA or after 10 cycles of such restriction, adaptation to the regimen had occurred (Katanbaf et al., 1988). Similar reports in the literature indicate that chickens adapt to prolonged cycles of alternate-day feeding (Gross and Siegel, 1983, 1986). In the present experiment, adequate time was allowed for adaptation to alternate-day feeding. Leg Deformities No differences were found between lines or between diets for incidence of leg deformities. There was, however, a difference between feeding regimens; incidence was 13.4 ± .2% for Regimen D and 2.0 ± . 1 % for Regimen R. According to Edwards and Sorensen (1987), increased growth and ash content of the long bones of birds undergoing feed restriction were due to cessation of calcification and increased mineralization of growth plates in these bones, which resulted in lower incidences of leg abnormalities. The present data suggest mat, under current practices of feed restriction for broiler breeder populations, leg problems are latent and such programs may preclude phenotypic expression. Chickens not on some form of feed restriction spend more time resting than those restricted (Boa-Amponsem et al., 1991b), suggesting lack of activity may be a contributing factor.

General Within the limits of the present experiment, particularly in regard to die range of lines, diets, and feeding regimens investigated, chickens were able to adapt to recurrent and prolonged nutritional modifications that did not result in malnutrition. Moreover, such adaptations did not interfere with traits associated with fitness. Generally, faster growth rates were associated with reduced immunocompetence, as was observed with Line A and males fed daily a high nutrient density diet for ad libitum intake. The results strongly suggest, therefore, that demands of fast growth, whether genetically induced or imposed by nutritional manipulation, result in deprivation of resources to systems that determine general fitness. ACKNOWLEDGMENTS

This research was supported, in part, by funds from the African-American Institute. The authors gratefully appreciate the assistance of A. S. Larsen and P. R. Morena. REFERENCES Barbato, G. F., P. B. SiegeL J. A. Cherry, and I. Nir, 1984. Selection for body weight at 8 weeks of age. 17. Overfeeding. Poultry Sci. 63:11-18. Boa-Amponsem, K., P. B. SiegeL and E. A. Dunnington, 1991a. Genotype, feeding regimen, and diet interactions in meat chickens. 1. Growth, organ size and feed utilization. Poultry Sci. 70:680-688. Boa-Amponsem, K., P. B. SiegeL and E. A. Dunnington, 1991b. Genotype, feeding regimen, and diet interactions in meat chickens. 2. Feeding behavior. Poultry Sci. 70:689-696. Burkhart, C. A., J. A. Cherry, H. P. Van Krey, and P. B. Siegel, 1983. Genetic selection for growth rate alters hypothalamic satiety mechanisms in chickens. Behav. Genet. 13:295-300.

GENOTYPE AND NUTRITION. 3. GENERAL FITNESS Cahaner, A., and P. B. Siegel, 1986. Evaluation of industry breeding programs for meat-type chickens and turkeys. In: Proc. 3rd World Congr. Genet. Appl. Livest. Prod. University of Nebraska, Lincoln, NE 10:337-346. Dunnington, E. A., 1990. Selection and homeostasis. Proc. 4th World Congr. Genet. Appl. Livest. Prod., Edinburgh, Scotland 16:5-12. Dunnington, E. A., A. Martin, and P. B. Siegel, 1987. Research Note: Antibody response to sheep erythrocytes in early (k) and late (K) feathering chicks in a broiler line. Poultry Sci. 66:2060-2062. Edwards, H. M. Jr., 1984. Studies on the etiology of tibial dyschondroplasia in chickens. J. Nutr. 114: 1001-1013. Edwards, H. M. Jr., and P. Sorensen, 1987. Effect of short fasts on the development of tibial dyschondroplasia in chickens. J. Nutr. 117:194-200. Fuller, H. L., D. K. Potter, and W. Kirkland, 1969. Effect of delayed maturity and carcass fat on reproductive performance of broiler breeder pullets. Poultry Sci. 48:801-«09. Glide, B., E. J. Day, and D. Thompson, 1981. Calorieprotein deficiencies and the immune response of the chicken. 1. Humoral immunity Poultry Sci. 60: 2494-2500. Gross, W. B., and H. S. Siegel, 1983. Evaluation of the heterophil/lymphocyte ratio as a measure of stress in chickens. Avian Dis. 27:972-979. Gross, W. B., and P. B. Siegel, 1986. Effect of initial and second periods of fasting on heterophil/lymphocyte ratios and body weight. Avian Dis. 30:345-346. Gross, W. B., and P. B. Siegel, 1988. Environment-genetic influences on immunocompetence. J. Anim. Sci. 66: 2091-2094.

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