Effect of p ,p′-DDT, o ,p′-DDT and p ,p′-DDE on the Reproductive Performance of Caged White Leghorns

Effect of p,p'-DDT, o,p'-DDT and p,p'-DDE on the Reproductive Performance of Caged White Leghorns R. J. LILLIE, C. A. DENTON, H. C. CECIL, J. BITMAN AND G. F. FRIES United States Department of Agriculture1 Beltsville, Maryland 20705 (Received for publication April 30, 1971)

POULTRY SCIENCE 51:

FFECTS of chlorinated hydrocarbon pesticides on avian reproduction have been documented in the literature since the beginning of their widespread use in the middle 1940's. Lowered efficiency of reproduction through reduced egg production, greater egg shell breakage and poor hatchability among raptorial and fish-eating birds have been reported by Hickey and Anderson (1968), Porter and Wiemeyer (1969) and Enderson and Berger (1970). Because of the adverse effects on wild birds, controlled experiments have been conducted in recent years to determine the degree of sensitivity to DDT toxicity in quail, pheasants, ducks and high egg-producing strains of chickens. Discrepancies have been observed in literature on the toxicity of DDT in quail. DeWitt (1955) reported that 200 p.p.m. of DDT in breeder quail diets exerted no adverse effects on egg production or fertility but did reduce hatchability significantly. However, the

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1

A.R.S., Animal Science Research Division.

122-129,

1972

adverse effect on hatchability was not duplicated in a later study (DeWitt, 1956). Negative results were obtained with the highest level of DDT (100 p.p.m.) on the reproductive performance of Japanese quail (Creger et al., 1970). In a 60-day feeding trial, Smith et al. (1969) showed that egg production of Japanese quail was not influenced by 400 p.p.m. of DDT (the highest level used) but that breeder livability, fertility and hatchability became affected after 3 days on this level. Conversely, Stickel and Rhodes (1970) stated that 2.5, 10 and 25 p.p.m. of DDT reduced egg production of Japanese quail in a 26-week period; however, hatchability was not significantly altered. Pheasants produced fewer eggs on either 50 or 100 p.p.m. DDT in the diet than the controls (DeWitt, 1956). However, neither fertility nor hatchability was affected. In studies with penned Mallard ducks fed 2.5, 10 and 40 p.p.m. of DDT, Heath et al. (1969) reported that the mortality among breeders fed 40 p.p.m. was so high

122

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ABSTRACT Nine groups of 20 caged White Leghorn pullets each were fed a standard breeder diet supplemented with 5, 25 or SO p.p.m. p,p'-DDT, o,p'-DDT or p,p'-DDE in Experiment 1 (28 weeks); the 5 and 25 p.p.m. levels were increased to 150 and 300 p.p.m., respectively, in Experiment 2 (additional 12 weeks). A tenth group fed no pesticides served as the control in both experiments. Least squares analysis of variance indicated in Experiment 1 pesticide effects for body weight gains which showed a rank of decreasing order: p,p'-DDT > o,p'-DDT > p,p'-DDE. The three pesticides produced significantly heavier body weights than the control. The level X pesticide effects indicated that the 5 and 25 p.p.m. levels of p,p'-DDE increased body weight gains more than the SO p.p.m. level and that the 5 and 50 p.p.m. levels of p,p'-DDT and o,p'-DDT, respectively, significantly reduced hatchability as compared with the other two levels within the pesticide. In Experiment 2, pesticide effects showed that the three pesticides significantly reduced egg production; no differences were noted between the pesticides for this trait. No significant differences due to pesticides, as compared with the control, were observed for mortality, fertility, hatchability and progeny growth in both experiments.

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EXPERIMENTAL PROCEDURE that the DDT level was reduced to 25 p.p.m. after the first season. Egg produc- Experiment 1. Single Comb White Leghorn tion and hatchability were not significantly pullets were obtained from a commercial affected by DDT. In the same study, DDE, hatchery at 20 weeks of age and placed in a metabolite of DDT, fed at the 10 and 40 individual cages in a gravity-ventilated, p.p.m. levels, significantly reduced hatch- open-front house equipped with windows. ability and duckling production. Supplementary heat was supplied during According to Smith et al. (1970), 10 the cold weather to maintain room temperp.p.m. of technical DDT appeared to de- ature at 50°F. The birds were fed a stanpress egg production of yearling White dard breeder diet containing 3.5% calcium Leghorns 10% below that of the control and exposed to a 14-hour light regime. At group after two months of DDT feeding. 26 weeks of age the pullets were individuDraper et al. (1952) concluded that levels ally weighed and randomly distributed into of 50, 100, and 200 p.p.m. of technical 10 groups of 20 each on the basis of body DDT in the feed decreased efficiency of weight and sexual maturity. The mean feed utilization and possibly egg production body weight of all groups was 1622 grams. of laying hens. The validity of their concluOne group was continued on the standard sion is doubtful because the authors used breeder diet (control); the other nine groups only four layers per treatment which does were fed the same diet supplemented with not constitute an adequate population sam- 5, 25 or 50 p.p.m. p,p'-DDT, o,p'-DDT, or ple. Rubin et al. (1947) reported that 310 p,p'-DDE. 2 The pesticides were dissolved in p.p.m. of technical DDT (the lowest level acetone and pipetted onto a portion of the used in the study) reduced egg production basal diet spread out in shallow pans. After but not hatchability of caged layers, that evaporation of the solvent, the premix was 620 p.p.m. affected hatchability, and that thoroughly mixed with the remainder of the 1250 and 2500 p.p.m. resulted in 90 and feed. Diets containing the pesticides were 100 percent mortality, respectively, by the prepared every two weeks. end of the 12th week. Weihe (1967) indiThe traits studied were egg production, cated that 20 p.p.m. of DDT exerted no feed consumption, body weights, mortality, effect on laying hens, that 200 p.p.m. re- fertility, hatchability, and progeny perforsulted in some mortality and that 1000 mance. p.p.m. resulted in 80 to 95 percent mortalIn the fertility studies, a composite samity by the end of one week. ple of undiluted semen obtained from caged Since very little information is known on White Leghorn males fed the same diet as the effects of pure p,p'-DDT, o,p'-DDT, the control pullets was used to inseminate and p,p'-DDE 2 on the reproductive per- the pullets once a month at the rate of 0.05 formance of chickens, studies were initiated cc. per bird. Two days after insemination, to compare such effects. The results of these eggs were saved for a 5-day period and set studies are presented herein. according to hen and group number. At hatching time the progeny from the 2 Thep,p'-DDT, [l,l,l-trichloro-2,2-bis (p-chlocontrol group and those groups fed 50 rophenyl)] ethane; o,p'-DDT, Ll,l,l-trichloro-2- p.p.m. of the three pesticides (a maximum (o-chlorophenyl), 2-(p-chlorophenyl)] ethane; and of 60 progeny per maternal group) were p,p'-DDE, [l,l-dichloro-2,2-bis(p-chlorophenyl)] placed in chick brooder batteries and fed a ethylene were from Aldrich Chemical Co. Our analstandard broiler diet without DDT suppleysis indicated that o,p'-DDT contained 1.2% p,p'mentation for a 4-week period. In the seven DDT on growing turkeys. Poultry Sci. 26: 3~6.

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LIIXIE, DENTON, CECIL, BITMAN AND FRIES

in Experiment 1, the pesticide levels of the groups on 5 and 25 p.p.m. were increased to 150 and 300 p.p.m., respectively, while the 50 p.p.m. diet remained the same in Experiment 2. The hens that diet in Experiment 1 were replaced by surplus birds of the same strain and age. Progeny from maternal groups fed 300 p.p.m. of the three pesticides were used instead of those from the groups fed the 50 p.p.m. level of the three pesticides for two progeny performance studies. The duration of Experiment 2 was 12 weeks.

Experiment 2. After the pullets had been on their respective diets for a 28-week period

RESULTS

Experiment 1. The data obtained on egg

TABLE 1.—Effects of p,p'-DDT, o,p-DDT and p,p'-DDE on egg production, body weights, mortality and feed consumption of layers in a 28-week period (Expt. 1) Pesticide supplementation

Level

Egg production (hen-day)

Adjusted body weight gains

Mortality

Average feed consumption per hen per day

p.p.m.

%

gms.

%

gms.

0.0+9.7

111.8

1

None (Control)

0

81.8+1.9

183 + 3l*

p,p'-DDT (P-l)

5 25 50

75.0 + 2.1 77.4+1.9 79.7 + 2.1

289 + 32 296+31 262 + 33

77.3+1.2

282+18 d

80.3 + 2.2 74.6+2.1 78.1 + 2.1

218 + 34 284+33 271 + 33

25.0 10.0 10.0

109.5 107.4 113.3

77.7 + 1.2

258+19°

15.0+5.6

110.1

81.5 + 2.4 74.9 + 2.0 78.9 + 2.1

267 + 38 289+32 168 + 34

35.0 10.0 15.0

110.7 112.7 108.4

78.5 + 1.3

241 + 20b

20.0 + 5.6

110.6

Means o,p'-DDT (P-2)

5 25 50

Means p,p'-DDE (P-3)

5 25 SO

Means

10.0 0.0 10.0 6.7 + 5.6

Approximate significance of F ratios Analysis of variance Total Reduction MU Pesticide (P) Level (L)/P-l L/P-2 L/P-3 BW(1) Error 1

df

df

176 11

10 4

1 3N.S. 2N.S. 2N.S. 2N.S. IN.S. 165

<0.5 N.S. N.S.

1 3 N.S.


6

Means with different superscripts are significantly different at the 5% level of probability.

110.3 112.2 113.5 112.0

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tests run, growth and mortality were the criteria used for progeny performance. All traits except feed consumption of layers and mortality of the progeny were subjected to the least squares analysis of variance. Whenever appropriate, the significant differences were determined by the least significance difference test (LeClerg, 1957). Data on egg weights, egg shell thickness, egg shell calcium content and pesticide residues will be presented in an accompanying paper (Cecil et al., 1972).

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TABLE 2.~EjJects of p,p'-DDT, n,p'-DDT, and p,p'-DDE on fertility, hatchability and progeny performance in Experiment 1 Pesticide supplementation

Progeny performance (4-week data) Growth Mortality

Fertility

Hatchability of fertile eggs

p.p.m.

%

%

gms.

%

None (control)

0

95.0 + 2.3

89.2+1.5

277 + 6

1.0(391) x

p,p'-DDT (P-l)

5 25 50

89.6 + 2.3 91.2 + 2.3 95.3 + 2.3

87.4+1.5 91.5+1.5 93.3+1.5

281 ± 6

1.0(391)

92.0+1.3

90.7 + 0.8

91.7 + 2.3 93.6±2.3 90.7 + 2.3

93.6+1.5 95.1 + 1.5 89.0+1.5

279 + 6

2.3(376)

92.0+1.3

92.6 + 0.8

95.6+2.3 91.8 + 2.3 93.2 + 2.3

89.0+1.5 91.7+1.5 89.9±1.5

292 + 6

1.0(380)

93.5+1.3

90.2 + 0.8

Means o,p'-DDT (P-2)

5 25 50

Means p,p'-DDE (P-3)

Means

5 25 50

Approximate significance of F ratios Analysis of variance

df

df

Total Reduction MU P L/P-1 L/P-2 L/P-3 Error

70 10

28 4

1

1 3N.S. 2N.S. 2N.S. 2N.S.

1 3 N.S.

N.S. <0.05 <0.05 N.S.

60

24

Number in parentheses represents survivors at 4 weeks of age.

production, body weight gains, mortality and average feed consumption per hen per day in the 2 8-week period are tabulated in Table 1, and the data on fertility, hatchability and progeny performance in Table 2. The only significant differences resulting from DDT or DDE supplementation in the feed were body weight gains (Table 1) and hatchability of fertile eggs (Table 2). The regression of initial body weight [BW(1)] on body weight change, significant at the 1% level, uncovered a source of variation which could affect the group means. Differences between the resulting adjusted group means could then be assessed free of this in-

fluence. The adjusted body weight data then indicated that (1) the three pesticides produced significantly heavier body weight gains than the control group at the 5% level, (2) there were significant differences between the three pesticides at the 5% level, (3) the 50 p.p.m. level of p,p'-DDE resulted in lower body weight gains than the 5 and 25 p.p.m. levels, the difference being significant at the 5 % level. The hatchability of fertile eggs was not significantly affected by the pesticides, as compared with the control. However, when pesticide levels were analyzed, the level X pesticide effects indicated that hatchability was significantly lower on 5 p.p.m. than on

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Level

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LILLIE, DENTON, CECIL, BITMAN AND FRIES

25 or 50 p.p.m. of p,p'-DDT and on 50 p.p.m. than on 5 or 25 p.p.m. of o,p'-DDT. No differences were observed between the three pesticides and the control for average feed consumption of the hens and mortality of the progeny. Experiment 2. As shown in Tables 3 and 4, the increased levels of DDT and DDE (150 and 300 p.p.m.) for the next 12 weeks of the 40-week study did not produce any adverse effects on all traits studied, as compared with the 50 p.p.m. level.

The only significant effect was egg production which was lowered by the three pesticides, as compared with the control, the difference being significant at the 1% level. No significant differences were observed between the three pesticides for egg production, nor were there any differences in feed consumption of layers and mortality of progeny. DISCUSSION

Although their egg production data were not statistically analyzed, Smith et al.

Pesticide supplementation

None (Control) p,p'-DDT (P-l)

Level

Egg production (hen-day)

Adjusted body weight changes

Mortality

Average feed consumption per hen per day

p.p.m. 1

%

gms.

%

gms.

0/0 5/150 25/300 50/50

Means o,p'-DDT (P-2)

5/150 25/300 50/50

Means p,p'-DDE (P-3)

Means

5/150 25/300 50/50

72.2±3.4*

2

90±31

5.0+1.7

114.2

0.0 0.0 0.0

107.8 110.9 110.9

0.0+0.96

108.4

5.0 5.0 0.0

106.7 108.9 108.5

3.3 + 0.96

108.0

60.7 + 3.3 67.8 + 3.3 66.9 + 3.3

2 + 31 -6+31 68 + 31

65.lil.9i>

21 + 18

56.8±3.3 59.1 + 3.3 57.1 + 3.3

26 + 31 12 + 31 -20+31

56.7+1.9»

6+18

67.7 + 3.3 60.9 + 3.3 64.3 + 3.3

- 1 8 + 31 - 2 7 + 31 43 + 31

0.0 0.0 0.0

112.2 105.0 111.3

64.3+1.9t>

-0.56+18

0.0+0.96

109.5

Approximate significance of F ratios Analysis of variance Total Reduction MU P L/P-1 L/P-2 L/P-3 BW(1) Error 1

df

df

197 11

10 4 1 3 2 2 2 1

186

<0.01 N.S. N.S. N.S. N.S.

1 3 N.S.

N.S. N.S. N.S. N.S. N.S. 6

The level on the left of / represented the level fed in Experiment 1 and that on the right of / the level fed in Experiment 2. 2 Means with different superscripts are significantly different at the 5% level of probability.

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TABLE 3.—Effects of increased levels of p,p'-DDT, o,p'-DDT, and p,p'-DDE on egg production, body weight changes, mortality and feed consumption in a 12-week period {Experiment Z)

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TABLE 4.—-Effects of p,p'-DDT, o,p'-DDT and p,p'-DDE on fertility, hatchability and progeny performance in Experiment 2 Pesticide supplementation

Progeny performance (4-week data) Growth Mortality

Fertility

Hatchability of fertile eggs

p.p.m. 1

%

%

gms.

%

None (control)

0/0

93.4±3.0

91.1 + 2.4

304+7

1.0 (100)2

p,p'-DDT (P-l)

5/150 25/300 50/50

94.2 + 3.0 95.5 + 3.0 93.8+3.0

93.4+2.4 95.0+2.4 91.6+2.4

297 + 7

0.0(113)

94.5+1.7

93.3+1.4

92.4+3.0 95.2 + 3.0 87.2 + 3.0

94.1 + 2.4 93.9 + 2.4 91.1 + 2.4

303 + 7

1.0(91)

91.6+1.7

93.0+1.4

92.5±3.0 90.8+3.0 94.3 + 3.0

91.2 + 2.4 90.8+2.4 92.5 + 2.4

303 + 7

0.0(94)

92.6+1.7

91.5+1.4

Means o,p'-DDT (P-2)

5/150 25/300 50/50

Means p,p'-DDE (P-3)

Means

5/150 25/300 50/50

Approximate significance of F ratios Analysis of variance

df

df

Total Reduction MU P L/P-1 L/P-2 L/P-3 Error

20 10

8 4

1 3 2 2 2

N.S. N.S. N.S. N.S.

10

N.S. N.S. N.S. N.S.

1 3 N.S.

4

1

The level on the left of / represented the level fed in Experiment 1 and that on the right of / the level in Experiment 2. 2 Number in parentheses represents survivors at 4 weeks of age.

(1970) reported that 10 p.p.m. of technical DDT appeared to depress egg production of yearling White Leghorns 10% below that of the control group after two months of DDT feeding. However, our studies showed that egg production was not significantly reduced by the 50 p.p.m. level after 28 weeks of pesticide feeding in Experiment 1 but was significantly reduced by the same level after the next 12 weeks of pesticide feeding in Experiment 2. The reduction in egg production was not a reflection of changes in feed consumption or body weights as reported in this paper or in egg

weights, egg shell thickness and egg shell calcium content as reported by Cecil et al. (1972). Possible explanations for the significant decrease in egg production in Experiment 2 may be the advancing age of the pullets and/or the hot weather. No explanation is offered for the increased body weight gains in Experiment 1 as a result of DDT or DDE supplementation. The increased body weight gains were not a reflection of feed intake because the feed intake on all treatments was essentially the same in both experiments. Nevertheless, the data deserve some consideration

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Level

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LILLIE, DENTON, CECIL, BITMAN AND FRIES

DeWitt (1955, 1956) with progeny from Japanese quail breeders fed 100 or 200 p.p.m. of DDT. Higher levels (400 p.p.m. of p,p'-DDT) caused ataxia, spasms and death in the progeny of Japanese quail breeders, according to Smith et al. (1969). The negative responses from high levels of p,p'-DDT, o,p'-DDT and p,p'-DDE on adult livability, fertility, hatchability and progeny performance, as reported in this paper, and on egg shell characteristics as reported by Cecil et al. (1972), appeared to be in conflict with some of the published results with wild birds. Therefore, the chicken appears to be more highly resistant to the effects of DDT than wild birds with respect to growth during the rearing period as reported by Noakes and Benfield (1965) and to reproductive performance as reported in this paper. ACKNOWLEDGMENT

We wish to express our gratitude for the valuable services of Dr. B. T. Weinland of the Biometrical Services staff, ARS, Beltsville, Maryland. REFERENCES Cecil, H. C , G. F. Fries, J. Bitman, S. J. Harris, R. J. Lillie and C. A. Denton, 1972. Dietary p,p'-DDT, o,p'-DDT or p,p'-DDE and changes in egg shell characteristics and pesticide accumulation in egg contents and body fat of caged White Leghorns. Poultry Sci. 5 1 : 130-139. Creger, C. R., J. R. Couch and M. R. Watkins, 1970. The effects of DDT on the reproductive performance of Coturnix quail. Poultry Sci. 49: 1378. DeWitt, J. B., 1955. Effects of chlorinated hydrocarbon insecticides upon quail and pheasants. J. Agric. Food Chem. 3 : 672-676. DeWitt, J. B., 1956. Chronic toxicity to quail and pheasants of some chlorinated insecticides. J. Agric. Food Chem. 4 : 863-866. Draper, C. I., J. R. Harris, D. A. Greenwood, C. Biddulph, L. E. Harris, F. Mangelson, W. Binns and M. L. Miner, 1952. The transfer of DDT from the feed to eggs and body tissues of White Leghorn hens. Poultry Sci. 3 1 : 388-393. Enderson, J. H., and D. D. Berger, 1970. Pesti-

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because Friend and Trainer (1970) observed significant body weight gains in Mallard ducklings as a result of polychlorinated biphenyl supplementation (25, 50 and 100 p.p.m.) in a 10-day feeding trial; the higher the level, the greater was the growth response. Since the authors could not account for the increased body weight gains and since polychlorinated biphenyls are closely related to DDT and DDE, more research is needed to explain the effect of chlorinated hydrocarbon pesticides on body weight changes in poultry. Although the differences were not significant, the mortality was higher for all but one of the pesticide-fed groups than for the control in Experiment 1. Most of the deaths which occurred before the birds reached 40 weeks of age were attributed to the avian leukosis complex. None of the birds that died exhibited symptoms typical of DDT poisoning (ataxia, tremors and paralysis). Since levels as high as 300 p.p.m. of DDT or DDE exerted no influence on fertility or hatchability in our studies, there is a possibility that higher levels may be needed to produce adverse effects on either trait, as suggested by Rubin et al. (1947) and Weihe (1967) who reported that 620 p.p.m. and 1000 p.p.m. of DDT, respectively, affected hatchability of chickens. However, levels as low as 10 p.p.m. of DDE, but not of DDT, did affect fertility and hatchability of penned Mallard ducks (Heath et al., 1969), indicating that a species difference might exist in the response to pesticide intake. The finding that high levels of p,p'-DDT, o,p'-DDT and p,p'-DDE in the maternal diet (50 p.p.m. and 300 p.p.m. in Experiments 1 and 2, respectively) did not influence the progeny livability at four weeks of age confirmed the work of DeWitt (1956) with progeny from pheasant breeders fed 100 p.p.m. of DDT but not the work of

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AND REPRODUCTION

and D D T : effects on sparrow hawk eggshells and reproduction. Science, 165 : 199-200. Rubin, M., H. R. Bird, N. Green and R. H. Carter, 1947. Toxicity of D D T to laying hens. Poultry Sci. 26:410-413. Smith, S. I., C. W. Weber and B. L. Reid, 1969. The effect of high levels of dietary DDT on egg production, mortality, fertility, hatchability and pesticide content of yolks in Japanese quail. Poultry Sci. 48: 1000-1004. Smith, S. I., C. W. Weber and B. L. Reid, 1970. Dietary pesticides and contamination of yolks and abdominal fat of laying hens. Poultry Sci. 49: 233-237. Stickel, L. F., and L. I. Rhodes, 1970. The thin eggshell problem. The Biological Impact of Pesticides in the Environment, Environ. Health Science Series 1: 31-35. Oregon State Univ., Corvallis. Weihe, M., 1967. Effects of DDT on reproduction in hens. Acta Pharmacol, et Toxicol. 25 (suppl. 4 ) : 54.

NEWS AND NOTES (Continued from page 116) ture, humidity, light, and air movement can be controlled and varied independently of the building. Also included in the building are offices for the personnel, and physiology and engineering laboratories. The research conducted in the building will be a cooperative effort between the Departments of Animal Sciences and Agricultural Engineering. The financing of the building illustrates cooperative effort of the poultry industry of Arkansas and the University of Arkansas. The facility cost approximately a hundred thousand dollars, and over seventy percent of this was donated by the poultry industry. RUTGERS NOTES On July 1st, a Department of Environmental Physiology was established at the College of Agriculture and Environmental Science with Dr. Paul D. Sturkie as its Chairman, with Dr. W. W. Weathers and Dr. J. J. McGrath as members. The Department also includes two technicians, seven farm workers and seven graduate students. This Department was formed from the old Department of Animal Sciences, which, in turn, represents the merger of the former Departments: Dairy Science, Animal Husbandry and Poultry Science.

Research in Poultry Physiology and Nutrition will be conducted mainly by the Departments of Physiology and Nutrition. The remaining members of the former Poultry Science Group, still in the Animal Sciences Department, include primarily Poultry Pathologists and ,the Extension Poultrymen. DELAWARE NOTES J. Frank Gordy, Director of the Georgetown Substation of the University of Delaware, and Extension Poultry Specialist, retired on June 30, ending more than 30 years of service at the University. He was instrumental in organizing the first Delmarva Chicken Festival held at Georgetown in 1948. From that beginning developed the Delmarva Poultry Industry, Inc., which today has more than 5,500 members on the Peninsula. Since 1955, Gordy has helped guide the Delmarva poultry industry as Executive Secretary of D.P.I. He will continue in this position following his retirement from the University. Raymond W. Lloyd, Associate Extension Specialist, has been promoted to Extension Poultry Specialist to take over Gordy's responsibilities in this field.

(Continued on page 146)

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cides: eggshell thinning and lowered production of young in prairie falcons. Bioscience, 20: 355-356. Friend, M., and D. O. Trainer, 1970. Polychlorinated biphenyl: interaction with duck hepatitis virus. Science, 170: 1314-1316. Heath, R. G., J. W. Spann and J. F. Kreitzer, 1969. Marked DDE impairment of Mallard reproduction in controlled studies. Nature, 224(5214): 47-48. Hickey, J. J., and D. W. Anderson, 1968. Chlorinated hydrocarbons and eggshell changes in raptorial and fish-eating birds. Science, 162: 271-273. LeClerg, E. L., 1957. Mean separation by the functional analysis of variance and multiple comparisons. Agric. Res. Serv. ARS-20-3 (May). Noakes, D. N., and C. A. Benfield, 1965. Tissue accumulation of DDT and its metabolites in the domestic fowl. J. Sci. Food Agric. 16: 693-697. Porter, R. D., and S. N. Wiemeyer, 1969. Dieldrin

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