Fearful and Associated Responses of White Leghorn Hens: Effects of Cage Environments and Genetic Stocks1,2

Fearful and Associated Responses of White Leghorn Hens: Effects of Cage Environments and Genetic Stocks 1 ' 2 J. V. CRAIG,3 J. VARGAS VARGAS,3 and G. A. MILLIKEN4 Departments of Animal Sciences and Industry and of Statistics, Kansas State University, Manhattan, Kansas 66506 (Received for publication May 1, 1986)

1986 Poultry Science 65:2199-2207 INTRODUCTION

High levels of escape of "flighty" behavior can cause increased feather loss of hens kept in large group, high density cages (Craig et al., 1983). "Hysteria" has been reported in cage environments by Elmslie et al. (1966) and Hansen (1976). As described by Hansen (1976), hysteria appears to consist of uncontrolled fear-related acts with exaggerated elements of escape behavior. Hysteria is likely to develop after hens have been kept in high density cages containing 14 or more hens for at least 15 to 20 weeks. When hysteria occurs, extreme feather loss is seen and egg production drops rapidly (Elmslie et al., 1966; Hansen, 1976). In the studies cited, comparisons among genetic stocks indicated an important genetic contribution.

'This investigation was supported in part by a grant from Humane Information Services, Inc. Contribution Number 86-428-J, Departments of Animal Sciences and Industry and of Statistics, Kansas Agricultural Experiment Station, Manhattan, KS. department of Animal Sciences and Industry. 4 Department of Statistics.

In addition to escape and avoidance behavior, another major type of fear-related response is reduced mobility. This is most evident when tonic immobility is induced by physical restraint. Duration of tonic immobility can be significantly increased by preexisting and parallel conditions known to increase the internal state of fear (Gallup, 1974a). Jones and Faure (1981) found that hens kept in 4-bird cages had longer duration of tonic immobility than hens kept in floor pens. Kujiyat et al. (1983) found that hens tested from larger, multiple hen cages were more fearful, by the same criterion, than those from floor pens, single-hen, and smaller group size cages. In a later study, Kujiyat et al. (1984) examined associations between fear-related behaviors and several quantitative traits of hens kept in 5-hen cages. Those results suggested that the longer duration of induced tonic immobility for hens tested late in the laying year appeared associated with reduced egg production . As is the case for escape and hysterical behavior, there is evidence of genetic influences on duration of tonic immobility (e.g., Gallup, 1974b; Craig etal., 1984). Studies with experimental stocks indicate that fearful behavior should be defined in terms of the particular testing situation. For example, some stocks identified as being more fearful by

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ABSTRACT Three measures of fearfulness were evaluated for hens of four genetic stocks after they had been kept in single-, 4-, and 6-bird cages for 26 or more weeks. Twelve hens of each stock and cage-environment combination were used (a total of 144 birds). Two tests involved latency of hungry hens to feed when confronted with fear-stimulating objects and one test was for latency to recover from induced tonic immobility. Results for the genetic stocks were inconsistent; strains identified as more fearful by a particular criterion were in some cases less fearful by another or did not differ. Hens kept in single-bird cages were either less fearful or showed a nonsignificant tendency, suggesting less fearfulness by all three criteria. Hens kept in 4-bird cages were typically similar in fearfulness to those in 6-bird cages. Fear-related responses were not clearly associated with plasma corticosteroids, body weights, mortality, or number of eggs laid. However, feather loss (in one test) was associated with escape and avoidance behavior of groups; stepwise increases in fearfulness with increasing group size were associated with similar increases in loss of feathers. (Key words: fear, hen, cage, environment, genetic)

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CRAIG ETAL.

the criteria of escape and avoidance behavior, as compared with other stocks (Craig et al., 1983), were either less fearful or failed to differ when judged by the alternative criterion of duration of induced tonic immobility (Craig et al., 1984). The present study evaluated three measures of fear-related behavior in terms of 1) effects of distinct cage environments, 2) genetic stock differences, and 3) associations with plasma corticosteroid concentrations, feather condition and loss, body weight, and egg production.

This study used different samples of birds, but they were hatched, brooded, reared, and placed in cages in the same house and at the same time as those involved in a previous experiment reported by Craig et al. (1986). General information regarding the stocks, rearing and management procedures, and cage housing environments may be obtained from that publication. Genetic Stocks. In brief, genetic stocks were derived from a White Leghorn Randombred population and consisted of strains Yj and Y2, selected alike for increased part-year egg mass, and strains Cj and C2 maintained as unselected controls. Laying House Management Procedures. At 22 weeks of age, pullets were moved into cages with 1, 4, or 6 birds per cage. Birds of the same genetic stock were placed in groups of 12 in random locations within each of the cage environments. This was achieved by using 12 adjacent cages for the single-hen cages, 3 adjacent cages for the 4-hen cages, and 2 adjacent cages for the 6-hen cages. Floor and feeder space per bird for the singlehen, 4-hen, and 6-hen cages were 930 cm2 and 20 cm, 464 cm2 and 10 cm, and 310 cm2 and 5 cm, respectively. Single- and 4-hen cages exceeded and met minimal space requirements, respectively, as defined in Great Britain (Ministry of Agriculture, Fisheries and Food, 1971), whereas the 6-bird cages allowed space indicated as adequate by the United Egg Producers (United Egg Producers, 1982). Behavioral Measures. At 48 weeks of age, two 6-hen and three 4-hen cages in which no mortality had occurred and 6 hens in consecutive cages in each of two single-hen cage sets were identified for each genetic stock. Each multiplehen cage and single-hen cage set representing a genetic stock was from a different group of

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MATERIALS AND METHODS

12 hens allotted to a particular location within the cage-housing environment. Those 144 hens (36 per strain) were used thereafter in obtaining all measurements except mortality. None of the individuals had been handled since housing. Each bird in the 4- and 6-hen cages was identified by a differently colored plastic wing badge. Some badges had turned under the wing; those were realigned with as little disturbance as possible and without removing birds from their cages. The first behavioral test conducted has been described as the "striking the cage" test (Craig et al., 1983). It did not require removing hens from their cages. This measure involves latencies until hungry hens return to feed when confronted with a human who has struck the cage. Details of the test as used in this study follow. 1) The feed trough was covered at 0800 hr after the early morning feeding period (lights were turned on at 0600 hr daily). 2) Testing began at 1400 hr. At the time each cage was tested, the feed was uncovered and the cage was struck on its top three times in rapid succession (for sets of 6 single-hen cages, one hand was used to strike above the partition separating cages 1 and 2 and the other to strike above the partition separating cages 5 and 6). 3) A stopwatch was then started for each hen and the time required to return to the feed trough and begin feeding (the beak touching the feed) was determined. The observer maintained eye contact with as many hens as possible during the test. A maximum of 20 min was allowed; any bird not returning to feed was recorded as responding at 20 min. This test was carried out twice when hens were 48 weeks old with a 3-day interval between tests. The second test was for recovery from induced tonic immobility as indicated by latency to first gross head movement and to "righting". Details of this test have been described by Craig et al. (1984). An attempt was made to test a hen from each genetic stock-cage environment subclass on each day of testing. Individual birds were removed to a separate room for tonic immobility tests. Testing began after the striking the cage test when birds were 48 weeks old. All birds were tested twice during a 2-week period. The third test involved removing one hen at a time to the small room where a metronome test was conducted. Whenever possible, one hen from each genetic group, cage environment subclass was tested on any one day. This test was similar to the striking the cage test, except that

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FEARFUL BEHAVIOR IN CAGED HENS

cation, feather scores and production-related traits were then examined to determine whether they were associated with those measures. Statistical Analysis. Chi-square analyses were used for data from the metronome test and for mortality data because of their "all or none'' characteristics. The general linear model for the analysis of variance was used for all other traits. First, however, latencies to return to "normal behavior" were transformed to log10 seconds for analysis of the striking the cage and tonic immobility data, because frequency distributions for these measures are highly skewed with many small values and long tails to the right (Craig et al., 1983; Kujiyat et al., 1984). Systems of selection and cage and housing environments were considered as fixed effects and strains within systems of selection as random variables. Differences among strains within selection systems should arise primarily because of random genetic drift. Both Y strains were selected on the same criterion and selection differentials were essentially the same in both. No conscious selection was imposed in the C strains. Expected components of mean squares were calculated to determine appropriate error terms. Because experimental units consisted of 6 birds in single and 6-hen cages and of 4 birds in 4-hen cages, different coefficients were used with the estimated variances to calculated standard errors and marginal means for contrasts of treatments, as described by Milliken and Johnson (1984). Computations were carried out by computer using SAS programs (SAS, 1982). RESULTS

Fear-Related Behavior Metronome. In the metronome test, only 29% of all birds responded by reaching the final criterion of feeding within the 20 min allowed (Table 1). Eighty percent took at least one step from their original position (placed facing the front of the cage) and 37% extended their heads above the feed trough. Differences existed among the environments; hens from single-bird cages were more likely to recover as indicated by all three criteria. For heads above the feeder and feeding, hens from multiple-bird cages were almost similar but responded less than hens from single-hen cages. Among genetic stocks, fewer C, hens became mobile as compared with C2 hens. The Y, birds

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a metronome was used as the fear-inducing stimulus, and hens were tested away from their home cage and group. The technique used was as follows. 1) Feed troughs of all groups were covered shortly before 2100 hr (lights were turned off at 2100 hr). 2) Testing was carried out the following morning, beginning at about 0800 hr. A single-hen cage was set up in the testing room with its feed trough covered. 3) The bird to be tested was caught, placed in the test cage, and the door was closed. 4) A metronome on a platform was attached to the cage so that it was immediately beyond the feed trough. 5) The feed was uncovered and the metronome was started, and it beat at the rate of 120 per min. 6) The observer moved 2 m away to a seat to record latency until the bird took its first step, until its head appeared above the feed trough, and until it began to feed. A maximum of 20 min was allowed, and any bird not responding was recorded as responding at 20 min. This testing was done when birds were between 50 and 58 weeks old. Other Measures. All hens were weighed at 58 weeks of age and feather damage and loss was scored by the method of Adams et al. (1978). Egg production was determined by palpating daily for an egg in the uterus over a 15-day period when hens were 58 to 60 weeks old. Preliminary observations indicated that essentially no eggs were laid before 0830 hr and all 144 hens could be palpated and their eggs recorded within a 1-hr period (by a three-person team). Therefore, palpations were carried out beginning at 0730 hr each day of the test period. Corticosteroid concentrations in plasma were obtained from blood samples collected during evening hours when hens were 67 weeks old. The method of blood collecting and assay procedures have been described in detail by Craig and Craig (1985). Unlike the other measures, mortality was calculated for all hens housed in cages (72 per genetic stock and housing environment subclass, 864 birds total). Within-Group Associations. Hens within 6bird groups, i.e., those housed in consecutive single-hen cages or together in 6-hen cages, were classified by pairs according to their status as having the longest, intermediate, or shortest latency to recover in the striking the cage and tonic immobility tests. (Results from the metronome test were excluded because a high proportion of hens failed to return to feed). With the fear-related measures as a treatment classifi-

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CRAIG ETAL. TABLE 1. Effects of cage and housing environments and genetic stock on percentage of bens recovering in the metronome test Percentage of hens recovering1 Became mobile

Head over feed

Began feeding

One hen/cage Four hens/cage Six hens/cage Chi-square test 2

90 69 81

54 25 33

42 23 21

33 47 -14 28 39 -11

28 36 -8 22 28 -6

Genetic stocks C,

58 86 -28** 83 92 -9

c.-c, Y, Y2 Y,

-Y, 1

2

Within a 20-min test period.

Chi-square test based on actual numbers: *P<.05; **P<.01.

showed a nonsignificant tendency, by all three criteria, to respond less than Y2s. Tonic Immobility. Although 13 and 18% of hens did not recover from induced tonic immobility (for righting) in the first and second rounds of testing, respectively, those percentages did not cause sufficient deviations from normal distributions to invalidate analyses of variance. Although there appeared to be a tendency for hens from single-bird cages to regain more rapidly their ability to move as compared with those in 4- and 6-hen cages, differences were not significant (Table 2).

Differences were found between Q and C2 strain pullets; Cj pullets required more time to recover from tonic immobility in both rounds (Table 2). The Y, pullets consistently required more time to recover than did Y2 pullets but only the difference in righting time in the second round attained significance. Selected Y strain pullets did not differ from those of the unselected C strains, and no interactions were found between genetic stocks and cage environments. Striking the Cage Test. Hens in single-bird cages returned more promptly to feed than did those in 4- and 6-hen cages (Table 3).

TABLE 2. Effects of cage and housing environments and genetic stocks on time to recover from induced tonic immobility by two criteria Second test

First test Environments

Head moves

Righting

Head moves

Righting

One hen/cage Four hens/cage Six hens/cage

217 250 223

345 397 379

194 206 306

284 305 421

529 159 370** 211 156 55 108

660 270 390** 388 279 109 281

461 154 307** 229 172 57 250

494 239 255** 510 248 262** -7

Genetic stock

c,

C2 Ci — C2 Y, Y, Y-, - Y s C-Y P<.01.

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Environments

FEARFUL BEHAVIOR IN CAGED HENS TABLE 3. Effects of cage and bousing environments and genetic stock on latency to return to feed in the striking the cage test Latency to begin feeding1 First test

Environments

Second test

, One hen/cage Four hens/cage Six hens/cage

N

55 302 146

18 a 49b 75b

t

**

Genetic stocks

c2 c, - c ,

Y, Y2 Y, - Y ,

35 49 -14 31 50

-19t

1 Time required for hungry hens to return to feeding after cage was struck three times.

**

+

P<.01. P<.10.

The C2 and Y2 strain birds took longer to return to feeding than C, and Y, birds, respectively. However, only the differences between the Y strains approached significance (P = .08 and .10 in the first and second tests, respectively). There was no suggestion of differences

between the means of the C and Y strains in either test, and genetic stock by environment interactions were absent. Measures of General Well-Being and Productivity Cage and housing environments affected • feather scores (P<.01), mortality (P<.05), and differences in egg production for the 15-day palpation period (P = .09) (Table 4). Hens in the 6-bird cages were adversely affected by that environment as compared with those in single-hen and 4-hen cages. Feather damage and loss increased stepwise with increasing group size and decreasing area per bird. Body weights trended nonsignificantly toward smaller values as number of hens per cage increased. Corticosteroid concentrations were essentially equal for birds in single- and 4-hen cages, but those for hens in 6-hen cages were nonsignificantly higher by about 17%. Differences among strains within the unselected C and the selected Y stocks were detected for egg production (C, > C2), feather score (Y, hens had more feathers), and corticosteroid concentrations (Y2 > Y,). Within-Group Associations Hens within experimental groups showed considerable variation in time required to return

TABLE 4. Effects of cage and housing environments and genetic stocks on : measures of well-being and productivity of hens

Environments

One hen/cage Four hens/cage Six hens/cage Genetic stocks

c, c2

c, - c ,

Y, Y2 Y, - Y , 1

Corticosteroids

Body weight

(ng/ml)

(g)

Feather condition score

Mortality

(%)

.93 .94 1.09

1,616 1,579 1,517

8.3a 6.3b 3.6C

2a 5a 15°

60.7 67.0 43.0

.93 .98 -.05 .91 1.13 -.22

1,582 1,501 81t 1,568 1,633 -65

6.0 5.7 .3 6.7 5.8 .9*

5.6 7.8 -2.2 6.1 9.3 -3.2

62.6 47.6 15.0* 59.4 58.2 1.2

t

Mortality data analyzed by chi-square, all other traits by analysis of variance.

*P<.05.

** P<.01. P-C.10.

Egg production 15 days

1

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129 147 -18 107 161 -54t

Ci

2203

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CRAIG ETAL. TABLE 5. Performance of hens for various traits when ranked by pairs within groups of six for latency to feed in the striking the cage test1

Latency duration by pairs

Latency to feed

Corticosteroids

(sec)

(ng/ml)

Body weight

Feather condition score

(g)

Eggs laid in 15 days (no.)

Single-hen cages Longest Intermediate Shortest

92 34 16

.99 .89 .92

Longest Intermediate Shortest

363 99 32

1.06 .95 1.16

1,583 1,678 1,587

8.4 8.2 8.3

8.6 10.3 9.2

3.4 4.1 3.4

7.9 6.8 6.6

Six-hen cages

1 None of the traits measured showed significant associations with latency, i.e., no differences were detected for other traits.

to feeding after their cages were struck (Table 5). However, those in single-hen cages were less variable than those in 6-hen cages; latencies were 92, 34, and 16 sec, respectively, for those ranked by pairs as having the longest, intermediate, and shortest latencies. Comparable figures for the 6-hen cages were 363, 99, and 32 sec. No significant differences associated with ranking were found for corticosteroid concentrations, body weights, feather scores, and number of eggs laid. When hens were ranked by pairs within groups for latency to recover from induced tonic immobility, large differences were found within both single-hen and 6-hen groups (Table 6). Those pairs recovering first required only about one-fifth as long as those pairs recovering most slowly. As was the case in the striking the cage test, no significant associations were found with the other traits among hens ranked on the basis of duration of induced tonic immobility.

DISCUSSION

Tests of Fearfulness Metronome. Hens from single-bird cages were more likely to recover in the 20-min maximum test period than were those from 4and 6-hen cages when they were caught and carried to the small room for the metronome test. This metronome test differs considerably from the metronome tests carried out on birds in their home cages (Craig et al., 1983). When testing in the home cage, hens have no direct

contact with the experimenter. When a hen is caught and restrained for 10 to 15 sec while being carried to and placed in the test cage, the situation becomes more like that used in the tonic immobility test. As a consequence, the results of this test are more like those from the tonic immobility test than they are to the results from the striking the cage test. [The striking the cage test is similar to the metronome test when applied to hens in their home cages (Craig et al., 1983).] The C, hens were less likely to become mobile (therefore, appeared more fearful) than were C2 hens in the metronome test. In the tonic immobility test (see next section), C] hens were clearly more fearful than C 2 hens as indicated by greater latency to recover mobility. Differences between the Y strain hens were not so evident, but Y : hens tended to be less likely to recover in the metronome test and also required longer periods to become mobile in tonic immobility tests. Tonic Immobility. Duration of tonic immobility tended to increase, although nonsignificantly, as group size increased from 1 to 6 hens and floor area decreased from 930 to 310 cm2. These results are similar to those of Kujiyat et al. (1983) in which birds from 5-hen cages had nonsignificantly longer immobility than hens from single-hen cages. However, Kujiyat et al. (1983) found a significant increase in immobility when group size was increased to 17 (but area per hen was about the same as in the 5-hen cages). Hens of the C, stock were clearly more fearful than C2 hens by the standards of the tonic immo-

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1,519 1,516 1,511

FEARFUL BEHAVIOR IN CAGED HENS

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TABLE 6. Performance of hens for various traits when ranked by pairs within groups of six for latency to recover from induced tonic immobility1 Feather condition score

III

Latency duration by pairs

Latency to recover

Corticosteroids

Body weight

(sec)

(ng/ml)

(g)

Longest Intermediate Shortest

535 222 82

.94 .93 .93

1,634 1,655 1,560

8.3 8.3 8.4

8.6 9.3 10.1

Longest Intermediate Shortest

592 237 122

1.11 1.04 1.16

1,550 1,533 1,489

3.8 3.8 3.5

7.9 7.7 5.5

(no.)

None of the traits measured showed significant associations with latency, i.e., no differences were detected for other traits.

bility test, as noted. The Y, hens had consistently longer immobility than Y2 hens. Results from this study and from previous comparisons (Craig et al., 1984) are consistent in terms of strain differences within systems of selection. Both studies are also consistent in failing to find any evidence that successful selection for greater egg mass had any influence on fearfulness, as indicated by the tonic immobility test. Differences found between the strains selected alike are most likely associated with random genetic drift occurring within these moderately inbred lines. Striking the Cage Test. In both rounds of testing, birds in single-hen cages fed more promptly than those in 4- and 6-hen cages. In the second test, the results were especially clear and indicated that hens in single-, 4-, and 6-hen cages returned to feeding in that order. It became obvious that this test may have been biased by feeder space constraints in both 4- and 6-hen cages. Four-hen cages allowed 10 cm of feeder space per bird, but hens in 6-hen cages had only 5 cm. It was observed that although a maximum of 4 hens could feed together at any one time, 1 or more hens could block some portion of the feeder by standing parallel to it. Another problem was that the observer, who also served as a fear-inducing stimulus, occupied less area relative to the feed space available when standing in front of the 6 single-hen cages than when in front of the multiple-hen cages. In earlier studies, hens tended to return first to feeding at both ends of the feed trough, thereby avoiding the fear-inducing object (either a person or a metronome) as much as possible.

Comparisons of the genetic stocks by the striking the cage test revealed tendencies for the C 2 hens to avoid the fear-inducing person longer than the C, hens and for the Y2 hens to be more fearful than the Y, hens. Those results agree with previous findings (Craig et al., 1984; Kujiyat et al., 1984). General. From the results presented, it is clear that the internal state of fearfulness is difficult to measure in terms of outward responses. Murphy (1978) and Duncan (1981) have discussed some practical difficulties in assessing fearfulness. Murphy (1977), in comparing genetic stocks, found that one strain showing more escape and avoidance behavior when confronted by a human, was, nevertheless, less fearful of novel food and unusual objects. Duncan and Filshie (1979), using radio telemetry techniques, compared three strains of chickens and found that a' 'flighty" strain showed much more avoidance and panic to visual stimuli than two "placid" strains. However, the heart rates of the placid birds took longer to return from initially accelerated rates to normal than the heart rates of the so-called flighty strain. Therefore, if heart rate is a suitable measure, behaviorally placid hens may be just as frightened as hens that overtly exhibit more fearful behavior. Genetic stocks having higher levels of escape and avoidance behavior lose more feathers when kept in larger group-size cages (Craig et al., 1983), and those strains that are susceptible to hysteria not only lose more feathers but also have greatly reduced egg production when they reach that state (Elmslie et al., 1966; Hansen,

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1

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CRAIG ETAL.

1976). Possible associations between duration of induced tonic immobility and general wellbeing and productivity are somewhat less evident, although the study of Kujiyat et al. (1984) suggested a possible relationship.

Within-Group Effects of Fearful Behavior Aside from considering the effects of fear-related behavior on groups of hens as indicated by data based on cage means, it is of interest to look at individuals within groups to determine whether their fearfulness is associated with measures of their own general well-being. As Tables 5 and 6 make clear, there is no indication that level of fearfulness, within a group or as an individual, was associated with any other measures.

REFERENCES Adams, A. W., J. V. Craig, and A. L. Bhagwat, 1978. Effects of flock size, age at housing and mating experience on two strains of egg-type chickens in colony cages. Poultry Sci. 57:48-53. Craig, J. V, and J. A. Craig, 1985. Corticosteroid levels in White Leghorn hens as affected by handling, layinghouse environment, and genetic stock. Poultry Sci. 64:809-816. Craig, J. V, T. P. Craig, and A. D. Dayton, 1983. Fearful behavior by caged hens of two genetic stocks. Appl. Anim. Ethol. 10:263-273. Craig, J. Y, J. A. Craig, and J. Vargas Vargas, 1986. Corticosteroids and other indicators of hens' well-being in four laying-house environments. Poultry Sci. 65:856-863. Craig, J. V, S. K. Kujiyat, and A. D. Dayton, 1984. Tonic immobility responses of White Leghorn hens affected by induction techniques and genetic stock differences. Poultry Sci. 63:1-10. Duncan, I.J.H., 1981. Animal rights-animal welfare: a scientist's assessment. Poultry Sci. 60:489-499. Duncan, I.J.H., and J. H. Filshie, 1979. The use of radio telemetry devices to measure temperature and heart rate in domestic fowl. In: A Handbook on Telemetry and Radio Tracking. C. J. Amlaner, and D. W. Macdonald, ed. Pergamon Press, Oxford, England. Edens, F. W., G. A. Martin, and T. W. Carter, 1982. Stress response of two layer stocks in five cage densities compared to floor birds. Poultry Sci. 61:1456. (Abstr.) Elmslie, L. J., R. H. Jones, and D. W. Knight, 1966. A general theory describing the effects of varying flock

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Housing Environment and Genetic Stock Effects Cage and Environment Effects. When a large number of blood samples were used for comparisons of hens in cage environments (11 sets of 36 each, collected over 22 weeks), hens in 6-bird cages had higher plasma corticosteroid concentrations than did those in single- and 4-hen cages, but the latter did not differ from each other (Craig et al., 1986). Results were similar in several (Lei et al, 1972; Edens et al., 1982; Mashaly et al., 1984) but not all (Koelkebeck and Cain, 1984) studies involving caged birds. Plasma corticosteroid concentrations in the present study, obtained after hens had been in cages for 45 wk, showed that hens in 6-bird cages had higher corticosteroid concentrations (although not significantly so) than birds in the single- and 4-hen cages. Hens in the high density, 6-bird cages experienced higher mortality and depressed egg production. However, those in the 1- and 4-hen cages did not differ from each other for either of those measures. Feather loss increased stepwise with increasing numbers of hens per cage; birds in 6-hen cages had considerable areas of exposed skin on their backs and wings, whereas those in 4-bird cages had only moderate loss. When all these measures are considered together, we conclude that birds in the single-hen and moderate density, 4-hen cages were at roughly equivalent levels of well-being and hens in the 6-bird cages were in a relatively adverse environment. Genetic Stock Effects. The C[ and Y, strains, in which hens regained mobility more slowly and, therefore, would be classified as more fearful when tested as individuals in a strange environment, were, nevertheless, the same strains that regained confidence and fed sooner when tested as groups in their home cages. Thus, it is not possible to indicate, in general terms, which of the paired strains (within selection schemes) was more "fearful". The C, strain hens laid more eggs late in the laying year than the C2 hens, suggesting that they were better adapted to cages. The Y! hens, which resembled those of the C, strain in fearfulness criteria, had lower plasma corticosteroid concentrations and

less feather loss than Y2 hens. These results suggest that strains in which hens are more likely to become immobile when confronted with fearinducing stimuli may be somewhat better adapted to life in cages. However, Kujiyat et al. (1984) found that hens from 5-bird cages in which induced tonic immobility persisted longer were less productive. The situation remains confused for cages with group sizes ranging from 1 to 6 hens, even though excessive nervousness and escape behavior is clearly detrimental in cages holding larger numbers of hens at high density (Elmslie et al., 1966; Hansen, 1976; Craig et al, 1983).

FEARFUL BEHAVIOR IN CAGED HENS

of population density on energy utilization, intestinal disaccharides, and adrenal function in hens. Can. J. Anim. Sci. 52:103-112. Mashaly, M. M., M. L. Webb, S. L. Youtz, W B. Roush, and H. B. Graves, 1984. Changes in serum corticosterone concentration of laying hens as a response to increased population density. Poultry Sci. 63:22712274. Milliken, G. A., and D. E. Johnson, 1984. Page 386 in: Analysis of Messy Data. Lifetime Learning Publ., Belmont, CA. Ministry of Agriculture, Fisheries, and Food, 1971. Codes of recommendations for the welfare of livestock. Code No. 3. Domestic fowls. Min. Agric, Fish. Food, London, Engl. Murphy, L. B., 1977. Responses of domestic fowl to novel food and objects. Appl. Anim. Ethol. 3:335-349. Murphy, L. B., 1978. The practical problems of recognizing and measuring fear and exploration behaviour in the domestic fowl. Anim. Behav. 26:422^431. Statistical Analysis Systems Institute. 1982. SAS User's Guide: Statistics. Cary, NC. United Egg Producers, 1982. Recommended guidelines of husbandry practices for laying chickens. 3951 Snapfinger Parkway, Decatur, GA.

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