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Effect of Age and Presence of Perches During Rearing on Tonic Immobility Fear Reactions of Broiler Breeder Pullets1
Effect of Age and Presence of Perches During Rearing on Tonic Immobility Fear Reactions of Broiler Breeder Pullets1 J. BRAKE2 and T. P. KEELEY Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695-7608 R. B. JONES Roslin Institute (Edinburgh), Department of Environment and Welfare, Roslin, Midlothian EH25 9PS, United Kingdom
1994 Poultry Science 73:1470-1474
INTRODUCTION A number of reports have suggested that the provision of perches may improve the productivity and welfare of chickens housed in cages or on the floor. First, the presence of perch poles during the rearing period decreased the incidence of floor laying in medium-weight hybrid layers (Appleby et al, 1983) and broiler breeders (Brake, 1987). Second, the strength of the tibia (Hughes and Appleby, 1989; Duncan et al., 1992) and tarsometatarsal trabecular bone volume (Hughes and Wilson, 1993) were increased in aged laying hens that had been given access to perches. Third, there was a slight trend toward greater weight gain and feed conversion efficiency when broilers housed in pens were
Received for publication January 7, 1994. Accepted for publication May 4, 1994. iTrade names used in this publication do not imply endorsement by the North Carolina Agricultural Research Service of the products mentioned, nor criticism of similar products not mentioned. 2 To whom correspondence should be addressed.
provided with perches (Hughes and Elson, 1977). On the other hand, the effects of perches on egg production by caged hens have been inconsistent, with reports of increased (Ruszler and Quisenberry, 1970), equivalent (Dorminey and Arscott, 1971), or reduced (Tauson, 1984) output. Heightened fearfulness (propensity to be easily frightened) and the elicitation of intense, prolonged, or inappropriate fear reactions can seriously harm the performance and welfare of poultry (Hemsworth and Barnett, 1989; Jones, 1989; Mills and Faure, 1990; Jones et al, 1993). Therefore, it is of interest that Brake (1987) reported a subjective impression that flightiness was reduced in broiler breeder pullets reared in the presence of perches. The objective of the present study was to objectively determine whether the provision of perches during rearing affected a fear-related behavior, namely tonic immobility (TI), in broiler breeder pullets. Tonic immobility is elicited by brief manual restraint, and it is characterized by a temporary state of motor inhibition, loss of the righting response, and reduced responsiveness to
1470
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
ABSTRACT Broiler breeders were housed in pens in an all-litter house with an 8-h photoperiod from hatching to 20 wk of age. They were reared either in the presence or absence of perches (7 cm per bird) and on either a 14% or a 17% CP diet. The duration of the tonic immobility (TI) fear response was measured in 15- and in 20-wk-old birds; each pullet was tested individually and once only. There was an apparent age-related increase in the duration of TI, which was attenuated by the provision of perches during rearing. The results are discussed in terms of maturational and environmental influences on the development and alleviation of fear. (Key words: age, broiler breeder, fear, perches, tonic immobility)
1471
RESEARCH NOTE TABLE 1. Diets during rearing period Dietary CP Ingredient
14%
17%
Corn Soy Wheat midds Limestone Poultry fat Poultry meal Dicalcium phosphate Salt DL-methionine Vitamins, minerals, and medications
67.73 10.46 15.00 1.24 1.00 2.00 1.53 .40 .07
63.58 10.69 15.00 .91 1.00 6.91 .85 .40 .09
.57
.57
MATERIALS AND METHODS Animals and Husbandry Arbor Acres slow-feathering strain broiler breeder females were grown as described by Brake (1987) and Brake and Baughman (1989) with the exceptions detailed below. Pullets were grown in groups of 65 in pens that were either equipped with 7 cm of wooden perch per pullet or left unequipped as controls. Perches were installed on one side of the pen in a configuration similar to that found on a conventional 12-hole nest box. The lower perch was 43 cm above the litter. Although systematic counts of the numbers of birds using the perches were not made, the perches were never observed to be fully
Treatments and Testing Tonic immobility tests were carried out using 15- and 20-wk-old pullets. Five pullets were randomly selected for test from each of two pens per treatment and diet combination when they were 15-wk-old, whereas samples of 13 pullets per each of 8 different pens (2 per treatment per diet combination) were taken at 20 wk of age. Thus, 10 and 26 pullets were tested (at 15 and 20 wk of age, respectively) from each of the following groups: perches +14% CP; no perches +14% CP; perches +17% CP; no perches +17% CP. Each pullet was tested individually and once only. All observations were taken on the afternoon of the "on-feed" day of the skip-a-day feeding program used to rear the birds. Pullets were carried to a separate room for TI testing. Tonic immobility was induced by restraining the bird on its back for 15 s in a U-shaped wooden cradle covered with cloth (Jones and Faure, 1981). One hand lightly cupped the head and the other was placed on the sternum with a downward force of approximately 3.5 kg. Pullets were considered induced into TI if they did not right themselves from the cradle within 10 s of release. The experimenter then retreated, sat 1 m away from and in full view of the bird, and recorded the duration of TI, i.e., the latency from the end of
TABLE 2. Feed allocation and BW of pullets at 15 and 20 wk of age „ Dietary CP
Feed per bird per day — 20 wk 15 wk
(%) 14 17
62 61
BW 15 wk
20 wk
1,158 1,230
2,029 2,020
(g)
95 95
•
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
external stimulation. It is considered to be an anti-predator reaction and to be positively related to the antecedent fear state, that is, the more frightened the bird is when TI is being induced, the longer it will remain immobile when released (Gallup, 1979; Jones, 1986).
occupied, and there was no evidence that the birds slept on the perches. The experimental birds were provided with perches from placement in the pens at hatch until testing ended at 20 wk of age. Pullets were reared at a density of 5.8/m2 and were fed one of two experimental diets shown in Table 1 (2,926 kcal ME/kg). Daily feed allocations and BW at 15 and 20 wk of age are shown in Table 2.
1472
BRAKE ET AL. TABLE 3. Effect of presence of perches during rearing on righting time of broiler breeder pullets after induced tonic immobility Age,1,2
Perches
Dietary CP
(%) With Without
14 14
With Without
17 17
x
(s) — 336 398 367 356 458 407 346 428 387
243 ± 43 217 ± 49 230 ± 32 284 ± 49 284 ± 75 284 ± 40 264 ± 2T2 251 ± 442B 257 ± 26"
±57 ± 60+ ±41 ±49 ± 52+ ± 36 ± 372 ± 392A ± 27 A
A B
- Means in a row across all treatments with no common superscript differ significantly (P £ .01). 'Values represent the x" ± SE of 10 observations at 15 wk and 26 observations at 20 wk of age. 2 Age by perch interaction across diets (P £ .10) when analyzed on a log10 (seconds + 1) basis. f Effect of age within diet (P S .10).
induction until self-righting. A silent unobtrusive observer is thought not to influence TI reactions in the domestic fowl (Jones, 1990). If TI could not be induced after five attempts, the bird was considered not to be susceptible and a score of 0 s was awarded. A ceiling of 15 min per test was set, and a maximum score of 900 s was afforded if the bird failed to right itself during the test period.
vations indicated that no significant effects were discernible on the "no-feed" day, presumably due to an overriding motivation to feed. Therefore, only data from the afternoon of feed days are included in this report. RESULTS
The effects of age, presence of perches, and diet upon TI duration are shown in Table 3. Overall, pullets tested at 20 wk of Statistical Analyses age showed longer TI reactions than did To further delineate discrete effects, the those tested at 15 wk, largely because the effects of age within perch type and the immobility episodes of birds reared witheffect of perch within age were determined out perches were longer at 20 wk. Indeed, by a one-way ANOVA. The data were the longer TI due to increasing age of analyzed using a multi-way ANOVA that birds grown without perches within each employed age, perch type, and diet as main diet approached significance (P < .08). effects using the General Linear Models Analysis on the basis of log10 (seconds + 1) (GLM) procedures of SAS® software (SAS also revealed an age by perch interaction Institute, 1989). The data were also sub- that approached significance (P < .10). jected to a two-way analysis of variance within diet type. Type III sum of squares DISCUSSION was used due to the unbalanced nature of the data. The error term in all cases was The duration of the domestic fowl's based upon variation among birds. The TI tonic immobility response is widely conduration was analyzed on the basis of both sidered to be positively related to the fear seconds and log10 (seconds + 1). The results state elicited at the time of induction were generally similar. Statements of because procedures designed to increase statistical significance were based on P < .05 fear prolong the reaction whereas fearunless otherwise stated. Preliminary obser- reducers attenuate it (Gallup, 1979; Jones,
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
With* Without 3? Overall 5c
20 w k
15 wk
1473
RESEARCH NOTE
one associated with the approach of sexual maturity and the accompanying hormonal events in broiler breeders. It seems to be a permanent change in White Leghorns (Campo and Camicer, 1993). It is of particular interest that this agerelated increase in the duration of the TI fear response was less pronounced in those pullets reared in the presence of perches. The present finding is therefore consistent with Brake's (1987) subjective report that the provision of perches during rearing reduced flightiness in broiler breeder pullets. A recent observation that the provision of low perches to growing meat-type broiler chickens facilitated handling and reduced wing flapping upon capture at 6 wk of age (Newberry and Blair, 1993) provides further support for this hypothesis. Because of the potentially deleterious effects of heightened fearfulness, the apparent fear-reducing effects of perches clearly merit further investigation, not only in broiler breeders but also in other varieties of the domestic fowl maintained under intensive conditions. We must also bear in mind that the present results may be conservative. Individual differences in perching behavior have been reported; some birds will readily perch, some will not (Faure and Jones, 1982). Thus, the possible unconscious inclusion of nonperchers in the present test groups may have diluted the effects of the provision of perches. The apparent sensitivity of the TI response to variables such as age, dietary protein, and the presence of perches sounds an important cautionary note for future investigations of fearfulness in sexually mature birds and in those approaching sexual maturity. ACKNOWLEDGMENTS
R. B. Jones' contribution to this study was commissioned and supported by the U. K. Ministry of Agriculture, Fisheries, and Food and by the Biotechnology and Biological Sciences Research Council.
REFERENCES Appleby, M. C, H. E. McRae, and I.J.H. Duncan, 1983. Nesting and floor-laying by domestic hens: Effects of individual variation in perching behaviour. Behav. Anal. Lett. 3:345-352.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
1986). Further, significant intra-individual correlations have been found in chicks and adult hens between their TI responses and their fear scores estimated in a variety of putatively frightening test situations (Jones and Mills, 1983; Jones, 1987; Jones and Waddington, 1992). These observations suggest that the duration of TI may be a useful index of nonspecific, underlying tearfulness. Broiler breeder pullets tested at 20 wk of age in the present study showed longer TI reactions man their 15-wk-old counterparts. Similar observations have been recently reported in White Leghorns (Campo and Camicer, 1993). This finding may reflect a direct effect of maturation; i.e., a progressive increase in underlying fearfulness with age, although a number of alternative explanations could be offered. First, the larger size and BW of the older birds might have proved a greater impediment to self-righting; that is, a heavier bird might have experienced greater mechanical restraint in the TI cradle. However, although BW might influence the overall effect of age on TI, the presence of an age by perch interaction that approached significance (P < .10), and of age effects (P < .08) within diet and perch treatments, suggest a more fundamental developmental effect. Second, we gained a subjective impression that the pullets were generally less active at 20 than at 15 wk of age. This may, in turn, have increased the likelihood of a passive coping strategy, such as TI, would be more persistent in older than in younger birds. Third, the age-related increase in TI may be associated with the approach of sexual maturity and the birds' changing endocrine state, as suggested by Campo and Camicer (1993). In this context, it is interesting to note that the pullets that received the 17% CP diet showed numerically longer TI durations than did the 14% CP birds. Feeding pullets a 17% rather than a 14% CP diet is known to accelerate their sexual maturity, as evidenced by reduced primary wing feather molt at 18 wk of age (Brake et al, 1992). An assessment of fear in older birds would clarify whether the longer TI found here at 20 wk represented a permanent developmental effect or just a transient
1474
BRAKE ET AL. Jones, R. B., 1987. Assessment of fear in adult laying hens: correlational analysis of methods and measures. Br. Poult. Sci. 28:319-326. Jones, R. B., 1989. Development and alleviation of fear. Pages 123-136 in: Proceedings of the Third European Symposium on Poultry Welfare. J. M. Faure and A. D. Mills, ed. World's Poultry Science Association, Tours, France. Jones, R. B., 1990. Is the experimenter an influential variable in studies of tonic immobility in the domestic fowl? Biol. Behav. 15:93-103. Jones, R. B., and J. M. Faure, 1981. Sex and strain comparisons of tonic immobility ("righting time") in the domestic fowl and the effects of various methods of induction. Behav. Proc. 6: 47-55. Jones, R. B., P. H. Hemsworth, and J. L. Barnett, 1993. Fear of humans and performance in commercial broiler flocks. Pages 292-294 in: Proceedings of the Fourth European Symposium on Poultry Welfare. C. J. Savory and B. O. Hughes, ed. Universities Federation for Animal Welfare, Potters Bar, U.K. Jones, R. S., and A. D. Mills, 1983. Estimation of fear in two lines of the domestic chick: correlation between various methods. Behav. Proc. 8: 243-253. Jones, R. B., and D. Waddington, 1992. Modification of fear in domestic chicks, Gallus gallus domesticu$, via regular handling and early environmental enrichment. Anim. Behav. 43:1021-1033. Mills, A. D., and J. M. Faure, 1990. Panic and hysteria in domestic fowl: A review. Pages 248-272 in: Social Stress in Domestic Animals. R. Zayan and R. Dantzer, ed. Kluwer, Dordrecht, The Netherlands. Newberry, R., and R. Blair, 1993. Perches ease handling of broiler chickens. Pages 270-271 in: Proceedings of the Fourth European Symposium on Poultry Welfare. C. J. Savory and B. O. Hughes, ed. Universities Federation for Animal Welfare, Potters Bar, U.K. Ruszler, P. L., and J. H. Quisenberry, 1970. The effect of perches on various performance factors of caged layers. Poultry Sci. 49:1433.(Abstr.) SAS Institute, 1989. SAS® User's Guide: Statistics. SAS Institute Inc., Cary, NC. Tauson, R., 1984. Effects of a perch in conventional cages for laying hens. Acta Agric. Scand. 34: 193-209.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
Brake, J., 1987. Influence of presence of perches during rearing on incidence of floor laying in broiler breeders. Poultry Sci. 66:1587-1589. Brake, J., and G. R. Baughman, 1989. A comparison of lighting regimens during growth on subsequent seasonal reproductive performance of broiler breeders. Poultry Sci. 68:79-85. Brake, J., T. J. Walsh, and S. E. Scheideler, 1992. Nutritional influences in broiler breeders: frame size, feather drop syndrome, and reproduction. Poultry Sci. 71(Suppl. l):16.(Abstr.) Campo, J. L., and C. Camicer, 1993. Realized heritability of tonic immobility in White Leghorn hens: A replicated single generation test. Poultry Sci. 72:2193-2199. Dorminey, R. W., and G. H. Arscott, 1971. Effects of bird density, nutrient density and perches on the performance of caged White Leghorn layers. Poultry Sci. 50:619-626. Duncan, E. T., M. C. Appleby, and B. O. Hughes, 1992. Effect of perches in laying cages on welfare and production of hens. Br. Poult. Sci. 33:25-35. Faure, J. M., and R. B. Jones, 1982. Effects of age, access and time of day on perching behaviour in the domestic fowl. Appl. Anim. Ethol. 8: 357-364. Gallup, G. G., Jr., 1979. Tonic immobility as a measure of fear in domestic fowl. Anim. Behav. 27:316-317. Hemsworth, P. H., and J. L. Barnett, 1989. Relationships between fear of humans, productivity and cage position of laying hens. Br. Poult. Sci. 30: 505-518. Hughes, B. O., and M. C. Appleby, 1989. Increase in bone strength of spent laying hens housed in modified cages with perches. Vet. Rec. 124: 483-484. Hughes, B. O., and H. A. Elson, 1977. The use of perches by broilers in floor pens. Br. Poult. Sci. 18:715-722. Hughes, B. O., and S. Wilson, 1993. Comparison of bone volume and strength as measures of skeletal integrity in caged laying hens with access to perches. Res. Vet. Sci. 54:202-206. Jones, R. B., 1986. The tonic immobility reaction of the domestic fowl: a review. World's Poult. Sci. J. 42:82-96.
1994 Poultry Science 73:1470-1474
INTRODUCTION A number of reports have suggested that the provision of perches may improve the productivity and welfare of chickens housed in cages or on the floor. First, the presence of perch poles during the rearing period decreased the incidence of floor laying in medium-weight hybrid layers (Appleby et al, 1983) and broiler breeders (Brake, 1987). Second, the strength of the tibia (Hughes and Appleby, 1989; Duncan et al., 1992) and tarsometatarsal trabecular bone volume (Hughes and Wilson, 1993) were increased in aged laying hens that had been given access to perches. Third, there was a slight trend toward greater weight gain and feed conversion efficiency when broilers housed in pens were
Received for publication January 7, 1994. Accepted for publication May 4, 1994. iTrade names used in this publication do not imply endorsement by the North Carolina Agricultural Research Service of the products mentioned, nor criticism of similar products not mentioned. 2 To whom correspondence should be addressed.
provided with perches (Hughes and Elson, 1977). On the other hand, the effects of perches on egg production by caged hens have been inconsistent, with reports of increased (Ruszler and Quisenberry, 1970), equivalent (Dorminey and Arscott, 1971), or reduced (Tauson, 1984) output. Heightened fearfulness (propensity to be easily frightened) and the elicitation of intense, prolonged, or inappropriate fear reactions can seriously harm the performance and welfare of poultry (Hemsworth and Barnett, 1989; Jones, 1989; Mills and Faure, 1990; Jones et al, 1993). Therefore, it is of interest that Brake (1987) reported a subjective impression that flightiness was reduced in broiler breeder pullets reared in the presence of perches. The objective of the present study was to objectively determine whether the provision of perches during rearing affected a fear-related behavior, namely tonic immobility (TI), in broiler breeder pullets. Tonic immobility is elicited by brief manual restraint, and it is characterized by a temporary state of motor inhibition, loss of the righting response, and reduced responsiveness to
1470
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
ABSTRACT Broiler breeders were housed in pens in an all-litter house with an 8-h photoperiod from hatching to 20 wk of age. They were reared either in the presence or absence of perches (7 cm per bird) and on either a 14% or a 17% CP diet. The duration of the tonic immobility (TI) fear response was measured in 15- and in 20-wk-old birds; each pullet was tested individually and once only. There was an apparent age-related increase in the duration of TI, which was attenuated by the provision of perches during rearing. The results are discussed in terms of maturational and environmental influences on the development and alleviation of fear. (Key words: age, broiler breeder, fear, perches, tonic immobility)
1471
RESEARCH NOTE TABLE 1. Diets during rearing period Dietary CP Ingredient
14%
17%
Corn Soy Wheat midds Limestone Poultry fat Poultry meal Dicalcium phosphate Salt DL-methionine Vitamins, minerals, and medications
67.73 10.46 15.00 1.24 1.00 2.00 1.53 .40 .07
63.58 10.69 15.00 .91 1.00 6.91 .85 .40 .09
.57
.57
MATERIALS AND METHODS Animals and Husbandry Arbor Acres slow-feathering strain broiler breeder females were grown as described by Brake (1987) and Brake and Baughman (1989) with the exceptions detailed below. Pullets were grown in groups of 65 in pens that were either equipped with 7 cm of wooden perch per pullet or left unequipped as controls. Perches were installed on one side of the pen in a configuration similar to that found on a conventional 12-hole nest box. The lower perch was 43 cm above the litter. Although systematic counts of the numbers of birds using the perches were not made, the perches were never observed to be fully
Treatments and Testing Tonic immobility tests were carried out using 15- and 20-wk-old pullets. Five pullets were randomly selected for test from each of two pens per treatment and diet combination when they were 15-wk-old, whereas samples of 13 pullets per each of 8 different pens (2 per treatment per diet combination) were taken at 20 wk of age. Thus, 10 and 26 pullets were tested (at 15 and 20 wk of age, respectively) from each of the following groups: perches +14% CP; no perches +14% CP; perches +17% CP; no perches +17% CP. Each pullet was tested individually and once only. All observations were taken on the afternoon of the "on-feed" day of the skip-a-day feeding program used to rear the birds. Pullets were carried to a separate room for TI testing. Tonic immobility was induced by restraining the bird on its back for 15 s in a U-shaped wooden cradle covered with cloth (Jones and Faure, 1981). One hand lightly cupped the head and the other was placed on the sternum with a downward force of approximately 3.5 kg. Pullets were considered induced into TI if they did not right themselves from the cradle within 10 s of release. The experimenter then retreated, sat 1 m away from and in full view of the bird, and recorded the duration of TI, i.e., the latency from the end of
TABLE 2. Feed allocation and BW of pullets at 15 and 20 wk of age „ Dietary CP
Feed per bird per day — 20 wk 15 wk
(%) 14 17
62 61
BW 15 wk
20 wk
1,158 1,230
2,029 2,020
(g)
95 95
•
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
external stimulation. It is considered to be an anti-predator reaction and to be positively related to the antecedent fear state, that is, the more frightened the bird is when TI is being induced, the longer it will remain immobile when released (Gallup, 1979; Jones, 1986).
occupied, and there was no evidence that the birds slept on the perches. The experimental birds were provided with perches from placement in the pens at hatch until testing ended at 20 wk of age. Pullets were reared at a density of 5.8/m2 and were fed one of two experimental diets shown in Table 1 (2,926 kcal ME/kg). Daily feed allocations and BW at 15 and 20 wk of age are shown in Table 2.
1472
BRAKE ET AL. TABLE 3. Effect of presence of perches during rearing on righting time of broiler breeder pullets after induced tonic immobility Age,1,2
Perches
Dietary CP
(%) With Without
14 14
With Without
17 17
x
(s) — 336 398 367 356 458 407 346 428 387
243 ± 43 217 ± 49 230 ± 32 284 ± 49 284 ± 75 284 ± 40 264 ± 2T2 251 ± 442B 257 ± 26"
±57 ± 60+ ±41 ±49 ± 52+ ± 36 ± 372 ± 392A ± 27 A
A B
- Means in a row across all treatments with no common superscript differ significantly (P £ .01). 'Values represent the x" ± SE of 10 observations at 15 wk and 26 observations at 20 wk of age. 2 Age by perch interaction across diets (P £ .10) when analyzed on a log10 (seconds + 1) basis. f Effect of age within diet (P S .10).
induction until self-righting. A silent unobtrusive observer is thought not to influence TI reactions in the domestic fowl (Jones, 1990). If TI could not be induced after five attempts, the bird was considered not to be susceptible and a score of 0 s was awarded. A ceiling of 15 min per test was set, and a maximum score of 900 s was afforded if the bird failed to right itself during the test period.
vations indicated that no significant effects were discernible on the "no-feed" day, presumably due to an overriding motivation to feed. Therefore, only data from the afternoon of feed days are included in this report. RESULTS
The effects of age, presence of perches, and diet upon TI duration are shown in Table 3. Overall, pullets tested at 20 wk of Statistical Analyses age showed longer TI reactions than did To further delineate discrete effects, the those tested at 15 wk, largely because the effects of age within perch type and the immobility episodes of birds reared witheffect of perch within age were determined out perches were longer at 20 wk. Indeed, by a one-way ANOVA. The data were the longer TI due to increasing age of analyzed using a multi-way ANOVA that birds grown without perches within each employed age, perch type, and diet as main diet approached significance (P < .08). effects using the General Linear Models Analysis on the basis of log10 (seconds + 1) (GLM) procedures of SAS® software (SAS also revealed an age by perch interaction Institute, 1989). The data were also sub- that approached significance (P < .10). jected to a two-way analysis of variance within diet type. Type III sum of squares DISCUSSION was used due to the unbalanced nature of the data. The error term in all cases was The duration of the domestic fowl's based upon variation among birds. The TI tonic immobility response is widely conduration was analyzed on the basis of both sidered to be positively related to the fear seconds and log10 (seconds + 1). The results state elicited at the time of induction were generally similar. Statements of because procedures designed to increase statistical significance were based on P < .05 fear prolong the reaction whereas fearunless otherwise stated. Preliminary obser- reducers attenuate it (Gallup, 1979; Jones,
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
With* Without 3? Overall 5c
20 w k
15 wk
1473
RESEARCH NOTE
one associated with the approach of sexual maturity and the accompanying hormonal events in broiler breeders. It seems to be a permanent change in White Leghorns (Campo and Camicer, 1993). It is of particular interest that this agerelated increase in the duration of the TI fear response was less pronounced in those pullets reared in the presence of perches. The present finding is therefore consistent with Brake's (1987) subjective report that the provision of perches during rearing reduced flightiness in broiler breeder pullets. A recent observation that the provision of low perches to growing meat-type broiler chickens facilitated handling and reduced wing flapping upon capture at 6 wk of age (Newberry and Blair, 1993) provides further support for this hypothesis. Because of the potentially deleterious effects of heightened fearfulness, the apparent fear-reducing effects of perches clearly merit further investigation, not only in broiler breeders but also in other varieties of the domestic fowl maintained under intensive conditions. We must also bear in mind that the present results may be conservative. Individual differences in perching behavior have been reported; some birds will readily perch, some will not (Faure and Jones, 1982). Thus, the possible unconscious inclusion of nonperchers in the present test groups may have diluted the effects of the provision of perches. The apparent sensitivity of the TI response to variables such as age, dietary protein, and the presence of perches sounds an important cautionary note for future investigations of fearfulness in sexually mature birds and in those approaching sexual maturity. ACKNOWLEDGMENTS
R. B. Jones' contribution to this study was commissioned and supported by the U. K. Ministry of Agriculture, Fisheries, and Food and by the Biotechnology and Biological Sciences Research Council.
REFERENCES Appleby, M. C, H. E. McRae, and I.J.H. Duncan, 1983. Nesting and floor-laying by domestic hens: Effects of individual variation in perching behaviour. Behav. Anal. Lett. 3:345-352.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 24, 2015
1986). Further, significant intra-individual correlations have been found in chicks and adult hens between their TI responses and their fear scores estimated in a variety of putatively frightening test situations (Jones and Mills, 1983; Jones, 1987; Jones and Waddington, 1992). These observations suggest that the duration of TI may be a useful index of nonspecific, underlying tearfulness. Broiler breeder pullets tested at 20 wk of age in the present study showed longer TI reactions man their 15-wk-old counterparts. Similar observations have been recently reported in White Leghorns (Campo and Camicer, 1993). This finding may reflect a direct effect of maturation; i.e., a progressive increase in underlying fearfulness with age, although a number of alternative explanations could be offered. First, the larger size and BW of the older birds might have proved a greater impediment to self-righting; that is, a heavier bird might have experienced greater mechanical restraint in the TI cradle. However, although BW might influence the overall effect of age on TI, the presence of an age by perch interaction that approached significance (P < .10), and of age effects (P < .08) within diet and perch treatments, suggest a more fundamental developmental effect. Second, we gained a subjective impression that the pullets were generally less active at 20 than at 15 wk of age. This may, in turn, have increased the likelihood of a passive coping strategy, such as TI, would be more persistent in older than in younger birds. Third, the age-related increase in TI may be associated with the approach of sexual maturity and the birds' changing endocrine state, as suggested by Campo and Camicer (1993). In this context, it is interesting to note that the pullets that received the 17% CP diet showed numerically longer TI durations than did the 14% CP birds. Feeding pullets a 17% rather than a 14% CP diet is known to accelerate their sexual maturity, as evidenced by reduced primary wing feather molt at 18 wk of age (Brake et al, 1992). An assessment of fear in older birds would clarify whether the longer TI found here at 20 wk represented a permanent developmental effect or just a transient
1474
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