Beak Trimming and Sex Effects on Behavior and Performance Traits of Large White Turkeys D. L. CUNNINGHAM, R. J. BUHR, and M. MAMPUTU Department of Poultry Science, The University of Georgia, Athens, Georgia 30602
1992 Poultry Science 71:1606-1614
INTRODUCTION Beak trimming is a management practice that has long been employed by poultry producers to reduce the deleterious effects of cannibalism and feather pecking. It is, however, a practice that has been severely criticized from an animal welfare perspective and one that continues to represent an emotionally sensitive and potentially difficult issue for the poultry industry. It is a practice that needs further investigation to evaluate alternatives and to address welfare concerns from a scientific perspective.
Received for publication February 10, 1992. Accepted for publication June 18, 1992.
Generally, studies of beak trimming in poultry have concentrated on the effects of this procedure on production and performance traits. Recent work by several authors (Gentle et al, 1982; Duncan et al, 1989; Lee and Craig, 1990,1991; Craig and Lee, 1990; Kuo et al, 1991), have demonstrated significant changes in feeding and drinking behaviors following beak trimming with chickens. Although beak trimming is a routine procedure employed throughout the turkey industry, only a few studies have investigated the effects of this procedure on the behavioral and performance criteria for this species (Denbow et al, 1984; Leighton et al, 1985). The purpose of the current study was to evaluate further the effects of beak trimming on certain behavioral and perfor-
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ABSTRACT The effects of beak trimming at day old on performance and behavioral activities of male and female Large White turkeys were evaluated. One hundred and twenty poults of each sex were evenly assigned to 20 treatment pens and evaluated for body weight, feed usage, and livability characteristics to 18 wk of age. Behavioral observations were conducted for feeding, drinking, sleeping, huddling, resting, and agonistic activities. Beak trirnming affected body weight and feed usage levels for the sexes differently. From 6 wk, trimmed males were significantly heavier than untrimmed males, whereas untrimmed females were heavier than trimmed females from 12 wk. Similar to body weights, feed usage levels from 13 to 18 wk were higher for trimmed males compared with untrimmed males and lower for trimmed females compared with untrimmed females. Feed conversion ratios after 12 wk and survival to 18 wk were not affected by trirnming treatment. Livability rates, however, were lowest for untrimmed males and highest for untrimmed females. Effects on behavioral activities were confined primarily to the brooding and early rearing phases. Beak trimming reduced feeding activity of females and drinking activity of both males and females during the first 2 wk. Sleeping, huddling, and resting activities were increased by beak trimming for both sexes during brooding. Agonistic acts were reduced by beak trimming main effect at 3 and 6 wk. Trimmed males committed fewer agonistic acts at 6 wk than untrimmed males. (Key words: beak trimming, sex, behavior, performance, turkeys)
BEAK TRIMMING AND SEX EFFECTS ON TURKEYS
mance traits of Large White male and female turkeys grown in confinement. MATERIALS AND METHODS
ing all birds in each replicate group on a 3-wk basis to 18 wk of age. In addition, feed usage was recorded per replicate for each 3-wk interval. Mortality was recorded on a daily basis. Behavioral activities were evaluated by observing each replicate group for a 15-min period four times a week during Weeks 1, 2, 3, 6, 12, and 18. Behavioral activities recorded during Weeks 1, 2, and 3 (brooding period) were feeding, drinking, sleeping, huddling, and resting. Behavioral activities recorded postbrooding were feeding, drinking, resting, and agonistic acts. Feeding and drinking behaviors were determined by recording the number of individual birds observed to be in the act of feeding or drinking at 5-min intervals during the observation sessions. Sleeping, huddling, and resting behaviors were recorded in the same manner. Individual poults were considered to be sleeping if they were observed in a crouched position with their eyes closed. Poults in a crouched position but with their eyes open were considered resting. Huddling activity was defined as two or more individuals in crouched positions with body contact. These behaviors were evaluated as possible indicators of differing responses to trimming treatments. The total agonistic acts (i.e., head pecks, fights, threats, and avoidance) committed were recorded for each replicate for each observational sessions. The data were analyzed by time periods using a 2 x 2 factorial arrangement of treatments (Steel and Torrie, 1960). When significant interactions were indicated, the data were analyzed within sex for each time period. The behavioral activities of feeding, drinking, sleeping, resting, and huddling were expressed as percentages with square root transformations applied prior to analyses. Logarithmic transformations were applied to the means for agonistic acts prior to analysis. Unless otherwise stated, significance refers to P < .05. RESULTS Body Weights and Livability
iBio-Beaker, Sterwin Laboratories, Inc., Millsboro, DE 19966. 2 B.U.T.A. Brooding Guide, British United Turkeys of America, P.O. Box 727, Lewisburg, WV 24901.
Body weights were not significantly affected by treatments during the first 3 wk of the study (Table 1). However, by 6 wk of
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One hundred and twenty Large White male and 120 Large White female turkeys of the Nicholas strain were used in the present study. The experimental design consisted of two beak-trimming treatments (trimmed versus untrimmed) for both sexes in a 2 x 2 factorial arrangement. Beak trimming was done at day old in a commercial hatchery using an electronic beak trimmer,1 which uses a high voltage electrical current to burn a small hole through the upper beak. The beak tip falls off after 3 to 7 days, leaving approximately two-thirds of the beak intact. Twelve males and 12 females were each assigned to 1 of 20 treatment pens measuring 1.37 x 1.52 m at Day 1. The poults were brooded using a combination of infrared heat lamps and forced-air furnaces. Standard brooding temperatures2 for turkeys were used for the first 3 wk, after which artificial heating was terminated. The lighting program consisted of 23 h of incandescent light followed by 1 h of darkness to 6 wk of age. At 6 wk the lighting was changed to 16 h of light and 8 h of darkness. Feed and water were provided for ad libitum consumption by the use of a single round tube feeder and a single bell drinker for each treatment group. During the 1st wk additional jar drinkers and feeder lids were used to start the poults eating and drinking quickly. The diets fed were standard University of Georgia starting, growing, and finishing turkey diets. The diets were fed as crumbles until 8 wk of age and then as pellets to the end of the study. Crude protein and metabolizable energy levels, respectively, for the diets ranged from 28% and 3,025 kcal/kg for the starter diet to 15% and 3,423 kcal/kg for the finisher diet. Performance data were evaluated for growth rate, feed usage, and mortality. Growth rates were determined by weigh-
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CUNNINGHAM ET AL.
kg and 9.23 versus 9.53 kg, respectively). A significant sex effect for livability was also observed (Table 1). Females had a higher percentage of birds reaching market age than did males (88.4 versus 81.7%) and trimming had no significant effect on livability. Feed Usage and Feed Conversion
Sex had significant effects on both feed usage and feed conversion values throughout most of the study (Table 1). Differences in treatments were observed by 6 wk of age when both trimmed and untrimmed males were eating significantly (P < .01) more feed than either trimmed or untrimmed females. Differences in trimming treatments, however, were not observed until 13 to 18 wk, during which significant sex by trim-
TABLE 1. Effects of sex and beak treatment on body weight, livability, feed usage, and feed conversion from 0 to 18 wk of age for Large White turkeys
Comparisons
0 to 3 wk 4 to 6 wk
Age 7 to 12 wk 13 to 18 wk 0 to 18 wk
Bi Ddy
Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
weigh*•
(%)
flrt-V
.61 .58
2.13** 1.96
7.48** 6.36
12.22** 9.38
81.7* 88.4
.61 .58
2.09 2.01
6.94 6.90
10.84 10.76
85.0 85.0
*
* * Feed usage (kg per bird) —
.76 .71
1.90" 1.63
13.55** 11.49
18.97** 14.30
35.18** 28.20
.75 .72
1.74 1.78
12.53 12.71
16.75 16.52
31.57 31.73
*
*
- Feed conversioi[1 Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
Livability (0 to 18 wk)
^Kg.K.g;
1.39 1.40
1.25* 1.17
2.54* 2.62
3.99** 4.74
2.89** 3.03
1.39 1.40
1.17* 1.25
2.55* 2.60
4.37 4.37
2.94 2.98
*
*
*
Represents body weight at end of time period. *P < .05. **P < .01.
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age significant (P < .01) sex effects as well as significant sex by trimming interaction effects were observed. Because of the significant interactions between main effects, body weights were presented by treatment groups (Table 2). By 6 wk of age, beaktrimmed males were significantly heavier (10.9%) than untrimmed males (2.24 versus 2.02 kg). Beak-trimmed males were consistently heavier than untrimmed males through the remainder of the study; their weight differential increased to .45 kg by 18 wk (12.45 versus 12.00 kg). Significant differences between trimmed and untrimmed females for body weights were not observed until 12 wk of age. In contrast to body weights of trimmed and untrimmed males, trimmed females weighed significantly less at 12 and 18 wk than their untrimmed counterparts (6.24 versus 6.48
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BEAK TRIMMING AND SEX EFFECTS ON TURKEYS TABLE 2. Treatment means for body weight, feed usage, and feed conversion of Large White turkeys in which sex and beak treatment interacted
Sex Male Female
Female
Male Female
0 to 3 wk
4 to 6 wk 2.24* 2.02 1.93 2.00
Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed
1.36* 1.41 1.41 1.38
Age 7 to 12 wk
13 to 18 wk 0 to 18 wk
7.63* 12.45* 7.32 12.00 6.24* 9.23* 6.48 9.53 • Feed usage (kg per bird) 19.50* 18.44 14.00* 14.60
1.18* 1.32 1.16 1.17
35.56* 34.82 27.50* 28.91
2.48* 2.59 2.62 2.61
Represents body weight at end of time period. •Means within sex are significantly different (P < .05).
ming interactions were observed (Table 2). During this period, trimmed males ate significantly more feed than untrimmed males (19.5 versus 18.44 kg per bird), whereas trimmed females ate significantly less feed than untrimmed females (14.0 versus 14.6 kg per bird). The significant sex by trimming interactions observed for 13 to 18 wk were large enough to effect the feed usage results for the entire study (0 to 18 wk) in the same manner. Significant sex and trimming main effects for feed conversions were present by 4 to 6 wk (Table 1) during which males and untrimmed poults had poorer values than females and trimmed poults. This situation changed, however, by 12 wk of age, when males demonstrated better weight gain to feed usage ratios (2.54 versus 2.62 kg:kg) than females. This sex effect for feed conversion performance remained to the end of the study, with males averaging a 2.89 kg:kg value compared with a ratio of 3.03 kg:kg for females. Significant interaction effects were present during the first 12 wk of the study for feed conversion. Trimmed males had significantly better feed conversion ratios than untrimmed males during the first 12 wk of the study but differences between females were not
present (Table 2). During the period of 13 to 18 wk, however, significant differences for feed conversion values between trimmed and untrimmed males were not observed, and, as a result, differences for the entire study were not present (2.87 versus 2.91 kg: kg).
Feeding and Drinking Activities Significant differences for feeding and drinking activities were observed for the first 2 wk of brooding (Tables 3 and 4). Untrimmed females were observed feeding more frequently (16.0 and 15.2% versus an average of 6.8%) than trimmed females (Table 4) during Weeks 1 and 2. By Week 3, differences in feeding activity were no longer present and all treatment groups demonstrated the same levels of activity to the end of the study. Untrimmed females were also observed drinking more frequently than trimmed females during Week 1 (14.3 versus 4.6%). During Week 2, untrimmed poults drank more frequently than trimmed poults (4.3 versus 2.4%). Similar to feeding activity, however, differences in drinking activity were not observed from 3 wk.
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Male
Beak treatment
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Sleeping, Huddling, and Resting Activity
TABLE 3. Effects of sex and beak treatment of feeding, drinking, sleeping, and huddling activity of Large White turkeys Age Comparisons Sex Males Females Beak treatment Trimmed Untrimmed Interaction Sex x beak Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
2 wk
3 wk
6 wk
12 wk
18 wk
8.5 8.4
8.5 11.0
11.2 12.6
6.2 7.3
8.9 9.0
7.7 7A
7.5* 12.3
7.6* 11.9
11.6 12.2
7.8 5.8
9.7 8.3
7.5 7.6
*
•f-
1 wk
4.3* 11.6
3.6 3.1
2.3 2.6
2.8 2.7
4.4 4.6
6.0 5.0
4.4* 9.4
2.4* 4.3
2.0 2.9
2.6 2.9
4.5 4.7
5.4 5.7
* C1nnni«A
Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
44.6 42.2
36.4* 27.3
29.4 27.2
47.9* 38.9
34.3* 29.4
28.8 27.9
*
*
n^4-^Trif^T
fO/
\
WiiHHlino- ar+ivifv (%.\
Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak *P < .05. **P < .01.
38.9* 27.2
31.7* 19.8
41.4* 26.0
38.4* 27.7
26.8 24.7
41.1* 26.3
*
**
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Sleeping and huddling activities were significantly affected by sex and trirnming treatments during the brooding period (Table 3). Trimmed males and trimmed females slept more frequently (48.0 and 47.7% versus 41.2 and 36.7%, respectively) than untrimmed males and females during Week 1 (Table 4). During Week 2, trimmed males continued to sleep more frequently than untrimmed males (39.9 versus 32.9%),
but differences were not observed between female treatment groups. During Week 3, sleeping activities were the same for all groups. Male poults and beak-trimmed poults had significantly increased huddling activity during the brooding period (Tables 3 and 4). The only exception to this observation occurred during Week 2, when trimmed and untrimmed females had the same levels of huddling activity. Differences in levels of resting activity were observed throughout the 18 wk study (Table 5). Significant (P < .01) sex effects and
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BEAK TRIMMING AND SEX EFFECTS ON TURKEYS
TABLE 4. Treatment means for feeding, drinking, sleeping, and huddling activity of Large White turkeys in which sex and beak treatment interacted
Sex
Male Female
1 wk
2 wk
Trimmed Untrimmed Trimmed Untrimmed
8.3 8.6 6.7* 16.0
8.3 8.6 6.8* 15.2
Trimmed Untrimmed Trimmed Untrimmed
4.2 4.4 4.6* 14.3
Trimmed Untrimmed Trimmed Untrimmed
48.0* 41.2 47.7* 36.7
Age 3 wk 6 wk Feeding activity (%)
12 wk
18 wk
Drinking activity (%) Male Female
Sleeping activity (%) Male Female
39.9* 32.9 28.6 25.9
35.0* 28.3 18.6 Female 21.0 *Means within sex differ significantly (P < .05). **Means within sex differ significantly (P < .01). Male
Trimmed Untrimmed Trimmed Untrimmed
Huddling activity (%) 44.6* 38.1 37.5** 14.5
significant (P < .05) trimming main effects were observed as early as Week 1, when males rested more often than females (60.8 versus 49.4%) and trimmed poults rested more often than untrimmed poults (57.3 versus 52.9%). Significant interactions between main effects were present during Weeks 1 to 3. Trimmed females rested more frequently than untrimmed at Week 1, however, differences between trimmed and untrimmed males were not observed until Week 2 (Table 6). The effects of beak trimming on resting activity remained through Week 6 of the study but were no longer present by Week 12. The significant sex effect for resting activity remained throughout the study.
or trimmed counterparts (Table 5). At 6 wk of age, a significant sex by trimming interaction was present; more agonistic acts were committed by untrimmed males than trimmed males and more agonistic acts were committed by trimmed females than untrimmed females (Table 6). By 12 wk, only sex differences for agonistic acts were present, with males committing more acts than females, and by 18 wk no differences were observed for any of the treatments. Overall, untrimmed males committed more agonistic acts than trimmed males whereas trimmed and untrimmed females committed the same level of agonistic acts.
Agonistic Behavior
Beak trimming resulted in significant effects on body weight and feed usage values. By 6 wk of age, beak-trimmed males were .22 kg heavier than untrimmed males. This difference in body weight remained to the end of the study, when trimmed males weighed .45 kg more
Significant sex and beak trimming main effects on agonistic activity were observed early in the study, when 3-wk-old males and untrimmed females committed significantly more agonistic acts than their female
DISCUSSION
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Beak treatment
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TABLE 5. Effects of sex and beak trimming on resting and agonistic activity from 1 to 18 weeks of age for Large White turkeys
Comparison
1 wk
2 wk
3 wk
Age 6 wk
12 wk
18 wk
3 to 18 wk
Resting activity (%) Sex
60.8*' 49.4
55.4*' 43.2
56.4*' 40.6
68.6*' 56.5
68.2*' 51.3
62.6* 53.7
57.3* 52.9
53.6* 45.0
58.7* 38.3
66.5* 58.7
58.2 61.3
57.0 59.3
Agonistic activity (acts per bird per hour) Sex
Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
4.0* 3.0
5.2* 4.4
1.1* .5
.5 .3
2.68 2.11
2.7* 4.4
3.8* 5.8
.7
.4 .4
1.93* 2.87
*P < .05. **P < .01.
than untrimmed males. Trimmed and untrimmed females were not different for body weight until 12 wk but, contrary to the males, trimmed females weighed less than their untrimmed counterparts. Similar to body weights, feed usage was greater for trimmed males but was significantly less for trimmed females. These results contrast somewhat to those of Denbow et al. (1984), who reported no significant differences between trimmed and untrimmed turkey males for body weights but, nevertheless, reported greater feed intake for trimmed males. The results in the current study are, however, in agreement with those of Leighton et al. (1985), who reported significant reductions in body weights for trimmed female turkeys along with lower feed intake values. Feed conversion or feed efficiency values were not affected by trimming treatment in these studies. Most studies of beak trimming for the domestic fowl have reported evidence of reduced body weights and feed intake immediately following trimming, but these are traits for which contradictory results have been reported (Cunningham, 1992). The results in the current study and those of Denbow
et al. (1984) and Leighton et al. (1985) suggest that the effects of beak trimming on these traits for turkeys are manifest primarily during the later stages of growth and are different for the sexes. Several recent studies have suggested that beak trimming results in perceptible pain to chickens, as evidenced by changes in certain behavioral activities (Duncan et al, 1989; Gentle et al, 1990; Lee and Craig, 1990; Kuo et al, 1991). These studies have reported significant decreases in activities such as feeding, drinking, and preening and increases in the amount of time spent standing inactive and crouching. Feeding and drinking activities were affected by trimming during the first 2 wk of the current study. Untrimmed females were observed feeding more frequently than trimmed females, whereas significant differences for males were not observed. Trimmed poults drank less frequently than untrimmed poults during Weeks 1 and 2 regardless of sex. There were no significant differences for feeding or drinking activity beyond 2 wk of age. These results are similar to those of Duncan et al. (1989), who reported reductions in feeding and drinking activities for
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Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
BEAK TRIMMING AND SEX EFFECTS ON TURKEYS
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TABLE 6. Treatment means for resting and agonistic activity of Large White turkeys in which sex and beak treatment interacted
Sex
Beak treatment
1 wk
2 wk
3 wk
Ag 6 wk
12 wk
18 wk
3 to 18 wk
Resting activity (%) Male
61.6 60.0 53.0* 45.8
58.8* 52.0 48.4* 38.0
63.9** 48.8 Female 53.5* 27.7 Agonistic activity (acts per bird per hour) Male Trimmed 2.93* Untrimmed 7.43 Female Trimmed 4.63 Untrimmed 4.16 'Means within sex differ significantly (P < .05). **Means within sex differ significantly (P < .01).
3 w k following beak trimming of 16-wk-old chickens and with the results of Lee and Craig (1990), who reported that pullets trimmed at 4 wk spent less time feeding for 3 wk following trimming. Gentle et al. (1990), on the other hand, reported changes in drinking behavior lasting as long as 6 wk posttrimming for 16-wk-old Brown Leghorn hens. Time spent sleeping, huddling, and resting (measures of inactivity) were significantly increased during brooding for males and trimmed poults. Duncan et al. (1989) also found an increase in time spent sitting and dozing for Leghorns immediately following trimming, but these activities returned to normal levels by 5 wk posttrimming. Resting activity remained significantly higher for trimmed poults through 6 wk of age. Beyond 6 wk, resting activity was only affected by sex, with males resting more frequently than females. Eskeland (1981) and Lee and Craig (1990) also reported reductions in bird activities following trimming. These results suggest some response to pain as a result of beak trimming may have been present early in the current study but any perception of pain as assessed by these behaviors was confined to the brooding or early rearing periods. Agonistic acts w e r e significantly reduced for females at 3, 6, and 12 wk and by beak trimming at 3 and 6 wk. Agonistic
1.90* 3.45 1.95 2.28
activities were at their highest levels at 3 and 6 wk of the study but beyond 6 wk of age agonistic activities were very low and not affected by trimming treatment. These results agree with those of Denbow et al. (1984) and Leighton et al. (1985), who reported nonsignificant beak trimming effects on agonistic activities of male and female turkeys as measured at 12 and 20 wk of age. Denbow et al. (1984) reported a significant reduction in 12 to 20 wk mortality for trimmed male turkeys, whereas Leighton et al. (1985) failed to find any significant effect of trimming on mortality rates of female turkeys. Beaktrimming effects on livability of turkeys were not present in the current study; however, it is worth noting that untrimmed males had the lowest survival rate of all groups (80.0%) whereas untrimmed females had the highest rate of survival (90.0%). The current study provides further evidence of differing responses to beak trimming by male and female turkeys. These results, along with those of Denbow et al. (1984), suggest that beak trimming of male turkeys is generally beneficial with regard to most performance traits and results in only minor or short-term alterations to measured behaviors. Additionally, the present results support those of Leighton et al. (1985), who observed adverse effects of beak trimming on growth
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Trimmed Untrimmed Trimmed Untrimmed
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CUNNINGHAM ET AL.
performances of female turkeys. The reasons for these different sex responses are still unclear, but the results strongly suggest that routine beak trimming of females may not be necessary and, in fact, may be detrimental. ACKNOWLEDGMENTS
REFERENCES Craig, J. V., and H. Y. Lee, 1990. Beak trimming and genetic stock effects on behavior and mortality from cannibalism in White Leghorn type pullets. Appl. Anim. Behav. Sci. 25:107-123. Cunningham, D. L., 1992. Beak trimming effects on performance, behavior and welfare of chickens: A review of literature. J. Appl. Poult. Res. 1: 129-134. Denbow, D. M., A. T. Leighton, Jr., and R. M. Hulet, 1984. Behavior and growth parameters of Large White turkeys as affected by floor space and beak trimming. I. Males. Poultry Sci. 63:31-37. Duncan, I.J.H., G. S. Slee, E. Seawright, and J. Breward, 1989. Behavioral consequences of par-
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Appreciation is expressed to Lynda Jones and Ariel and Maria Rolon for their help with this project. Appreciation is also expressed to Cuddy Farms, Marshville, NC 28103, and to the Georgia Turkey Federation, Athens, GA 30605, for their partial support of this study.
tial beak amputation (Beak Trimming) in poultry. Br. Poult. Sci. 30:479-488. Eskeland, B., 1981. Effects of beak trimming. Pages 193-200 in: First European Symposium on Poultry Welfare. Edited by L. Y. Sorensen, Danish Branch of World's Poultry Science Association, Copenhagen, Denmark. Gentle, M. J., B. O. Hughes, and R. C. Hubrecht, 1982. The effect of beak trimming on food intake, feeding behavior and body weight in adult hens. Appl. Anim. Ethol. 8:147-159. Gentle, M. J., D. Waddington, L. N. Hunter, and R. Bryan Jones, 1990. Behavioral evidence for persistent pain following partial beak amputation in chickens. Appl. Anim. Behav. Sci. 27: 149-157. Kuo, F.-L., J. V. Craig, and W. M. Muir, 1991. Selection and beak trimming effects on behavior, cannibalism and short-term production traits in White Leghorn pullets. Poultry Sci. 70: 1057-1068. Lee, H. Y., and J. V. Craig, 1990. Beak-trimming effects on the behavior and weight gain of floorreared, egg strain pullets from three genetic stocks during the rearing period. Poultry Sci. 69: 568-575. Lee, H. Y., and J. V. Craig, 1991. Beak trimming effects on behavior patterns, fearfulness, feathering and mortality among three stocks of White Leghorn pullets in cages or floor pens. Poultry Sci. 70:211-221. Leighton, A. T., Jr., D. M. Denbow, and R. M. Hulet, 1985. Behavior and growth parameters of Large White turkeys as affected by floor space and beak trimming, n. Females. Poultry Sci. 64: 440-446. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., New York, NY.
1992 Poultry Science 71:1606-1614
INTRODUCTION Beak trimming is a management practice that has long been employed by poultry producers to reduce the deleterious effects of cannibalism and feather pecking. It is, however, a practice that has been severely criticized from an animal welfare perspective and one that continues to represent an emotionally sensitive and potentially difficult issue for the poultry industry. It is a practice that needs further investigation to evaluate alternatives and to address welfare concerns from a scientific perspective.
Received for publication February 10, 1992. Accepted for publication June 18, 1992.
Generally, studies of beak trimming in poultry have concentrated on the effects of this procedure on production and performance traits. Recent work by several authors (Gentle et al, 1982; Duncan et al, 1989; Lee and Craig, 1990,1991; Craig and Lee, 1990; Kuo et al, 1991), have demonstrated significant changes in feeding and drinking behaviors following beak trimming with chickens. Although beak trimming is a routine procedure employed throughout the turkey industry, only a few studies have investigated the effects of this procedure on the behavioral and performance criteria for this species (Denbow et al, 1984; Leighton et al, 1985). The purpose of the current study was to evaluate further the effects of beak trimming on certain behavioral and perfor-
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ABSTRACT The effects of beak trimming at day old on performance and behavioral activities of male and female Large White turkeys were evaluated. One hundred and twenty poults of each sex were evenly assigned to 20 treatment pens and evaluated for body weight, feed usage, and livability characteristics to 18 wk of age. Behavioral observations were conducted for feeding, drinking, sleeping, huddling, resting, and agonistic activities. Beak trirnming affected body weight and feed usage levels for the sexes differently. From 6 wk, trimmed males were significantly heavier than untrimmed males, whereas untrimmed females were heavier than trimmed females from 12 wk. Similar to body weights, feed usage levels from 13 to 18 wk were higher for trimmed males compared with untrimmed males and lower for trimmed females compared with untrimmed females. Feed conversion ratios after 12 wk and survival to 18 wk were not affected by trirnming treatment. Livability rates, however, were lowest for untrimmed males and highest for untrimmed females. Effects on behavioral activities were confined primarily to the brooding and early rearing phases. Beak trimming reduced feeding activity of females and drinking activity of both males and females during the first 2 wk. Sleeping, huddling, and resting activities were increased by beak trimming for both sexes during brooding. Agonistic acts were reduced by beak trimming main effect at 3 and 6 wk. Trimmed males committed fewer agonistic acts at 6 wk than untrimmed males. (Key words: beak trimming, sex, behavior, performance, turkeys)
BEAK TRIMMING AND SEX EFFECTS ON TURKEYS
mance traits of Large White male and female turkeys grown in confinement. MATERIALS AND METHODS
ing all birds in each replicate group on a 3-wk basis to 18 wk of age. In addition, feed usage was recorded per replicate for each 3-wk interval. Mortality was recorded on a daily basis. Behavioral activities were evaluated by observing each replicate group for a 15-min period four times a week during Weeks 1, 2, 3, 6, 12, and 18. Behavioral activities recorded during Weeks 1, 2, and 3 (brooding period) were feeding, drinking, sleeping, huddling, and resting. Behavioral activities recorded postbrooding were feeding, drinking, resting, and agonistic acts. Feeding and drinking behaviors were determined by recording the number of individual birds observed to be in the act of feeding or drinking at 5-min intervals during the observation sessions. Sleeping, huddling, and resting behaviors were recorded in the same manner. Individual poults were considered to be sleeping if they were observed in a crouched position with their eyes closed. Poults in a crouched position but with their eyes open were considered resting. Huddling activity was defined as two or more individuals in crouched positions with body contact. These behaviors were evaluated as possible indicators of differing responses to trimming treatments. The total agonistic acts (i.e., head pecks, fights, threats, and avoidance) committed were recorded for each replicate for each observational sessions. The data were analyzed by time periods using a 2 x 2 factorial arrangement of treatments (Steel and Torrie, 1960). When significant interactions were indicated, the data were analyzed within sex for each time period. The behavioral activities of feeding, drinking, sleeping, resting, and huddling were expressed as percentages with square root transformations applied prior to analyses. Logarithmic transformations were applied to the means for agonistic acts prior to analysis. Unless otherwise stated, significance refers to P < .05. RESULTS Body Weights and Livability
iBio-Beaker, Sterwin Laboratories, Inc., Millsboro, DE 19966. 2 B.U.T.A. Brooding Guide, British United Turkeys of America, P.O. Box 727, Lewisburg, WV 24901.
Body weights were not significantly affected by treatments during the first 3 wk of the study (Table 1). However, by 6 wk of
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One hundred and twenty Large White male and 120 Large White female turkeys of the Nicholas strain were used in the present study. The experimental design consisted of two beak-trimming treatments (trimmed versus untrimmed) for both sexes in a 2 x 2 factorial arrangement. Beak trimming was done at day old in a commercial hatchery using an electronic beak trimmer,1 which uses a high voltage electrical current to burn a small hole through the upper beak. The beak tip falls off after 3 to 7 days, leaving approximately two-thirds of the beak intact. Twelve males and 12 females were each assigned to 1 of 20 treatment pens measuring 1.37 x 1.52 m at Day 1. The poults were brooded using a combination of infrared heat lamps and forced-air furnaces. Standard brooding temperatures2 for turkeys were used for the first 3 wk, after which artificial heating was terminated. The lighting program consisted of 23 h of incandescent light followed by 1 h of darkness to 6 wk of age. At 6 wk the lighting was changed to 16 h of light and 8 h of darkness. Feed and water were provided for ad libitum consumption by the use of a single round tube feeder and a single bell drinker for each treatment group. During the 1st wk additional jar drinkers and feeder lids were used to start the poults eating and drinking quickly. The diets fed were standard University of Georgia starting, growing, and finishing turkey diets. The diets were fed as crumbles until 8 wk of age and then as pellets to the end of the study. Crude protein and metabolizable energy levels, respectively, for the diets ranged from 28% and 3,025 kcal/kg for the starter diet to 15% and 3,423 kcal/kg for the finisher diet. Performance data were evaluated for growth rate, feed usage, and mortality. Growth rates were determined by weigh-
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kg and 9.23 versus 9.53 kg, respectively). A significant sex effect for livability was also observed (Table 1). Females had a higher percentage of birds reaching market age than did males (88.4 versus 81.7%) and trimming had no significant effect on livability. Feed Usage and Feed Conversion
Sex had significant effects on both feed usage and feed conversion values throughout most of the study (Table 1). Differences in treatments were observed by 6 wk of age when both trimmed and untrimmed males were eating significantly (P < .01) more feed than either trimmed or untrimmed females. Differences in trimming treatments, however, were not observed until 13 to 18 wk, during which significant sex by trim-
TABLE 1. Effects of sex and beak treatment on body weight, livability, feed usage, and feed conversion from 0 to 18 wk of age for Large White turkeys
Comparisons
0 to 3 wk 4 to 6 wk
Age 7 to 12 wk 13 to 18 wk 0 to 18 wk
Bi Ddy
Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
weigh*•
(%)
flrt-V
.61 .58
2.13** 1.96
7.48** 6.36
12.22** 9.38
81.7* 88.4
.61 .58
2.09 2.01
6.94 6.90
10.84 10.76
85.0 85.0
*
* * Feed usage (kg per bird) —
.76 .71
1.90" 1.63
13.55** 11.49
18.97** 14.30
35.18** 28.20
.75 .72
1.74 1.78
12.53 12.71
16.75 16.52
31.57 31.73
*
*
- Feed conversioi[1 Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
Livability (0 to 18 wk)
^Kg.K.g;
1.39 1.40
1.25* 1.17
2.54* 2.62
3.99** 4.74
2.89** 3.03
1.39 1.40
1.17* 1.25
2.55* 2.60
4.37 4.37
2.94 2.98
*
*
*
Represents body weight at end of time period. *P < .05. **P < .01.
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age significant (P < .01) sex effects as well as significant sex by trimming interaction effects were observed. Because of the significant interactions between main effects, body weights were presented by treatment groups (Table 2). By 6 wk of age, beaktrimmed males were significantly heavier (10.9%) than untrimmed males (2.24 versus 2.02 kg). Beak-trimmed males were consistently heavier than untrimmed males through the remainder of the study; their weight differential increased to .45 kg by 18 wk (12.45 versus 12.00 kg). Significant differences between trimmed and untrimmed females for body weights were not observed until 12 wk of age. In contrast to body weights of trimmed and untrimmed males, trimmed females weighed significantly less at 12 and 18 wk than their untrimmed counterparts (6.24 versus 6.48
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BEAK TRIMMING AND SEX EFFECTS ON TURKEYS TABLE 2. Treatment means for body weight, feed usage, and feed conversion of Large White turkeys in which sex and beak treatment interacted
Sex Male Female
Female
Male Female
0 to 3 wk
4 to 6 wk 2.24* 2.02 1.93 2.00
Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed Trimmed Untrimmed
1.36* 1.41 1.41 1.38
Age 7 to 12 wk
13 to 18 wk 0 to 18 wk
7.63* 12.45* 7.32 12.00 6.24* 9.23* 6.48 9.53 • Feed usage (kg per bird) 19.50* 18.44 14.00* 14.60
1.18* 1.32 1.16 1.17
35.56* 34.82 27.50* 28.91
2.48* 2.59 2.62 2.61
Represents body weight at end of time period. •Means within sex are significantly different (P < .05).
ming interactions were observed (Table 2). During this period, trimmed males ate significantly more feed than untrimmed males (19.5 versus 18.44 kg per bird), whereas trimmed females ate significantly less feed than untrimmed females (14.0 versus 14.6 kg per bird). The significant sex by trimming interactions observed for 13 to 18 wk were large enough to effect the feed usage results for the entire study (0 to 18 wk) in the same manner. Significant sex and trimming main effects for feed conversions were present by 4 to 6 wk (Table 1) during which males and untrimmed poults had poorer values than females and trimmed poults. This situation changed, however, by 12 wk of age, when males demonstrated better weight gain to feed usage ratios (2.54 versus 2.62 kg:kg) than females. This sex effect for feed conversion performance remained to the end of the study, with males averaging a 2.89 kg:kg value compared with a ratio of 3.03 kg:kg for females. Significant interaction effects were present during the first 12 wk of the study for feed conversion. Trimmed males had significantly better feed conversion ratios than untrimmed males during the first 12 wk of the study but differences between females were not
present (Table 2). During the period of 13 to 18 wk, however, significant differences for feed conversion values between trimmed and untrimmed males were not observed, and, as a result, differences for the entire study were not present (2.87 versus 2.91 kg: kg).
Feeding and Drinking Activities Significant differences for feeding and drinking activities were observed for the first 2 wk of brooding (Tables 3 and 4). Untrimmed females were observed feeding more frequently (16.0 and 15.2% versus an average of 6.8%) than trimmed females (Table 4) during Weeks 1 and 2. By Week 3, differences in feeding activity were no longer present and all treatment groups demonstrated the same levels of activity to the end of the study. Untrimmed females were also observed drinking more frequently than trimmed females during Week 1 (14.3 versus 4.6%). During Week 2, untrimmed poults drank more frequently than trimmed poults (4.3 versus 2.4%). Similar to feeding activity, however, differences in drinking activity were not observed from 3 wk.
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Male
Beak treatment
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Sleeping, Huddling, and Resting Activity
TABLE 3. Effects of sex and beak treatment of feeding, drinking, sleeping, and huddling activity of Large White turkeys Age Comparisons Sex Males Females Beak treatment Trimmed Untrimmed Interaction Sex x beak Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
2 wk
3 wk
6 wk
12 wk
18 wk
8.5 8.4
8.5 11.0
11.2 12.6
6.2 7.3
8.9 9.0
7.7 7A
7.5* 12.3
7.6* 11.9
11.6 12.2
7.8 5.8
9.7 8.3
7.5 7.6
*
•f-
1 wk
4.3* 11.6
3.6 3.1
2.3 2.6
2.8 2.7
4.4 4.6
6.0 5.0
4.4* 9.4
2.4* 4.3
2.0 2.9
2.6 2.9
4.5 4.7
5.4 5.7
* C1nnni«A
Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
44.6 42.2
36.4* 27.3
29.4 27.2
47.9* 38.9
34.3* 29.4
28.8 27.9
*
*
n^4-^Trif^T
fO/
\
WiiHHlino- ar+ivifv (%.\
Sex Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak *P < .05. **P < .01.
38.9* 27.2
31.7* 19.8
41.4* 26.0
38.4* 27.7
26.8 24.7
41.1* 26.3
*
**
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Sleeping and huddling activities were significantly affected by sex and trirnming treatments during the brooding period (Table 3). Trimmed males and trimmed females slept more frequently (48.0 and 47.7% versus 41.2 and 36.7%, respectively) than untrimmed males and females during Week 1 (Table 4). During Week 2, trimmed males continued to sleep more frequently than untrimmed males (39.9 versus 32.9%),
but differences were not observed between female treatment groups. During Week 3, sleeping activities were the same for all groups. Male poults and beak-trimmed poults had significantly increased huddling activity during the brooding period (Tables 3 and 4). The only exception to this observation occurred during Week 2, when trimmed and untrimmed females had the same levels of huddling activity. Differences in levels of resting activity were observed throughout the 18 wk study (Table 5). Significant (P < .01) sex effects and
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BEAK TRIMMING AND SEX EFFECTS ON TURKEYS
TABLE 4. Treatment means for feeding, drinking, sleeping, and huddling activity of Large White turkeys in which sex and beak treatment interacted
Sex
Male Female
1 wk
2 wk
Trimmed Untrimmed Trimmed Untrimmed
8.3 8.6 6.7* 16.0
8.3 8.6 6.8* 15.2
Trimmed Untrimmed Trimmed Untrimmed
4.2 4.4 4.6* 14.3
Trimmed Untrimmed Trimmed Untrimmed
48.0* 41.2 47.7* 36.7
Age 3 wk 6 wk Feeding activity (%)
12 wk
18 wk
Drinking activity (%) Male Female
Sleeping activity (%) Male Female
39.9* 32.9 28.6 25.9
35.0* 28.3 18.6 Female 21.0 *Means within sex differ significantly (P < .05). **Means within sex differ significantly (P < .01). Male
Trimmed Untrimmed Trimmed Untrimmed
Huddling activity (%) 44.6* 38.1 37.5** 14.5
significant (P < .05) trimming main effects were observed as early as Week 1, when males rested more often than females (60.8 versus 49.4%) and trimmed poults rested more often than untrimmed poults (57.3 versus 52.9%). Significant interactions between main effects were present during Weeks 1 to 3. Trimmed females rested more frequently than untrimmed at Week 1, however, differences between trimmed and untrimmed males were not observed until Week 2 (Table 6). The effects of beak trimming on resting activity remained through Week 6 of the study but were no longer present by Week 12. The significant sex effect for resting activity remained throughout the study.
or trimmed counterparts (Table 5). At 6 wk of age, a significant sex by trimming interaction was present; more agonistic acts were committed by untrimmed males than trimmed males and more agonistic acts were committed by trimmed females than untrimmed females (Table 6). By 12 wk, only sex differences for agonistic acts were present, with males committing more acts than females, and by 18 wk no differences were observed for any of the treatments. Overall, untrimmed males committed more agonistic acts than trimmed males whereas trimmed and untrimmed females committed the same level of agonistic acts.
Agonistic Behavior
Beak trimming resulted in significant effects on body weight and feed usage values. By 6 wk of age, beak-trimmed males were .22 kg heavier than untrimmed males. This difference in body weight remained to the end of the study, when trimmed males weighed .45 kg more
Significant sex and beak trimming main effects on agonistic activity were observed early in the study, when 3-wk-old males and untrimmed females committed significantly more agonistic acts than their female
DISCUSSION
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Beak treatment
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TABLE 5. Effects of sex and beak trimming on resting and agonistic activity from 1 to 18 weeks of age for Large White turkeys
Comparison
1 wk
2 wk
3 wk
Age 6 wk
12 wk
18 wk
3 to 18 wk
Resting activity (%) Sex
60.8*' 49.4
55.4*' 43.2
56.4*' 40.6
68.6*' 56.5
68.2*' 51.3
62.6* 53.7
57.3* 52.9
53.6* 45.0
58.7* 38.3
66.5* 58.7
58.2 61.3
57.0 59.3
Agonistic activity (acts per bird per hour) Sex
Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
4.0* 3.0
5.2* 4.4
1.1* .5
.5 .3
2.68 2.11
2.7* 4.4
3.8* 5.8
.7
.4 .4
1.93* 2.87
*P < .05. **P < .01.
than untrimmed males. Trimmed and untrimmed females were not different for body weight until 12 wk but, contrary to the males, trimmed females weighed less than their untrimmed counterparts. Similar to body weights, feed usage was greater for trimmed males but was significantly less for trimmed females. These results contrast somewhat to those of Denbow et al. (1984), who reported no significant differences between trimmed and untrimmed turkey males for body weights but, nevertheless, reported greater feed intake for trimmed males. The results in the current study are, however, in agreement with those of Leighton et al. (1985), who reported significant reductions in body weights for trimmed female turkeys along with lower feed intake values. Feed conversion or feed efficiency values were not affected by trimming treatment in these studies. Most studies of beak trimming for the domestic fowl have reported evidence of reduced body weights and feed intake immediately following trimming, but these are traits for which contradictory results have been reported (Cunningham, 1992). The results in the current study and those of Denbow
et al. (1984) and Leighton et al. (1985) suggest that the effects of beak trimming on these traits for turkeys are manifest primarily during the later stages of growth and are different for the sexes. Several recent studies have suggested that beak trimming results in perceptible pain to chickens, as evidenced by changes in certain behavioral activities (Duncan et al, 1989; Gentle et al, 1990; Lee and Craig, 1990; Kuo et al, 1991). These studies have reported significant decreases in activities such as feeding, drinking, and preening and increases in the amount of time spent standing inactive and crouching. Feeding and drinking activities were affected by trimming during the first 2 wk of the current study. Untrimmed females were observed feeding more frequently than trimmed females, whereas significant differences for males were not observed. Trimmed poults drank less frequently than untrimmed poults during Weeks 1 and 2 regardless of sex. There were no significant differences for feeding or drinking activity beyond 2 wk of age. These results are similar to those of Duncan et al. (1989), who reported reductions in feeding and drinking activities for
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Males Females Beak treatment Trimmed Untrimmed Interactions Sex x beak
BEAK TRIMMING AND SEX EFFECTS ON TURKEYS
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TABLE 6. Treatment means for resting and agonistic activity of Large White turkeys in which sex and beak treatment interacted
Sex
Beak treatment
1 wk
2 wk
3 wk
Ag 6 wk
12 wk
18 wk
3 to 18 wk
Resting activity (%) Male
61.6 60.0 53.0* 45.8
58.8* 52.0 48.4* 38.0
63.9** 48.8 Female 53.5* 27.7 Agonistic activity (acts per bird per hour) Male Trimmed 2.93* Untrimmed 7.43 Female Trimmed 4.63 Untrimmed 4.16 'Means within sex differ significantly (P < .05). **Means within sex differ significantly (P < .01).
3 w k following beak trimming of 16-wk-old chickens and with the results of Lee and Craig (1990), who reported that pullets trimmed at 4 wk spent less time feeding for 3 wk following trimming. Gentle et al. (1990), on the other hand, reported changes in drinking behavior lasting as long as 6 wk posttrimming for 16-wk-old Brown Leghorn hens. Time spent sleeping, huddling, and resting (measures of inactivity) were significantly increased during brooding for males and trimmed poults. Duncan et al. (1989) also found an increase in time spent sitting and dozing for Leghorns immediately following trimming, but these activities returned to normal levels by 5 wk posttrimming. Resting activity remained significantly higher for trimmed poults through 6 wk of age. Beyond 6 wk, resting activity was only affected by sex, with males resting more frequently than females. Eskeland (1981) and Lee and Craig (1990) also reported reductions in bird activities following trimming. These results suggest some response to pain as a result of beak trimming may have been present early in the current study but any perception of pain as assessed by these behaviors was confined to the brooding or early rearing periods. Agonistic acts w e r e significantly reduced for females at 3, 6, and 12 wk and by beak trimming at 3 and 6 wk. Agonistic
1.90* 3.45 1.95 2.28
activities were at their highest levels at 3 and 6 wk of the study but beyond 6 wk of age agonistic activities were very low and not affected by trimming treatment. These results agree with those of Denbow et al. (1984) and Leighton et al. (1985), who reported nonsignificant beak trimming effects on agonistic activities of male and female turkeys as measured at 12 and 20 wk of age. Denbow et al. (1984) reported a significant reduction in 12 to 20 wk mortality for trimmed male turkeys, whereas Leighton et al. (1985) failed to find any significant effect of trimming on mortality rates of female turkeys. Beaktrimming effects on livability of turkeys were not present in the current study; however, it is worth noting that untrimmed males had the lowest survival rate of all groups (80.0%) whereas untrimmed females had the highest rate of survival (90.0%). The current study provides further evidence of differing responses to beak trimming by male and female turkeys. These results, along with those of Denbow et al. (1984), suggest that beak trimming of male turkeys is generally beneficial with regard to most performance traits and results in only minor or short-term alterations to measured behaviors. Additionally, the present results support those of Leighton et al. (1985), who observed adverse effects of beak trimming on growth
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Trimmed Untrimmed Trimmed Untrimmed
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CUNNINGHAM ET AL.
performances of female turkeys. The reasons for these different sex responses are still unclear, but the results strongly suggest that routine beak trimming of females may not be necessary and, in fact, may be detrimental. ACKNOWLEDGMENTS
REFERENCES Craig, J. V., and H. Y. Lee, 1990. Beak trimming and genetic stock effects on behavior and mortality from cannibalism in White Leghorn type pullets. Appl. Anim. Behav. Sci. 25:107-123. Cunningham, D. L., 1992. Beak trimming effects on performance, behavior and welfare of chickens: A review of literature. J. Appl. Poult. Res. 1: 129-134. Denbow, D. M., A. T. Leighton, Jr., and R. M. Hulet, 1984. Behavior and growth parameters of Large White turkeys as affected by floor space and beak trimming. I. Males. Poultry Sci. 63:31-37. Duncan, I.J.H., G. S. Slee, E. Seawright, and J. Breward, 1989. Behavioral consequences of par-
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Appreciation is expressed to Lynda Jones and Ariel and Maria Rolon for their help with this project. Appreciation is also expressed to Cuddy Farms, Marshville, NC 28103, and to the Georgia Turkey Federation, Athens, GA 30605, for their partial support of this study.
tial beak amputation (Beak Trimming) in poultry. Br. Poult. Sci. 30:479-488. Eskeland, B., 1981. Effects of beak trimming. Pages 193-200 in: First European Symposium on Poultry Welfare. Edited by L. Y. Sorensen, Danish Branch of World's Poultry Science Association, Copenhagen, Denmark. Gentle, M. J., B. O. Hughes, and R. C. Hubrecht, 1982. The effect of beak trimming on food intake, feeding behavior and body weight in adult hens. Appl. Anim. Ethol. 8:147-159. Gentle, M. J., D. Waddington, L. N. Hunter, and R. Bryan Jones, 1990. Behavioral evidence for persistent pain following partial beak amputation in chickens. Appl. Anim. Behav. Sci. 27: 149-157. Kuo, F.-L., J. V. Craig, and W. M. Muir, 1991. Selection and beak trimming effects on behavior, cannibalism and short-term production traits in White Leghorn pullets. Poultry Sci. 70: 1057-1068. Lee, H. Y., and J. V. Craig, 1990. Beak-trimming effects on the behavior and weight gain of floorreared, egg strain pullets from three genetic stocks during the rearing period. Poultry Sci. 69: 568-575. Lee, H. Y., and J. V. Craig, 1991. Beak trimming effects on behavior patterns, fearfulness, feathering and mortality among three stocks of White Leghorn pullets in cages or floor pens. Poultry Sci. 70:211-221. Leighton, A. T., Jr., D. M. Denbow, and R. M. Hulet, 1985. Behavior and growth parameters of Large White turkeys as affected by floor space and beak trimming, n. Females. Poultry Sci. 64: 440-446. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., New York, NY.
