Motor ability and self-selection of an analgesic drug by fast-growing chickens

Abstract

Breeding programs designed for broiler production have resulted in a chicken that, when fully fed, grows rapidly and has a body conformation that enhances yield at market weight. Compared with chickens bred for high egg production, the motor ability of broilers has been compromised and is of increasing concern in broiler breeding and production. Broilers with intermediate gait scores of 2, 3, and 4 were provided choices among diets containing different doses of a nonsteroidal anti-inflammatory drug (carprofen). Broilers with no identifiable gait abnormality (score of 1) or unable to walk (score of 5) were excluded from the study. The hypothesis that broilers with higher gait scores, if experiencing pain, would prefer diets with higher doses of carprofen was rejected because no differences were observed in feed consumption among treatment groups. Although males and females responded similarly, there was an interaction of sex with left-right preference for feeder location.

Full text

DESCRIPTION OF PROBLEM
During the past 60+ yr, the dual-purpose
chicken has been replaced by stocks bred spe-
cifically for the production of eggs or meat.
These programs have contributed to distinct
differences in the body types of egg and meat
stocks. For broilers, changes in conformation,
early growth rate, FE, and yield have been dra-
matic [1, 2]. These changes have influenced
their motor ability and have generated con-
siderable research interest that has taken sev-
eral forms, with emphasis including anatomical
factors [3–5], tibia dyschondroplasia and hus-
bandry [6–10], pain [11–14], large field studies
[15], and comprehensive reviews and discus-
sion [16, 17].
That chickens, including broilers, can self-se-
lect feed to satisfy nutrient requirements is well
documented from choice-feeding experiments
[18–21]. Choice feeding was used to compare
preferences by “lame” and “sound” broilers for
diets containing the analgesic drug carprofen
[14], with the assumption being that individuals
experiencing pain should prefer diets contain-
ing the carprofen to a placebo. In this paper, we
describe experiments designed to compare feed
intake of fast-growing, high-yield broilers that
differ in motor ability when fed diets with and
without the analgesic drug carprofen.
© 2011 Poultry Science Association, Inc.
Motor ability and self-selection of an analgesic
drug by fast-growing chickens
P. B. Siegel ,*1 S. J. Gustin ,† and M. N. Katanbaf ‡
* Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg 24061;
† Cobb-Vantress Inc., Siloam Springs, AR 72761;
and ‡ Cobb-Vantress Inc., Monticello, KY 42633
Primary Audience: Behaviorists, Breeders, Production Managers, Veterinarians
SUMMARY
Breeding programs designed for broiler production have resulted in a chicken that, when
fully fed, grows rapidly and has a body conformation that enhances yield at market weight.
Compared with chickens bred for high egg production, the motor ability of broilers has been
compromised and is of increasing concern in broiler breeding and production. Broilers with
intermediate gait scores of 2, 3, and 4 were provided choices among diets containing differ-
ent doses of a nonsteroidal anti-inflammatory drug (carprofen). Broilers with no identifiable
gait abnormality (score of 1) or unable to walk (score of 5) were excluded from the study. The
hypothesis that broilers with higher gait scores, if experiencing pain, would prefer diets with
higher doses of carprofen was rejected because no differences were observed in feed consump-
tion among treatment groups. Although males and females responded similarly, there was an
interaction of sex with left-right preference for feeder location.
Key words: broiler , carprofen , choice feeding , gait
2011 J. Appl. Poult. Res. 20 :249–252
doi: 10.3382/japr.2009-00118
1 Corresponding author: pbsiegel@vt.edu

250 JAPR: Research Report
MATERIALS AND METHODS
Experiment 1
This experiment was designed to ascertain if
training was necessary for broilers to discrimi-
nate among varying dosages of the nonsteroidal
anti-inflammatory drug carprofen [22] in their
feed. The main effects were dosage of carprofen
(0, 34.3, or 102.9 mg/kg of feed), sex (male, fe-
male), and laterality (left, right).
At 35 d of age, broilers from a large sex-in-
termingled flock reared on wood shavings, with
feed and water available ad libitum, were indi-
vidually weighed and gait scored (scores from 1
to 5) [23]. The scores used were a slight modifi-
cation [9] of those described by Kestin et al. [3].
From broilers with a score of 3, we randomly
selected 36 males and 36 females for transfer
to preassigned individual cages [24]. Each cage
was equipped with 2 feeders that contained feed
at all times. The assignment of carprofen dos-
ages was at random in a manner such that all
combinations were available. To balance for lat-
erality, the feed with the lowest dosage was on
the left side for half the cages and on the right
side for the other half. The basal diet [25] was
a broiler finisher in pellet form. Carprofen [14,
22] at each dosage was mixed with 100 mL of
distilled water and sprayed on the feed. For the
0-mg level, only 100 mL of water was sprayed
on the feed.
Feed consumption from each feeder was re-
corded daily on d 36, 37, and 38 (considered the
training period). Individual BW were obtained
again on d 39 and 43, with ADFI recorded for d
39 to 43. Because of variations in BW among in-
dividuals, the trait analyzed was ADFI corrected
for BW (%ADFI). Data were analyzed using a
split-plot design [26], with significance consid-
ered at P < 0.05.
Experiment 2
The experimental protocol for this experi-
ment was based on the results from experiment
1. Added to the main effects in experiment 1
were individuals with gait scores of 2, 3, and
4 [23]. The objective was to compare %ADFI
among broilers with intermediate gait scores.
Thus, of the 36 males and 36 females selected,
12 males and 12 females had gait scores of 2,
3, or 4. Consistent with experiment 1, broilers
at 35 d of age were weighed, gait scored, and
transferred to preassigned cages. Their %ADFI
was measured for d 37, 38, and 39 (i.e., d 2, 3,
and 4 after caging). Data were analyzed using a
split-plot design [26], with significance consid-
ered at P < 0.05.
RESULTS AND DISCUSSION
Experiment 1
A significant difference was observed in
%ADFI among carprofen doses. The %ADFI
for the 0-mg dose (1.97 ± 0.07) was intermedi-
ate and was not different from the 34.3 mg/kg of
feed (2.11 ± 0.07) and the 102.9 mg/kg of feed
(1.88 ± 0.07), which differed. Sex × laterality
was the only significant interaction. This inter-
action occurred because although females had
no left-right preference in %ADFI (2.00 ± 0.08
for left vs. 1.96 ± 0.07 for right), males had a
significant preference for the left compared with
the right feeder (2.25 ± 0.07 vs. 1.73 ± 0.07).
Experiment 2
Analysis of variance of %ADFI for this ex-
periment is presented in Table 1. None of the
14 higher order interactions and only 1 (sex ×
laterality) of the 10 first-order interactions was
significant. The interaction was because al-
though males showed no left-right preference
(3.90 ± 0.15 for left vs. 4.14 ± 0.21 for right),
females had a significant preference for the left
compared with the right feeder (3.97 ± 0.13 vs.
3.52 ± 0.14).
Means and SE for the other main effects (day,
gait score, and carprofen dose) are summarized
in Table 2. Fluctuation was observed among
days, with %ADFI being less for d 3 than for
d 2 and 4, which did not differ. For gait score,
a trend was observed, with higher values for
score 2 than 4 and the values for 3 being inter-
mediate. Because intake was expressed relative
to BW, those broilers with the lower gait score
had a higher relative food intake. No differences
were observed in %ADFI among carprofen dos-
ages. We can conclude, based on the lack of a
carprofen dose × gait score interaction, that

251
SIEGEL ET AL.: MOTOR ABILITY OF BROILERS
among these treatment groups, no self-selection
occurred for the feed containing the nonsteroidal
anti-inflammatory analgesic.
General
We suggest, based on the lack of a preference
among diets for chickens with gait scores of 2,
3, or 4, that although their motor ability may
have been considered phenotypically compro-
mised, it was not sufficient to elicit a preference
for diets containing carprofen at these levels.
Moreover, we did not measure a progression of
gait scores over time. Pain is a vague term that
is defined as “a state of physical or mental lack
of well-being or physical or mental uneasiness
that ranges from mild discomfort or dull distress
to acute, often unbearable agony” [27]. For the
population studied, individuals with intermedi-
ate gait scores did not exhibit a preference for
a veterinary compound routinely prescribed for
animals with joint pain. Although these results
may appear inconsistent with results in which
this was observed [12, 14, 17], it may be due
in part to the testing procedures (traverse an ob-
stacle course [12], feed color [14], vertical force
[17]), underlying pathology, differences in ac-
tivity levels of the broilers, or a combination of
these factors, which could have altered the need
to self-select the analgesic because of pain.
CONCLUSIONS AND APPLICATIONS
1. Individual broilers differed in their mo-
tor ability. Those with gait scores of 2,
3, and 4 did not exhibit a preference for
an analgesic at the dosages used, sug-
gesting that although abnormalities may
have been identified, they were not suf-
ficient for those chickens to prefer a diet
containing an analgesic compound.
2. When given choices among diets, chick-
ens exhibited laterality in dietary selec-
tion. The direction (left vs. right) was not
necessarily predictable. Thus, laterality
should be included in the experimental
design of choice-feeding experiments.
3. Because no differences were observed
among the intermediate gait scores, con-
Table 1. Analysis of variance for %ADFI,1 experiment 2
Source of
variation2df Mean squares × 10−4
Sex (S) 1 1.14
Gait (G) 2 11.19**
Feed type (FT) 2 0.05
Day (D) 2 11.14**
Laterality (L) 1 0.81
S × G 2 1.38
S × FT 2 5.34
S × D 2 2.34
S × L 1 12.37**
G × FT 4 1.13
G × D 4 0.76
G × L 2 1.61
FT × D 4 1.74
FT × L 2 2.01
D × L 2 2.89
S × G × FT 4 0.81
S × F × D 4 0.73
S × D × L 2 5.36
S × G × D 4 0.15
S × G × L 2 1.73
G × FT × D 8 1.06
G × FT × L 4 3.67
FT × D × L 4 1.37
S × G × FT × D 8 1.72
S × G × FT × L 6 1.82
S × G × D × L 8 2.59
S × FT × D × L 4 0.22
G × FT × D × L 8 1.73
S × G × FT × D × L 8 1.88
1%ADFI = ADFI corrected for BW.
2Sex (male, female), gait (score 2, 3, 4), feed type (carpro-
fen dose of 0, 34.3, 102.9), day (2, 3, 4), and laterality (left,
right).
**P < 0.01.
Table 2. Means and SE for %ADFI1 by day, gait, and
carprofen dose
Item Mean ± SE
Day1
2 4.05 ± 0.13a
3 3.56 ± 0.09b
4 4.04 ± 0.12a
Gait score2
2 4.17 ± 0.12a
3 3.86 ± 0.11ab
4 3.61 ± 0.12b
Carprofen dose, mg/kg of feed
0 3.91 ± 0.13a
34.3 3.90 ± 0.11a
102.9 3.84 ± 0.12a
a,bMeans within a treatment with the same superscript are not
different (P < 0.05).
1%ADFI = ADFI corrected for BW. %ADFI was measured
on d 2, 3, and 4 after caging.
2See [23] for detailed descriptions.

252 JAPR: Research Report
sideration should be given to reducing
the classifications used in measuring the
motor ability of meat-type poultry.
REFERENCES AND NOTES
1. Havenstein, G. B., P. R. Ferket, and M. A. Qureshi.
2003. Growth, liveability, and feed conversion of 1957 ver-
sus 2001 broilers when fed representative 1957 and 2001
broiler diets. Poult. Sci. 82:1500–1508.
2. Emmerson, D. A., N. B. Anthony, K. E. Nester, and Y.
M. Saif. 1991. Genetic association of selection for increased
leg muscle and increased shank diameter with body compo-
sition and walking ability. Poult. Sci. 70:739–745.
3. Kestin, S. C., T. G. Knowles, A. E. Tinch, and N. G.
Gregory. 1992. Prevalence of leg weakness in broiler chick-
ens and its relationship with genotype. Vet. Rec. 131:190–
194.
4. Skinner-Noble, D. O., and R. G. Teeter. 2009. An ex-
amination of anatomic, physiologic, and metabolic factors
associated with well-being of broilers differing in field gait
score. Poult. Sci. 88:2–9.
5. Weeks, C. A., T. D. Danbury, H. C. Davies, P. Hunt,
and S. C. Kestin. 2000. The behavior of broiler chickens
and its modification by lameness. Appl. Anim. Behav. Sci.
67:111–125.
6. Sørensen, P., G. Su, and S. C. Kestin. 2000. Effects of
age and stocking density on leg weakness in broiler chick-
ens. Poult. Sci. 79:864–870.
7. Su, G., P. Sorenson, and S. C. Kestin. 1999. Meal
feeding is more effective than early feed restriction at re-
ducing the prevalence of leg weakness in broiler chickens.
Poult. Sci. 78:949–955.
8. Sanotra, G. S., L. G. Lawson, and K. S. Vertergaard.
2001. Influence of stocking density on tonic immobility,
lameness and tibial dyschondroplasia in broilers. J. Appl.
Anim. Welf. Sci. 12:677–683.
9. Garner, J. P., C. Falcone, P. Wakenell, M. Martin, and
J. A. Mench. 2002. Reliability and validity of a modified gait
scoring system and its use in accessing tibial dyschondropla-
sia in broilers. Br. Poult. Sci. 43:355–363.
10. Blatchford, R. A., K. C. Klasing, H. L. Shivaprusad,
P. S. Wakenell, G. S. Archer, and J. A. Mench. 2009. The ef-
fect of light intensity on the behavior, eye and leg health, and
immune function of broiler chickens. Poult. Sci. 88:20–28.
11. Weary, D. M., L. Niel, C. F. Flower, and D. Fraser.
2006. Identifying and preventing pain in animals. Appl.
Anim. Behav. Sci. 100:64–76.
12. McGeown, D., T. C. Danbury, A. E. Waterman-Pear-
son, and S. C. Kestin. 1999. Effect of carprofen on lameness
in broiler chickens. Vet. Rec. 144:668–671.
13. Hocking, P. M., R. Bernard, and M. H. Maxwell.
1999. Assessment of pain during locomotion and the wel-
fare of adult male turkeys with destructive cartilage loss of
the hip joint. Br. Poult. Sci. 40:30–34.
14. Danbury, T. C., C. A. Weeks, J. P. Chambers, A. E.
Waterman-Pearson, and S. C. Kestin. 2000. Self-selection of
the analgesic drug carprofen by lame broiler chickens. Vet.
Rec. 146:307–311.
15. Knowles, T. G., S. C. Kestin, S. M. Haslam, S. N.
Brown, L. E. Green, A Butterworth, S. J. Pope, D. Pfei-
ffer, and C. J. Nicol. 2008. Leg disorders in broiler chick-
ens: Prevalence, risk factors, and prevention. PLoS One
3:e1545. doi:10/1371/journal.pone.0001545.
16. Manning, L., S. C. Chadd, and R. N. Baines. 2007.
Key health and welfare indicators for broiler performance.
World’s Poult. Sci. J. 63:43–62.
17. Naas, I. A., I. C. L. A. Paz, M. S. Barache, G. Mene-
zos, L. G. F. Bueno, I. C. L. Almeida, and D. T. Moura. 2009.
Impact of lameness on broiler well-being. J. Appl. Poult.
Res. 18:432–439.
18. Siegel, P. B., M. Picard, I. Nir, E. A. Dunnington, M.
H. A. Willemson, and P. E. V. Williams. 1997. Responses of
meat-type chickens to choice feeding of diets differing in
protein and energy from hatch to market weight. Poult. Sci.
76:1183–1192.
19. Rose, S. P., and I. Kyriazakis. 1991. Diet selection in
pigs and poultry. Proc. Nutr. Soc. 50:87–98.
20. Noble, D. O., M. L. Picard, E. A. Dunnington, G.
Uzu, A. S. Larsen, and P. B. Siegel. 1993. Food intake ad-
justments of chicks: Short term reactions of genetic stocks to
deficiencies in lysine, methionine or tryptophan. Br. Poult.
Sci. 34:725–735.
21. Picard, M. L., G. Uzu, E. A. Dunnington, and P. B.
Siegel. 1993. Food intake adjustments of chicks: Short term
reactions to deficiencies in lysine, methionine and trypto-
phan. Br. Poult. Sci. 34:737–746.
22. Carprofen (Rimadyl, injectable, manufactured by
Pfizer Animal Health, New York, NY) is a nonsteroidal anti-
inflammatory drug commonly used in veterinary practice
to provide relief of joint pain by reducing inflammation by
inhibiting production of cyclooxygenase-2 and other sources
of inflammatory prostaglandins.
23. Gait scores: 1 = no identifiable abnormality; 2 = iden-
tifiable abnormality that has little impact on overall func-
tion; 3 = identifiable abnormality that impairs function; 4 =
severe impairment of function, but still capable of walking;
5 = unable to walk.
24. Cages were 50.8 cm wide, 50.8 cm deep, and 61.0 cm
high with plastic slatted floors.
25. Basal diet contained 19% CP and 3,208 kcal of ME/
kg of feed.
26. SAS Institute. 2003. Statistical Analysis Software
Version 9.3.1. SAS Inst. Inc., Cary, NC, for split plot design.
Sources of variation are shown in Table 1 for experiment 2.
The analysis for experiment 1 is the same except that gait
and interactions involving it were not sources of variation.
Multiple means were compared by Duncan’s multiple range
test.
27. Merriam-Webster. 1961. Webster’s 3rd New Interna-
tional Dictionary—Unabridged. G. & C. Merriam Co., Chi-
cago, IL.