This article was downloaded by: [Monash University Library] On: 06 March 2015, At: 16:42 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
British Poultry Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/cbps20
Comparative gait analysis of two strains of turkey, meleagris gallopavo A. Abourachid
a b
a
University of Rennes I, National Museum of Natural History , Paris b
Laboratory of Comparative Anatomy , 55 rue Buffon, Paris, 75005, France Published online: 08 Nov 2007.
To cite this article: A. Abourachid (1991) Comparative gait analysis of two strains of turkey, meleagris gallopavo , British Poultry Science, 32:2, 271-277, DOI: 10.1080/00071669108417350 To link to this article: http://dx.doi.org/10.1080/00071669108417350
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/ page/terms-and-conditions
British Poultry Science (1991) 32: 271-277
COMPARATIVE GAIT ANALYSIS OF TWO STRAINS OF TURKEY, MELEAGRIS GALLOPAVO A. ABOURACHID University of Rennes 1 and National Museum of Natural History, Paris
Downloaded by [Monash University Library] at 16:42 06 March 2015
Received for publication 28th November 1989
Abstract 1. Economic requirements have encouraged farmers to select broad-breasted strains of turkeys (Meleagris gallopavo). These birds are very heavy (more than 30 kg), have pectoral hypertrophy and are frequently lame. Traditional turkeys, closer to wild birds, weigh 9 kg on average. 2. Gaits, which are motor pattern expressions, seem to be linked to species morphology. However, no significant differences are evident between the gaits of traditional and broad-breasted strains. 3. Yet, posterior views of the walk of both strains show lateral oscillations, which are very slight in the traditional one but very marked in the broad-breasted one. 4. In the latter, modification of the centre of gravity path may increase the energetic cost of walking and be associated with problems of lameness. 5. Therefore, if the genetic pool permits an increase in weight of broad-breasted turkeys, then extrinsic factors, such as gravity constraints, may limit this evolution. INTRODUCTION
Domestic animals have been selected for traits that are viewed as beneficial from an economic, cultural or aesthetic point of view. Domestication can generate an imbalance in growth rate of different parts of the body (CluttonBrock, 1981) to produce very different adult morphology proportions in domestic animals versus wild ones. Turkeys are a good example of this phenomenon. One of the domestic strains which preserves the most "natural" characteristics are the traditional turkeys raised by the Betina Society (Crawford, 1984). However, most commercial turkey strains come from a heavy strain selected since 1927 (Davey, 1974). These birds have hypertrophiée! pectoral muscles, associated with fast growth. Traditional male adult turkeys have a mean weight of 9 kg, whereas broad-breasted breeder males can weigh Present address: Laboratory of Comparative Anatomy, 55 rue Buffon, 75005 Paris, France. 271
Downloaded by [Monash University Library] at 16:42 06 March 2015
272
A. ABOURACHID
over 40 kg. Such heavy birds are frequently lame: Dugg et al. (1987) noted that more than half of the adult male breeding turkeys studied were lame at 55 weeks of age. Bipedal locomotion results from the repetition of coordinated hindlimb movements. Spatio-temporal coordination is linked to different gaits and is an expression of a species-specific locomotor pattern. This locomotor pattern is linked to morphological organisation and corresponds with the relatively low variation of body proportions observed in nature. The major morphological modifications produced by selection in broad-breasted turkeys causes them to be outside the natural phenotypic variation of the species Meleagris gallopavo. Besides the considerable weight increase in the broad-breasted strain, an altered distribution of body mass results from pectoral hypertrophy. Pectoral muscles represent 13% of body weight in traditional turkeys at 105 d and 20% in broad-breasted turkeys at the same age. It is of interest to compare the gait of broad-breasted turkeys with that of traditional turkeys to see if changes appear in the locomotor pattern of the species and if such morphological differences interfere in the bird's balance and its locomotor movements.
MATERIALS AND METHODS
Adult male turkeys of the 2 strains (traditional and breeder broadbreasted) selected by the Betina Society (St Nolff, 56250 Elven, France) were studied. Average weight of adult birds of the traditional strain was 8 kg; the broad-breasted turkeys' average weight was about 30 kg. All animals studied were healthy and without any lameness. Sixteen millimetre films were made on the farm and in the laboratory; 4 broad-breasted and 5 traditional turkeys were filmed. The walking speed was slow and a film frequency of 25 frames/s was sufficient. Reference spots were placed in the frame field to allow measurement of the birds' displacement. Turkeys were filmed in both lateral and posterior views. Films were analysed frame by frame. The gait analysis followed the method of Hildebrand (1966) for quadrupeds, modified by Hayes and Alexander (1983). Two main variables were recorded (1) the duration of the stance phase, i.e. contact with the substrate (which starts with the placement of all the toes and ends with the removal of the last toe); (2) the length of time between the start of the stance phases for the two limbs, expressed as a percentage of the cycle duration. The cycle includes both the swing phase, i.e. no contact with the substrate (beginning with the removal of the last toe and ending with the placement of all the toes) and the stance phase of a reference limb. On each sequence, frame number was used as a time base for events of the walk (i.e. the beginning and the end of each phase). Stride length was also measured, as the distance between two placement points of a given element of
273
COMPARATIVE GAIT ANALYSIS OF TURKEYS
i
(a)
œ w
(b)
3-
3-
2-
2-
1-
1-
I SÎ
Downloaded by [Monash University Library] at 16:42 06 March 2015
'>*''
'0'
/S' 'S/
f J
-F -
1
2 Cycle duration
3
1
2 Cycle duration
h.
3
(c) 3-
g
1 •o
a)
I
2-
H
-''•''
ÜB Traditional turkeys = ï î Broad-breasted turkeys
i
I
I
1
2 Cycle duration
3
FIG. 1.—Regression between stance-phase duration and cycle duration (in seconds). Dotted lines represent the predicted limits and fine dashed lines the 95% confidence limits; (a) broad-breasted turkeys, (b) traditional turkeys, and (c) both strains.
the foot; 42 cycles were analysed for traditional turkeys and 44 for the broadbreasted ones. In posterior views, lateral oscillations of the body could be estimated by the inclination of the line joining two points: the vent and the middle of the support base when the two feet were in contact with the ground. RESULTS
In the cycles analysed (42 in 4 broad-breasted birds and 44 in 5 traditional birds), mean values were calculated for the variables that are not linked to speed. Regression lines relating the duration of the stance phase to the cycle duration were calculated by minimising the sum of squares of the residuals (see
274
A. ABOURACHID
20100-10-
Downloaded by [Monash University Library] at 16:42 06 March 2015
-20-
20
50
70
100
% cycle
FIG. 2.—Lateral body oscillations during walking in broad-breasted turkeys (BB) and traditional turkeys (T). Horizontal lines below the graph represent the stance phases of the right and left limbs. Table). T h e difference between the start of the stance phases, in b o t h strains,
was close to 50% of the cycle: the gait was a normal walk as defined by Hayes and Alexander (1983). TABLE
Results of gait analysis. Means ± standard deviations Difference between the start of stance of stance phases (% of cycle duration) Stride length (ra) Hip height (m) Regression of stance-phase duration (Y) on cycle duration (X)
Broad-breasted
Traditional
47±8 0-36±0-03 0-48
52±9 0-30 ±0-02 0-40
-0-20±0-01 + 0-99±0-08XK = -0-23±0-02 + 0-96±0-01X
The stride length of traditional turkeys was shorter than that of broadbreasted ones. However, this value is generally related to hip height. Here, in both cases, it was 0-75 times the hip height. As the birds did not always walk at the same speed, and as the duration of the stance phase is linked to speed, it was necessary to investigate whether the function that relates stance phase to speed was similar in both cases. In order to calculate regressions for this relationship, cycle duration was substituted for speed, which could not be calculated for all cycles. These two values (speed and cycle duration) were closely correlated (r2 = 0-86). In both strains the intercepts were very close (—0-23 for traditional turkeys and —0-20 for broadbreasted ones) and the standard errors overlapped. The slopes were slightly, but not significantly, different (0-96 for traditional birds and 0-99 for broadbreasted ones) (Fig. 1). Analysis of the posterior views showed lateral oscillations of the body, very
COMPARATIVE GAIT ANALYSIS OF TURKEYS
275
Downloaded by [Monash University Library] at 16:42 06 March 2015
(a)
BB
(b)
BB
FIG. 3.—Lateral (a) and posterior (b) views of gait in broad-breasted (BB) and traditional (T) turkeys. Lateral views show almost no difference between strains but lateral oscillations are clearly seen in posterior view.
slight in traditional birds but very marked in broad-breasted ones (Fig. 2). The line that passes between the vent and the middle of the support base showed angular variations of 5° to either side of a vertical line during the traditional turkey's walk and more than 15° for the broad-breasted ones.
DISCUSSION
A classical analysis of gait, based on durations of stance and swing phases,
Downloaded by [Monash University Library] at 16:42 06 March 2015
276
A. ABOURACHID
did not detect any differences between the gait of the two turkey strains. There was no apparent modification by artificial selection of the locomotor pattern responsible for hindlimb synchronisation during walking. Broad-breasted turkey locomotion remained under the locomotor coordination which characterises the species. Posterior views of the birds showed that the morphological modifications produced by selection affect the birds' balance. However, because of the broadening of the breast resulting from the increase in pectoral volume, the legs of heavy turkeys were much further apart than in traditional birds. The support base was thus wider. During walking, the centre of gravity was brought over the stance foot to allow equilibrium (Fig. 3). The resulting modification of the gravity centre's path in broad-breasted turkeys contributed to balance but not to progression. The lateral oscillations, therefore, constituted a type of "parasitic" movement. In bipedal locomotion, lateral speed variation of the centre of gravity is negligible (Cavagna et al., 1963) and lateral movements are very small. This was the case in traditional turkeys but in broad-breasted ones the "parasitic" lateral oscillations must increase the energetic cost of walking. The muscular effort necessary to move the body from side to side would also produce fatigue which would accompany lameness. A dynamometric study, measuring the forces exerted on the ground by the feet, Avould allow verification of this point. If this is so, the general relationship that the cost of moving a gramme of body mass a given distance decreases as a function of increasing body mass (e.g. a 30 g quail uses approximately 13 times as much energy to move each gramme of its body as would a 100 kg ostrich (Taylor et al., 1982) would not be true for different strains of the same species. Conclusions
No changes in locomotor pattern, i.e. the coordination of hind limb movements were observed in broad-breasted turkeys as results of the morphological modifications produced by artificial selection. However, their gait had very marked lateral oscillations that possibly increase the energetic cost of walking and may be linked to lameness. Genotypic variability within a species may permit an increase in weight (Crawford, 1984), but mechanical constraints produce selection pressures which limit such evolution. The multiplication of locomotor problems, associated with weight increase in broad-breasted turkeys, is a first indication of this phenomenon. The question is how far can the phenotypic limits of the species be extended without serious functional problems.
ACKNOWLEDGEMENTS
I thank S. Renous for her useful comments and advice, J. P. Gase for valuable suggestions and G. Dingerkus for correction of English. I also thank the Laboratory of Comparative Anatomy of the Muséum National d'Histoire
COMPARATIVE GAIT ANALYSIS OF TURKEYS
277
Naturelle in Paris and UA1137 of the CNRS for technical assistance. This work was supported by the Betina Society and the Conseil Regional de Bretagne.
Downloaded by [Monash University Library] at 16:42 06 March 2015
REFERENCES CAVAGNA, G.A., SAIBENE, F.P. & MARGARIA, R. (1963) External work in walking. Journal of Applied Physiology, 18: 1-9. CLUTTON-BROCK, J. (1981) Domesticated animals from early times. Heinemann British Museum (Natural History), 208 pp. CRAWFORD, R.D. (1984) Turkey, in: I. L. MASON (Ed.) Evolution of domesticated animals, pp. 325-334 (London & N.Y., Longman). DAVEY, A.D. (1974) Canada, in: J. L. SKINNER (Ed.) American Poultry History 1823-1973, chapter 17 (Madison, Wisconsin, American Printing and Publishing). DUFF, S.R.I., HOCKING, P.M. & FIELD, R.K. (1987) The gross morphology of skeletal disease in adult male breeding turkeys. Avian Pathology, 16: 635-651. HAYES, G. & ALEXANDER, R . M C N . (1983) The hopping gaits of Crows (Corvidae) and other bipeds. Journal of Zoology, 200: 205-213. HILDEBRAND, M. (1966) Analysis of symmetrical gaits of Tetrapods. Folia Biotheoretica, 6: 1-22. TAYLOR, C.R., HEGLUND, N.C. & MALOY, G.M.O. (1982) Energetics and mechanics of terrestrial locomotion. I. Metabolic energy consumption as a function of speed and body size in birds and mammals. Journal of Experimental Biology, 97: 1-21.
British Poultry Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/cbps20
Comparative gait analysis of two strains of turkey, meleagris gallopavo A. Abourachid
a b
a
University of Rennes I, National Museum of Natural History , Paris b
Laboratory of Comparative Anatomy , 55 rue Buffon, Paris, 75005, France Published online: 08 Nov 2007.
To cite this article: A. Abourachid (1991) Comparative gait analysis of two strains of turkey, meleagris gallopavo , British Poultry Science, 32:2, 271-277, DOI: 10.1080/00071669108417350 To link to this article: http://dx.doi.org/10.1080/00071669108417350
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/ page/terms-and-conditions
British Poultry Science (1991) 32: 271-277
COMPARATIVE GAIT ANALYSIS OF TWO STRAINS OF TURKEY, MELEAGRIS GALLOPAVO A. ABOURACHID University of Rennes 1 and National Museum of Natural History, Paris
Downloaded by [Monash University Library] at 16:42 06 March 2015
Received for publication 28th November 1989
Abstract 1. Economic requirements have encouraged farmers to select broad-breasted strains of turkeys (Meleagris gallopavo). These birds are very heavy (more than 30 kg), have pectoral hypertrophy and are frequently lame. Traditional turkeys, closer to wild birds, weigh 9 kg on average. 2. Gaits, which are motor pattern expressions, seem to be linked to species morphology. However, no significant differences are evident between the gaits of traditional and broad-breasted strains. 3. Yet, posterior views of the walk of both strains show lateral oscillations, which are very slight in the traditional one but very marked in the broad-breasted one. 4. In the latter, modification of the centre of gravity path may increase the energetic cost of walking and be associated with problems of lameness. 5. Therefore, if the genetic pool permits an increase in weight of broad-breasted turkeys, then extrinsic factors, such as gravity constraints, may limit this evolution. INTRODUCTION
Domestic animals have been selected for traits that are viewed as beneficial from an economic, cultural or aesthetic point of view. Domestication can generate an imbalance in growth rate of different parts of the body (CluttonBrock, 1981) to produce very different adult morphology proportions in domestic animals versus wild ones. Turkeys are a good example of this phenomenon. One of the domestic strains which preserves the most "natural" characteristics are the traditional turkeys raised by the Betina Society (Crawford, 1984). However, most commercial turkey strains come from a heavy strain selected since 1927 (Davey, 1974). These birds have hypertrophiée! pectoral muscles, associated with fast growth. Traditional male adult turkeys have a mean weight of 9 kg, whereas broad-breasted breeder males can weigh Present address: Laboratory of Comparative Anatomy, 55 rue Buffon, 75005 Paris, France. 271
Downloaded by [Monash University Library] at 16:42 06 March 2015
272
A. ABOURACHID
over 40 kg. Such heavy birds are frequently lame: Dugg et al. (1987) noted that more than half of the adult male breeding turkeys studied were lame at 55 weeks of age. Bipedal locomotion results from the repetition of coordinated hindlimb movements. Spatio-temporal coordination is linked to different gaits and is an expression of a species-specific locomotor pattern. This locomotor pattern is linked to morphological organisation and corresponds with the relatively low variation of body proportions observed in nature. The major morphological modifications produced by selection in broad-breasted turkeys causes them to be outside the natural phenotypic variation of the species Meleagris gallopavo. Besides the considerable weight increase in the broad-breasted strain, an altered distribution of body mass results from pectoral hypertrophy. Pectoral muscles represent 13% of body weight in traditional turkeys at 105 d and 20% in broad-breasted turkeys at the same age. It is of interest to compare the gait of broad-breasted turkeys with that of traditional turkeys to see if changes appear in the locomotor pattern of the species and if such morphological differences interfere in the bird's balance and its locomotor movements.
MATERIALS AND METHODS
Adult male turkeys of the 2 strains (traditional and breeder broadbreasted) selected by the Betina Society (St Nolff, 56250 Elven, France) were studied. Average weight of adult birds of the traditional strain was 8 kg; the broad-breasted turkeys' average weight was about 30 kg. All animals studied were healthy and without any lameness. Sixteen millimetre films were made on the farm and in the laboratory; 4 broad-breasted and 5 traditional turkeys were filmed. The walking speed was slow and a film frequency of 25 frames/s was sufficient. Reference spots were placed in the frame field to allow measurement of the birds' displacement. Turkeys were filmed in both lateral and posterior views. Films were analysed frame by frame. The gait analysis followed the method of Hildebrand (1966) for quadrupeds, modified by Hayes and Alexander (1983). Two main variables were recorded (1) the duration of the stance phase, i.e. contact with the substrate (which starts with the placement of all the toes and ends with the removal of the last toe); (2) the length of time between the start of the stance phases for the two limbs, expressed as a percentage of the cycle duration. The cycle includes both the swing phase, i.e. no contact with the substrate (beginning with the removal of the last toe and ending with the placement of all the toes) and the stance phase of a reference limb. On each sequence, frame number was used as a time base for events of the walk (i.e. the beginning and the end of each phase). Stride length was also measured, as the distance between two placement points of a given element of
273
COMPARATIVE GAIT ANALYSIS OF TURKEYS
i
(a)
œ w
(b)
3-
3-
2-
2-
1-
1-
I SÎ
Downloaded by [Monash University Library] at 16:42 06 March 2015
'>*''
'0'
/S' 'S/
f J
-F -
1
2 Cycle duration
3
1
2 Cycle duration
h.
3
(c) 3-
g
1 •o
a)
I
2-
H
-''•''
ÜB Traditional turkeys = ï î Broad-breasted turkeys
i
I
I
1
2 Cycle duration
3
FIG. 1.—Regression between stance-phase duration and cycle duration (in seconds). Dotted lines represent the predicted limits and fine dashed lines the 95% confidence limits; (a) broad-breasted turkeys, (b) traditional turkeys, and (c) both strains.
the foot; 42 cycles were analysed for traditional turkeys and 44 for the broadbreasted ones. In posterior views, lateral oscillations of the body could be estimated by the inclination of the line joining two points: the vent and the middle of the support base when the two feet were in contact with the ground. RESULTS
In the cycles analysed (42 in 4 broad-breasted birds and 44 in 5 traditional birds), mean values were calculated for the variables that are not linked to speed. Regression lines relating the duration of the stance phase to the cycle duration were calculated by minimising the sum of squares of the residuals (see
274
A. ABOURACHID
20100-10-
Downloaded by [Monash University Library] at 16:42 06 March 2015
-20-
20
50
70
100
% cycle
FIG. 2.—Lateral body oscillations during walking in broad-breasted turkeys (BB) and traditional turkeys (T). Horizontal lines below the graph represent the stance phases of the right and left limbs. Table). T h e difference between the start of the stance phases, in b o t h strains,
was close to 50% of the cycle: the gait was a normal walk as defined by Hayes and Alexander (1983). TABLE
Results of gait analysis. Means ± standard deviations Difference between the start of stance of stance phases (% of cycle duration) Stride length (ra) Hip height (m) Regression of stance-phase duration (Y) on cycle duration (X)
Broad-breasted
Traditional
47±8 0-36±0-03 0-48
52±9 0-30 ±0-02 0-40
-0-20±0-01 + 0-99±0-08XK = -0-23±0-02 + 0-96±0-01X
The stride length of traditional turkeys was shorter than that of broadbreasted ones. However, this value is generally related to hip height. Here, in both cases, it was 0-75 times the hip height. As the birds did not always walk at the same speed, and as the duration of the stance phase is linked to speed, it was necessary to investigate whether the function that relates stance phase to speed was similar in both cases. In order to calculate regressions for this relationship, cycle duration was substituted for speed, which could not be calculated for all cycles. These two values (speed and cycle duration) were closely correlated (r2 = 0-86). In both strains the intercepts were very close (—0-23 for traditional turkeys and —0-20 for broadbreasted ones) and the standard errors overlapped. The slopes were slightly, but not significantly, different (0-96 for traditional birds and 0-99 for broadbreasted ones) (Fig. 1). Analysis of the posterior views showed lateral oscillations of the body, very
COMPARATIVE GAIT ANALYSIS OF TURKEYS
275
Downloaded by [Monash University Library] at 16:42 06 March 2015
(a)
BB
(b)
BB
FIG. 3.—Lateral (a) and posterior (b) views of gait in broad-breasted (BB) and traditional (T) turkeys. Lateral views show almost no difference between strains but lateral oscillations are clearly seen in posterior view.
slight in traditional birds but very marked in broad-breasted ones (Fig. 2). The line that passes between the vent and the middle of the support base showed angular variations of 5° to either side of a vertical line during the traditional turkey's walk and more than 15° for the broad-breasted ones.
DISCUSSION
A classical analysis of gait, based on durations of stance and swing phases,
Downloaded by [Monash University Library] at 16:42 06 March 2015
276
A. ABOURACHID
did not detect any differences between the gait of the two turkey strains. There was no apparent modification by artificial selection of the locomotor pattern responsible for hindlimb synchronisation during walking. Broad-breasted turkey locomotion remained under the locomotor coordination which characterises the species. Posterior views of the birds showed that the morphological modifications produced by selection affect the birds' balance. However, because of the broadening of the breast resulting from the increase in pectoral volume, the legs of heavy turkeys were much further apart than in traditional birds. The support base was thus wider. During walking, the centre of gravity was brought over the stance foot to allow equilibrium (Fig. 3). The resulting modification of the gravity centre's path in broad-breasted turkeys contributed to balance but not to progression. The lateral oscillations, therefore, constituted a type of "parasitic" movement. In bipedal locomotion, lateral speed variation of the centre of gravity is negligible (Cavagna et al., 1963) and lateral movements are very small. This was the case in traditional turkeys but in broad-breasted ones the "parasitic" lateral oscillations must increase the energetic cost of walking. The muscular effort necessary to move the body from side to side would also produce fatigue which would accompany lameness. A dynamometric study, measuring the forces exerted on the ground by the feet, Avould allow verification of this point. If this is so, the general relationship that the cost of moving a gramme of body mass a given distance decreases as a function of increasing body mass (e.g. a 30 g quail uses approximately 13 times as much energy to move each gramme of its body as would a 100 kg ostrich (Taylor et al., 1982) would not be true for different strains of the same species. Conclusions
No changes in locomotor pattern, i.e. the coordination of hind limb movements were observed in broad-breasted turkeys as results of the morphological modifications produced by artificial selection. However, their gait had very marked lateral oscillations that possibly increase the energetic cost of walking and may be linked to lameness. Genotypic variability within a species may permit an increase in weight (Crawford, 1984), but mechanical constraints produce selection pressures which limit such evolution. The multiplication of locomotor problems, associated with weight increase in broad-breasted turkeys, is a first indication of this phenomenon. The question is how far can the phenotypic limits of the species be extended without serious functional problems.
ACKNOWLEDGEMENTS
I thank S. Renous for her useful comments and advice, J. P. Gase for valuable suggestions and G. Dingerkus for correction of English. I also thank the Laboratory of Comparative Anatomy of the Muséum National d'Histoire
COMPARATIVE GAIT ANALYSIS OF TURKEYS
277
Naturelle in Paris and UA1137 of the CNRS for technical assistance. This work was supported by the Betina Society and the Conseil Regional de Bretagne.
Downloaded by [Monash University Library] at 16:42 06 March 2015
REFERENCES CAVAGNA, G.A., SAIBENE, F.P. & MARGARIA, R. (1963) External work in walking. Journal of Applied Physiology, 18: 1-9. CLUTTON-BROCK, J. (1981) Domesticated animals from early times. Heinemann British Museum (Natural History), 208 pp. CRAWFORD, R.D. (1984) Turkey, in: I. L. MASON (Ed.) Evolution of domesticated animals, pp. 325-334 (London & N.Y., Longman). DAVEY, A.D. (1974) Canada, in: J. L. SKINNER (Ed.) American Poultry History 1823-1973, chapter 17 (Madison, Wisconsin, American Printing and Publishing). DUFF, S.R.I., HOCKING, P.M. & FIELD, R.K. (1987) The gross morphology of skeletal disease in adult male breeding turkeys. Avian Pathology, 16: 635-651. HAYES, G. & ALEXANDER, R . M C N . (1983) The hopping gaits of Crows (Corvidae) and other bipeds. Journal of Zoology, 200: 205-213. HILDEBRAND, M. (1966) Analysis of symmetrical gaits of Tetrapods. Folia Biotheoretica, 6: 1-22. TAYLOR, C.R., HEGLUND, N.C. & MALOY, G.M.O. (1982) Energetics and mechanics of terrestrial locomotion. I. Metabolic energy consumption as a function of speed and body size in birds and mammals. Journal of Experimental Biology, 97: 1-21.
