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Relationship of Feed Efficiency to Carcass Composition and Metabolic Rate in Laying Birds
Relationship of Feed Efficiency to Carcass Composition and Metabolic Rate in Laying Birds W. D. MORRISON and S. LEESON Department of Animal and Poultry Science, University of Guelph, Guelpb, Ontario, Canada (Received for publication September 30, 1977)
INTRODUCTION
Little attention has been given to date on studies of feed efficiency of the laying hen. With refined systems of management and nutrition, and an apparent plateau in egg numbers, future economic advantages may accrue from selection for the efficiency of conversion of feed into eggs. Joshi et al. (1948) showed considerable variation within full sister families for feed efficiency suggesting the possibility of genetical selection. More recently Hurnik (1977) demonstrated large differences in individual bird feed efficiency within a genetically controlled flock; some 37% of this variation remained unexplained after normal production characteristics were considered. In an attempt to explain some of the residual variability in feed efficiency, certain aspects of energy metabolism of birds selected for this trait have been studied. MATERIALS AND METHODS One thousand first generation individually caged SCWL birds selected on the basis of dam feed efficiency were themselves identified for this trait. Feed intake and production characteristics were measured according to the procedure described by Hurnik et al. (1977). After four months of production, 100 of these birds, which were excess genetical replicates, were made available for studies on energy metabo1978 Poultry Sci 57:735-739
lism. Feed wastage was measured and found not to be causative in feed efficiency variability. Carcass Analysis. In studying factors affecting feed efficiency, it is evident that differences in body weight gain and carcass composition are of prime importance. To this end the majority of birds were maintained through the production cycle on a crumbled corn-soybean diet with production data being recorded as previously described. After 12 months of production all birds were killed by cervical dislocation, and duplicate analyses for fat and protein were conducted on freeze-dried samples prepared from individual carcasses. Metabolic Rate. Due to the significance of basal metabolism in energy utilization, the involvement of this parameter in feed utilization was investigated. From the 100 bird population, four "efficient" and three "inefficient" (in terms of feed efficiency) birds were identified. The basis for selection was similarity in body weight, egg production, and egg size (Table 1). These birds were transferred to the metabolism chambers of an open circuit calorimeter. The efficient and inefficient birds were individually caged in identical chambers, maintained at 22 C and 70% relative humidity and provided with 14 hr of light per day. A crumbled diet (Table 2) was provided ad lib. throughout a 14 day acclimatization period. During this period the metabolizable energy level of the diet was measured by a total
735
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
ABSTRACT From a population of SCWL laying hens, 100 birds were classified according to their efficiency of conversion of feed to egg mass. From these, 4 "efficient" and 3 "inefficient" birds were used in energy metabolism studies involving indirect calorimetry, while the remainder were used for carcass analysis. Birds maintaining a criteria of 13.5—15.5 kg egg/48 weeks and classified as efficient or inefficient with respect to feed conversion had comparable body weight gains and did not differ significantly (P<.05) in the protein or fat content of their carcasses. In terms of energy metabolism, efficient and inefficient birds (selected on the basis of similar body size and egg mass production) showed no significant (P<.05) difference in their ability to metabolize dietary energy. In metabolism chambers, however, inefficient birds produced significantly (P<.01) more heat under conditions of ad lib. feeding (.148 vs. .121 kcal/min/kg ) and starvation (.110 vs. .090 kcal/min/kg ). From a videotaped study of bird activity there was an indication that this difference in metabolic rate was related to bird movement since inefficient birds spent less time resting and more time standing and feeding than did the efficient birds.
MORRISON AND LEESON
736
TABLE 1 .—Characteristics of experimental birds Efficient
Inefficient SE
Mean 1. 2. 3. 4. 5.
Feed efficiency Body weight (g) Feed intake (g/b/d) Egg production (%) Egg weight (g)
Mean
.02 65 1.6 3.6 1.8
2.02 1818 91.6 83.6 54.2
SE
2.48 1832 102.9 74.7 55.6
.01 53 4.4 1.9 3.0
Number of birds
Ingredient Ground corn Soybean meal (49%) Tallow Limestone Dicalcium phosphate Iodized salt Mineral/vitamin3DL-methionine L-lysine HC1
64.00 23.00 3.29 6.65 2.00 .25 .75 .03 .03
Calculated analysis Crude protein
16.8%
See Leeson and Summers (1976).
collection procedure comparable to that described by Leeson and Summers (1976). Heat production was measured by indirect calorimetry over 22 to 24 hr collection periods. Throughout this period, a continuous sampling of exhaust chamber gases resulted in a final sample of approximately 20 liters which was used for gas analysis. Two samples were simul-
tanously collected from each chamber. This continuous sampling system removed variation due to diurnal activity. Three replicate determinations were made over a 5 day period. After this time, feed was removed and measurements of fasting metabolic rate (FMR) were made over 24 to 48, 48 to 72, and 72 to 96 hr periods of starvation. Bird Activity. A measure of bird activity was thought necessary due to differences in FMR observed for the two groups of birds. As none of the birds showed any sign of molting after the 4 day starvation period, they were removed immediately to individual cages maintained in a windowless room. The dietary treatment and lighting program as used in the metabolism chambers were continued. After a 7 day acclimatization period, bird activity throughout the 14 hr light period was monitored by means of video equipment. Feeding and egg collection was carried out at the same time each day. Activity was monitored for 3 consecutive days. Individual bird activity was subsequently measured at the start of each 5 min period, giving a total of 168 observations per 14 hr day. Activities recorded were resting vs. standing,
TABLE 3 .—Production parameters and carcass composition of laying birds classified according to feed efficiency with no constraints imposed relating to egg mass production
Feed efficiency classification
Body weight gain (g)
Egg mass production (g)
Feed efficiency (g feed/ gegg)
1. Efficient (1.86-1.98) 2. Intermediate (2.55-2.61) 3. Inefficient (3.20-32.59)
529.4 545.0 772.8
16,393 12,504 3,232
1.92 2.58 11.36
'' Means followed by different letters are significantly different (P<.05).
Carcass composition (% DM) Crude protein
Fat
38.7 C 34.8 b 31.7^
55.7 a 60.8 b 62.2b
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
TABLE 2.—Experimental diet
737
RELATIONSHIP OF FEED EFFICIENCY IN LAYING BIRDS TABLE A.—Production parameters and carcass composition of laying birds producing 13.5—15.5 kg egg per year when classified according to feed efficiency Carcass composition a (% DM)
Feed efficiency classification
Body weight gain (g)
Egg mass production (g)
Feed efficiency (g feed/ gegg)
Crude protein
Fat
1. Efficient (X1.98) 2. Intermediate (2.32- 2.38) 3. Inefficient 0 2 . 6 2 )
508.1 502.1 563.7
14,799 14,210 14,139
1.93 2.36 2.74
36.6 36.6 36.5
57.5 57.6 59.8
TABLE 5.—Determined dietary energy
Metabolizable energy 0 (kcal/kg) a
metabolizable
Efficient birds a
Inefficient birds3-
3034
3009
54
33
See Table 1. Mean ± SE.
and within the latter category, whether or not the bird was feeding. RESULTS AND DISCUSSION The relationship between feed efficiency and carcass composition was arbitrarily classified according to differences in feed efficiency. When no constraint was imposed on egg mass production, body weight gain increased with deterioration in the level of feed efficiency and
was accompanied by significant (P=C05) decreases in carcass protien and increases in carcass fat content (Table 3). It is assumed that inefficiency was due to the production of carcass fat rather than egg mass. Within the population, however, it was possible to isolate approximately 16 birds per group that were efficient, intermediate, or inefficient in terms of feed efficiency, but produced a comparable egg mass (Table 4). In this situation body weight gain was comparable for all three groups, and there were no significant (P^.05) differences in the protein or fat content of their carcasses (Table 4). These data suggest that for high-producing birds, factors other than carcass size and composition are responsible for observed differences in feed efficiency confirming the observation of Hurnik (1977). When selected birds (Table 2) were transferred to metabolism chambers, no difference in the ability to metabolize dietary energy was observed (Table 5) for the two groups. With ad lib. feeding, inefficient birds produced significantly (P^.01) more heat per unit of metabolic
TABLE 6.—Energy metabolism with ad libitum feeding Replicate 1
2
3
Efficient birds c RQ Heat production kcal per min/kg-75
.69 .118
.80 .122
.80 .122
.76 .121
.06 .002a
Inefficient birds c RQ Heat production kcal permin/kg-75
.74 .147
.78 .149
.77 .149
.76 .148
.02 .001b
a,b
Means followed by different letters are significantly different (P<.01).
See Table 1.
Mean + SE
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
No significant differences (P<.05).
738
MORRISON AND LEESON TABLE 7 .—Fasting energy metabolism Replicate id
2e
3f
Efficient birds c RQ Heat production kcal per m i n / k g - "
.58 .105
.65 .093
.57 .087
.61 .090
.04 .01a
Inefficient birds c RQ Heat production kcal per min/kg-75
.60 .116
.64 .105
.60 .108
.62 .107
.02 .006°
Mean ± SE?
c
See Table 1.
d e f
' ' 2 4 - 4 8 hr, 4 8 - 7 2 hr, and 7 2 - 9 6 hr of fasting, respectively.
^Mean of replicate observations 2 and 3.
body size than did the efficient birds (Table 6). This difference in heat output was maintained when birds were starved (Table 7), demonstrating true differences in FMR. As no eggs were produced after 36 hr of starvation, this difference in FMR was not related to egg production, although Balnave (1974) cites evidence that even under conditions of starvation, hens utilize body reserves for eggs with an associated heat production. Ota and McNally (1961), however, failed to show any relationship between egg and heat production. The difference in FMR observed between the two groups of birds is substantially greater than the variability in FMR noted for individual animals (Blaxter, 1969). Since activity can represent a substantial proportion of the maintenance requirement, the results obtained for bird activity during the
light period are of importance (Table 8). They indicated that efficient birds were less active, and spent more time resting and less time standing than inefficient birds. The inefficient birds also spent considerably more time at the feed trough (Table 8). Such effects may be of importance in explaining differences in FMR since standing and associated activities, and eating per se, can increase heat production by 25% and 37% respectively (Van Kampen, 1976). However, the variability noted in replicate observations (Table 8) precludes any definite answer to the relationship between activity and FMR in this situation. In search for alternate explanations for differences in FMR obsered for the efficient and inefficient birds, it is evident that feather cover may be of importance. Although feather cover was not measured in this work, O'Neill et
TABLE 8.—Bird activity (hr/14 hr light period) Replicate observation
Resting
Standing
Eating
Efficient birds a
1 2 3 Mean
1.69 4.38 5.48 3.85
12.32 9.62 8.52 10.15
4.19 2.66 1.51 2.79
Inefficient birds a
1 2 3 Mean
1.11 2.35 2.80 2.08
12.89 11.15 11.20 11.91
5.44 2.12 1.96 3.18
See Table 1.
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
a ' b Means followed by different letters are significantly different (P<.01).
RELATIONSHIP OF FEED EFFICIENCY IN LAYING BIRDS al. ( 1 9 7 1 ) indicated t h a t at 22 C (the temperature maintained in this study) the F M R of defeathered cockerels was 2.5 X greater than t h a t of feathered cockerels. Since this same work indicated n o such differences at 38 C, it m a y be useful t o use elevated t e m p e r a t u r e s in future work of this t y p e . A t t h e same time it m a y also be advantageous t o test for differences in F M R a t different ages of bird, since Leeson and Porter-Smith ( 1 9 7 0 ) indicated an increase in F M R with d u r a t i o n of t h e p r o d u c t i o n cycle.
T h e a u t h o r s are i n d e b t e d t o Dr. H. S. Bayley for making available calorimetry facilities and to Dr. F. Hurnik for providing t h e e x p e r i m e n t a l birds. This work was s u p p o r t e d by t h e National Research Council and t h e Ontario Ministry of Agriculture and F o o d . REFERENCES Balnave, D., 1974. Biological factors affecting energy expenditure. In Energy requirements for poultry. T. R. Morris and B. M. Freeman, ed. Br. Poultry Sci., Edinburgh. Blaxter, K. L., 1969. The energy metabolism of ruminants. Hutchinson Sci. and Techn., London, p.
95.
Hurnik, J. F., 1977. The effect of feed consumption, feeding behaviour and feed conversion on the individual profitability of birds. Proc. Poultry Industr. School, Guelph, Ontario. Hurnik, J. F., J. D. Summers, B. S. Reinhart, and E. M. Swierczewska, 1977. Effect of age on the performance of laying hens during the first year of production. Poultry Sci. 56:222-230. Joshi, B. C , C. S. Shaffner and M. A. Jull, 1948. Studies on feed efficiency in relation to egg production. Poultry Sci., 27:670. Leeson, S., and A. J. Porter-Smith, 1970. A study of changes in fasting metabolic rate with duration of egg production in the domestic fowl. Br. Poultry Sci., 11:275-279. Leeson, S., and J. D. Summers, 1976. Effect of adverse growing conditions on corn maturity and feeding value for poultry. Poultry Sci., 55:588-593. O'Neill, S. J. B., 1971. Calorimetric studies on the effect of feathering and environmental temperature on heat production by the domestic fowl. Ph.D. Thesis. Queen's University, Belfast, N. Ireland. Ota, H., and McNally, E. H., 1961. Poultry respiration calorimetric studies of laying hens—Single Comb White Leghorns, Rhode Island Reds and New Hampshire X Cornish crosses. ARS 42—43. U.S. Dept. Agri. Washington, DC. Van Kampen, M., 1976. Activity and energy expenditure in laying hens. 3. The energy cost of eating and posture. J. Agr. Sci., Camb., 87:85-88.
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
ACKNOWLEDGEMENTS
739
INTRODUCTION
Little attention has been given to date on studies of feed efficiency of the laying hen. With refined systems of management and nutrition, and an apparent plateau in egg numbers, future economic advantages may accrue from selection for the efficiency of conversion of feed into eggs. Joshi et al. (1948) showed considerable variation within full sister families for feed efficiency suggesting the possibility of genetical selection. More recently Hurnik (1977) demonstrated large differences in individual bird feed efficiency within a genetically controlled flock; some 37% of this variation remained unexplained after normal production characteristics were considered. In an attempt to explain some of the residual variability in feed efficiency, certain aspects of energy metabolism of birds selected for this trait have been studied. MATERIALS AND METHODS One thousand first generation individually caged SCWL birds selected on the basis of dam feed efficiency were themselves identified for this trait. Feed intake and production characteristics were measured according to the procedure described by Hurnik et al. (1977). After four months of production, 100 of these birds, which were excess genetical replicates, were made available for studies on energy metabo1978 Poultry Sci 57:735-739
lism. Feed wastage was measured and found not to be causative in feed efficiency variability. Carcass Analysis. In studying factors affecting feed efficiency, it is evident that differences in body weight gain and carcass composition are of prime importance. To this end the majority of birds were maintained through the production cycle on a crumbled corn-soybean diet with production data being recorded as previously described. After 12 months of production all birds were killed by cervical dislocation, and duplicate analyses for fat and protein were conducted on freeze-dried samples prepared from individual carcasses. Metabolic Rate. Due to the significance of basal metabolism in energy utilization, the involvement of this parameter in feed utilization was investigated. From the 100 bird population, four "efficient" and three "inefficient" (in terms of feed efficiency) birds were identified. The basis for selection was similarity in body weight, egg production, and egg size (Table 1). These birds were transferred to the metabolism chambers of an open circuit calorimeter. The efficient and inefficient birds were individually caged in identical chambers, maintained at 22 C and 70% relative humidity and provided with 14 hr of light per day. A crumbled diet (Table 2) was provided ad lib. throughout a 14 day acclimatization period. During this period the metabolizable energy level of the diet was measured by a total
735
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
ABSTRACT From a population of SCWL laying hens, 100 birds were classified according to their efficiency of conversion of feed to egg mass. From these, 4 "efficient" and 3 "inefficient" birds were used in energy metabolism studies involving indirect calorimetry, while the remainder were used for carcass analysis. Birds maintaining a criteria of 13.5—15.5 kg egg/48 weeks and classified as efficient or inefficient with respect to feed conversion had comparable body weight gains and did not differ significantly (P<.05) in the protein or fat content of their carcasses. In terms of energy metabolism, efficient and inefficient birds (selected on the basis of similar body size and egg mass production) showed no significant (P<.05) difference in their ability to metabolize dietary energy. In metabolism chambers, however, inefficient birds produced significantly (P<.01) more heat under conditions of ad lib. feeding (.148 vs. .121 kcal/min/kg ) and starvation (.110 vs. .090 kcal/min/kg ). From a videotaped study of bird activity there was an indication that this difference in metabolic rate was related to bird movement since inefficient birds spent less time resting and more time standing and feeding than did the efficient birds.
MORRISON AND LEESON
736
TABLE 1 .—Characteristics of experimental birds Efficient
Inefficient SE
Mean 1. 2. 3. 4. 5.
Feed efficiency Body weight (g) Feed intake (g/b/d) Egg production (%) Egg weight (g)
Mean
.02 65 1.6 3.6 1.8
2.02 1818 91.6 83.6 54.2
SE
2.48 1832 102.9 74.7 55.6
.01 53 4.4 1.9 3.0
Number of birds
Ingredient Ground corn Soybean meal (49%) Tallow Limestone Dicalcium phosphate Iodized salt Mineral/vitamin3DL-methionine L-lysine HC1
64.00 23.00 3.29 6.65 2.00 .25 .75 .03 .03
Calculated analysis Crude protein
16.8%
See Leeson and Summers (1976).
collection procedure comparable to that described by Leeson and Summers (1976). Heat production was measured by indirect calorimetry over 22 to 24 hr collection periods. Throughout this period, a continuous sampling of exhaust chamber gases resulted in a final sample of approximately 20 liters which was used for gas analysis. Two samples were simul-
tanously collected from each chamber. This continuous sampling system removed variation due to diurnal activity. Three replicate determinations were made over a 5 day period. After this time, feed was removed and measurements of fasting metabolic rate (FMR) were made over 24 to 48, 48 to 72, and 72 to 96 hr periods of starvation. Bird Activity. A measure of bird activity was thought necessary due to differences in FMR observed for the two groups of birds. As none of the birds showed any sign of molting after the 4 day starvation period, they were removed immediately to individual cages maintained in a windowless room. The dietary treatment and lighting program as used in the metabolism chambers were continued. After a 7 day acclimatization period, bird activity throughout the 14 hr light period was monitored by means of video equipment. Feeding and egg collection was carried out at the same time each day. Activity was monitored for 3 consecutive days. Individual bird activity was subsequently measured at the start of each 5 min period, giving a total of 168 observations per 14 hr day. Activities recorded were resting vs. standing,
TABLE 3 .—Production parameters and carcass composition of laying birds classified according to feed efficiency with no constraints imposed relating to egg mass production
Feed efficiency classification
Body weight gain (g)
Egg mass production (g)
Feed efficiency (g feed/ gegg)
1. Efficient (1.86-1.98) 2. Intermediate (2.55-2.61) 3. Inefficient (3.20-32.59)
529.4 545.0 772.8
16,393 12,504 3,232
1.92 2.58 11.36
'' Means followed by different letters are significantly different (P<.05).
Carcass composition (% DM) Crude protein
Fat
38.7 C 34.8 b 31.7^
55.7 a 60.8 b 62.2b
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
TABLE 2.—Experimental diet
737
RELATIONSHIP OF FEED EFFICIENCY IN LAYING BIRDS TABLE A.—Production parameters and carcass composition of laying birds producing 13.5—15.5 kg egg per year when classified according to feed efficiency Carcass composition a (% DM)
Feed efficiency classification
Body weight gain (g)
Egg mass production (g)
Feed efficiency (g feed/ gegg)
Crude protein
Fat
1. Efficient (X1.98) 2. Intermediate (2.32- 2.38) 3. Inefficient 0 2 . 6 2 )
508.1 502.1 563.7
14,799 14,210 14,139
1.93 2.36 2.74
36.6 36.6 36.5
57.5 57.6 59.8
TABLE 5.—Determined dietary energy
Metabolizable energy 0 (kcal/kg) a
metabolizable
Efficient birds a
Inefficient birds3-
3034
3009
54
33
See Table 1. Mean ± SE.
and within the latter category, whether or not the bird was feeding. RESULTS AND DISCUSSION The relationship between feed efficiency and carcass composition was arbitrarily classified according to differences in feed efficiency. When no constraint was imposed on egg mass production, body weight gain increased with deterioration in the level of feed efficiency and
was accompanied by significant (P=C05) decreases in carcass protien and increases in carcass fat content (Table 3). It is assumed that inefficiency was due to the production of carcass fat rather than egg mass. Within the population, however, it was possible to isolate approximately 16 birds per group that were efficient, intermediate, or inefficient in terms of feed efficiency, but produced a comparable egg mass (Table 4). In this situation body weight gain was comparable for all three groups, and there were no significant (P^.05) differences in the protein or fat content of their carcasses (Table 4). These data suggest that for high-producing birds, factors other than carcass size and composition are responsible for observed differences in feed efficiency confirming the observation of Hurnik (1977). When selected birds (Table 2) were transferred to metabolism chambers, no difference in the ability to metabolize dietary energy was observed (Table 5) for the two groups. With ad lib. feeding, inefficient birds produced significantly (P^.01) more heat per unit of metabolic
TABLE 6.—Energy metabolism with ad libitum feeding Replicate 1
2
3
Efficient birds c RQ Heat production kcal per min/kg-75
.69 .118
.80 .122
.80 .122
.76 .121
.06 .002a
Inefficient birds c RQ Heat production kcal permin/kg-75
.74 .147
.78 .149
.77 .149
.76 .148
.02 .001b
a,b
Means followed by different letters are significantly different (P<.01).
See Table 1.
Mean + SE
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
No significant differences (P<.05).
738
MORRISON AND LEESON TABLE 7 .—Fasting energy metabolism Replicate id
2e
3f
Efficient birds c RQ Heat production kcal per m i n / k g - "
.58 .105
.65 .093
.57 .087
.61 .090
.04 .01a
Inefficient birds c RQ Heat production kcal per min/kg-75
.60 .116
.64 .105
.60 .108
.62 .107
.02 .006°
Mean ± SE?
c
See Table 1.
d e f
' ' 2 4 - 4 8 hr, 4 8 - 7 2 hr, and 7 2 - 9 6 hr of fasting, respectively.
^Mean of replicate observations 2 and 3.
body size than did the efficient birds (Table 6). This difference in heat output was maintained when birds were starved (Table 7), demonstrating true differences in FMR. As no eggs were produced after 36 hr of starvation, this difference in FMR was not related to egg production, although Balnave (1974) cites evidence that even under conditions of starvation, hens utilize body reserves for eggs with an associated heat production. Ota and McNally (1961), however, failed to show any relationship between egg and heat production. The difference in FMR observed between the two groups of birds is substantially greater than the variability in FMR noted for individual animals (Blaxter, 1969). Since activity can represent a substantial proportion of the maintenance requirement, the results obtained for bird activity during the
light period are of importance (Table 8). They indicated that efficient birds were less active, and spent more time resting and less time standing than inefficient birds. The inefficient birds also spent considerably more time at the feed trough (Table 8). Such effects may be of importance in explaining differences in FMR since standing and associated activities, and eating per se, can increase heat production by 25% and 37% respectively (Van Kampen, 1976). However, the variability noted in replicate observations (Table 8) precludes any definite answer to the relationship between activity and FMR in this situation. In search for alternate explanations for differences in FMR obsered for the efficient and inefficient birds, it is evident that feather cover may be of importance. Although feather cover was not measured in this work, O'Neill et
TABLE 8.—Bird activity (hr/14 hr light period) Replicate observation
Resting
Standing
Eating
Efficient birds a
1 2 3 Mean
1.69 4.38 5.48 3.85
12.32 9.62 8.52 10.15
4.19 2.66 1.51 2.79
Inefficient birds a
1 2 3 Mean
1.11 2.35 2.80 2.08
12.89 11.15 11.20 11.91
5.44 2.12 1.96 3.18
See Table 1.
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
a ' b Means followed by different letters are significantly different (P<.01).
RELATIONSHIP OF FEED EFFICIENCY IN LAYING BIRDS al. ( 1 9 7 1 ) indicated t h a t at 22 C (the temperature maintained in this study) the F M R of defeathered cockerels was 2.5 X greater than t h a t of feathered cockerels. Since this same work indicated n o such differences at 38 C, it m a y be useful t o use elevated t e m p e r a t u r e s in future work of this t y p e . A t t h e same time it m a y also be advantageous t o test for differences in F M R a t different ages of bird, since Leeson and Porter-Smith ( 1 9 7 0 ) indicated an increase in F M R with d u r a t i o n of t h e p r o d u c t i o n cycle.
T h e a u t h o r s are i n d e b t e d t o Dr. H. S. Bayley for making available calorimetry facilities and to Dr. F. Hurnik for providing t h e e x p e r i m e n t a l birds. This work was s u p p o r t e d by t h e National Research Council and t h e Ontario Ministry of Agriculture and F o o d . REFERENCES Balnave, D., 1974. Biological factors affecting energy expenditure. In Energy requirements for poultry. T. R. Morris and B. M. Freeman, ed. Br. Poultry Sci., Edinburgh. Blaxter, K. L., 1969. The energy metabolism of ruminants. Hutchinson Sci. and Techn., London, p.
95.
Hurnik, J. F., 1977. The effect of feed consumption, feeding behaviour and feed conversion on the individual profitability of birds. Proc. Poultry Industr. School, Guelph, Ontario. Hurnik, J. F., J. D. Summers, B. S. Reinhart, and E. M. Swierczewska, 1977. Effect of age on the performance of laying hens during the first year of production. Poultry Sci. 56:222-230. Joshi, B. C , C. S. Shaffner and M. A. Jull, 1948. Studies on feed efficiency in relation to egg production. Poultry Sci., 27:670. Leeson, S., and A. J. Porter-Smith, 1970. A study of changes in fasting metabolic rate with duration of egg production in the domestic fowl. Br. Poultry Sci., 11:275-279. Leeson, S., and J. D. Summers, 1976. Effect of adverse growing conditions on corn maturity and feeding value for poultry. Poultry Sci., 55:588-593. O'Neill, S. J. B., 1971. Calorimetric studies on the effect of feathering and environmental temperature on heat production by the domestic fowl. Ph.D. Thesis. Queen's University, Belfast, N. Ireland. Ota, H., and McNally, E. H., 1961. Poultry respiration calorimetric studies of laying hens—Single Comb White Leghorns, Rhode Island Reds and New Hampshire X Cornish crosses. ARS 42—43. U.S. Dept. Agri. Washington, DC. Van Kampen, M., 1976. Activity and energy expenditure in laying hens. 3. The energy cost of eating and posture. J. Agr. Sci., Camb., 87:85-88.
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 6, 2015
ACKNOWLEDGEMENTS
739