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Effects of Reduced Feeding Time Using All Mash or Crumble-Pellet Dietary Regimens on Chicken Broiler Performance, Including the Incidence of Acute Death Syndrome1
Effects of Reduced Feeding Time Using All Mash or Crumble-Pellet Dietary Regimens on Chicken Broiler Performance, Including - the Incidence of Acute Death Syndrome1 F. G. PROUDFOOT and H. W. HULAN Agriculture Canada, Research Station, Kentville, Nova Scotia B4N 1J5 (Received for publication June 17, 1981) ABSTRACT A total of 2400 commercial broiler chickens (1200 males and 1200 females) were used in an experiment designed to estimate the effect on performances of restricting feeding time to 8, 10, 12, 14, 16, or 24 hr per day from 21 to 49 days of age (slaughter age) and the effect of using an all-mash versus a crumble-pellet feeding regimen. Restricting the feeding time had a significant effect on the body weights of both males and females at 28 and 49 days, with body weights being heavier as feeding time increased. Significant effects among feeding times also occurred for monetary returns per bird over feed and chick cost, but a linear trend was not evident. Feeding crumble-pellet diets resulted in increased body weights at 21, 28, and 49 days, improved feed conversion, more grade A carcasses, and increased monetary returns. Mortality was also significantly higher for birds grown on the crumble-pellet feeding regimen. This higher mortality was attributed to deaths due to acute death syndrome ("flip-over"), which was significantly higher among males on the crumble-pellet dietary regimen than on the all-mash dietary regimen. There is no evidence that interactions between feeding time and feed texture occurred for any of the traits measured. (Key words: feeding time, feed texture, acute death syndrome, broilers, growth, feed conversion) 1982 Poultry Science 61:750-754
INTRODUCTION
An earlier report revealed that broiler chickens on a crumble-pellet dietary regimen could withstand a feeding time of as short as 16 hr per day commencing as early as 21 days of age (Proudfoot and Hulan, 1982). There is considerable evidence that broiler chickens on a crumble-pellet dietary regimen will outperform birds on an all-mash program (Calet, 1965; Proudfoot and Sefton, 1978). With the cost of pelleting continuing to increase, the question arises whether this superior biological performance is currently reflected in an economic advantage. This experiment was conducted to estimate the effects of reducing the feeding time to as low as 8 hr per day, commencing at 21 days of age, on broiler chickens fed either an all-mash or crumble-pellet dietary regimen. MATERIALS AND METHODS
A windowless brooding and rearing house containing 24 pens, each with a floor area of
'Contribution No. 1732.
13.54 m , was used for this experiment. The 24 pens used in this experiment were separated by a central alleyway with 12 pens on each side of the alleyway. A total of 2400 Cobb (feathersexed) chicken broilers were randomly assigned to 24 pens with 50 male and 50 female chickens in each pen. All birds received continuous lighting. Light intensity was reduced from 25 lx at day-old to .5 lx at 21 days through to the end of the experiment. Each pen was equipped with one hanging circular type waterer with a pan diameter of 35.6 cm. Cylindrical feeders were used with a pan diameter of 36.8 cm. Four feeders were allotted to each pen initially with an increase to 5 per pen at 28 days of age. Diets (starter and finisher) fed are shown in Table 1. The starter was fed as crumbles to 28 days and the finisher fed as pellets from 29 to 49 days (slaughter age). All feeds were pelleted and/or crumbled using a steam-pressure-die process. Pellet diameter was .48 cm with pellet length being approximately 1.25 cm. All-mash feeding was randomly assigned to 6 pens on each side of the central alleyway with the remaining pens assigned to the crumble-pellet dietary regimen. Duplicate pens for 750
FEED RESTRICTION AND TEXTURE EFFECTS TABLE 1. Diet composition Starter
Finisher (g/kg)
Ground corn Ground wheat Stabilized tallow Soybean meal (50%) Fishmeal (63%) Ground limestone Dical-phosphate Iodized salt Micronutrients a Calculated analyses: Crude protein (%) ME (MJ/kg)
450 160 20 295 50 9 6 5 5
24.0 12.45
580 220 30 94 50 8 8 5 5
15.9 13.28
Supplied per kilogram of diet: 9000 IU vitamin A; 2000 ICU vitamin D 3 ; 8 mg riboflavin; 12 mg dcalcium pantothenate; 12 Mg vitamin B 12 ; 30mgniacin; 3 mg vitamin K; 1 mg folic acid; 100 Mg biotin; 800 mg choline chloride (50%); 7 IU vitamin E; 5 mg pyridoxine; 3 mg thiamine; 450 mg DL-methionine; 112 mg manganese oxide (60% Mn); 83 mg zinc oxide (72% Zn); 20 mg copper sulfate (25% Cu); 219 Mg sodium selenite (45% Se); 100 mg ethoxyquin; 680 mg amprolium (250 g/kg); enough ground corn to make 5
g-
each dietary regimen, one on each side of the alleyway, were randomly assigned to each continuous reduced feeding time treatment. Feed denial treatments consisted of removing feeders for a period of 0, 8, 10, 12, 14, and 16 hr each day, commencing at 21 days of age. Traits measured were: percentage mortality of males and females from 0 to 49 days; incidence of birds dying from acute death syndrome; body weights of males and females at 21, 28, and 49 days; feed conversion up to 21, 28, and 49 days, calculated as the unit weight of feed per unit body weight. The calculation of monetary returns over the cost of feed and chicks was based on current market prices (Canadian monetary system). Feed prices were as follows: starter crumbles, 36.65
751
means and all percentage data converted to angles for statistical analysis, while counts of birds dying from acute death syndrome were treated as Poisson counts and transformed to the V x + 1 scale (Steel and Torrie, 1960).
RESULTS AND DISCUSSION Because the density of feed is enhanced by the crumbling and pelleting process, it was considered probable that first-order interactions between feed texture and feeding time might occur for at least some of the traits measured. There was, however, a complete absence of such interactions for all traits measured. In the absence of significant first-order interactions between feed texture and restricted feeding treatments, the two main effects are considered separately. Feed Restriction Treatments. As feed restriction treatments commenced when birds were 21 days of age, there were no feed restriction treatment effects for traits measured at that age (i.e., body weights and feed conversion). Although somewhat variable, mortality of males and females was unaffected by the different time periods of feed restriction (Table 2). Body weight measurements conducted at 28 and 49 days were significantly altered in a linear fashion by the duration of feeding time with body weights of both males and females being heavier with the longer daily feeding periods. Although feed conversion at 28 days was not significantly affected by duration of feeding time, feed conversion at 49 days improved as feeding time was reduced from 24 to 8 hr per day. These results may appear to be contrary to our earlier report (Proudfoot and Hulan, 1982), but in the earlier work a feeding time of 16 hr per day was compared with full feeding time (24 hr). Eight hours of restriction did not appear to be a sufficiently long enough period of time to effect an improvement in feed conversion. Similarly, Beane et al. (1979) reported that restricting feed intake to 85% of full fed controls between 15 and 42 days of age resulted in the full-fed controls exhibiting greater gains and better feed conversion. However, enhanced feed conversion associated with restricted feeding time is supported by Yule and Fuelling (1979), Yule et al. (1979), and McCartney and Brown (1977). The proportion of Grade A carcasses were not significantly affected by feeding time restriction. Monetary returns over the cost of
**
7.07 12.27 1.251
NS
13.64 4.07 7.61 11.91 9.03 11.80 2.167
(angles)
*
5.68 9.67 1.301
NS
9.12 10.50 7.91 6.43 8.46 3.64 5.081
(angles)
(2.0) (3.5)
(3.5) (3.5) (2.6) (2.5) (3.0) (1.6)
(%)
Significant **P<.01; *P<.05;and NS; not significant PX05.
Standard error of the mean with the number of observations in parentheses.
(2.2) (5.2)
(6.0) (1.0) (2.5) (4.5) (3.5) (4.6)
(%)
Females
Mortality 0 to 49 days
Males
Detransformed from •«Jx — 1 scale.
Feed texture Ali mash Crumbles and pellets SE(ll) Significance
SE (4) b Significance0
8 10 12 14 16 24
Feed period (hr)
Main effects
*
1.187 1.617 .0996
NS
1.699 1.207 1.287 1.433 1.433 1.353 .1725
(N/X^T)
Males
(.41) (1.62)
(1.89) (.46) (.65) (1.05) (1.05) (.83)
(no.)*
NS
1.103 1.234 .0974
NS
1.000 1.207 1.286 1.207 1.207 1.104 .0562
(Vx-1)
Females
Mortality due to acute death syndrome
(.22) (.52)
(.46) (.65) (.46) (.46) (.22)
(0)
(no.)
**
563 629 3.8
594 605 592 599 595 590 6.5 NS
Male
21
TABLE 2. Effect of restricting feeding time and feed texture on mortality, incidence of acute d and body weights of broiler chickens
c
See footnote c, Table 2.
See footnote b, Table 2.
Detransformed angles.
**
**
1.576 1.616 1.552 1.559 1.564 1.607 .0164 NS
1.599 1.558 .0095
Feed period (hr) 8 10 12 14 16 24 SE (4)b Significance0
28 days
Feed conversion
1.484 1.404 .0058
1.452 1.438 1.444 1.441 1.438 1.450 .0101 NS
Main effects
Feed texture All-mash Crumbles and pellets SE(12) Significance
21 days
*
2.008 1.959 .0164
*
1.952 1.917 1.934 2.054 2.023 2.022 .0285
49 days
**
49.90 56.34 1.185
51.72 55.06 50.16 53.63 51.31 56.83 2.053 NS
(angles)
Males
(58.4) (69.1)
(61.4) (67.1) (58.8) (64.7) (60.6) (70.0)
(%)a
Grade
TABLE 3. Effect of restricted feeding time and feed texture on feed conversion, and monetary returns of chicken broilers
754
PROUDFOOT AND HULAN
feed and chicks were significantly affected by duration of feeding. However, no particular trends associated with feeding time were evident as results were highly variable. The advantages of improved feed conversion were offset in part by the disadvantage of lighter body weights. Also, there appeared to be more food retention prior to slaughter among birds which were on the shorter daily feeding times. As revenue for the sale of meat is based on live weights, the method used to estimate economic gain associated with these treatments may be inadequate. General observations also revealed that birds subjected to reduced feeding time tended to have enlarged crops with more feed retention prior to slaughter and to have a tendency toward pendulous crops, particularly among those birds fed the all-mash diets. It may be possible to use a feed restriction procedure early in the life of the broiler chicken to stimulate an enlargement of the crop and possibly other digestive organs, so that birds returned to full-feeding would have increased capacity in the digestive tract to enable improved growth rates. Feed Texture. Birds fed crumbled starter and pelleted finisher diets exhibited superior performance for practically all traits measured compared to birds on all-mash starter and finisher diets (Tables 2 and 3). Mortality was higher for both males and females fed the crumble-pellet diets than for those on all-mash. This higher mortality is attributed to the significantly larger number of males dying from acute death syndrome (flip-over) when fed on the crumble-pellet feeds compared with those fed the all-mash dietary regimen (Hulan et al., 1980). Further experimentation is being undertaken to collect more data before conclusions are drawn. Not only did the crumble-pelleting process result in body weights being heavier at all ages (21, 28, and 49 days) for both males and females, but feed conversion was also significantly improved and the percentage of carcasses graded A was also increased. Birds fed crumbled-pelleted diets had their profit margin increased by 8
despite a feed cost increase of l<£/kg of feed for the crumbling-pelleting process. These results support those of Proudfoot and Sefton (1978) and Calet (1965) who reported that the performance of broiler chicks fed pelleted diets was superior compared to birds on all-mash diets. It is concluded that, despite the increased incidence of acute death syndrome associated with crumble-pelletfed feed, it continues to be advantageous both biologically and economically to feed broiler chickens crumbled starter and pelleted finisher diets compared with an all-mash dietary regimen.
ACKNOWLEDGMENT The authors acknowledge the advice and assistance freely given by Ken McRae for statistical analysis of the data presented. REFERENCES Beane, W. L., J. A. Cherry, and W. D. Weaver, Jr., 1979. Intermittant light and restricted feeding of broiler chickens. Poultry Sci. 58:567-571. Calet, C , 1965. The relative value of pellets versus mash and grain in poultry nutrition. World's Poultry Sci. J. 21:23-52. Hulan, H. W., F. G. Proudfoot, and K. B. McRae, 1980. Effect of vitamins on the incidence of mortality and acute death syndrome ('flip-over") in broiler chickens. Poultry Sci. 59:927—931. McCartney, M. G., and H. B. Brown, 1977. The effects of feed restriction time on the growth and feed conversion of broiler males. Poultry Sci. 56: 713-715. Proudfoot, F. G., and H. W. Hulan, 1982. The effect of toe clipping and reduced feeding time on the general performance of broiler chickens. Can. J. Anim. Sci. (In press). Proudfoot, F. G., and A. E. Sefton, 1978. Feed texture and light treatment effects on the performance of chicken broilers. Poultry Sci. 57:408— 416. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw Hill Book Co., New York, NY. Yule, W. J., K. M. Barrum, and H. W. Burton, 1979. Effect of access time to food on broilers fed on diets of differing nutrient concentration. Brit. Poultry Sci. 20:311-316. Yule, W. J., and D. E. Fuelling, 1979. Effect of different patterns of food restriction from different ages on growth and efficiency of broilers. Brit. Poultry Sci. 20:273-279.
INTRODUCTION
An earlier report revealed that broiler chickens on a crumble-pellet dietary regimen could withstand a feeding time of as short as 16 hr per day commencing as early as 21 days of age (Proudfoot and Hulan, 1982). There is considerable evidence that broiler chickens on a crumble-pellet dietary regimen will outperform birds on an all-mash program (Calet, 1965; Proudfoot and Sefton, 1978). With the cost of pelleting continuing to increase, the question arises whether this superior biological performance is currently reflected in an economic advantage. This experiment was conducted to estimate the effects of reducing the feeding time to as low as 8 hr per day, commencing at 21 days of age, on broiler chickens fed either an all-mash or crumble-pellet dietary regimen. MATERIALS AND METHODS
A windowless brooding and rearing house containing 24 pens, each with a floor area of
'Contribution No. 1732.
13.54 m , was used for this experiment. The 24 pens used in this experiment were separated by a central alleyway with 12 pens on each side of the alleyway. A total of 2400 Cobb (feathersexed) chicken broilers were randomly assigned to 24 pens with 50 male and 50 female chickens in each pen. All birds received continuous lighting. Light intensity was reduced from 25 lx at day-old to .5 lx at 21 days through to the end of the experiment. Each pen was equipped with one hanging circular type waterer with a pan diameter of 35.6 cm. Cylindrical feeders were used with a pan diameter of 36.8 cm. Four feeders were allotted to each pen initially with an increase to 5 per pen at 28 days of age. Diets (starter and finisher) fed are shown in Table 1. The starter was fed as crumbles to 28 days and the finisher fed as pellets from 29 to 49 days (slaughter age). All feeds were pelleted and/or crumbled using a steam-pressure-die process. Pellet diameter was .48 cm with pellet length being approximately 1.25 cm. All-mash feeding was randomly assigned to 6 pens on each side of the central alleyway with the remaining pens assigned to the crumble-pellet dietary regimen. Duplicate pens for 750
FEED RESTRICTION AND TEXTURE EFFECTS TABLE 1. Diet composition Starter
Finisher (g/kg)
Ground corn Ground wheat Stabilized tallow Soybean meal (50%) Fishmeal (63%) Ground limestone Dical-phosphate Iodized salt Micronutrients a Calculated analyses: Crude protein (%) ME (MJ/kg)
450 160 20 295 50 9 6 5 5
24.0 12.45
580 220 30 94 50 8 8 5 5
15.9 13.28
Supplied per kilogram of diet: 9000 IU vitamin A; 2000 ICU vitamin D 3 ; 8 mg riboflavin; 12 mg dcalcium pantothenate; 12 Mg vitamin B 12 ; 30mgniacin; 3 mg vitamin K; 1 mg folic acid; 100 Mg biotin; 800 mg choline chloride (50%); 7 IU vitamin E; 5 mg pyridoxine; 3 mg thiamine; 450 mg DL-methionine; 112 mg manganese oxide (60% Mn); 83 mg zinc oxide (72% Zn); 20 mg copper sulfate (25% Cu); 219 Mg sodium selenite (45% Se); 100 mg ethoxyquin; 680 mg amprolium (250 g/kg); enough ground corn to make 5
g-
each dietary regimen, one on each side of the alleyway, were randomly assigned to each continuous reduced feeding time treatment. Feed denial treatments consisted of removing feeders for a period of 0, 8, 10, 12, 14, and 16 hr each day, commencing at 21 days of age. Traits measured were: percentage mortality of males and females from 0 to 49 days; incidence of birds dying from acute death syndrome; body weights of males and females at 21, 28, and 49 days; feed conversion up to 21, 28, and 49 days, calculated as the unit weight of feed per unit body weight. The calculation of monetary returns over the cost of feed and chicks was based on current market prices (Canadian monetary system). Feed prices were as follows: starter crumbles, 36.65
751
means and all percentage data converted to angles for statistical analysis, while counts of birds dying from acute death syndrome were treated as Poisson counts and transformed to the V x + 1 scale (Steel and Torrie, 1960).
RESULTS AND DISCUSSION Because the density of feed is enhanced by the crumbling and pelleting process, it was considered probable that first-order interactions between feed texture and feeding time might occur for at least some of the traits measured. There was, however, a complete absence of such interactions for all traits measured. In the absence of significant first-order interactions between feed texture and restricted feeding treatments, the two main effects are considered separately. Feed Restriction Treatments. As feed restriction treatments commenced when birds were 21 days of age, there were no feed restriction treatment effects for traits measured at that age (i.e., body weights and feed conversion). Although somewhat variable, mortality of males and females was unaffected by the different time periods of feed restriction (Table 2). Body weight measurements conducted at 28 and 49 days were significantly altered in a linear fashion by the duration of feeding time with body weights of both males and females being heavier with the longer daily feeding periods. Although feed conversion at 28 days was not significantly affected by duration of feeding time, feed conversion at 49 days improved as feeding time was reduced from 24 to 8 hr per day. These results may appear to be contrary to our earlier report (Proudfoot and Hulan, 1982), but in the earlier work a feeding time of 16 hr per day was compared with full feeding time (24 hr). Eight hours of restriction did not appear to be a sufficiently long enough period of time to effect an improvement in feed conversion. Similarly, Beane et al. (1979) reported that restricting feed intake to 85% of full fed controls between 15 and 42 days of age resulted in the full-fed controls exhibiting greater gains and better feed conversion. However, enhanced feed conversion associated with restricted feeding time is supported by Yule and Fuelling (1979), Yule et al. (1979), and McCartney and Brown (1977). The proportion of Grade A carcasses were not significantly affected by feeding time restriction. Monetary returns over the cost of
**
7.07 12.27 1.251
NS
13.64 4.07 7.61 11.91 9.03 11.80 2.167
(angles)
*
5.68 9.67 1.301
NS
9.12 10.50 7.91 6.43 8.46 3.64 5.081
(angles)
(2.0) (3.5)
(3.5) (3.5) (2.6) (2.5) (3.0) (1.6)
(%)
Significant **P<.01; *P<.05;and NS; not significant PX05.
Standard error of the mean with the number of observations in parentheses.
(2.2) (5.2)
(6.0) (1.0) (2.5) (4.5) (3.5) (4.6)
(%)
Females
Mortality 0 to 49 days
Males
Detransformed from •«Jx — 1 scale.
Feed texture Ali mash Crumbles and pellets SE(ll) Significance
SE (4) b Significance0
8 10 12 14 16 24
Feed period (hr)
Main effects
*
1.187 1.617 .0996
NS
1.699 1.207 1.287 1.433 1.433 1.353 .1725
(N/X^T)
Males
(.41) (1.62)
(1.89) (.46) (.65) (1.05) (1.05) (.83)
(no.)*
NS
1.103 1.234 .0974
NS
1.000 1.207 1.286 1.207 1.207 1.104 .0562
(Vx-1)
Females
Mortality due to acute death syndrome
(.22) (.52)
(.46) (.65) (.46) (.46) (.22)
(0)
(no.)
**
563 629 3.8
594 605 592 599 595 590 6.5 NS
Male
21
TABLE 2. Effect of restricting feeding time and feed texture on mortality, incidence of acute d and body weights of broiler chickens
c
See footnote c, Table 2.
See footnote b, Table 2.
Detransformed angles.
**
**
1.576 1.616 1.552 1.559 1.564 1.607 .0164 NS
1.599 1.558 .0095
Feed period (hr) 8 10 12 14 16 24 SE (4)b Significance0
28 days
Feed conversion
1.484 1.404 .0058
1.452 1.438 1.444 1.441 1.438 1.450 .0101 NS
Main effects
Feed texture All-mash Crumbles and pellets SE(12) Significance
21 days
*
2.008 1.959 .0164
*
1.952 1.917 1.934 2.054 2.023 2.022 .0285
49 days
**
49.90 56.34 1.185
51.72 55.06 50.16 53.63 51.31 56.83 2.053 NS
(angles)
Males
(58.4) (69.1)
(61.4) (67.1) (58.8) (64.7) (60.6) (70.0)
(%)a
Grade
TABLE 3. Effect of restricted feeding time and feed texture on feed conversion, and monetary returns of chicken broilers
754
PROUDFOOT AND HULAN
feed and chicks were significantly affected by duration of feeding. However, no particular trends associated with feeding time were evident as results were highly variable. The advantages of improved feed conversion were offset in part by the disadvantage of lighter body weights. Also, there appeared to be more food retention prior to slaughter among birds which were on the shorter daily feeding times. As revenue for the sale of meat is based on live weights, the method used to estimate economic gain associated with these treatments may be inadequate. General observations also revealed that birds subjected to reduced feeding time tended to have enlarged crops with more feed retention prior to slaughter and to have a tendency toward pendulous crops, particularly among those birds fed the all-mash diets. It may be possible to use a feed restriction procedure early in the life of the broiler chicken to stimulate an enlargement of the crop and possibly other digestive organs, so that birds returned to full-feeding would have increased capacity in the digestive tract to enable improved growth rates. Feed Texture. Birds fed crumbled starter and pelleted finisher diets exhibited superior performance for practically all traits measured compared to birds on all-mash starter and finisher diets (Tables 2 and 3). Mortality was higher for both males and females fed the crumble-pellet diets than for those on all-mash. This higher mortality is attributed to the significantly larger number of males dying from acute death syndrome (flip-over) when fed on the crumble-pellet feeds compared with those fed the all-mash dietary regimen (Hulan et al., 1980). Further experimentation is being undertaken to collect more data before conclusions are drawn. Not only did the crumble-pelleting process result in body weights being heavier at all ages (21, 28, and 49 days) for both males and females, but feed conversion was also significantly improved and the percentage of carcasses graded A was also increased. Birds fed crumbled-pelleted diets had their profit margin increased by 8
despite a feed cost increase of l<£/kg of feed for the crumbling-pelleting process. These results support those of Proudfoot and Sefton (1978) and Calet (1965) who reported that the performance of broiler chicks fed pelleted diets was superior compared to birds on all-mash diets. It is concluded that, despite the increased incidence of acute death syndrome associated with crumble-pelletfed feed, it continues to be advantageous both biologically and economically to feed broiler chickens crumbled starter and pelleted finisher diets compared with an all-mash dietary regimen.
ACKNOWLEDGMENT The authors acknowledge the advice and assistance freely given by Ken McRae for statistical analysis of the data presented. REFERENCES Beane, W. L., J. A. Cherry, and W. D. Weaver, Jr., 1979. Intermittant light and restricted feeding of broiler chickens. Poultry Sci. 58:567-571. Calet, C , 1965. The relative value of pellets versus mash and grain in poultry nutrition. World's Poultry Sci. J. 21:23-52. Hulan, H. W., F. G. Proudfoot, and K. B. McRae, 1980. Effect of vitamins on the incidence of mortality and acute death syndrome ('flip-over") in broiler chickens. Poultry Sci. 59:927—931. McCartney, M. G., and H. B. Brown, 1977. The effects of feed restriction time on the growth and feed conversion of broiler males. Poultry Sci. 56: 713-715. Proudfoot, F. G., and H. W. Hulan, 1982. The effect of toe clipping and reduced feeding time on the general performance of broiler chickens. Can. J. Anim. Sci. (In press). Proudfoot, F. G., and A. E. Sefton, 1978. Feed texture and light treatment effects on the performance of chicken broilers. Poultry Sci. 57:408— 416. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw Hill Book Co., New York, NY. Yule, W. J., K. M. Barrum, and H. W. Burton, 1979. Effect of access time to food on broilers fed on diets of differing nutrient concentration. Brit. Poultry Sci. 20:311-316. Yule, W. J., and D. E. Fuelling, 1979. Effect of different patterns of food restriction from different ages on growth and efficiency of broilers. Brit. Poultry Sci. 20:273-279.