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The Effect of Different Dietary Energy Regimens on the Performance of Two Commercial Chicken Broiler Genotypes Reared to Roaster Weight1
The Effect of Different Dietary Energy Regimens on the Performance of Two Commercial Chicken Broiler Genotypes Reared to Roaster Weight1 H. W. HULAN and F. G. PROUDFOOT Research Station, Agriculture Canada, Kentville, Nova Scotia, Canada B4N 1J5 (Received for publication April 25, 1981)
1982 Poultry Science 61:510-515 INTRODUCTION A previous study d e m o n s t r a t e d t h a t general biological performance and incidence of leg weakness differ a m o n g commercial broiler g e n o t y p e s reared t o roaster weight (Hulan et al, 1980). In addition, t h a t s t u d y d e m o n s t r a t e d t h a t as t h e protein c o n t e n t of the diet decreased, feed conversion improved, t h e incid e n c e of leg abnormalities declined, a n d m o n e tary returns improved. A s u b s e q u e n t s t u d y (Hulan and P r o u d f o o t , 1981) d e m o n s t r a t e d t h a t roaster chickens can b e reared successfully on a three-stage (starter, grower, finisher) feeding regimen rather t h a n a four- o r fivestage regimen. Also, it was evident t h a t a dietary regimen which included starter, grower, and finisher diets with 16, 2 0 , and 16% p r o t e i n , respectively, resulted in o p t i m u m biological response and m o n e t a r y returns. Although t h e o p t i m u m level of dietary p r o tein at each stage of p r o d u c t i o n has been established for roasters, such is n o t necessarily t h e case with regard t o energy. In our previous studies we have used energy levels (kcal/kg) of: 3 0 0 0 (starters); 3 1 0 0 , 3 2 0 0 (growers); 3 3 0 0 , 3 4 0 0 (finishers). In all of o u r roaster studies, as well as in t h e commercial p r o d u c t i o n of
'Contribution No. 1724.
roasters, there is a t e n d e n c y for t h e birds to be overly fat, indicating an excess of dietary energy b e y o n d t h a t required for m a i n t e n a n c e and p r o d u c t i o n . T h e s t u d y reported here was designed to ascertain t h e optimal level of energy for roasters a t each stage of p r o d u c t i o n using t h e low protein (16-20-16) dietary regimen developed at this l a b o r a t o r y earlier (Hulan and Proudfoot, 1981). EXPERIMENTAL PROCEDURES A total of 2 4 0 0 male day-old chicks of two commercial Shaver g e n o t y p e s ( 1 2 0 0 of each) were randomized into 2 4 pens, each with a floor area of 13.54 m 2 ( 1 4 6 f t 2 ) . T h e genotypes were reared separately, and each pen housed 1 0 0 birds. F o u r cylindrical t y p e feeders and one bell shaped waterer were provided in each p e n . Initial hover t e m p e r a t u r e was set at 35 C and reduced 3 C per week until a temperat u r e of 2 3 C was o b t a i n e d . All stock was started on c o n t i n u o u s lighting of 3 ft-c (30 lx) which was reduced gradually so t h a t at 21 days the birds were receiving .5 ft-c (5 lx) intensity white light. T h e diets fed are s h o w n in Table 1. T h e energy c o n t e n t of t h e diets was attained by varying t h e a m o u n t of animal fat and g r o u n d corn. T h e diets were calculated t o be isonitrogenous b y m a k i n g a p p r o p r i a t e adjustments in 510
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ABSTRACT An experiment was conducted involving two commercial male Shaver genotypes (1200 of each) to ascertain the optimal level of dietary energy for roasters at each stage of production using a three-stage (starter, grower, finisher) feeding system of 16-20-16% dietary protein, respectively. Of the regimens examined, a starter-grower-finisher regimen with 3000, 3100, 3200 kcal/kg metabolizable energy resulted in the heaviest body weights and best feed conversion and monetary returns. Detailed examination of the leg bones of approximately one-half the population showed the true incidence of leg abnormalities in this type ot bird to range between 37 and 41%, depending on genotype. Although the incidence of slipped tendons tended to increasejsignjficant for the highest energy regimen) with increasing levels ot dietary energy, the incidence of total leg abnormalit-ips (all types) wasnot altered significantly by dietary energy level per se. (Key words: dietary energy, roasters, broilers, body weight, leg abnormalities)
16.0 2900 26.38
18 23 5 10
5 852 82 5
1
Starter
16.0 3000 27.75
590 180 163 10 1 18 23 5 10
2
20.0 3000 29.69
435 254 225 30 14 12 15 5 10
1
Grower
20.0 3100 30.46
451 210 225 35 37 12 15 5 10
2
16.0 3100 27.60
584 202 160 6 11 10 12 5 10
1
1 Supplied per kilogram diet: 12,000 IU vitamin A; 2000 ICU vitamin D 3 ; 8 mg riboflavin; 13 mg calcium pantothe K; 1 mg folic acid; 15 IU vitamin E; 300 Mg biotin; 5 mg pyridoxine; 3 mg thiamine; 4.5 mg procaine penicillin; 187 ethoxyquin; 120 mgmanganous oxide (60% Mn); 90 mgzinc oxide (72% Zn); 25 mg copper oxide (25% Cu); 220 Mg so
J
Calculated analysis Crude protein (%) ,E (kcal/kg) ost(<}ykg)
Ground corn Ground wheat Soybean meal (490 g/kg) Fishmeal (630 g/kg) Animal fat Limestone Dicalcium phosphate Iodized salt Vitamin-mineral premix 1
Ingredients
TABLE 1. Composition (g/kg) roaster diets tested
m http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
512
HULAN AND PROUDFOOT TABLE 2. Feeding regimens tested Regimen
Stage (duration)
2
3
4
Starter ( 1 - 2 1 days) Protein (%) ME (kcal/kg)
16.0 2900
16.0 2900
16.0 3000
16.0 3000
Grower ( 2 2 - 4 9 days) Protein (%) ME (kcal/kg)
20.0 3000
20.0 3000
20.0 3100
20.0 3100
Finisher ( 5 0 - 7 0 days) Protein (%) ME (kcal/kg)
16.0 3100
16.0 3150
16.0 3200
16.0 3250
the amount of ground wheat, soybean meal, and fishmeal. In order to determine the level of energy required in each stage to achieve optimum biological performance and/or monetary returns, the feeding regimens outlined in Table 2 were tested. The choice of these feeding regimens was based on the information obtained in our previous roaster studies (Hulan et al, 1980; Hulan and Proudfoot, 1981). Triplicate pens of each genotype were assigned at random to these dietary regimens. Starters were fed as crumbles from 1 to 21 days, while the grower and finisher diets were fed as pellets from 22 to 49 days and from 50 to 70 days, respectively. Traits measured were: percentage mortality and live weight at 21, 49, and 70 days. Feed consumption was recorded and feed conversion calculated as the unit weight of feed per unit live weight at 21, 49, and 70 days. Percentage of Grade A carcasses was determined at slaughter using the Canadian Grade Standards. The calculation of monetary returns over the cost of feed and chicks was based on current market prices. Feed costs were as shown in Table 1. Meat sold for 91
by examining closely the tarsometatarsus, then opening and sagittally cutting both jj}ints_oi-the tibiotairsus and femur, and by removing the muscle tissue from the tibiotarsus and femur and carefully examining the bones. The analysis of variance (Snedecor and Cochran, 1980) was conducted on pen means. Percent mortality and percent Grade A carcasses were transformed to angles for the analysis. Differences among genotypic and treatment means were tested using the Duncan (1955) new multiple range procedure. RESULTS AND DISCUSSION
There were no significant differences observed for live body weight and feed conversion between the two genotypes tested (Table 3). Birds fed the lower energy regimens 1 and 2 grew at a slower rate and weighed significantly less at each weigh period compared to those fed the higher energy regimens 3 and 4. On the average, birds fed the lower energy regimens (1 and 2) did not reach the marketable weight (3.2 kg) of a roaster, while those fed the higher energy regimens (3 and 4) surpassed the marketable weight. Feed conversion of birds was significantly lower for the higher energy regimens at 21 days only. At 70 days the best (numerically) feed conversion was attained for birds fed regimen 3 followed by those fed one of the lower energy regimens, regimen 2. Feeding of regimen 3 resulted in a considerable improvement in live weights and feed conversion compared to our previous investigation (Hulan and Proudfoot, 1981) when these broiler genotypes were
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
1
ENERGY, GENOTYPE, AND ROASTERS
513
TABLE 3. Mean live body weight and feed conversion of roaster chickens fed different levels of dietary energy during the starter-grower-finisher periods Feed conversion
Live body weight (g)
SEM (n = 6)
49 days
70 days
21 days
49 days
70 days
295 a 287 a 5.5 207a 210a 375b 372b
2053a 2032a 14.0 1865 a 1862a 2238b 2206 b
3326 a 3327a 14.9 3109 a 3137a 3535 b 3525b
.91a .96 a .019 1.05a 1.07a .81b .81b
1.61 a 1.63 a .017 1.67a 1.61 a 1.60a 1.60a
2.34a 2.35a .019 2.36 a 2.33a 2.31 a 2.36 a
7.8
19.9
21.1
.028
.024
.027
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
Shaver 1 Shaver 2 SEM (n = 12) Regimen 1 2 3 4
21 days
a ' b Means within a column and factor (strain or dietary regimen) with a common superscript letter are not significantly different (P<.01).
fed the same low protein (16-20-16) regimen but with energy levels of 3000, 3150, and 3 300 kcal/kg metabolizable energy (ME) for starter, grower, and finisher diets, respectively. Throughout the test, mortality and Grade A carcasses (Table 4) tended to be slightly higher for Shaver 1 compared to Shaver 2 and on average higher for birds fed the higher energy regimens (3 and 4) compared to those fed the lower energy regimens (1 and 2), but these differences were not significant. The mortality observed at 70 days (total over experiment) compared quite favorably with the mortality observed in our previous investigation (Hulan and Proudfoot, 1981) with the same low protein (but higher energy) regimen. The percentage Grade A carcasses observed in the current study were considerably lower for both genotypes and dietary regimens compared to that observed in our previous investigations (Hulan et al, 1980; Hulan and Proudfoot, 1981). A concomitant increase in the percentage of birds grading Utility followed the decrease in Grade A carcasses. The Utility grade includes birds that would have been normally graded A for conformation, flesh, and fat but had a limb missing, were bruised, or had skin slashes (on-line damage). Because of the frequent handling of the birds during the course of the experiment, many birds were bruised, which resulted in those carcasses being graded Utility at the time of slaughter. The grading process, therefore, would tend to underestimate carcass quality. Had a treatment in this experiment adversely affected conformation, flesh, or fat of the
birds, there would have been a pronounced increase in Grade B carcasses. However, the percentage of birds graded B were quite low and well within the expected range for this type of heavy meat bird. The difference in monetary returns between the two genotypes was not significant, although returns were slightly (.5
1 / / \ \ | \
cant effect on f'Ta 1
\
lp
S abnormalities suggest-
ing that the energy component of the diet per se had less influence on leg weakness than the
| I
1.71
SEM (n = 6)
1.42
12.23(4.7) 10.6 a (3.6) 1.00 11.6 a (4.2) 11.8 a (4.5) 11.9a (4.5) 10.2 a (3.5)
49 days
1.21
15.03(6.8) 14.5a (6.6) .86 15.1 a (6.8) 14.0 a (6.4) 15.6 a (7.3) 14.4a (6.4)
70 days
2.12
47.0 a (53.5) 46.0 a (51.7) 1.50 49.9 a (58.5) 46.9 a (53.3) 43.9 a (48.1) 4 5 . 3 a (50.4)
a
1
295 284 293 282
583 571
1.93
37.2 41.0
37.6 a 40.0 a 1.36 39.4 a 36.7 a 38.2 a 38.8 a
40.3 35.7 38.2 39.3
(%)
(Angle)
Total
1.61
5.1 4.3
13.0 a 12.0 a 1.14 10.9 a 10.3 a 12.9 a 16. l b 3.6 3.2 5.0 7.7
(%)
ST (Angle)
1.83
28.4228.6 a 1.29 30.3 s 28.3 a 28.7 a 27.la
(Angle)
TD
25.6 22.5 23.1 20.8
22.6 22.9
(%)
1.71
15.4 a 17.ia 1.21 16.0a 16.4a 16.0 a 16.6 a
(Angle)
EFH
Leg abnormali
' Means within a column with a common superscript letter are not significantly different (P<.05).
ST = slipped tendon; TD = tibial dyschondroplasia; EFH = erosion of femoral head; FHN = femoral head necrosis; SA
SEM (n = 6)
Shaver 1 Shaver 2 SEM(n = 12) Regimen 1 2 3 4
No. examined
3.1
9.4 9.5 2.2 11.3 13.5 8.6 4.3
B
Carca
TABLE 5. Incidence of various types of leg abnormalities of roaster chicken fed different le during the starter-grower-finisher periods
Mean angle with percent in parentheses. ab . ' Means within a column with a common superscript letter are not significantly different (P<.05).
6.8a(1.9) 6.1 a (1.6) 1.21 4.9 a (1.4) 5.4 a (1.5) 8.9 a (2.7) 6.5 a (1.3)
Shaver 1 Shaver 2 SEM (n = 12) Regimen 1 2 3 4
21 days
Mortality.'
TABLE 4. Mortality, carcass grade, and mean monetary returns of roaster chickens fed differen during the starter-grower-finisher periods
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ENERGY, GENOTYPE, AND ROASTERS
Within the limitations of this experiment, it may be concluded that optimum biological
response (body weights and feed conversion) and monetary returns can be achieved in the rearing of chicken broiler genotypes to roaster weight (3.2 kg) by using a three-stage feeding system of starter-grower-finisher with protein — %(energy, kcal/kg ME) of 16(3000) - 20(3100) — 16(3200). Tjie_results would also suggest that dietary energy per se within the range.studied has little effect on the incidence of mortality arid leg abnormalities of broiler genotypes reared to roaster weight.
ACKNOWLEDGMENT To K. B. McRae for advice on experimental design and statistical analyses of the data; W. DeWitt, Nova Scotia Department of Agriculture, Truro, Nova Scota, and R. Bishop, Cornwallis Veterinarians, Kentville, Nova Scota, for assisting in the postmortem examination of the birds for leg abnormalities.
REFERENCES Duncan, D. B., 1955. The new multiple range and multiple F tests. Biometrics 11:1—2. Hulan, H. W., and F. G. Proudfoot, 1981. The effect of different dietary protein levels in a three stage diet system on general performance of chickens reared to roaster weight. Poultry Sci. 60:172— 178. Hulan, H. W., F. G. Proudfoot, D. Ramey and K. B. McRae, 1980. Influence of genotype and diet on general performance and incidence of leg abnormalities of commercial broilers reared to roaster weight. Poultry Sci. 59:748-757. Snedecor, G. W., and W. G. Cochran, 1980. Statistical Methods. 8th ed. Iowa State Press, Ames, IA.
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protein content of the diet, as demonstrated in our previous studies (Hulan et al, 1980: Hulan and Proudfoot, 1981). There was some evidence to suggest that the increased energy content of the dietary regimen resulted in an increase in the incidence of slipped tendons. When the highest energy regimen was fed, a significantly higher incidence of slipped tendons resulted. There were, however, no significant differences among the different dietary regimens tested for the incidence of the other specific leg abnormalities. The higher incidence of leg abnormalities in the current study compared to that of our previous studies (Hulan et al, 1980; Hulan and Proudfoot, 1981) is worthy of special note. In the earlier studies, leg abnormalities were identified by postmortem examination of birds which either died during the experiment, or were removed during the experiment because they were unable to reach the feed and water as a result of leg problems, or were removed from the killing line because of an obvious leg abnormality. In addition to the postmortem examination, a detailed examination (described in Experimental Procedures) of the legs of onehalf the birds in each genotype remaining at 70 days was carried out in the current study. The results presented here would suggest that the magnitude of the leg weakness problems in this type of bird was underestimated in our previous studies. The results also indicate that the incidence is high regardless of genotype and was not affected by dietary regimen.
515
1982 Poultry Science 61:510-515 INTRODUCTION A previous study d e m o n s t r a t e d t h a t general biological performance and incidence of leg weakness differ a m o n g commercial broiler g e n o t y p e s reared t o roaster weight (Hulan et al, 1980). In addition, t h a t s t u d y d e m o n s t r a t e d t h a t as t h e protein c o n t e n t of the diet decreased, feed conversion improved, t h e incid e n c e of leg abnormalities declined, a n d m o n e tary returns improved. A s u b s e q u e n t s t u d y (Hulan and P r o u d f o o t , 1981) d e m o n s t r a t e d t h a t roaster chickens can b e reared successfully on a three-stage (starter, grower, finisher) feeding regimen rather t h a n a four- o r fivestage regimen. Also, it was evident t h a t a dietary regimen which included starter, grower, and finisher diets with 16, 2 0 , and 16% p r o t e i n , respectively, resulted in o p t i m u m biological response and m o n e t a r y returns. Although t h e o p t i m u m level of dietary p r o tein at each stage of p r o d u c t i o n has been established for roasters, such is n o t necessarily t h e case with regard t o energy. In our previous studies we have used energy levels (kcal/kg) of: 3 0 0 0 (starters); 3 1 0 0 , 3 2 0 0 (growers); 3 3 0 0 , 3 4 0 0 (finishers). In all of o u r roaster studies, as well as in t h e commercial p r o d u c t i o n of
'Contribution No. 1724.
roasters, there is a t e n d e n c y for t h e birds to be overly fat, indicating an excess of dietary energy b e y o n d t h a t required for m a i n t e n a n c e and p r o d u c t i o n . T h e s t u d y reported here was designed to ascertain t h e optimal level of energy for roasters a t each stage of p r o d u c t i o n using t h e low protein (16-20-16) dietary regimen developed at this l a b o r a t o r y earlier (Hulan and Proudfoot, 1981). EXPERIMENTAL PROCEDURES A total of 2 4 0 0 male day-old chicks of two commercial Shaver g e n o t y p e s ( 1 2 0 0 of each) were randomized into 2 4 pens, each with a floor area of 13.54 m 2 ( 1 4 6 f t 2 ) . T h e genotypes were reared separately, and each pen housed 1 0 0 birds. F o u r cylindrical t y p e feeders and one bell shaped waterer were provided in each p e n . Initial hover t e m p e r a t u r e was set at 35 C and reduced 3 C per week until a temperat u r e of 2 3 C was o b t a i n e d . All stock was started on c o n t i n u o u s lighting of 3 ft-c (30 lx) which was reduced gradually so t h a t at 21 days the birds were receiving .5 ft-c (5 lx) intensity white light. T h e diets fed are s h o w n in Table 1. T h e energy c o n t e n t of t h e diets was attained by varying t h e a m o u n t of animal fat and g r o u n d corn. T h e diets were calculated t o be isonitrogenous b y m a k i n g a p p r o p r i a t e adjustments in 510
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
ABSTRACT An experiment was conducted involving two commercial male Shaver genotypes (1200 of each) to ascertain the optimal level of dietary energy for roasters at each stage of production using a three-stage (starter, grower, finisher) feeding system of 16-20-16% dietary protein, respectively. Of the regimens examined, a starter-grower-finisher regimen with 3000, 3100, 3200 kcal/kg metabolizable energy resulted in the heaviest body weights and best feed conversion and monetary returns. Detailed examination of the leg bones of approximately one-half the population showed the true incidence of leg abnormalities in this type ot bird to range between 37 and 41%, depending on genotype. Although the incidence of slipped tendons tended to increasejsignjficant for the highest energy regimen) with increasing levels ot dietary energy, the incidence of total leg abnormalit-ips (all types) wasnot altered significantly by dietary energy level per se. (Key words: dietary energy, roasters, broilers, body weight, leg abnormalities)
16.0 2900 26.38
18 23 5 10
5 852 82 5
1
Starter
16.0 3000 27.75
590 180 163 10 1 18 23 5 10
2
20.0 3000 29.69
435 254 225 30 14 12 15 5 10
1
Grower
20.0 3100 30.46
451 210 225 35 37 12 15 5 10
2
16.0 3100 27.60
584 202 160 6 11 10 12 5 10
1
1 Supplied per kilogram diet: 12,000 IU vitamin A; 2000 ICU vitamin D 3 ; 8 mg riboflavin; 13 mg calcium pantothe K; 1 mg folic acid; 15 IU vitamin E; 300 Mg biotin; 5 mg pyridoxine; 3 mg thiamine; 4.5 mg procaine penicillin; 187 ethoxyquin; 120 mgmanganous oxide (60% Mn); 90 mgzinc oxide (72% Zn); 25 mg copper oxide (25% Cu); 220 Mg so
J
Calculated analysis Crude protein (%) ,E (kcal/kg) ost(<}ykg)
Ground corn Ground wheat Soybean meal (490 g/kg) Fishmeal (630 g/kg) Animal fat Limestone Dicalcium phosphate Iodized salt Vitamin-mineral premix 1
Ingredients
TABLE 1. Composition (g/kg) roaster diets tested
m http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
512
HULAN AND PROUDFOOT TABLE 2. Feeding regimens tested Regimen
Stage (duration)
2
3
4
Starter ( 1 - 2 1 days) Protein (%) ME (kcal/kg)
16.0 2900
16.0 2900
16.0 3000
16.0 3000
Grower ( 2 2 - 4 9 days) Protein (%) ME (kcal/kg)
20.0 3000
20.0 3000
20.0 3100
20.0 3100
Finisher ( 5 0 - 7 0 days) Protein (%) ME (kcal/kg)
16.0 3100
16.0 3150
16.0 3200
16.0 3250
the amount of ground wheat, soybean meal, and fishmeal. In order to determine the level of energy required in each stage to achieve optimum biological performance and/or monetary returns, the feeding regimens outlined in Table 2 were tested. The choice of these feeding regimens was based on the information obtained in our previous roaster studies (Hulan et al, 1980; Hulan and Proudfoot, 1981). Triplicate pens of each genotype were assigned at random to these dietary regimens. Starters were fed as crumbles from 1 to 21 days, while the grower and finisher diets were fed as pellets from 22 to 49 days and from 50 to 70 days, respectively. Traits measured were: percentage mortality and live weight at 21, 49, and 70 days. Feed consumption was recorded and feed conversion calculated as the unit weight of feed per unit live weight at 21, 49, and 70 days. Percentage of Grade A carcasses was determined at slaughter using the Canadian Grade Standards. The calculation of monetary returns over the cost of feed and chicks was based on current market prices. Feed costs were as shown in Table 1. Meat sold for 91
by examining closely the tarsometatarsus, then opening and sagittally cutting both jj}ints_oi-the tibiotairsus and femur, and by removing the muscle tissue from the tibiotarsus and femur and carefully examining the bones. The analysis of variance (Snedecor and Cochran, 1980) was conducted on pen means. Percent mortality and percent Grade A carcasses were transformed to angles for the analysis. Differences among genotypic and treatment means were tested using the Duncan (1955) new multiple range procedure. RESULTS AND DISCUSSION
There were no significant differences observed for live body weight and feed conversion between the two genotypes tested (Table 3). Birds fed the lower energy regimens 1 and 2 grew at a slower rate and weighed significantly less at each weigh period compared to those fed the higher energy regimens 3 and 4. On the average, birds fed the lower energy regimens (1 and 2) did not reach the marketable weight (3.2 kg) of a roaster, while those fed the higher energy regimens (3 and 4) surpassed the marketable weight. Feed conversion of birds was significantly lower for the higher energy regimens at 21 days only. At 70 days the best (numerically) feed conversion was attained for birds fed regimen 3 followed by those fed one of the lower energy regimens, regimen 2. Feeding of regimen 3 resulted in a considerable improvement in live weights and feed conversion compared to our previous investigation (Hulan and Proudfoot, 1981) when these broiler genotypes were
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
1
ENERGY, GENOTYPE, AND ROASTERS
513
TABLE 3. Mean live body weight and feed conversion of roaster chickens fed different levels of dietary energy during the starter-grower-finisher periods Feed conversion
Live body weight (g)
SEM (n = 6)
49 days
70 days
21 days
49 days
70 days
295 a 287 a 5.5 207a 210a 375b 372b
2053a 2032a 14.0 1865 a 1862a 2238b 2206 b
3326 a 3327a 14.9 3109 a 3137a 3535 b 3525b
.91a .96 a .019 1.05a 1.07a .81b .81b
1.61 a 1.63 a .017 1.67a 1.61 a 1.60a 1.60a
2.34a 2.35a .019 2.36 a 2.33a 2.31 a 2.36 a
7.8
19.9
21.1
.028
.024
.027
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on June 3, 2015
Shaver 1 Shaver 2 SEM (n = 12) Regimen 1 2 3 4
21 days
a ' b Means within a column and factor (strain or dietary regimen) with a common superscript letter are not significantly different (P<.01).
fed the same low protein (16-20-16) regimen but with energy levels of 3000, 3150, and 3 300 kcal/kg metabolizable energy (ME) for starter, grower, and finisher diets, respectively. Throughout the test, mortality and Grade A carcasses (Table 4) tended to be slightly higher for Shaver 1 compared to Shaver 2 and on average higher for birds fed the higher energy regimens (3 and 4) compared to those fed the lower energy regimens (1 and 2), but these differences were not significant. The mortality observed at 70 days (total over experiment) compared quite favorably with the mortality observed in our previous investigation (Hulan and Proudfoot, 1981) with the same low protein (but higher energy) regimen. The percentage Grade A carcasses observed in the current study were considerably lower for both genotypes and dietary regimens compared to that observed in our previous investigations (Hulan et al, 1980; Hulan and Proudfoot, 1981). A concomitant increase in the percentage of birds grading Utility followed the decrease in Grade A carcasses. The Utility grade includes birds that would have been normally graded A for conformation, flesh, and fat but had a limb missing, were bruised, or had skin slashes (on-line damage). Because of the frequent handling of the birds during the course of the experiment, many birds were bruised, which resulted in those carcasses being graded Utility at the time of slaughter. The grading process, therefore, would tend to underestimate carcass quality. Had a treatment in this experiment adversely affected conformation, flesh, or fat of the
birds, there would have been a pronounced increase in Grade B carcasses. However, the percentage of birds graded B were quite low and well within the expected range for this type of heavy meat bird. The difference in monetary returns between the two genotypes was not significant, although returns were slightly (.5
1 / / \ \ | \
cant effect on f'Ta 1
\
lp
S abnormalities suggest-
ing that the energy component of the diet per se had less influence on leg weakness than the
| I
1.71
SEM (n = 6)
1.42
12.23(4.7) 10.6 a (3.6) 1.00 11.6 a (4.2) 11.8 a (4.5) 11.9a (4.5) 10.2 a (3.5)
49 days
1.21
15.03(6.8) 14.5a (6.6) .86 15.1 a (6.8) 14.0 a (6.4) 15.6 a (7.3) 14.4a (6.4)
70 days
2.12
47.0 a (53.5) 46.0 a (51.7) 1.50 49.9 a (58.5) 46.9 a (53.3) 43.9 a (48.1) 4 5 . 3 a (50.4)
a
1
295 284 293 282
583 571
1.93
37.2 41.0
37.6 a 40.0 a 1.36 39.4 a 36.7 a 38.2 a 38.8 a
40.3 35.7 38.2 39.3
(%)
(Angle)
Total
1.61
5.1 4.3
13.0 a 12.0 a 1.14 10.9 a 10.3 a 12.9 a 16. l b 3.6 3.2 5.0 7.7
(%)
ST (Angle)
1.83
28.4228.6 a 1.29 30.3 s 28.3 a 28.7 a 27.la
(Angle)
TD
25.6 22.5 23.1 20.8
22.6 22.9
(%)
1.71
15.4 a 17.ia 1.21 16.0a 16.4a 16.0 a 16.6 a
(Angle)
EFH
Leg abnormali
' Means within a column with a common superscript letter are not significantly different (P<.05).
ST = slipped tendon; TD = tibial dyschondroplasia; EFH = erosion of femoral head; FHN = femoral head necrosis; SA
SEM (n = 6)
Shaver 1 Shaver 2 SEM(n = 12) Regimen 1 2 3 4
No. examined
3.1
9.4 9.5 2.2 11.3 13.5 8.6 4.3
B
Carca
TABLE 5. Incidence of various types of leg abnormalities of roaster chicken fed different le during the starter-grower-finisher periods
Mean angle with percent in parentheses. ab . ' Means within a column with a common superscript letter are not significantly different (P<.05).
6.8a(1.9) 6.1 a (1.6) 1.21 4.9 a (1.4) 5.4 a (1.5) 8.9 a (2.7) 6.5 a (1.3)
Shaver 1 Shaver 2 SEM (n = 12) Regimen 1 2 3 4
21 days
Mortality.'
TABLE 4. Mortality, carcass grade, and mean monetary returns of roaster chickens fed differen during the starter-grower-finisher periods
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ENERGY, GENOTYPE, AND ROASTERS
Within the limitations of this experiment, it may be concluded that optimum biological
response (body weights and feed conversion) and monetary returns can be achieved in the rearing of chicken broiler genotypes to roaster weight (3.2 kg) by using a three-stage feeding system of starter-grower-finisher with protein — %(energy, kcal/kg ME) of 16(3000) - 20(3100) — 16(3200). Tjie_results would also suggest that dietary energy per se within the range.studied has little effect on the incidence of mortality arid leg abnormalities of broiler genotypes reared to roaster weight.
ACKNOWLEDGMENT To K. B. McRae for advice on experimental design and statistical analyses of the data; W. DeWitt, Nova Scotia Department of Agriculture, Truro, Nova Scota, and R. Bishop, Cornwallis Veterinarians, Kentville, Nova Scota, for assisting in the postmortem examination of the birds for leg abnormalities.
REFERENCES Duncan, D. B., 1955. The new multiple range and multiple F tests. Biometrics 11:1—2. Hulan, H. W., and F. G. Proudfoot, 1981. The effect of different dietary protein levels in a three stage diet system on general performance of chickens reared to roaster weight. Poultry Sci. 60:172— 178. Hulan, H. W., F. G. Proudfoot, D. Ramey and K. B. McRae, 1980. Influence of genotype and diet on general performance and incidence of leg abnormalities of commercial broilers reared to roaster weight. Poultry Sci. 59:748-757. Snedecor, G. W., and W. G. Cochran, 1980. Statistical Methods. 8th ed. Iowa State Press, Ames, IA.
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protein content of the diet, as demonstrated in our previous studies (Hulan et al, 1980: Hulan and Proudfoot, 1981). There was some evidence to suggest that the increased energy content of the dietary regimen resulted in an increase in the incidence of slipped tendons. When the highest energy regimen was fed, a significantly higher incidence of slipped tendons resulted. There were, however, no significant differences among the different dietary regimens tested for the incidence of the other specific leg abnormalities. The higher incidence of leg abnormalities in the current study compared to that of our previous studies (Hulan et al, 1980; Hulan and Proudfoot, 1981) is worthy of special note. In the earlier studies, leg abnormalities were identified by postmortem examination of birds which either died during the experiment, or were removed during the experiment because they were unable to reach the feed and water as a result of leg problems, or were removed from the killing line because of an obvious leg abnormality. In addition to the postmortem examination, a detailed examination (described in Experimental Procedures) of the legs of onehalf the birds in each genotype remaining at 70 days was carried out in the current study. The results presented here would suggest that the magnitude of the leg weakness problems in this type of bird was underestimated in our previous studies. The results also indicate that the incidence is high regardless of genotype and was not affected by dietary regimen.
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