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GENETICS |
* Department of Poultry Science, College of Agriculture and Life Sciences, North Carolina State University, Raleigh 27695; USDA/CSREES, Washington, DC 20250; and Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691
2 Corresponding author: Gerald_Havenstein{at}ncsu.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: turkey • body weight • feed conversion • livability • genetic change
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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In the late 1950s, poultry geneticists had the foresight to develop random breeding populations of broilers and turkeys using crosses of several current commercial and research strains as their base. McCartney (1964) reported the development of the first randombred turkey strain that was developed at the Ohio Agricultural Research and Development Center (OARDC; Wooster, OH) in 1957. That strain has become known as the RBC1 and is still maintained at the OARDC. A second randombred turkey strain (now known as the RBC2) was initiated in 1966 by Nestor (Nestor et al., 1969), and it was developed using 2 of the most popular commercial strains in 1966. It also continues to be maintained at the OARDC. Those randombred turkey strains, like their broiler counterparts, are extremely valuable for measuring genetic change in various performance traits of turkey populations over time. Several different experiments have been reported using randombred broilers to estimate genetic change of commercial stocks (Marks, 1971; Chambers et al., 1981; Qureshi and Havenstein, 1994; Sherwood, 1977; Cheema et al., 2003: Havenstein et al., 1994a,b, 2003a,: Havenstein et al., b), but none other than 2 preliminary reports from the current study (Havenstein et al., 2004a,b) have been reported using randombred turkeys to measure changes in commercial turkey performance over time.
The objective of the current study was to compare the relative performance of the RBC2 vs. composite pens of 3 modern primary turkey breeds placed during 2003 when they were grown on dietary regimens that were representative of what was being fed to commercial turkeys in 1966 and 2003. The study was designed to measure the relative contribution of genetics and nutritional management to the changes in production and processing traits, both edible and inedible, during the 37-yr period from 1966 to 2003. Growth, feed efficiency, and livability of the progeny turkeys used in the present study are given here.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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The study consisted of a 2 x 2 x 2 factorial arrangement of treatments with 4 replicate blocks of 8 treatment pens. With the exception of FC and livability, which were collected and analyzed on a pen basis, all other data were collected and summarized on an individual bird basis. That is, the overall factorial experiment consisted of 2 strains (RBC2 vs. modern), 2 sexes (toms and hens), and 2 dietary regimens that were thought to be representative of what was being fed to turkeys in 1966 and 2003. All treatment pens for the modern strain consisted of a composite of 5 birds each of Nicholas, British United Turkeys of America, and Hybrid turkeys. Poults from the RBC2 strain were hatched and sexed at the OARDC and were then transported by van on the evening of March 5, 2003, to the North Carolina State University Turkey Educational Unit. The Hybrid and British United Turkeys of America poults were hatched, sexed, and delivered by company employees, and Nicholas poults were hatched and sexed by Sleepy Creek Hatchery (Goldsboro, NC) and were then transported by North Carolina State University personnel to the test site early on the day of placement. All poults were then neck-tagged for individual identification and were placed 15 birds/8.55 m2 of pen early on the morning following hatch, with the exception that, due to a shortage of poults, the RBC2 female pens received only 14 birds/pen. The test flock was placed into 32 pens within a 40-pen curtain-sided house in a randomized block design using the factorial arrangement described above with 4 replicate blocks of 8 treatment pens. Warm-room brooding was accomplished using 2 propane heaters mounted near the ceiling in each end of the building. The hot air from the heaters was directed into stirring fans aimed at the ceiling that mixed and distributed the warm air evenly into all pens. Each pen was also equipped with an incandescent infrared heat lamp for spot brooding during the first 10 d of age. Each pen also contained 1 bell-type hanging waterer and 1 tube-type hanging feeder. Continuous light was provided for the first 3 d, and 23L:1D was provided thereafter. Brooder temperature was 32°C and was to the degree possible reduced 2.6°C/wk until an ambient temperature of 21°C was reached. Thereafter, the temperature of the facility was maintained as close as possible to an average of 21°C. Due to the time of year that the birds were grown (8 to 28 wk of age during mid-May to mid-September), however, and due to the fact that they were grown in an open curtain-sided house, the ambient temperatures were considerably above 21°C during most of the growout period (Figure 1
). Water and feed were supplied for ad libitum consumption. Neck tags were replaced with wing badges at approximately 6 wk of age.
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and 2.
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Statistical Analysis
The overall design consisted of a 2 x 2 x 2 factorial with 2 strains (RBC2 and modern), 2 sexes, and 2 dietary regimens with 4 replicate blocks of the 8 factorial treatment pens. The data, with the exception of FC and livability, were recorded and analyzed on an individual bird basis. All data were analyzed using the GLM procedure of SAS (SAS Institute, 1996). When possible, the 2- and 3-way interactions of strain, sex, and diet were included in the model for the analysis of all traits measured. At 196 d of age, the first 3 replicate blocks had already been slaughtered, so only 1 pen/treatment was available and therefore only the main effects and 1-way interactions of strain, sex, and diet could be included in the 196-d analysis. No analysis could be performed on the single observation per test group for FC from the last block at 196 d of age. All mortality data were transformed by arc sin before analysis. Mortalities after 112 d were not analyzed due to the first block of cages having been slaughtered for processing at 112 d of age.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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. For reasons that are not totally clear, the growth rate for all of the turkeys used in the current study was below normal. For example, the RBC2 toms in this study weighed 2.47, 6.29, and 7.85 kg when grown during the late spring and summer, whereas their full sibs produced and grown during the winter and early spring in Wooster, Ohio, weighed 2.87, 7.77, and 9.86 kg at 56, 84, and 140 d of age (K. E. Nestor, personal communication). Likewise, the modern toms weighed 4.80, 13.17, and 15.54 kg at these same ages, whereas field data from around the world compiled by Ferket (2003) indicates that toms should have weighed about 3.58, 12.32, and 17.00 kg at these ages. Thus, the RBC2 was 15 to 20% lighter in weight than its sib flocks in Ohio, and the modern strain was 7% above and 9% below year 2003 field flocks at 112 and 140 d of age. It is believed that the depression in growth rate was largely due to the fact that North Carolina experienced an extremely hot, humid spring and summer throughout the time when these birds were 70 to 196 d of age. Nevertheless, no signs of disease were observed at any time during the growing period for this flock, and all of the birds involved were subjected to the same ambient conditions, so the relative performance levels of the 2 types of turkeys should not have been affected.
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). As expected, there were no significant differences among the poults that were randomly assigned to the different blocks or to the different feeding programs at the time of hatch. Measurements of BW at the different ages revealed significant block or area of the house effects for most of the ages measured, so those effects were statistically removed in the analyses. Highly significant differences were observed (P < 0.001) between the strains, diets and sexes, and in the strain x diet interaction at all ages measured from 14 through 112 d of age. The same level of significance continued to be observed for strain and sex at the later 3 ages studied (Table 1). Not surprisingly, in light of the large difference in growth rate between these 2 strains, highly significant 2- and 3-way interactions were also observed. If one compares the relative performance utilizing the average for both sexes for the modern strain on the modern feed vs. the old strain on the modern feed, the modern 2003 strain was approximately twice as heavy (i.e., 2.17, 2.05, 1.93, and 1.89 times) as the 1966 RBC2 at 112, 140, 168, and 196 d of age. Using the BW performance of the 2 strains on the modern feed as the basis, one can estimate that tom weights have increased by 186, 208, 227, and 241 g/yr, and hens weights have increased by 164, 179, 186, and 205 g/yr at 112, 140, 168, and 196 d of age, respectively, over the past 37 yr. This is somewhat more than what the field data collected and summarized by Ferket (2003) showed, which indicated that tom weights at 126 d of age increased at a rate of 195 g/yr from 1966 to 2003. Market turkey hens are not normally kept to these ages, so comparable field data are not available. The field data from 98 d of age (Ferket, 2003) shows an increase of 65 g/yr for hens, whereas, the 98-d data from this experiment (not shown herein) shows a change of 141 g/yr. It is not clear as to why there is this discrepancy between the results from the 2 sexes herein with the field data.
Contribution of Genetics and Nutrition to Changes in Growth Rate.
Sherwood (1977) and Havenstein et al. (1994a, 2003a) reported that about 85 to 90% of the change in commercial broiler performance from 1957 until the years they conducted their comparisons have been due to the genetic selection practiced by commercial breeding companies and that the other 10 to 15% has taken place due to changes in nutritional management. One cannot reach such a clear conclusion from the data reported on turkeys herein. In fact, if one examines the growth rate data in Table 3 and compares the relative performance of the strain-sex groups on the 2003 vs. the 1966 rations, one can see a considerable difference as to how the strains and sexes react to the 2 dietary regimes over the course of the experiment. The calculations in Table 4 are an attempt to demonstrate the relative differences in response to the 2 dietary regimens.
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and 4). Thereafter, with the exception of the modern hens, the birds on the 1966 diets performed better than those on the 2003 diets. As can be seen from Figure 1, after 9 to 10 wk of age, the ambient temperatures started rising, and the birds on the 1966 diet, which contained higher protein and lower energy, started performing better than those on the higher energy and lower protein modern diets. It appeared that the birds consuming the modern high-energy diets reduced their intake as an adaptive measure to minimize their heat stress, and, consequently, the reduced protein intake limited their growth. In contrast, the birds consuming the 1966 diet containing lower energy and higher protein were able to consume more feed during heat stress and therefore more protein and other nutrients to support greater weight gain. Veldkamp et al. (2002) reported that turkeys modulate feed intake when exposed to high ambient temperatures in relation to the caloric density of the diet. Although data to confirm their observation are not available from the present study, this seems to be the most logical explanation for this switch in performance on the 2 diets. Follow-up studies need to be conducted to better understand how to feed market turkeys under high ambient temperatures. From the current study, however, the answer one would give as to whether nutrition and nutritional management has improved performance during the 37-yr period from 1966 to 2003 is clearly dependent upon the flock’s age and the ambient temperature under which the birds are grown.
Feed Efficiency
Feed consumption and BW records were collected by 14-d periods from hatch to 112 d of age and then by 28-d periods from 112 to 196 d of age. The FC was calculated for each pen by individual period and cumulative overall periods to the age involved. The FC by period of age is summarized by strain, diet, and sex in Table 5. The 2003 turkeys had consistently better FC during the first six 2-wk age periods through 84 d of age than did the 1966 RBC2 strain. Once the temperatures began to increase, the FC of both strains increased dramatically, and those birds fed the 1966 diet in most of the comparisons had numerically or significantly better FC than did those on the modern high-calorie diets. The FC was consistently poorer in both strains on the 1966 diets than on the 2003 diets through 84 d of age, but, consistent with the BW data, FC was in most cases (except during the last period when temperatures began to decrease) better on the 1966 diet after that age.
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provide a summary of the cumulative FC data by strain, sex, and feeding regimen for each age measured. Highly significant differences in FC were observed between the strains and diets at all ages, but not between the sexes. The lack of a significant effect due to sex is probably due to a problem that arose when the poults of one of the modern strains were received from the commercial hatchery. Although the 2 groups were labeled as toms and hens, they turned out to be all toms. This was not realized until the birds had been weighed several times, and it was then decided to leave the pens intact. Because the birds were individually identified, this problem was easily handled for the analysis of the other traits but could not be rectified due to the confounding of having both males and females consuming feed in the modern female pens for FC. So, all pens of modern females were comprised of 10 hens and 5 toms. Thus, the sex effect was undoubtedly less than what it should be for FC.
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Livability
Cumulative mortality rates by strain, age, sex, and diet group through 112 d of age are provided in Table 7. The mortality data from 112 to 196 d of age is not included, because 25% of the pens were killed to obtain processing data at 113 d of age, and another 25% were killed each 28-d period thereafter. None of the statistical comparisons were significant at any age period shown (Table 7), and overall livability to 112 d of age was very good for all groups. A few birds were culled during the course of the study and were included in the mortality due to the presence of leg problems or pendulous crops (data not shown), but there didn’t appear to be any consistent pattern to the presence of these abnormalities by strain or diet.
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summarizes the relative differences in response to the 2 dietary regimens. Both sexes of both strains performed much better on the 2003 diets from hatch to 4 to 6 wk of age than on the 1966 diets. Thereafter, with the exception of the modern hens, the birds on the 1966 diets began to perform better than those on the 2003 diets. After 9 to 10 wk of age (mid-May), it became very hot and humid and the birds on the 1966 diet, which contained higher protein and lower energy, started performing better than those on the higher energy and lower protein modern diets. It appears that the birds consuming the modern high-energy diets reduced their intake as an adaptive measure to minimize their heat stress, and, consequently, the reduced protein intake limited their growth. In contrast, the birds consuming the 1966 diet containing lower energy and higher protein were able to consume more feed during heat stress and therefore enough protein and other nutrients to support greater weight gain. This is not too surprising, because Veldkamp et al. (2002) recently reported that turkeys modulate feed intake when exposed to high ambient temperatures in relation to the caloric density of the diet. Follow-up studies need to be conducted to better understand how to feed market turkeys under high ambient temperatures. Thus, from this study, the answer one would give as to whether nutrition and nutritional management has improved performance during the past 37 yr (i.e., from 1966 to 2003) is clearly dependent upon the age and the ambient temperature under which the measurement was taken. In conclusion, the performance of modern market turkeys produced in 2003 was compared with that of randombred turkeys started in 1966, when grown using representative 1966 and 2003 diets. The data indicated that growth rate to market age has approximately doubled during this 37-yr period, and the BW of toms and hens have been increasing by approximately 208 and 140 g/yr during this period. Feed efficiency was approximately 20% better in the 2003 tom turkey on the 2003 feed (2.638) than in the RBC2 tom on the 1966 feed (3.278) at 20 wk of age. Feed efficiency to 11 kg of BW in the 2003 toms (2.132 at 98 d of age) was approximately 50% better than in the RBC2 toms (4.208 at 196 d of age). The number of days to reach that weight was halved during this period. Livability was numerically better in the modern than in the randombred control line of turkeys, so the doubling of the growth rate, with its consequent reduction in FC in the modern turkeys, has not increased the mortality levels in modern turkeys to the ages studied.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Received for publication May 2, 2006. Accepted for publication October 8, 2006.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Cheema, M. A., M. A. Qureshi, and G. B. Havenstein. 2003. A comparison of the immune response of a 2001 commercial broiler with a 1957 randombred broiler strain when fed representative 1957 and 2001 broiler diets. Poult. Sci. 82:1519–1529.
Ensminger, M. E. 1967. Page 80 in Poultry Science. 1st ed. M. E. Ensminger. The Interstate Printers and Publishers Inc., Danville, IL.
Ferket, P. R. 2003. Growth of toms improves substantially. Watt USA (Jul.): 38.
Havenstein, G. B., P. R. Ferket, J. L. Grimes, M. A. Qureshi, and K. E. Nestor. 2004a. Changes in the performance of turkeys –1966–2003. Pages 1–13 in Proc. 27th Tech. Turkeys Conf., Macclesfield, Cheshire, UK.
Havenstein, G. B., P. R. Ferket, J. L. Grimes, M. A. Qureshi, and K. E. Nestor. 2004b. Performance of 1966 vs. 2003-type turkeys when fed representative 1966 and 2003 turkey diets. Proc. World’s Poult. Congr., Istanbul, Turkey. WPSA, Izmir, Turkey.
Havenstein, G. B., P. R. Ferket, S. E. Scheideler, and B. T. Larson. 1994a. Growth, livability and feed conversion of 1991 vs. 1957 broilers when fed "typical" 1957 and 1991 broiler diets. Poult. Sci. 73:1785–1794.[ISI][Medline]
Havenstein, G. B., P. R. Ferket, S. E. Scheideler, and D. V. Rives. 1994b. Carcass composition and yield of 1991 vs. 1957 broilers when fed "typical" 1957 and 1991 diets. Poult. Sci. 73:1795–1804.[ISI][Medline]
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Havenstein, G. B., P. R. Ferket, and M. A. Qureshi. 2003b. Carcass composition and yield of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci. 82:1509–1518.
Marks, H. L. 1971. Growth rate and feed intake of selected and non-selected broilers. Growth 43:80–90.
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Qureshi, M. A., and G. B. Havenstein. 1994. A comparison of the immune performance of a 1991 commercial broiler with a 1957 randombred broiler strain when fed "typical" 1957 and 1991 broiler diets. Poult. Sci. 73:1805–1812.[ISI][Medline]
SAS Institute. 1996. SAS User’s Guide: Statistics. Version 6 ed. SAS Inst. Inc., Cary, NC.
Sherwood, D. H. 1977. Modern broiler feeds and strains: What two decades of improvement have done. Feedstuffs 49:70.
USDA. 2005. Food consumption (per capita) data system. http://www.ers.usda.gov Accessed Oct. 2005.
Veldkamp, T., R. P. Kwakkel, P. R. Ferket, and M. A. Verstegen. 2002. Impact of ambient temperature and age on dietary lysine and energy in turkey production. World’s Poult. Sci. J. 58:475–491.
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