The Effects of Genetic Selection on Production Parameters of Single Comb White Leghorn Hens1

The Effects of Genetic Selection on Production Parameters of Single Comb White Leghorn Hens1

ENVIRONMENT AND HEALTH The Effects of Genetic Selection on Production Parameters of Single Comb White Leghorn Hens1 D. R. Jones,2 K. E. Anderson,3 and...

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ENVIRONMENT AND HEALTH The Effects of Genetic Selection on Production Parameters of Single Comb White Leghorn Hens1 D. R. Jones,2 K. E. Anderson,3 and G. S. Davis Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695 for the more modern strains with CS5 being the heaviest and CCS maintaining the smallest body weight throughout the production periods. The CCS had the highest (P < 0.0001) hen-day production rate, which resulted in the greatest daily egg mass among the strains. The CCS consumed the greatest amount of feed and exhibited the highest gross egg income among the strains. We concluded that genetic selection has improved production parameters in commercial layers as determined by measurements in this study.

(Key words: genetic selection, egg production) 2001 Poultry Science 80:1139–1143

INTRODUCTION During the past four decades, the primary breeders have selected for traits in the commercial strains of Leghorns that have enhanced the efficiency of egg production. Selection emphasis changed periodically for numerous traits, some of which included the size of eggs, number of eggs produced, or age at first egg. Studies conducted throughout the years have isolated some general traits that could be associated with the different control strains and that could be used as a basis for comparison. For example, Fairfull and Gowe (1986) reported that body weight steadily declined from the older stocks to the more current stocks. Lower body weights of more current stocks have also been reported by Grady (1960, 1973) and Anderson (1994). Primary breeders have been selecting for early sexual maturity in commercial layers for many years. Fairfull et al. (1983), Fairfull and Gowe (1986), and Jackson et al. (1986) have shown that age at first egg has steadily decreased, whereas egg weight has increased (Fairfull and

2001 Poultry Science Association, Inc. Received for publication August 21, 2000. Accepted for publication April 9, 2000. 1 Mention of trade mark, proprietary product, or specific equipment does not constitute a warranty by North Carolina State University and does not imply its approval to the exclusion of other products that may be suitable. 2 Current address: USDA-ARS, Russell Research Center, Athens, GA 30604. 3 To whom correspondence should be addressed: [email protected] ncsu.edu.

Gowe, 1986; Jackson et al., 1986; McMillan et al., 1990) in the control strains formed in 1950, 1959, and 1972. This selection emphasis has been in response to consumer demands for larger eggs. Due to this selection pressure, egg size distribution also has changed (Akbar et al., 1983). Fairfull et al. (1983), Fairfull and Gowe (1986), and Jackson et al. (1986) have reported that hen-day egg production is higher in the more current strains. Therefore, the objectives of this study were to document changes that have occurred in the commercial laying hen and to evaluate the effect of selection on egg quality and size distribution throughout the laying cycle.

MATERIALS AND METHODS Four genetic stocks were used in this study. Three of the Ottawa Control Strains were acquired from Agriculture Canada; Strains 5 (CS5), 7 (CS7), and 10 (CS10) were used as comparisons against a current commercial laying stock. Gowe et al. (1993) and Fairfull et al. (1983) described the composition of these three random-bred, control strains. CS5 was formed from a common base population of laying hens in 1950. The CS7 was formed in 1959 from four Leghorn strains: H&N “Nick Chick,” Hy-Line威 934A, Kimber K137, and Shaver 288. CS10 was formed in 1972 from four Leghorn strains: Babcock B300, H&N “Nick Chick,” Hy-Line威 934, and Shaver 288. These strains have

Abbreviation Key: CS5 = Ottawa Control Strain 5, CS7 = Ottawa Control Strain 7, CS10 = Ottawa Control Strain 10, CCS = Current commercial stock.

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ABSTRACT Four commercial table egg genetic stocks consisting of the Ottawa Control Strains 5, 7, and 10 (CS5, CS7, and CS10) and the 1993 H&N “Nick Chick” (CCS) were housed in the same environment and compared for production characteristics. These birds were housed in an environmentally controlled laying facility with trideck cages. Feed consumption, egg production, and mortality were monitored daily and compiled every 28 d. The study was conducted for two egg production cycles, including the molt period. Body weight was progressively lower

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JONES ET AL.

cantly different were separated by least-squares means according to SAS威 software. Interactions of hen age by genetic strain that occurred were due to the Ottawa Control Strains interacting among one another over time. Due to the lack of interaction between the control strains and the CCS, we can account for differences in main effects among the strains.

RESULTS AND DISCUSSION Body weights are shown in Table 1. The CCS and CS5 had similar 18-wk body weights but were heavier (P < 0.001) than CS7 and CS10. However, at the end of the first production cycle (62 wk), the CS5 hens (2157.2 g) were heavier (P < 0.001) than the CS7 (1964.4 g) and CS10 (1927.3 g). After the molt period (64 wk), the CS7, CS10, and CCS had similar body weights that were significantly (P < 0.001) lower than those weights observed for CS5. Final body weights (86 wk) also resulted the same. Fairfull and Gowe (1986) found that when comparing CS5, CS7, and CS10, body weight decreased, respectively. Fairfull et al. (1983) also found similar results when comparing CS7 and CS10. Both of these reports support the findings of this study, in that the CCS birds weighed less than their predecessors at the end of the production period. The age at 50% egg production among the strains is shown in Table 2. The CCS was the earliest maturing strain, reaching 50% production in 154.9 d, which was less (P < 0.001) than the control strains that matured later. CS5 took the longest (182.86 d) to reach 50% production. In a comparison of reports published by Grady (1960) Grady (1973) and Anderson (1994) found a decrease in the age of hens at 50% production in more modern commercial strains. These reported findings are similar to the findings of Fairfull et al. (1983). Grady (1973) and Anderson (1994) reported that henday production levels increases in more modern commercial strains, and similar results were observed in the current study (Table 2). Fairfull et al. (1983), Fairfull and Gowe (1986), and Jackson et al. (1986) found that henday egg production increases among the later-formed control strains, with the more current strains producing more eggs. In the present study, a significant (P < 0.0001) interaction between strain and hen age was found for hen-day egg production. Interactions among the control

TABLE 1. Effects of strain on initial, premolt, postmolt, and final body weights and percentages of gain and loss during the total production cycle1 Strain

18-wk body weight (g)

62-wk body weight (g)

Gain (%)

64-wk body weight (g)

Loss (%)

86-wk body weight (g)

CS5 CS7 CS10 CCS Pooled SE

1,399.7y 1,336.0z 1,330.7z 1,429.3y ± 7.8

2,157.2a 1,964.4b 1,927.3b 2,042.7ab ± 47.0

54.3a 47.2b 45.1b 37.2c ± 1.8

1,545.3y 1,354.6z 1,331.1z 1,335.9z ± 20.5

28.4b 31.1a 30.9a 31.8a ± 0.6

2,348.9y 2,141.9z 2,074.7z 2,073.9z ± 20.5

Means with different superscripts differ within a column (P < 0.01). Means with different superscripts differ within a column (P < 0.001). 1 CS5 = Ottawa Control Strain 5; CS7 = Ottawa Control Strain 7; CS10 = Ottawa Control Strain 10; CCS = Current commercial stock. a–c y,z

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been maintained in a random-bred, unselected manner since their formation. The current commercial stock used in this study was the 1993 H&N “Nick Chick” because of its common ancestry with the control strains. Hatching eggs were obtained and hatched simultaneously at the North Carolina Department of Agriculture Piedmont Research Station, Poultry Unit, located in Salisbury, North Carolina. The eggs from the four strains were randomly placed in two incubators to reduce variation between strains due to potential incubator differences. The chicks were housed, 40 females per cage, with a density of 310 cm2/bird in a flat-deck, brood-grow cage facility. The rearing and lighting programs were identical as outlined by Anderson (1996). At 18 wk of age, the pullets were moved to an environmentally controlled laying house containing four rows of trideck layer cages. Six hens were housed per cage with density and feeder space being 361 cm210.2 cm, respectively. The strains were equally represented in all cage levels and rows in a complete random block design. The birds were maintained using a phase feeding program regulated based on flock performance and feed intake. Birds were molted at 62 wk according to the methods of Anderson (1994). Body weights were recorded at four ages: 18, 62, 64, and 86 wk. These dates correspond with housing, premolt, postmolt, and experiment termination. Age at 50% egg production was considered a measure of maturity in each of the strains. Feed consumption was monitored every 28 d and was recorded as the kilograms of feed consumed daily per 100 hens. Feed conversion was also monitored every 28 d and recorded as the grams of eggs produced per gram of feed consumed. Egg income was calculated on a per bird basis, based on a 3-yr regional average egg price. Eggs were collected daily, and hen-day egg production and daily egg mass were calculated for each 28-d period. Egg grades and size distributions were determined utilizing the grading standard, size classifications, and specified weights for market eggs (USDA, 1982). All egg size and quality grade outs were done concurrently to ensure consistency of data collection. The data were subjected to ANOVA with the general linear models procedure of SAS威 software (SAS Institute, 1989). Percentage mortality was subjected to an arc sin transformation prior to analysis. Means that were signifi-

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GENETIC SELECTION IN SINGLE COMB WHITE LEGHORNS TABLE 2. Effect of strain on the age at 50% production, hen-day egg production, daily egg mass, and egg weight1 Strain

Age at 50% production (d)

CS5 CS7 CS10 CCS

± ± ± ±

182.9 172.6 166.3 154.9

Hen-day egg production (%)

w

0.9 0.9x 0.9y 0.9z

56.88 59.67 64.20 73.38 ****

± ± ± ±

Daily egg mass (g)

Z

0.18 0.18Y 0.18X 0.18W

34.18 37.02 41.17 49.34 ****

± ± ± ±

Egg weight (g)

Z

0.18 0.16Y 0.16X 0.16W

56.49 61.76 61.03 63.63 ****

± ± ± ±

0.74c 0.67b 0.67b 0.67a

Means with different superscripts within a column are significantly different (P < 0.05). Means with different superscripts within a column are significantly different (P < 0.001). W–Z Means with different superscripts within a column are significantly different (P < 0.0001). 1 CS5 = Ottawa Control Strain 5; CS7 = Ottawa Control Strain 7; CS10 = Ottawa Control Strain 10; CCS = Current commercial stock. ****Interaction of strain and age (P < 0.0001). a–c

w–z

strains interacted with each other throughout the production cycles. An increase in the percentage of large and extra-large eggs was observed in the late stages of the first production cycle, which is a natural progression of egg size development in the laying hen. The percentage of large eggs gradually decreased during the second production cycle for all strains. The CCS exhibited the highest (P < 0.0001) percentage of extralarge eggs for both cycles. This result parallels the egg weight data in that the CCS produced the heaviest eggs, whereas the CS5 produced the lightest eggs. Thus, the more current strains produce more of the larger-sized eggs due to breeder selection. Akbar et al. (1983), in a study with the CS5 and CS7, found a similar distribution of egg size. In the present study, there was an increase in the percentage of extra-large eggs as hens aged. A summary of egg quality grades is shown in Table 4. The CS7 had the lowest (P < 0.05) percentage of A grade eggs and the highest (P < 0.05) percentage of B grade eggs. These results suggest that egg quality suffered during genetic selection in the early 1970s. Egg quality was increased in CS10 and CCS, with CCS maintaining the highest (P < 0.05) percentage of A grade eggs and the lowest (P < 0.05) percentage of B grade and loss eggs. There were no differences among the strains for the percentage of check grade eggs. It is also important to note that all strains in this study were subjected to the same environment and management practices. Both of these factors have been linked to the incidence of check grade eggs. Thus, selection does not appear to have affected shell soundness.

TABLE 3. Effect of strain on percentage of egg size distribution1 Strain

Pee wee (%)

CS5 CS7 CS10 CCS

± ± ± ±

7.57 5.55 2.42 0.83 ****

W

0.39 0.36X 0.35Y 0.35Z

Small (%) 7.00 5.30 4.08 2.17 ****

± ± ± ±

Medium (%) a

0.43 0.40b 0.39c 0.39d

23.24 18.96 14.64 9.03 ****

± ± ± ±

W

0.60 0.55X 0.55Y 0.55Z

Large (%) 38.75 39.60 34.54 27.78 ****

± ± ± ±

Extra large (%) X

0.90 0.65X 0.64Y 0.64Z

22.69 30.81 44.01 59.78 ****

± ± ± ±

0.61Z 0.56Y 0.55X 0.55W

Means with different superscripts within a column are significantly different (P < 0.05). Means with different superscripts within a column are significantly different (P < 0.0001). 1 CS5 = Ottawa Control Strain 5; CS7 = Ottawa Control Strain 7; CS10 = Ottawa Control Strain 10; CCS = Current commercial stock. ****Interaction of strain and age (P < 0.0001). a–d

W–Z

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strains occurred during peak production of the first and second egg production cycles. The CCS maintained maximal hen-day production levels among the strains throughout both production cycles. Daily egg mass was greater (P < 0.0001) for the CCS compared to the control strains (Table 2). Anderson (1994) found a similar daily egg mass of 49.7 g among the white egg strains housed in environmentally controlled facilities. A significant (P < 0.0001) strain by hen age interaction occurred during the study. There was also a significant interaction between CS5 and CS7 during the second production cycle peak. Egg weight values were significant (P < 0.05) for strain, as shown in Table 2. The CCS had the greatest (P < 0.05) average egg weight (63.63 g) for the complete production cycle, which is similar to egg weights observed by Anderson (1996) for white egg layers and Jin and Craig (1988) for the H&N “Nick Chick.” The CS5 birds had the lowest egg weights for the overall production period, which was also reported by Fairfull and Gowe (1986), Jackson et al. (1986), and McMillan et al. (1990). Egg size distribution values are shown in Table 3. The CS5 had the greatest percentage of pee wee (P < 0.0001), small (P < 0.05), medium (P < 0.0001), and large (P < 0.0001) eggs and the lowest (P < 0.0001) percentage of extra-large eggs. The CCS had inverse results. These results follow the trends in genetic selection for increased egg size due to consumer demands for large and extralarge eggs. A significant (P < 0.0001) strain by hen age interaction exists for each egg size category. The control

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JONES ET AL. TABLE 4. Effect of strain on egg grades1 Strain

Grade A (%)

CS5 CS7 CS10 CCS

94.66 93.97 94.99 95.54

± ± ± ±

Grade B (%)

0.37ab 0.33b 0.33a 0.33a

3.06 3.82 2.98 2.72

± ± ± ±

Check (%)

0.30b 0.27a 0.27b 0.27b

2.16 2.01 1.77 1.69

± ± ± ±

0.22 0.20 0.19 0.19

Loss (%) 0.12 0.18 0.26 0.04

± ± ± ±

0.05bc 0.05ab 0.05a 0.05c

Means with different superscripts within a column are significantly different (P < 0.05). CS5 = Ottawa Control Strain 5; CS7 = Ottawa Control Strain 7; CS10 = Ottawa Control Strain 10; CCS = Current commercial stock. a–c 1

of an induced molt. The high levels of mortality of the CCS could be due in part to the high levels of egg production in comparison to the other strains. There was also a higher incidence of prolapse, which was associated with the increased egg production. Feed cost was significantly (P < 0.0001) greater for the more modern strains (Table 5). The CCS had the greatest feed cost ($8.75/bird), and the CS5 had the least feed cost ($8.09/bird) for the present study. The increase in feed cost coincides with increased feed consumption. Egg income was greatest (P < 0.001) for the CCS ($19.98/bird) with the CS5 exhibiting the lowest income ($14.81/bird), as shown in Table 5. The higher egg income for the more current stocks was in part due to the greater level of egg production and the higher levels of production of large and extra-large eggs by these strains. In conclusion, the traits examined in this study clearly illustrate the advances made in hen production due to genetic selection during the past 40 yr. Genetic selection has influenced egg production characteristics and economic factors. Body weight in the more current strain has decreased, whereas feed consumption has increased with a concurrent gain in the grams of egg per gram of feed. It is clearly evident that the CCS provided the greatest egg income among the four strains. Hen-day production has increased with CS5 exhibiting the lowest production rates and the CCS the highest production rate. This trend was also observed for average daily egg mass and average egg weight, which have both increased. More-current strains had greater percentages of extra-large eggs produced. The most current strain did exhibit the highest percentage of average mortality

TABLE 5. Effect of strain on feed consumption, feed conversion, total mortality, egg income, and feed cost1 Strain CS5 CS7 CS10 CCS

Feed consumption (kg/100 birds/d) 10.43 10.45 10.59 11.30 ****

± ± ± ±

0.04Z 0.04Y 0.04Y 0.04X

Feed conversion (g eggs/g feed) 0.319 0.345 0.378 0.426 ****

± ± ± ±

0.002Z 0.002Y 0.002Y 0.002W

Total mortality (%) 16.05 12.00 11.66 17.09

± ± ± ±

1.22a 1.22b 1.22b 1.22a

Feed cost ($/bird) 8.09 8.15 8.28 8.75

± ± ± ±

0.06Z 0.06XY 0.06Y 0.06X

Egg income ($/bird) 14.81 16.02 17.55 19.98 ****

± ± ± ±

0.15z 0.15y 0.15x 0.15w

Means with different superscripts within a column are significantly different (P < 0.05). Means with different superscripts within a column are significantly different (P < 0.001). W–Z Means with different superscripts within a column are significantly different (P < 0.0001). 1 CS5 = Ottawa Control Strain 5; CS7 = Ottawa Control Strain 7; CS10 = Ottawa Control Strain 10; CCS = Current commercial stock. ****Interaction of strain and age (P < 0.0001). a,b

w–z

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The CCS had the greatest (P < 0.0001) overall average feed consumption rate of 11.30 kg/100 birds per day (Table 5). The greater feed consumption found in the CCS could be associated with the higher productivity of this strain. There was an interaction among the control strains (P < 0.0001) during the complete cycle, which was due to variations in the feeding level of the control strains. Jackson et al. (1986) reported that feed consumption was similar for CS5 and CS7, which further supports the findings from the current study. Feed conversion was most efficient for the CCS for the entire study (Table 5). The feed conversion shown here is similar to that reported by Anderson (1996) for commercially available white egg strains that were established at the same time as the CCS. Selection pressures for early maturity, egg size, and persistency of lay for current strains appear to have resulted in greater yields at lower costs. There was a significant interaction between strain and hen age (P < 0.0001) for feed conversion. The interaction occurred at the beginning of the first production cycle between CS7 and CS10. There was also an interaction between CS5 and CS7 at the end of the second cycle. The total mortality for each strain is shown in Table 5. The CCS had the highest (P < 0.05) level of mortality among the strains at molt (17.09%), which was similar to the findings of Anderson (1996) for the same strain. Jackson et al. (1986) reported a higher level of mortality for the CS7 than the CS5 to 273 d, whereas Fairfull et al. (1983) found the CS7 percentage of mortality to be lower than that of the CS10 through 371 d. The higher level of mortality in the CCS observed in the present study may be attributed to the length of the study and the inclusion

GENETIC SELECTION IN SINGLE COMB WHITE LEGHORNS

among the four strains. The increased mortality of this current commercial strain could be an effect of the enhanced egg production rate of these hens. This finding supports the need for research in the areas of nutrition, physiology, and management to better care for the higher physiological needs of these new production stocks, based on productivity and body mass. Additional work in nutritional supplementation during periods of high productivity may be able to eliminate some of the mortality observed in this study. Furthermore, alterations in management practices such as lighting and feed withdrawal programs could prove beneficial in reducing mortality rates in high producing flocks.

REFERENCES

method, caging density, and lymphoid leukosis infection on adult performance in egg stocks of chickens. Poultry Sci. 62:2360–2370. Fairfull, R. W., and R. S. Gowe, 1986. Genotypic and phenotypic parameters of spur incidence and length in White Leghorn hens. Poultry Sci. 65:1995–2001. Gowe, R. S., R. W. Fairfull, I. McMillan, and G. S. Schmidt, 1993. Strategy for maintaining high fertility and hatchability in multiple-trait egg stock selection program. Poultry Sci. 72:1433–1448. Grady, G. A., 1960. Final report of the first North Carolina random sample egg laying test. North Carolina State University Cooperative Extension Service, Raleigh, NC 1(4). Grady, G. A., 1973. Final report of the fourteenth North Carolina random sample egg laying test. North Carolina State University Cooperative Extension Service, Raleigh, NC 14(4). Jackson, M. E., G. W. Friars, J. S. Gavora, C. Y. Lin, R. S. Gowe, I. McMillan, and E. T. Moran, 1986. Comparisons of control and selected strains, strain crosses, and commercial stocks of leghorns for egg production efficiency. Poultry Sci. 65:16–25. Jin, L. and J. V. Craig, 1988. Some effects of cage and floor rearing on commercial White Leghorn pullets during growth and the first year of egg production. Poultry Sci. 67:1400– 1406. McMillan, I., R. W. Fairfull, R. S. Gowe, and J. S. Gavora, 1990. Evidence for genetic improvement of layer stocks of chickens during 1950–1980. World’s Poultry Sci. J. 46:235–245. SAS Institute, 1989. A User’s Guide to SAS威. Sparks Press, Inc., Cary, NC. United States Department of Agriculture, Agricultural Marketing Service, Poultry Division, 1982. United States standards, grades, and weight classes for shell eggs. USDA, Washington, DC.

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Akbar, M. K., J. S. Gavora, G. W. Friars, and R. S. Gowe, 1983. Composition of eggs by commercial size categories: Effects of genetic group, age, and diet. Poultry Sci. 62:925–933. Anderson, K. E., 1994. Final report of the thirtieth North Carolina layer performance and management test. North Carolina State University Cooperative Extension Service, Raleigh, NC 30(4). Anderson, K. E., 1996. Final report of the thirty-first North Carolina layer performance and management test. North Carolina State University Cooperative Extension Service, Raleigh, NC 31(4). Fairfull, R. W., V. A. Garwood, J. L. Spencer, R. S. Gowe, and P. C. Lowe, 1983. The effects of geographical area, rearing

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