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Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo) a
b
b
O. W. Willems , N. J. H. Buddiger & B. J. Wood a
Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada b
Hybrid Turkeys, Suite C, 650 Riverbend Drive, Kitchener, ON, Canada Accepted author version posted online: 23 Sep 2014.Published online: 18 Dec 2014.
Click for updates To cite this article: O. W. Willems, N. J. H. Buddiger & B. J. Wood (2014) Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo), British Poultry Science, 55:6, 715-719, DOI: 10.1080/00071668.2014.966058 To link to this article: http://dx.doi.org/10.1080/00071668.2014.966058
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British Poultry Science, 2014 Vol. 55, No. 6, 715–719, http://dx.doi.org/10.1080/00071668.2014.966058
Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo) O. W. WILLEMS, N. J. H. BUDDIGER1,
AND
B. J. WOOD1
Downloaded by [University of Cambridge] at 23:55 29 December 2014
Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada, and 1Hybrid Turkeys, Suite C, 650 Riverbend Drive, Kitchener, ON, Canada
Abstract 1. Genetic parameters for production and feed efficiency traits in the Orlopp line of turkeys were estimated to determine breeding goals and future potential of the line in a long-term genetic improvement programme. 2. Body weight, egg production and fertility traits were recorded and feed conversion ratio (FCR) was assessed from 16–20 weeks of age. 3. Moderate heritabilities were found for feed intake and body weight gain (0.25 to 0.31). Average FCR was 3.14, with heritability of 0.10. Body weight, breast conformation score and egg production traits showed moderate heritabilities (0.22 to 0.52), while both fertility and hatch of fertile eggs were low (0.04 and 0.09, respectively). 4. Genetic correlations between breast confirmation score, 10- and 18-week body weights were moderate, 0.50 and 0.45, respectively. Average egg weight also showed moderate genetic correlations with 10- and 18week body weights (0.59 and 0.42).
INTRODUCTION The Orlopp line of turkeys originated in the San Joaquin Valley, CA, USA. This population formed one of the oldest foundation turkey breeding programmes in the world. Like most early commercial turkey breeding programmes, the breeding goals were primarily focused on increasing body weight via phenotypic selection. In 2005, a Canadian primary turkey breeder purchased the Orlopp line of turkeys and the lines were transported from California, USA northwards to Ontario, Canada. Modern turkey breeding programmes generally consist of two different selection strategies, one for the sire lines and one for the dam lines. Sire line breeding goals more closely resemble the original selection strategy for turkey programmes, focusing on body weight and growth rate, but are also likely to incorporate breast meat yield, feed efficiency and a walking/survivability
score. Dam line breeding programmes include traits from the sire line programmes, with additional traits such as fertility, hatchability and egg production also included in the breeding goals. Previous genetic parameter estimates in turkeys have reported moderate heritabilities (0.36 to 0.43) for body weight in populations between the ages of 17 to 24 weeks and 0.45 in a random control bred population (Nestor et al., 1967; Havenstein et al., 1988). Heritability estimates for 15-week body weight in sire lines ranged from 0.30 to 0.35 (Case et al., 2012a; Willems et al., 2013). In a dam line, heritability for 15-week body weight was higher (0.39), and total egg production heritability has been reported between 0.16 and 0.32 (Case et al., 2010; Quinton et al., 2011). Estimates of heritability for fertility and hatchability for a dam line already included in a commercial breeding programme were 0.08 and 0.09, respectively (Case et al., 2010).
Correspondence to: Owen W. Willems, Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada. E-mail: [email protected] Accepted for publication 25 July 2014.
© 2014 British Poultry Science Ltd
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The purpose of the current study was to estimate the genetic parameters for an Orlopp dam line of turkeys. Genetic parameters for this particular line have not previously been examined and will serve as a starting point for further analyses. Estimation of genetic parameters and genetic correlations between traits is important in determining the potential of continuing to use a particular line within a breeding programme. Typically, to include a line of birds into a breeding programme, the traits that it expresses must be heritable, contain genetic variation and be useful either currently or going forward.
Traits Egg production was evaluated as the percentage of days with an egg produced between 210 and 420 d of age. Fertility was measured as the proportion of eggs that had a live embryo when candled at 14 d. Hatchability was calculated as the percentage of fertile eggs that produced a live poult. Body weights for birds in the general population were taken at both 10 and 18 weeks. Breast confirmation scores were done at 18 weeks of age. Body weights for birds removed from the general population to be assessed for feed efficiency were measured at both 16 and 20 weeks, as opposed to 18 weeks. Feed conversion ratio (FCR) was calculated as FCR ¼
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MATERIALS AND METHODS Turkey population Birds from an Orlopp primary breeder turkey line (n = 13339) with data collected over a 4year period with pedigree information were used. Rearing until 15 weeks of age was under a standard commercial production environment and feeding regime, which involved group housing with shared feeders and drinkers. At 15 weeks of age, stags were placed in individual pens (0.60 m wide, 0.85 m long and 0.82 m high) to acclimatise and they remained in the same pen throughout the feeding trial, from approximately 16 to 20 weeks of age. Body weight was measured at the start (16 weeks of age) and the end of the trial (20 weeks of age). Feed intake was recorded by weighing feeders at the beginning of the trial; weighing the feed added to each feeder and weighing the remaining feed at the end of the trial. During this period, stags were fed a standard commercial diet. Feed was available ad libitum, with access to feed from individual feeders within a pen and a shared water source between pens. Hens were reared to 16 weeks of age under the same standard commercial production environment as the stags. After 16 weeks of age, hens were placed onto a qualitatively restricted commercial parent stock body weight diet. Qualitatively restricted diets contained less protein and less energy than the standard commercial diets. Lighting conditions consisted of equal 12-h periods of light and dark to 16 weeks of age. From 16 to 30 weeks birds were exposed to 6-h periods of light and 18-h of dark. Light intensities varied with flock requirement, temperament, and other management factors. From 30 weeks of age the photoperiod consisted of 16-h of light and 8-h of dark periods. Feed and water were available ad libitum, with access to shared feeders and drinkers.
feed consumed ðkgÞ body weight gain ðkgÞ
Metabolic mid-weight (MMW) was calculated as MMW
weight at start of trial þ weight at end of trial 0:75 ¼ 2
To determine residual feed intake (RFI), expected feed intake was calculated as a multiple regression with observed feed intake as the dependent variable (Model 1). Model 1 : FI ¼ μ þ b1 MMW þ b2 WG þ hatch þ e where FI is the feed intake over the test period, MMW is the metabolic mid-weight, WG is body weight gain over the test period, μ is the intercept, b1 and b2 are partial regression coefficients and e is the residual. The fixed contemporary group effect (hatch) was used to account for the common environment effect that influenced birds hatched on the same date and managed in the same group. Regression coefficients from Model 1 were used to calculate RFI (Model 2): Model 2 : RFI ¼ FI μ þ ^b 1 MMW þ ^b 2 WG Genetic analyses Heritability for each trait as well as phenotypic and genetic correlations was estimated using ASREML 3.0 (Gilmour et al., 2009). The model for all traits was Trait ¼ hatch þ animal þ e where “trait” is 10-week body weight (BW10), 18week body weight (BW18), breast conformation score (BCS), RFI, FCR, feed intake, MMW and body weight gain. “Hatch” was a fixed
GENETICS OF ORLOPP TURKEYS
contemporary group effect to account for the common environment of group of birds hatched and managed together, “animal” represents the random additive genetic effect, and e the residual random effect. The random effects were assumed to be normally distributed with a mean of zero. Heritability estimates were calculated using a univariate model. Phenotypic and genetic correlations were estimated pair-wise using a bivariate model.
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RESULTS Means and heritabilities for body weight at 10 and 18 weeks of age, breast conformation score, average egg weight, fertility, hatch of fertile, total egg production, FCR and RFI are shown in Table 1. Body weight traits had moderate heritabilities (0.48 and 0.52) for 10- and 18-week body weight, respectively. Egg weight was also moderately heritable with an estimated value of 0.49. Fertility traits were lowly heritable, with fertility at 0.04 and hatch of fertile at 0.09, while total egg production had a heritability of 0.22. Breast conformation Table 1. Descriptive statistics and heritabilities for production, fertility and feed efficiency traits in a dam line of Orlopp turkeys Trait
Number Mean
10-week body weight (kg) 18-week body weight (kg) Breast conformation score Egg weight (g) Fertility (%) Hatch of fertile (%) Total egg production Feed intake (kg) 16-week body weight (kg) 20-week body weight (kg) Body weight gain (kg) Feed conversion ratio (kg/kg) Residual feed intake (kg)
13 339 8711 8710 652 622 617 566 271 271 271 271 271 271
4.75 11.88 2.16
SD
Heritability (SE)
0.61 2.67 0.75
0.52 (0.03) 0.48 (0.03) 0.29 (0.03)
73.51 4.77 80.53 15.53 91.62 11.33 52.86 11.95 14.16 2.22 9.82 1.00 14.55 1.32 4.73 1.00 3.14 0.26 0.00
1.09
0.49 0.04 0.09 0.22 0.27 0.20 0.35 0.31 0.10
(0.09) (0.06) (0.08) (0.08) (0.16) (0.15) (0.17) (0.17) (0.13)
0.18 (0.16)
717
score had a heritability of 0.29. The feed efficiency traits of FCR and RFI had heritabilities of 0.10 and 0.18, respectively. Phenotypic and genetic correlations among body weights, conformation scores, egg production, fertility and feed efficiency traits can be found in Table 2. Both phenotypic and genetic correlations between body weight traits were high and positive. Breast conformation score was moderately positively correlated both phenotypically and genetically with the body weight traits. Egg weight also showed low to moderate positive phenotypic and genetic correlations with the body weight traits, while hatch of fertile had high genetic correlations with the body weight traits (0.85 and 0.90), however standard errors were also high (0.32 and 0.30). Total egg production was not genetically correlated to 10-week body weight, but had a moderate positive genetic correlation with 18-week body weight (0.25). Total egg production had a negative genetic correlation with both average egg weight (−0.18) and fertility (−0.33). Average egg weight had a moderately positive genetic correlation with hatch of fertile (0.46), while hatch of fertile was negatively genetically correlated with fertility (0.40). Total egg production had a low genetic correlation with hatch of fertile (0.10). FCR had positive genetic correlations with all traits (0.09 to 0.60) except for total egg production (−0.55). Residual feed intake had positive genetic correlations with 10- and 18-week body weights (0.13 and 0.23), breast conformation score (0.07) and fertility (0.78), and negative genetic correlations with average egg weight (−0.67), hatch of fertile (−0.28) and total egg production (−0.56).
DISCUSSION The estimated heritabilities of the two body weight traits (10- and 18-weeks of age) are slightly higher than previous estimates in both dam and sire line turkeys (Nestor et al., 2000; Case et al., 2010). Breast
Table 2.
Phenotypic (above diagonal) and genetic (below diagonal) correlations for a dam line of Orlopp turkeys, standard errors in parentheses
Traits1
BW10
BW10 BW18 BCS EW FERT HOF EP FCR RFI 1
0.81 0.50 0.59 −0.14 0.85 −0.01 0.52 0.13
(0.02) (0.05) (0.07) (0.29) (0.32) (0.13) (0.34) (0.24)
BW18
BCS
EW
0.60 (0.01)
0.31 (0.01) 0.37 (0.01)
0.21 (0.05) 0.15 (0.05) −0.20 (0.05)
0.45 0.42 −0.56 0.90 0.25 0.60 0.23
(0.06) (0.08) (0.34) (0.30) (0.20) (0.38) (0.25)
0.22 −0.30 0.24 −0.35 0.58 0.07
(0.10) (0.32) (0.20) (0.15) (0.47) (0.28)
0.37 0.46 −0.18 0.16 −0.67
(0.45) (0.30) (0.21) (0.38) (0.40)
FERT 0.00 −0.06 0.00 0.03
(0.05) (0.06) (0.06) (0.04)
−0.40 −0.33 0.67 0.78
(0.62) (0.77) (078) (0.84)
HOF 0.09 0.17 −0.07 0.10 0.11
(0.06) (0.06) (0.06) (0.04) (0.04)
0.10 (0.38) 0.09 (0.72) −0.28 (0.54)
EP 0.01 −0.03 −0.13 0.07 0.16 0.27
(0.06) (0.06) (0.06) (0.05) (0.04) (0.05)
−0.55 (0.58) −0.56 (0.46)
FCR 0.07 −0.20 −0.11 0.04 0.04 0.01 −0.08
(0.07) (0.06) (0.08) (0.08) (0.06) (0.07) (0.07)
RFI −0.08 −0.03 −0.03 −0.18 0.08 −0.04 −0.11 0.19
(0.08) (0.07) (0.08) (0.09) (0.07) (0.08) (0.08) (0.06)
0.97 (0.55)
10-week body weight (BW10), 18-week body weight (BW18), breast conformation score (BCS), average egg weight (EW), fertility (FERT), hatch of fertile (HOF), total egg production (EP), feed conversion ratio (FCR), residual feed intake (RFI).
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conformation score heritability was within the range of previous estimates where conformation was assessed visually, and slightly higher than studies which measured both the length and the width of the turkey breast by callipers (Aslam et al., 2011; Case et al., 2012b). Estimates of total egg production heritability were on the lower end of previous estimates in turkeys, which have been shown to range from 0.13 to 0.61 (Nestor and Noble, 1995; Chapuis et al., 1996; Nestor et al., 1996). The heritability for average egg weight was also similar to previous reports in the literature at 0.49 (Nestor et al., 1972; Arthur and Abplanalp, 1975). Fertility and hatch of fertile were both low, as expected in fertility traits, and both were below even the lowest limit of previous estimates in turkeys, with a previous range reported between 0.16 and 0.34 (Mccartney et al., 1968; Nestor et al., 1972). For the feed efficiency traits, the heritabilities of both FCR and RFI are within estimates of earlier findings in turkeys, with Case et al. (2012a) reporting 0.16 and 0.21, and Willems et al. (2013) publishing estimates of 0.05 and 0.23 for FCR and RFI, respectively. The genetic correlation between 10- and 18week body weight was 0.80, which is similar to the 0.86 reported between 11- and 17-week body weight in turkeys (Aslam et al., 2011). Correlations between 18-week body weight and egg production were found to be moderately positive; this is in contrast to previous findings in female turkey lines with selection placed heavily on body weight, where Kranis et al. (2006) report the genetic correlation as a weighted average between four different studies as −0.53 (Chapuis et al., 1996; Nestor et al., 1996; Emmerson et al., 2002). This problem is further exacerbated, as the 10-week body weight also shows zero correlations, both phenotypically and genetically with total egg production. Typically, a negative correlation is seen between body weight and egg production; this may be due to more energy being allocated for egg production as opposed to depositing protein and fat for body weight gain. This is also the case in laying hens where Luiting (1990) notes that net energy for production is divided between the processes of egg production and body weight gain. However, in the Orlopp line, that does not seem to be the case, as body weight remains largely unrelated to egg production. This may be one cause of the lower than normal total egg production values in this line of turkeys. However, as stated by Nestor et al. (1996), the genetic correlation between body weight and egg production can change rapidly and must therefore be re-estimated each generation. This was echoed in a more recent study where changes in genetic variance were examined across a 10-year period by a primary turkey breeder (Proulx et al., 2014). While not possible in this study, once
subsequent generational data has been collected, a re-examination of the genetic parameters would be necessary to determine if the genetic correlation between body weight and egg production is changing from year to year as previously suggested. Genetic correlation estimates between average egg weight, fertility and hatch of fertile, as well as between hatch of fertile and total egg production were similar to previous estimates (Nestor et al., 1972). However, genetic correlations between fertility and hatch of fertile, and fertility and egg production were moderately negative, whereas in previous studies these correlations have been found to be positive (Nestor et al., 1972; Nestor and Noble, 1995). In this case, the cause for the opposing correlation is likely due to a high standard error, 0.62 and 0.77, respectively, caused by low numbers of records for the population studied. FCR was below what is generally reported in male line turkeys, which average closer to 2.95 (Case et al., 2012a; Willems et al., 2013); however this result is expected due to selection pressures being placed not only on production traits, but also fertility and egg production traits in the female line. The negative genetic correlation for RFI with average egg weight, hatch of fertile and total egg production appears to be in line with previous studies where RFI was examined alongside egg production and fertility traits. In an experiment on divergent RFI lines in laying hens, hatchability was 20 points higher in the more efficient RFI line (Morisson et al., 1997). In addition, Basso et al. (2012) state the following in the laying duck: correlated responses on reproductive traits seem favourable, as lower RFI values increase the number of total egg produced, as well as the hatchability and fertility rates. Genetic correlations between body weight traits and total egg production in this dam line of Orlopp turkeys appear to be abnormally positive, which could be useful in a breeding programme. Negative correlations are generally expected between body weight and total egg production in a dam line. In this case, estimated correlations between body weight and total egg production are close to zero or positive, which is more indicative of a sire line of turkeys. However, the genetic correlations estimated in this study may be unreliable due to large standard errors in their estimation. This problem is largely due to the small data set that was used in the estimation process. Prior to deciding whether or not to include this line in a breeding programme, a larger data set should be used to complete similar estimates for this line. This study does however begin to put together the framework on which initial decisions can be made concerning the Orlopp line of turkeys and its usefulness in a breeding programme.
GENETICS OF ORLOPP TURKEYS
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REFERENCES ARTHUR, J.A. & ABPLANALP, H. (1975) Linear estimates of heritability and genetic correlation for egg production, body weight, conformation and egg weight of turkeys. Poultry Science, 54: 11–23. doi:10.3382/ps.0540011 ASLAM, M.L., BASTIAANSEN, J.W.M., CROOIJMANS, R.P.M.A., DUCRO, B.J., VEREIJKEN, A.L.J. & GROENEN, M.A.M. (2011) Genetic variances, heritabilities and maternal effects on body weight, breast meat yield, meat quality traits and the shape of the growth curve in turkey birds. BMC Genetics, 12: 14–23. doi:10.1186/1471-2156-12-14 BASSO, B., BORDAS, A., DUBOS, F., MORGANX, P. & MARIEETANCELIN, C. (2012) Feed efficiency in the laying duck: appropriate measurements and genetic parameters. Poultry Science, 91: 1065–1073. doi:10.3382/ps.2011-02008 CASE, L.A., KELLY, M.J., MILLER, S.P. & WOOD, B.J. (2010) Genotype x environment interaction as it relates to egg production in turkeys (Meleagris gallopavo). Journal of Animal Science, 88: 1957–1966. doi:10.2527/jas.2009-2004 CASE, L.A., WOOD, B.J. & MILLER, S.P. (2012a) The genetic parameters of feed efficiency and its component traits in the turkey (Meleagris gallopavo). Genetics Selection Evolution, 44: 2–6. doi:10.1186/1297-9686-44-2 CASE, L.A., WOOD, B.J. & MILLER, S.P. (2012b) The investigation of ultrasound technology to measure breast muscle depth as a correlated trait to breast meat yield in turkey (Meleagris gallopavo). Journal of Animal Science, 90: 3410–3417. doi:10.2527/jas.2011-4822 CHAPUIS, H., TIXIER-BOICHARD, M., DELABROSSE, Y. & DUCROCQ, V. (1996) Multivariate restricted maximum likelihood estimation of genetic parameters for production traits in three selected turkey strains. Genetics Selection Evolution, 28: 299–317. doi:10.1186/1297-9686-28-3-299 EMMERSON, D.A., VELLEMAN, S.G. & NESTOR, K.E. (2002) Genetics of growth and reproduction in the turkey. 15. Effect of long-term selection for increased egg production on the genetics of growth and egg production traits. Poultry Science, 81: 316–320. doi:10.1093/ps/81.3.316 GILMOUR, A.R., GOGEL, B.J., CULLIS, B.R., WELHAM, S.J. & THOMPSON, R. (2009). Asreml User Guide Release 3.0., pp. 1–267 (Hemel Hempstead, UK, VSN International Ltd). HAVENSTEIN, G., NESTOR, K., TOELLE, V. & BACON, W. (1988) Estimates of genetic parameters in turkeys. 1. Body weight and skeletal characteristics. Poultry Science, 67: 1378–1387. doi:10.3382/ps.0671378 KRANIS, D.A., HOCKING, P.M., HILL, W.G. & WOOLLIAMS, J. (2006) Genetic parameters for a heavy female turkey line: impact of simultaneous selection for body weight and total egg number. British Poultry Science, 47: 685–693. doi:10.1080/ 00071660601053304
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LUITING, P. (1990) Genetic variation of energy partitioning in laying hens: causes of variation in residual feed consumption. World’s Poultry Science Journal, 46: 133–152. doi:10. 1079/WPS19900017 MCCARTNEY, M.G., NESTOR, K.E. & HARVEY, W.R. (1968) Genetics of growth and reproduction in the turkey: 2. Selection for increased body weight and egg production. Poultry Science, 47: 981–990. doi:10.3382/ps.0470981 MORISSON, M., BORDAS, A., PETIT, J., JAYAT-VIGNOLES, C., JULIEN, R. & MINVIELLE, F. (1997) Associated effects of divergent selection for residual feed consumption on reproduction, sperm characteristics, and mitochondria of spermatozoa. Poultry Science, 76: 425–431. doi:10.1093/ps/ 76.3.425 NESTOR, K.E., ANDERSON, J.W. & PATTERSON, R.A. (2000) Genetics of growth and reproduction in the turkey. 14. Changes in genetic parameters over thirty generations of selection for increased body weight. Poultry Science, 79: 445–452. doi:10.1093/ps/79.4.445 NESTOR, K.E., BROWN, K.I. & WEAVER, C.R. (1972) Egg quality and poult production in turkeys: 2. Inheritance and relationship among traits. Poultry Science, 51: 147–158. doi:10.3382/ps.0510147 NESTOR, K.E., MCCARTNEY, M.G. & HARVEY, W.R. (1967) Genetics of growth and reproduction in the turkey: 1. Genetic and non-genetic variation in body weight and body measurements. Poultry Science, 46: 1374–1384. doi:10. 3382/ps.0461374 NESTOR, K.E. & NOBLE, D.O. (1995) Influence of selection for increased egg production, body weight, and shank width of turkeys on egg composition and the relationship of the egg traits to hatchability. Poultry Science, 74: 427–433. doi:10.3382/ps.0740427 NESTOR, K.E., NOBLE, D.O., ZHU, J. & MORITSU, Y. (1996) Direct and correlated responses to long-term selection for increased body weight and egg production in turkeys. Poultry Science, 75: 1180–1191. doi:10.3382/ps.0751180 PROULX, J., WILLEMS, O.W. & WOOD, B.J. (2014) Evaluating genetic variance of reproductive traits across ten years of selection in the turkey (Meleagris gallopavo). Proceedings of the 10th World Congress on Genetics Applied to Livestock Production, Vancouver, Canada. Abstract number: 150. QUINTON, C.D., WOOD, B.J. & MILLER, S.P. (2011) Genetic analysis of survival and fitness in turkeys with multiple-trait animal models. Poultry Science, 90: 2479–2486. doi:10.3382/ ps.2011-01604 WILLEMS, O.W., MILLER, S.P. & WOOD, B.J. (2013) Assessment of residual body weight gain and residual intake and body weight gain as feed efficiency traits in the turkey (Meleagris gallopavo). Genetics Selection Evolution, 45: 26–34. doi:10. 1186/1297-9686-45-26
British Poultry Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/cbps20
Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo) a
b
b
O. W. Willems , N. J. H. Buddiger & B. J. Wood a
Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada b
Hybrid Turkeys, Suite C, 650 Riverbend Drive, Kitchener, ON, Canada Accepted author version posted online: 23 Sep 2014.Published online: 18 Dec 2014.
Click for updates To cite this article: O. W. Willems, N. J. H. Buddiger & B. J. Wood (2014) Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo), British Poultry Science, 55:6, 715-719, DOI: 10.1080/00071668.2014.966058 To link to this article: http://dx.doi.org/10.1080/00071668.2014.966058
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
British Poultry Science, 2014 Vol. 55, No. 6, 715–719, http://dx.doi.org/10.1080/00071668.2014.966058
Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo) O. W. WILLEMS, N. J. H. BUDDIGER1,
AND
B. J. WOOD1
Downloaded by [University of Cambridge] at 23:55 29 December 2014
Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada, and 1Hybrid Turkeys, Suite C, 650 Riverbend Drive, Kitchener, ON, Canada
Abstract 1. Genetic parameters for production and feed efficiency traits in the Orlopp line of turkeys were estimated to determine breeding goals and future potential of the line in a long-term genetic improvement programme. 2. Body weight, egg production and fertility traits were recorded and feed conversion ratio (FCR) was assessed from 16–20 weeks of age. 3. Moderate heritabilities were found for feed intake and body weight gain (0.25 to 0.31). Average FCR was 3.14, with heritability of 0.10. Body weight, breast conformation score and egg production traits showed moderate heritabilities (0.22 to 0.52), while both fertility and hatch of fertile eggs were low (0.04 and 0.09, respectively). 4. Genetic correlations between breast confirmation score, 10- and 18-week body weights were moderate, 0.50 and 0.45, respectively. Average egg weight also showed moderate genetic correlations with 10- and 18week body weights (0.59 and 0.42).
INTRODUCTION The Orlopp line of turkeys originated in the San Joaquin Valley, CA, USA. This population formed one of the oldest foundation turkey breeding programmes in the world. Like most early commercial turkey breeding programmes, the breeding goals were primarily focused on increasing body weight via phenotypic selection. In 2005, a Canadian primary turkey breeder purchased the Orlopp line of turkeys and the lines were transported from California, USA northwards to Ontario, Canada. Modern turkey breeding programmes generally consist of two different selection strategies, one for the sire lines and one for the dam lines. Sire line breeding goals more closely resemble the original selection strategy for turkey programmes, focusing on body weight and growth rate, but are also likely to incorporate breast meat yield, feed efficiency and a walking/survivability
score. Dam line breeding programmes include traits from the sire line programmes, with additional traits such as fertility, hatchability and egg production also included in the breeding goals. Previous genetic parameter estimates in turkeys have reported moderate heritabilities (0.36 to 0.43) for body weight in populations between the ages of 17 to 24 weeks and 0.45 in a random control bred population (Nestor et al., 1967; Havenstein et al., 1988). Heritability estimates for 15-week body weight in sire lines ranged from 0.30 to 0.35 (Case et al., 2012a; Willems et al., 2013). In a dam line, heritability for 15-week body weight was higher (0.39), and total egg production heritability has been reported between 0.16 and 0.32 (Case et al., 2010; Quinton et al., 2011). Estimates of heritability for fertility and hatchability for a dam line already included in a commercial breeding programme were 0.08 and 0.09, respectively (Case et al., 2010).
Correspondence to: Owen W. Willems, Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada. E-mail: [email protected] Accepted for publication 25 July 2014.
© 2014 British Poultry Science Ltd
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The purpose of the current study was to estimate the genetic parameters for an Orlopp dam line of turkeys. Genetic parameters for this particular line have not previously been examined and will serve as a starting point for further analyses. Estimation of genetic parameters and genetic correlations between traits is important in determining the potential of continuing to use a particular line within a breeding programme. Typically, to include a line of birds into a breeding programme, the traits that it expresses must be heritable, contain genetic variation and be useful either currently or going forward.
Traits Egg production was evaluated as the percentage of days with an egg produced between 210 and 420 d of age. Fertility was measured as the proportion of eggs that had a live embryo when candled at 14 d. Hatchability was calculated as the percentage of fertile eggs that produced a live poult. Body weights for birds in the general population were taken at both 10 and 18 weeks. Breast confirmation scores were done at 18 weeks of age. Body weights for birds removed from the general population to be assessed for feed efficiency were measured at both 16 and 20 weeks, as opposed to 18 weeks. Feed conversion ratio (FCR) was calculated as FCR ¼
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MATERIALS AND METHODS Turkey population Birds from an Orlopp primary breeder turkey line (n = 13339) with data collected over a 4year period with pedigree information were used. Rearing until 15 weeks of age was under a standard commercial production environment and feeding regime, which involved group housing with shared feeders and drinkers. At 15 weeks of age, stags were placed in individual pens (0.60 m wide, 0.85 m long and 0.82 m high) to acclimatise and they remained in the same pen throughout the feeding trial, from approximately 16 to 20 weeks of age. Body weight was measured at the start (16 weeks of age) and the end of the trial (20 weeks of age). Feed intake was recorded by weighing feeders at the beginning of the trial; weighing the feed added to each feeder and weighing the remaining feed at the end of the trial. During this period, stags were fed a standard commercial diet. Feed was available ad libitum, with access to feed from individual feeders within a pen and a shared water source between pens. Hens were reared to 16 weeks of age under the same standard commercial production environment as the stags. After 16 weeks of age, hens were placed onto a qualitatively restricted commercial parent stock body weight diet. Qualitatively restricted diets contained less protein and less energy than the standard commercial diets. Lighting conditions consisted of equal 12-h periods of light and dark to 16 weeks of age. From 16 to 30 weeks birds were exposed to 6-h periods of light and 18-h of dark. Light intensities varied with flock requirement, temperament, and other management factors. From 30 weeks of age the photoperiod consisted of 16-h of light and 8-h of dark periods. Feed and water were available ad libitum, with access to shared feeders and drinkers.
feed consumed ðkgÞ body weight gain ðkgÞ
Metabolic mid-weight (MMW) was calculated as MMW
weight at start of trial þ weight at end of trial 0:75 ¼ 2
To determine residual feed intake (RFI), expected feed intake was calculated as a multiple regression with observed feed intake as the dependent variable (Model 1). Model 1 : FI ¼ μ þ b1 MMW þ b2 WG þ hatch þ e where FI is the feed intake over the test period, MMW is the metabolic mid-weight, WG is body weight gain over the test period, μ is the intercept, b1 and b2 are partial regression coefficients and e is the residual. The fixed contemporary group effect (hatch) was used to account for the common environment effect that influenced birds hatched on the same date and managed in the same group. Regression coefficients from Model 1 were used to calculate RFI (Model 2): Model 2 : RFI ¼ FI μ þ ^b 1 MMW þ ^b 2 WG Genetic analyses Heritability for each trait as well as phenotypic and genetic correlations was estimated using ASREML 3.0 (Gilmour et al., 2009). The model for all traits was Trait ¼ hatch þ animal þ e where “trait” is 10-week body weight (BW10), 18week body weight (BW18), breast conformation score (BCS), RFI, FCR, feed intake, MMW and body weight gain. “Hatch” was a fixed
GENETICS OF ORLOPP TURKEYS
contemporary group effect to account for the common environment of group of birds hatched and managed together, “animal” represents the random additive genetic effect, and e the residual random effect. The random effects were assumed to be normally distributed with a mean of zero. Heritability estimates were calculated using a univariate model. Phenotypic and genetic correlations were estimated pair-wise using a bivariate model.
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RESULTS Means and heritabilities for body weight at 10 and 18 weeks of age, breast conformation score, average egg weight, fertility, hatch of fertile, total egg production, FCR and RFI are shown in Table 1. Body weight traits had moderate heritabilities (0.48 and 0.52) for 10- and 18-week body weight, respectively. Egg weight was also moderately heritable with an estimated value of 0.49. Fertility traits were lowly heritable, with fertility at 0.04 and hatch of fertile at 0.09, while total egg production had a heritability of 0.22. Breast conformation Table 1. Descriptive statistics and heritabilities for production, fertility and feed efficiency traits in a dam line of Orlopp turkeys Trait
Number Mean
10-week body weight (kg) 18-week body weight (kg) Breast conformation score Egg weight (g) Fertility (%) Hatch of fertile (%) Total egg production Feed intake (kg) 16-week body weight (kg) 20-week body weight (kg) Body weight gain (kg) Feed conversion ratio (kg/kg) Residual feed intake (kg)
13 339 8711 8710 652 622 617 566 271 271 271 271 271 271
4.75 11.88 2.16
SD
Heritability (SE)
0.61 2.67 0.75
0.52 (0.03) 0.48 (0.03) 0.29 (0.03)
73.51 4.77 80.53 15.53 91.62 11.33 52.86 11.95 14.16 2.22 9.82 1.00 14.55 1.32 4.73 1.00 3.14 0.26 0.00
1.09
0.49 0.04 0.09 0.22 0.27 0.20 0.35 0.31 0.10
(0.09) (0.06) (0.08) (0.08) (0.16) (0.15) (0.17) (0.17) (0.13)
0.18 (0.16)
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score had a heritability of 0.29. The feed efficiency traits of FCR and RFI had heritabilities of 0.10 and 0.18, respectively. Phenotypic and genetic correlations among body weights, conformation scores, egg production, fertility and feed efficiency traits can be found in Table 2. Both phenotypic and genetic correlations between body weight traits were high and positive. Breast conformation score was moderately positively correlated both phenotypically and genetically with the body weight traits. Egg weight also showed low to moderate positive phenotypic and genetic correlations with the body weight traits, while hatch of fertile had high genetic correlations with the body weight traits (0.85 and 0.90), however standard errors were also high (0.32 and 0.30). Total egg production was not genetically correlated to 10-week body weight, but had a moderate positive genetic correlation with 18-week body weight (0.25). Total egg production had a negative genetic correlation with both average egg weight (−0.18) and fertility (−0.33). Average egg weight had a moderately positive genetic correlation with hatch of fertile (0.46), while hatch of fertile was negatively genetically correlated with fertility (0.40). Total egg production had a low genetic correlation with hatch of fertile (0.10). FCR had positive genetic correlations with all traits (0.09 to 0.60) except for total egg production (−0.55). Residual feed intake had positive genetic correlations with 10- and 18-week body weights (0.13 and 0.23), breast conformation score (0.07) and fertility (0.78), and negative genetic correlations with average egg weight (−0.67), hatch of fertile (−0.28) and total egg production (−0.56).
DISCUSSION The estimated heritabilities of the two body weight traits (10- and 18-weeks of age) are slightly higher than previous estimates in both dam and sire line turkeys (Nestor et al., 2000; Case et al., 2010). Breast
Table 2.
Phenotypic (above diagonal) and genetic (below diagonal) correlations for a dam line of Orlopp turkeys, standard errors in parentheses
Traits1
BW10
BW10 BW18 BCS EW FERT HOF EP FCR RFI 1
0.81 0.50 0.59 −0.14 0.85 −0.01 0.52 0.13
(0.02) (0.05) (0.07) (0.29) (0.32) (0.13) (0.34) (0.24)
BW18
BCS
EW
0.60 (0.01)
0.31 (0.01) 0.37 (0.01)
0.21 (0.05) 0.15 (0.05) −0.20 (0.05)
0.45 0.42 −0.56 0.90 0.25 0.60 0.23
(0.06) (0.08) (0.34) (0.30) (0.20) (0.38) (0.25)
0.22 −0.30 0.24 −0.35 0.58 0.07
(0.10) (0.32) (0.20) (0.15) (0.47) (0.28)
0.37 0.46 −0.18 0.16 −0.67
(0.45) (0.30) (0.21) (0.38) (0.40)
FERT 0.00 −0.06 0.00 0.03
(0.05) (0.06) (0.06) (0.04)
−0.40 −0.33 0.67 0.78
(0.62) (0.77) (078) (0.84)
HOF 0.09 0.17 −0.07 0.10 0.11
(0.06) (0.06) (0.06) (0.04) (0.04)
0.10 (0.38) 0.09 (0.72) −0.28 (0.54)
EP 0.01 −0.03 −0.13 0.07 0.16 0.27
(0.06) (0.06) (0.06) (0.05) (0.04) (0.05)
−0.55 (0.58) −0.56 (0.46)
FCR 0.07 −0.20 −0.11 0.04 0.04 0.01 −0.08
(0.07) (0.06) (0.08) (0.08) (0.06) (0.07) (0.07)
RFI −0.08 −0.03 −0.03 −0.18 0.08 −0.04 −0.11 0.19
(0.08) (0.07) (0.08) (0.09) (0.07) (0.08) (0.08) (0.06)
0.97 (0.55)
10-week body weight (BW10), 18-week body weight (BW18), breast conformation score (BCS), average egg weight (EW), fertility (FERT), hatch of fertile (HOF), total egg production (EP), feed conversion ratio (FCR), residual feed intake (RFI).
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conformation score heritability was within the range of previous estimates where conformation was assessed visually, and slightly higher than studies which measured both the length and the width of the turkey breast by callipers (Aslam et al., 2011; Case et al., 2012b). Estimates of total egg production heritability were on the lower end of previous estimates in turkeys, which have been shown to range from 0.13 to 0.61 (Nestor and Noble, 1995; Chapuis et al., 1996; Nestor et al., 1996). The heritability for average egg weight was also similar to previous reports in the literature at 0.49 (Nestor et al., 1972; Arthur and Abplanalp, 1975). Fertility and hatch of fertile were both low, as expected in fertility traits, and both were below even the lowest limit of previous estimates in turkeys, with a previous range reported between 0.16 and 0.34 (Mccartney et al., 1968; Nestor et al., 1972). For the feed efficiency traits, the heritabilities of both FCR and RFI are within estimates of earlier findings in turkeys, with Case et al. (2012a) reporting 0.16 and 0.21, and Willems et al. (2013) publishing estimates of 0.05 and 0.23 for FCR and RFI, respectively. The genetic correlation between 10- and 18week body weight was 0.80, which is similar to the 0.86 reported between 11- and 17-week body weight in turkeys (Aslam et al., 2011). Correlations between 18-week body weight and egg production were found to be moderately positive; this is in contrast to previous findings in female turkey lines with selection placed heavily on body weight, where Kranis et al. (2006) report the genetic correlation as a weighted average between four different studies as −0.53 (Chapuis et al., 1996; Nestor et al., 1996; Emmerson et al., 2002). This problem is further exacerbated, as the 10-week body weight also shows zero correlations, both phenotypically and genetically with total egg production. Typically, a negative correlation is seen between body weight and egg production; this may be due to more energy being allocated for egg production as opposed to depositing protein and fat for body weight gain. This is also the case in laying hens where Luiting (1990) notes that net energy for production is divided between the processes of egg production and body weight gain. However, in the Orlopp line, that does not seem to be the case, as body weight remains largely unrelated to egg production. This may be one cause of the lower than normal total egg production values in this line of turkeys. However, as stated by Nestor et al. (1996), the genetic correlation between body weight and egg production can change rapidly and must therefore be re-estimated each generation. This was echoed in a more recent study where changes in genetic variance were examined across a 10-year period by a primary turkey breeder (Proulx et al., 2014). While not possible in this study, once
subsequent generational data has been collected, a re-examination of the genetic parameters would be necessary to determine if the genetic correlation between body weight and egg production is changing from year to year as previously suggested. Genetic correlation estimates between average egg weight, fertility and hatch of fertile, as well as between hatch of fertile and total egg production were similar to previous estimates (Nestor et al., 1972). However, genetic correlations between fertility and hatch of fertile, and fertility and egg production were moderately negative, whereas in previous studies these correlations have been found to be positive (Nestor et al., 1972; Nestor and Noble, 1995). In this case, the cause for the opposing correlation is likely due to a high standard error, 0.62 and 0.77, respectively, caused by low numbers of records for the population studied. FCR was below what is generally reported in male line turkeys, which average closer to 2.95 (Case et al., 2012a; Willems et al., 2013); however this result is expected due to selection pressures being placed not only on production traits, but also fertility and egg production traits in the female line. The negative genetic correlation for RFI with average egg weight, hatch of fertile and total egg production appears to be in line with previous studies where RFI was examined alongside egg production and fertility traits. In an experiment on divergent RFI lines in laying hens, hatchability was 20 points higher in the more efficient RFI line (Morisson et al., 1997). In addition, Basso et al. (2012) state the following in the laying duck: correlated responses on reproductive traits seem favourable, as lower RFI values increase the number of total egg produced, as well as the hatchability and fertility rates. Genetic correlations between body weight traits and total egg production in this dam line of Orlopp turkeys appear to be abnormally positive, which could be useful in a breeding programme. Negative correlations are generally expected between body weight and total egg production in a dam line. In this case, estimated correlations between body weight and total egg production are close to zero or positive, which is more indicative of a sire line of turkeys. However, the genetic correlations estimated in this study may be unreliable due to large standard errors in their estimation. This problem is largely due to the small data set that was used in the estimation process. Prior to deciding whether or not to include this line in a breeding programme, a larger data set should be used to complete similar estimates for this line. This study does however begin to put together the framework on which initial decisions can be made concerning the Orlopp line of turkeys and its usefulness in a breeding programme.
GENETICS OF ORLOPP TURKEYS
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REFERENCES ARTHUR, J.A. & ABPLANALP, H. (1975) Linear estimates of heritability and genetic correlation for egg production, body weight, conformation and egg weight of turkeys. Poultry Science, 54: 11–23. doi:10.3382/ps.0540011 ASLAM, M.L., BASTIAANSEN, J.W.M., CROOIJMANS, R.P.M.A., DUCRO, B.J., VEREIJKEN, A.L.J. & GROENEN, M.A.M. (2011) Genetic variances, heritabilities and maternal effects on body weight, breast meat yield, meat quality traits and the shape of the growth curve in turkey birds. BMC Genetics, 12: 14–23. doi:10.1186/1471-2156-12-14 BASSO, B., BORDAS, A., DUBOS, F., MORGANX, P. & MARIEETANCELIN, C. (2012) Feed efficiency in the laying duck: appropriate measurements and genetic parameters. Poultry Science, 91: 1065–1073. doi:10.3382/ps.2011-02008 CASE, L.A., KELLY, M.J., MILLER, S.P. & WOOD, B.J. (2010) Genotype x environment interaction as it relates to egg production in turkeys (Meleagris gallopavo). Journal of Animal Science, 88: 1957–1966. doi:10.2527/jas.2009-2004 CASE, L.A., WOOD, B.J. & MILLER, S.P. (2012a) The genetic parameters of feed efficiency and its component traits in the turkey (Meleagris gallopavo). Genetics Selection Evolution, 44: 2–6. doi:10.1186/1297-9686-44-2 CASE, L.A., WOOD, B.J. & MILLER, S.P. (2012b) The investigation of ultrasound technology to measure breast muscle depth as a correlated trait to breast meat yield in turkey (Meleagris gallopavo). Journal of Animal Science, 90: 3410–3417. doi:10.2527/jas.2011-4822 CHAPUIS, H., TIXIER-BOICHARD, M., DELABROSSE, Y. & DUCROCQ, V. (1996) Multivariate restricted maximum likelihood estimation of genetic parameters for production traits in three selected turkey strains. Genetics Selection Evolution, 28: 299–317. doi:10.1186/1297-9686-28-3-299 EMMERSON, D.A., VELLEMAN, S.G. & NESTOR, K.E. (2002) Genetics of growth and reproduction in the turkey. 15. Effect of long-term selection for increased egg production on the genetics of growth and egg production traits. Poultry Science, 81: 316–320. doi:10.1093/ps/81.3.316 GILMOUR, A.R., GOGEL, B.J., CULLIS, B.R., WELHAM, S.J. & THOMPSON, R. (2009). Asreml User Guide Release 3.0., pp. 1–267 (Hemel Hempstead, UK, VSN International Ltd). HAVENSTEIN, G., NESTOR, K., TOELLE, V. & BACON, W. (1988) Estimates of genetic parameters in turkeys. 1. Body weight and skeletal characteristics. Poultry Science, 67: 1378–1387. doi:10.3382/ps.0671378 KRANIS, D.A., HOCKING, P.M., HILL, W.G. & WOOLLIAMS, J. (2006) Genetic parameters for a heavy female turkey line: impact of simultaneous selection for body weight and total egg number. British Poultry Science, 47: 685–693. doi:10.1080/ 00071660601053304
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LUITING, P. (1990) Genetic variation of energy partitioning in laying hens: causes of variation in residual feed consumption. World’s Poultry Science Journal, 46: 133–152. doi:10. 1079/WPS19900017 MCCARTNEY, M.G., NESTOR, K.E. & HARVEY, W.R. (1968) Genetics of growth and reproduction in the turkey: 2. Selection for increased body weight and egg production. Poultry Science, 47: 981–990. doi:10.3382/ps.0470981 MORISSON, M., BORDAS, A., PETIT, J., JAYAT-VIGNOLES, C., JULIEN, R. & MINVIELLE, F. (1997) Associated effects of divergent selection for residual feed consumption on reproduction, sperm characteristics, and mitochondria of spermatozoa. Poultry Science, 76: 425–431. doi:10.1093/ps/ 76.3.425 NESTOR, K.E., ANDERSON, J.W. & PATTERSON, R.A. (2000) Genetics of growth and reproduction in the turkey. 14. Changes in genetic parameters over thirty generations of selection for increased body weight. Poultry Science, 79: 445–452. doi:10.1093/ps/79.4.445 NESTOR, K.E., BROWN, K.I. & WEAVER, C.R. (1972) Egg quality and poult production in turkeys: 2. Inheritance and relationship among traits. Poultry Science, 51: 147–158. doi:10.3382/ps.0510147 NESTOR, K.E., MCCARTNEY, M.G. & HARVEY, W.R. (1967) Genetics of growth and reproduction in the turkey: 1. Genetic and non-genetic variation in body weight and body measurements. Poultry Science, 46: 1374–1384. doi:10. 3382/ps.0461374 NESTOR, K.E. & NOBLE, D.O. (1995) Influence of selection for increased egg production, body weight, and shank width of turkeys on egg composition and the relationship of the egg traits to hatchability. Poultry Science, 74: 427–433. doi:10.3382/ps.0740427 NESTOR, K.E., NOBLE, D.O., ZHU, J. & MORITSU, Y. (1996) Direct and correlated responses to long-term selection for increased body weight and egg production in turkeys. Poultry Science, 75: 1180–1191. doi:10.3382/ps.0751180 PROULX, J., WILLEMS, O.W. & WOOD, B.J. (2014) Evaluating genetic variance of reproductive traits across ten years of selection in the turkey (Meleagris gallopavo). Proceedings of the 10th World Congress on Genetics Applied to Livestock Production, Vancouver, Canada. Abstract number: 150. QUINTON, C.D., WOOD, B.J. & MILLER, S.P. (2011) Genetic analysis of survival and fitness in turkeys with multiple-trait animal models. Poultry Science, 90: 2479–2486. doi:10.3382/ ps.2011-01604 WILLEMS, O.W., MILLER, S.P. & WOOD, B.J. (2013) Assessment of residual body weight gain and residual intake and body weight gain as feed efficiency traits in the turkey (Meleagris gallopavo). Genetics Selection Evolution, 45: 26–34. doi:10. 1186/1297-9686-45-26
