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Genetic parameters of body weight, egg production, and shell quality traits in the Shan Ma laying duck (Anas platyrhynchos)
Genetic parameters of body weight, egg production, and shell quality traits in the Shan Ma laying duck (Anas platyrhynchos) R. L. Lin,∗ H. P. Chen,∗ R. Rouvier,† and C. Marie-Etancelin†,1,2 ∗
Fujian Longyan Honglong Poultry Industrial Company limited, Longyan, 364000 China; and † GenPhySE, INRA, INPT, INP-ENVT, Universit´e de Toulouse, 31076 Castanet Tolosan, France (ranging from 0.38 to 0.43), and low for the age at first egg (0.13). Heritability’s for egg shell quality traits varied from 0.20 for the breaking strength to 0.44 for egg length, with in-between values of 0.28 for shell thickness and 0.34 for the shape index. The number of eggs laid was not genetically correlated with the age at first egg or egg weight, but was correlated with body weight (rg = +0.54 ± 0.23). High positive correlations were found between egg weight and body weight traits, and both of these traits (except egg weight at first egg) were highly and positively correlated with egg length and width. Breaking strength was genetically correlated with egg shell thickness (rg = +0.54 ± 0.19) and the shape index (rg = +0.71 ± 0.23). These results suggest that an efficient selection strategy could be implemented to improve the egg production of the pure Shan Ma duck line.
Key words: egg quality, laying duck, genetic parameter 2016 Poultry Science 0:1–6 http://dx.doi.org/10.3382/ps/pew222
INTRODUCTION
estimating the genetic parameters for such economically important traits is to better understand the genetic variation of these traits and to define an optimized breeding program leading to genetic improvement of the breed. As yet, very few studies have focused on estimating the genetic parameters of egg production and egg shell quality in laying ducks, except in Brown Tsaiya ducks (Tai et al., 1989; Cheng et al., 1995). The purpose of this study was to estimate and discuss the genetic parameters for body weight, egg production, and egg shell quality traits of the Chinese Shan Ma duck.
Duck egg production is an important economic activity in China because duck eggs represent approximately 15% of all eggs produced for human consumption (Pingel, 2009). The Shan Ma duck (Anas Platyrhynchos) is one of the main Chinese indigenous egg laying duck breeds mentioned in the photograph album of China indigenous poultry breeds (Xu and Chen, 2003). In a first study, in order to obtain homogeneous plumage color phenotypes, Shan Ma ducks were crossbred with two other Chinese laying duck breeds, the Putian White and the Putian Black, and its plumage color inheritance was established (Lin et al., 2014). Nevertheless, the genetic variation of the quantitative traits related to egg production and egg shell quality remained unknown for Shan Ma ducks. The aim of
MATERIALS AND METHODS The present study was carried out in agreement with the guidelines on live animals research approved by the US Institutional Animal Care and Use Committee (IACUC).
C 2016 Poultry Science Association Inc. Received January 20, 2016. Accepted May 25, 2016. 1 Corresponding author: [email protected] 2 Current address: Institut National de la Recherche Agronomique, UMR GenPhySE, B.P. 52627, 31326 Castanet-Tolosan, Tel: (+33) 5 61 28 51 93 , Fax: (+33) 5 61 28 53 53.
Ducks A total of 304 female laying Shan Ma ducks were hatched from 11 sire families. More specifically, each of 1
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ABSTRACT Three hundred and four female ducks of the Chinese indigenous Shan Ma breed, progeny of 11 sires and 104 dams, were used to study laying traits. Among them, 264 ducks were used to study the egg shell quality traits of eggs laid at 300 days of age. The mean age at first egg was 109 days with an average egg weight of 49.6 ± 3.7 g. Between 210 and 300 days of age, egg weight increased from 65.0 ± 3.9 g to 67.0 ± 4.2 g and the mean of the number of eggs laid up to 300 days was 161 ± 15.0. Egg length was 59.57 ± 3.01 mm and egg width was 45.02 ± 1.98 mm, leading to a shape index of 1.32 ± 0.08. Egg shell thickness was about 0.31 mm whatever the shell region, and the breaking strength was 28.80 ± 8.29 N. The heritability’s estimated using restricted maximum likelihood (REML) methodology were high for egg weights (ranging from 0.43 to 0.61), intermediate for the number of eggs laid
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Traits Measured The individual body weights and egg laying traits were measured for 269 to 304 ducks, depending on the trait. Body weights were measured at 110 days of age (BW110) and 300 days of age (BW300). The age at first egg (A1EGG), the averaged weights of the 10 first eggs laid (EW1ST), the average weights of the 5 consecutive eggs laid from 210, 280, and 300 days of age (EW210, EW280, EW300), and the number of eggs laid up to 210, 280, and 300 days of age (NE210, NE280, NE300) were recorded. The egg shell quality traits were measured for eggs laid on 3 consecutive days starting at 300 days of age: 3, 2, and 1 eggs were measured for 243, 16, and 5 female ducks, respectively, leading to a total of 766 eggs. The following external traits were recorded for each egg: egg weight (EW), egg length or vertical diameter (LE), egg width or horizontal diameter (WE), shape index (SI) which was defined as the ratio of the length on the width measured to the nearest 0.1 mm, egg shell breaking strength (BS), egg shell thickness at the blunt region (STB), equatorial region (STE), and sharp region (STS), and the average of these 3 thicknesses (STA). Broken eggs were not used. Egg weight was measured to the nearest 0.01 g while the shell thickness was measured with a precision of 0.01 mm using a Vernier caliper. Breaking strength was measured by pole-to-pole pressing of the egg with a digital concrete compression testing machine with capacity range of 0 N to 500 N.
Statistical Analysis The normal distribution of the traits was tested using the Univariate procedure of the SAS software package (SAS Institute, 2009). The hypothesis of normal distribution was accepted except for A1EGG, NE210, NE280, NE300, and WE. In order to achieve normality, the number of eggs laid up to 210, 280, and 300 days of age were transformed using log (N-number of eggs)
with N = 96, N = 165, and N = 185 respectively at 210, 280, and 300 days of age. Because these transformations change the sign of the correlations, they have been reversed in the Tables 2 and 5 to match the biological results. The same transformation, with different parameters, was used by Dunn et al. (2005) for egg production traits in domestic hens. The means and phenotypic standard deviations of the traits were computed with the Means procedure of the SAS software package, while the “pen” fixed effect was tested with the GLM procedure of SAS. No significant within-sire pen effect was observed on body weight or egg production traits except for BW110 in family 1. The phenotypic correlations between traits were obtained using the CORR procedure of SAS. To estimate the genetic parameters, an animal model was constructed as follows: Yij = μ + ai + eij Where Yij is the ijth phenotypic record of a trait, μ the common mean, ai the ith individual breeding value, and eij the error. The restricted maximum likelihood (REML) procedure was applied to estimate heritability’s and genetic correlations using the VCE 6.0 software package (Neumaier and Groeneveld, 1998). Heritability’s were estimated using single-trait analysis, while genetic correlations between traits were estimated using 2-trait analysis. A multitrait REML procedure was also performed on a reduced number of egg shell quality traits, in order to obtain more accurate estimates while achieving convergence. The two data sets for egg production traits and egg shell quality traits were first analyzed separately, then genetic correlations between the traits of the two sets were estimated.
RESULTS AND DISCUSSION Body Weight and Egg Laying Traits Table 1 shows the means, standard deviations, and coefficients of variation for the body weight and egg laying traits. Duck body weights increased by more than 100 g from 110 days of age (1,269 ± 110 g) to 300 days of age (1,381 ± 117 g). On average, animals laid their first egg at 109.5 days of age, with a very small coefficient of variation (1.7%). The means and standard deviations for the NE210, NE280, and NE 300 were respectively 82 ± 8.5, 143 ± 13.6, and 161 ± 15.0 eggs, and the EW210, EW280, and EW300 were 65.0 ± 3.9, 65.9 ± 4.6, and 67.0 ± 4.2 g, respectively. The body weights for Shan Ma ducks are similar to those published by Tai et al. (1989), who reported body weights of 1,270 ± 136 g at 16 weeks of age and 1,407 ± 133 g at 40 weeks of age in Brown Tsaiya ducks. As regards to laying traits, our results are close to those reported in Brown Tsaiya ducks with 139 ± 15 eggs laid up to 280 days of age, and egg weights of 64.2 ± 4.3 g
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the 11 Shan Ma drakes was mated to 8 to 10 Shan Ma female ducks producing a progeny of 25 to 29 daughter ducks per sire family. The 11 sires and the 104 dams, parents of the study set of 304 female ducks, were selected at random in a large population and were assumed not to be related. All ducks in the study set were individually identified. In all, 22 pens were used for breeding the whole study population: progenies of each of the 11 drakes were raised into 2 separate pens, taking care that the full sisters of each sire family were well split into these 2 pens. Individual egg production was measured by caging each duck in the evening, taking it out of the cage early in the morning and recording the characteristics of the eggs laid. Animals were fed ad libitum with standard pellets and watered with a nipple drinker.
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GENETICS OF SHELL QUALITY IN DUCKS Table 1. Statistical parameters for body weights and egg laying traits. Unit
Sample size (N)
Mean
Standard deviation
Coefficient of variation (%)
BW110 BW300 A1EGG EW1ST EW210 EW280 EW300 NE210 NE280 NE300
g g day g g g g egg egg egg
304 304 304 304 295 292 269 304 298 298
1,269 1,381 109.5 49.6 65.0 65.9 67.0 82 143 161
110 117 1.85 3.7 3.9 4.6 4.2 8.5 13.6 15.0
8.7 8.5 1.7 7.5 6.0 7.0 6.3 10.4 9.5 9.3
N: number of ducks. BW110 and BW300: body weights at 110 days and 300 days of age. A1EGG: age at first egg. EW1ST: mean weight of the 10 first eggs. EW210, EW280, and EW300: mean weights of 5 eggs at 210, 280 and 300 days of age. NE210, NE280, and NE300: number of eggs laid up to 210, 280 and 300 days of age.
and 67.8 ± 4.3 g at 210 and 280 days of age, respectively. The age at first egg was earlier and less variable in Shan Ma than in Brown Tsaiya ducks (109.5 days for Shan Ma versus 126 days for Brown Tsaiya, coefficient of variation of 1.7% versus 8.7% respectively). Table 2 shows the heritability, the genetic correlation estimates and the phenotypic correlations. The heritability values for the body weights were medium to high, with values of 0.345 ± 0.117 for BW110 and 0.540 ± 0.142 for BW300. Tai et al. (1989) found similar heritability values for Brown Tsaiya ducks, with value of 0.47 ± 0.09 for both body weights at 16 weeks and at 40 weeks of age. The heritability estimates for the number of eggs laid were high with average values of 0.425 ± 0.139, 0.428 ± 0.152, and 0.376 ± 0.147, for the number of eggs laid up to 210, 280, and 300 days of age, respectively. These estimates were higher than those found in Brown Tsaiya ducks by both Tai et al. (1989) and Cheng et al. (1995) who reported heritability values for the number of eggs laid up to 280 days of age of 0.15 and 0.16, respectively. However, Pingel (1990) reported higher values in Pekin ducks with a heritability for the number of eggs laid ranging from 0.23 to 0.32. The phenotypic and genetic correlations between these three egg laying traits (NE210, NE280, and NE300) were extremely high, with a genetic correlation of 0.997 ± 0.004 between NE280 and NE300 so the number of eggs laid up to 280 days and up to 300 days of age seem to be the same trait. A1EGG showed a low heritability value (0.128 ± 0.076), compared to those published by Cheng et al. (1995) in Brown Tsaiya (0.191 ± 0.004) and Brun and Larzul (2003) in common ducks (0.47 ± 0.04). A1EGG did not seem to be correlated with the other traits, except for EW280 (+0.618 ± 0.299) but the standard error for this estimate was high. The heritability’s for egg weights were high with values of 0.426 ± 0.108, 0.468 ± 0.131, 0.507 ± 0.128, and 0.614 ± 0.148 respectively for the EW1ST, EW210, EW280, and EW300. These heritability values were higher than those described by Pingel (1990) who reported values ranging from 0.23 to 0.47
in Pekin ducks, and seemed to increase with the age of duck. The phenotypic correlations between body weight measurements and egg weights were low to moderate, ranging from +0.17 to +0.36. The phenotypic correlation between egg weights at two successive ages increased as the duck got older, with values of +0.36 between EW1ST and EW210, +0.56 between EW210 and EW280, and +0.72 between EW280 and EW300. Regarding the number of eggs laid, the phenotypic correlations at successive ages increased from +0.75 (between NE210 and NE280) to +0.97 (between NE280 and NE300). EW280 and EW300 were demonstrated to be the same trait with a genetic correlation estimate of +1 ± 0.001. The egg weights were highly genetically correlated with the body weights − for instance the genetic correlation between EW300 and BW300 was +0.816 ± 0.101 - but they were not correlated with the numbers of eggs laid since the genetic correlation between NE300 and EW300 of +0.112 ± 0.259 was not significantly different from 0. The genetic correlation between NE300 and BW300 was found to be significant although the standard error of the estimate was high (+0.545 ± 0.227), indicating a tendency for larger ducks to produce more eggs. Genetic correlation patterns between the three biological traits of economic importance, NE300, EW300, and BW300, were quite different from those observed in Brown Tsaiya ducks (Cheng et al., 1995) for which the genetic correlations, estimated on a large data set, between the number of eggs laid and the egg weight were found to be negative (−0.354 for the number of eggs laid up to 40 weeks of age and −0.323 for the number of eggs laid up to 52 weeks of age), and the genetic correlations between the number of eggs laid up to 40 weeks or 52 weeks of age and the body weight were null. Both at 40 weeks of age and at 52 weeks of age, there was a positive genetic correlation between the egg weight and the body weight. Unlike for laying hens, very little data is available on the genetic parameters of laying duck traits and apart
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Traits
4 0.287 0.227 0.370 0.240 0.264 0.263 0.259 0.087 0.004 0.147 ± ± ± ± ± ± ± ± ± ± +0.410 +0.545 +0.045 +0.191 +0.091 − 0.162 +0.112 +0.840 +0.997 0.376 0.290 0.237 0.380 0.228 0.256 0.285 0.255 0.062 0.152 0.152 0.189 0.336 0.163 0.131
+0.700 +0.780 +0.618 +0.551 +0.861 0.507 +0.72 +0.05 +0.14 +0.19
± ± ± ± ± ±
0.156 0.089 0.299 0.177 0.095 0.128
+0.798 +0.816 +0.471 +0.680 +0.995 +1.000 0.614 +0.05 +0.08 +0.11
± ± ± ± ± ± ±
0.127 0.101 0.328 0.145 0.058 0.001 0.148
+0.318 +0.186 − 0.351 +0.189 +0.092 − 0.144 − 0.065 0.425 +0.75 +0.69
± ± ± ± ± ± ± ±
0.275 0.272 0.359 0.228 0.240 0.249 0.229 0.139
+0.364 +0.427 − 0.044 +0.142 +0.020 − 0.165 +0.047 +0.888 0.428 +0.97
± ± ± ± ± ± ± ± ±
Egg Shell Quality Traits
BW110 and BW300: body weights at 110 days and 300 days of age. A1EGG: age at first egg. EW1ST: mean weight of the 10 first eggs. EW210, EW280 and EW300: mean weights of 5 eggs at 210, 280 and 300 days of age. NE210, NE280, and NE300: number of eggs laid up to 210, 280 and 300 days of age.
± ± ± ± ± +0.879 +0.664 +0.221 +0.757 0.468 +0.56 +0.53 +0.13 +0.11 +0.12 0.193 0.194 0.286 0.108 ± ± ± ± +0.502 +0.483 − 0.144 0.426 +0.36 +0.29 +0.32 +0.02 +0.10 +0.10 +0.808 ± 0.099 0.540 ± 0.142 − 0.05 +0.26 +0.32 +0.34 +0.36 +0.13 +0.09 +0.09 0.345 ± 0.117 +0.68 − 0.07 +0.27 +0.21 +0.24 +0.17 +0.06 +0.05 +0.06 BW110 BW300 A1EGG EW1ST EW210 EW280 EW300 NE210 NE280 NE300
− 0.166 ± 0.332 +0.491 ± 0.297 0.128 ± 0.076 − 0.02 +0.03 +0.02 +0.06 − 0.11 − 0.03 +0.01
NE300 NE280 NE210 EW300 EW280 EW210 EW1ST BW300 BW110 Traits
A1EGG
from the Brown Tsaiya duck, there was no other data with which to compare our Shan Ma estimates. These results show that a selection program could be implemented in Shan Ma ducks to increase NE300 without a detrimental effect on egg weight and while maintaining body weight.
Table 3 shows the means, standard deviations, coefficients of variation, and repeatability estimates for the 9 egg shell quality traits. The heritability’s and genetic/phenotypic correlations are provided in the Table 4. The genetic correlations between egg quality traits and body weights and egg production traits are shown in Table 5. The average egg weight of the subset of 264 Shan Ma ducks (67.3 g) is not different from the average egg weight (67.0 g) in the total population (n = 304) studied for body weights and laying traits. For all traits, the coefficients of variation were lower than 11.50% except for BS which was highly variable (coefficient of variation of 28.78%) and showed the lowest repeatability (0.23). LE, WE, and SI, for which the mean values were 59.57 mm, 45.02 mm, and 1.32 respectively, presented low coefficients of variation indicating homogeneity of these traits. Although the repeatability of LE was moderate (0.53), the estimated repeatability of WE (Table 3) was low (0.28). The difference between the mean values of STB and STS indicated that egg shells were thicker at the sharp end than at the blunt end of the eggs (Table 3). The STE was of an intermediate value. The average value for BS was 28.80 N, which could be converted to 2.88 kg/cm2 . In Brown Tsaiya ducks, Cheng et al. (1995) found that the egg shell strength at 40 weeks of age was lower than that at 30 weeks of age (3.5 kg/cm2 vs. 3.8 kg/cm2 ). Such a decrease in shell strength as the ducks get older could explain, at least partly, the value observed for the Shan Ma ducks at 300 days of age. The heritability of egg weight (0.652 ± 0.093) was similar to that computed with the entire population of 304 ducks at 300 days of age (Table 2). The heritability’s for the LE (0.443 ± 0.090) and SI (0.342 ± 0.146) were moderate, while the heritability’s for the BS and STE were lower with values of 0.204 ± 0.106 and 0.280 ± 0.097, respectively. In Brown Tsaiya ducks, Tai et al. (1989) found an average shell thickness of 0.37 mm and reported a heritability of 0.13 ± 0.08 for the egg shell strength at 30 weeks of age and a heritability of 0.25 ± 0.09 for the egg shell thickness. In a large population of Brown Tsaiya ducks, the heritability values for egg shell strength at 30 weeks and 40 weeks of age reported by Cheng et al. (1995) were quite similar (0.107 and 0.094, respectively). As far as we know, no other studies are available on the egg shell quality traits of ducks, and our results on the SI are the first to be reported. Conversely, numerous studies have
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Table 2. Heritability (diagonal), genetic correlations (above the main diagonal), and phenotypic correlations (below the diagonal) for body weights and egg production traits.
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GENETICS OF SHELL QUALITY IN DUCKS Table 3. Statistical parameters (mean, standard deviation, coefficient of variation) and repeatability of egg shell quality traits. Unit
EW LE WE SI BS STB STE STS STA
g mm mm N mm mm mm mm
Sample size (n)
Mean
Standard deviation
Coefficient of variation (%)
Repeatability
766 766 766 766 766 766 766 766 766
67.30 59.57 45.02 1.32 28.80 0.309 0.311 0.313 0.311
5.23 3.01 1.98 0.08 8.29 0.033 0.033 0.036 0.030
7.8 5.1 4.4 6.1 28.8 10.7 10.6 11.5 9.6
0.66 0.53 0.28 0.57 0.23 0.32 0.37 0.39 0.37
EW: egg weight. LE: egg length (vertical diameter). WE: egg width (horizontal diameter). SI: shape index (egg length/egg width). BS: breaking strength. STB: egg shell thickness at blunt region. STE: egg shell thickness at equatorial region. STS: egg shell thickness at sharp region. STA: average egg shell thickness.
Table 4. Heritability’s (diagonal), genetic correlations (above the diagonal), and phenotypic correlations (below the diagonal) for egg quality traits.
EW LE SI BS STE
EW
LE
SI
0.652 ± 0.093 +0.62 +0.15 +0.10 +0.15
+0.737 ± 0.097 0.443 ± 0.090 +0.79 +0.16 +0.16
+0.137 ± 0.155 +0.712 ± 0.118 0.342 ± 0.146 +0.19 +0.20
BS +0.125 +0.499 +0.713 0.204 +0.52
± ± ± ±
STE 0.163 0.176 0.229 0.106
+0.071 +0.253 +0.390 +0.537 0.280
± ± ± ± ±
0.173 0.191 0.239 0.190 0.097
EW: egg weight. LE: egg length (vertical diameter). SI: shape index (egg length/egg width). BS: breaking strength. STE: egg shell thickness at equatorial region.
Table 5. Genetic correlations between egg quality traits and body weight and egg production traits. LE BW110 BW300 EW1ST EW210 EW280 EW300 NE210 NE280 NE300
+0.660 +0.625 +0.372 +0.637 +0.900 +0.833 +0.090 +0.159 +0.151
± ± ± ± ± ± ± ± ±
SI 0.202 0.181 0.242 0.213 0.114 0.109 0.258 0.277 0.274
+0.215 +0.375 +0.063 −0.055 +0.190 +0.255 +0.442 +0.422 +0.341
± ± ± ± ± ± ± ± ±
BS 0.325 0.298 0.284 0.310 0.285 0.265 0.312 0.309 0.322
+0.054 +0.038 −0.191 −0.113 +0.104 +0.261 +0.369 +0.405 +0.391
± ± ± ± ± ± ± ± ±
STE 0.389 0.362 0.377 0.368 0.338 0.310 0.424 0.402 0.421
−0.040 +0.374 −0.087 −0.079 −0.136 +0.029 +0.543 +0.193 +0.130
± ± ± ± ± ± ± ± ±
0.327 0.252 0.290 0.126 0.311 0.287 0.349 0.327 0.328
LE: egg length (vertical diameter). SI: shape index (egg length/egg width). BS: breaking strength. STE: egg shell thickness at equatorial region. BW110 and BW300: body weights at 110 days and 300 days of age. EW1ST: mean weight of the 10 first eggs. EW210, EW280 and EW300: mean weights of 5 eggs at 210, 280 and 300 days of age. NE210, NE280 and NE300: number of eggs laid up to 210, 280 and 300 days of age.
been carried out in hens. In different pedigrees of laying hens, Blanco et al. (2014) found heritability estimates ranging from 0.23 to 0.35 for BS and from 0.27 to 0.44 for STE. Heritability levels for SI defined as the ratio width/length, i.e., the inverse of our SI, were moderate in some lines and showed higher heritability values
in other lines (ranging from 0.35 to 0.58). In brownegg dwarf layers, Zhang et al. (2005) found heritability values of 0.40 for the shape index (defined as the ratio width/length), 0.24 for BS and 0.34 for egg shell thickness. In domestic hens, Dunn et al. (2005) reported heritability values of 0.30 for the shape index (defined
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Traits
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CONCLUSION On the whole, the heritability’s of egg shell quality traits were moderate and no unfavorable genetic
correlations with egg production traits could be demonstrated. Although results needed to be confirm on a larger data set, it seemed possible to improve egg shell quality by selection. However, to implement their selection, breeders must have information about the heritability’s and genetic correlations between the traits of interest in their own breed. This study has evidenced genetic variations which should allow breeders to design efficient genetic selection strategies for the Shan Ma duck aimed at improving both egg production traits and egg shell quality traits.
REFERENCES Blanco, A. E., W. Icken, D. Ould-Ali, D. Cavero, and M. Schmutz. 2014. Genetic parameters of egg quality traits on different pedigree layers with special focus on dynamic stiffness. Poult. Sci. 93:2457–2463. Brun, J.-M., and C. Larzul. 2003. Inheritance of reproductive traits of female common ducks (Anas platyrhynchos) in pure breeding and in inter-generic crossbreeding with muscovy ducks (Cairina moschata). Br. Poult. Sci. 44:40–45. Cheng, Y. S., R. Rouvier, J. P. Poivey, and C. Tai. 1995. Genetic parameters of body weight, egg production and shell quality traits in the Brown Tsaiya laying duck. Genet. Sel. Evol. 27: 459–472. Dunn, I. C., M. Bain, A. Edmond, P. W. Wilson, N. Joseph, S. Solomon, B. De Ketelaere, J. De Baerdemaeker, M. Schmutz, R. Preisinger, and D. Waddington. 2005. Heritability and genetic correlation of measurements derived from acoustic resonance frequency analysis; a novel method of determining eggshell quality in domestic hens. Brit. Poult. Sci. 46:280–286. Lin, R. L., H. P. Chen, R. Rouvier, and J. P. Poivey. 2014. Selection and Crossbreeding in Relation to Plumage Color Inheritance in three Chinese Egg Type Duck Breeds (Anas Platyrhynchos). Asian Austr. J. Anim. Sci. 27:1069–1074. Neumaier, A., and E. Groeneveld. 1998. Restricted maximum likelihood estimation of covariances in sparse linear models. Genet. Sel. Evol. 30:3–26. Pingel, H. 2009. Waterfowl Production for Food Security. Conference at the 4th world waterfowl conference, Thrissur, India, 6p. Pingel, H. 1990. Genetics of egg production and reproduction in waterfowl. In: Poultry Breeding and Genetics, R. D. Crawford ed. Elsevier, Amsterdam, 771–780. SAS Institute, 2009. SAS/STAT Software Release 9.3. SAS Institute Inc., Cary, NC, USA. Tai, C., R. Rouvier, and J. P. Poivey. 1989. Genetic parameters of some growth and egg production traits in laying Brown Tsaiya (Anas platyrynchos). Genet. Sel. Evol. 21:377–384. Xu, G. F., and K. W. Chen. 2003. Photograph Album of China Indigeneous Poultry Breeds. Beijing, China Agricultural Press. Zhang, L. C., Z. H. Ning, G. Y. Xu, Z. C. Hou, and N. Yang. 2005. Heritabilities and genetic and phenotypic correlations of egg quality traits in brown-egg dwarf layers. Poult Sci. 84: 1209–1213.
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as our ratio) and 0.18 for breaking strength. These values were similar to the results we describe in ducks. Egg weight was not genetically correlated with the shell quality traits (Table 4) − except LE − and phenotypic correlations were low, inferring that heavier eggs were not more breakable than lighter ones. In particular, genetic correlation between BS and EW (+0.125 ± 0.163) was not significantly different from zero, while phenotypic correlation was +0.10. Zhang et al. (2005) concluded that both phenotypic and genetic correlations between EW and egg shell strength were low (−0.05 and −0.19 ± 0.20, respectively), inferring that larger eggs were not weaker than smaller ones. Cheng et al. (1995) reported a positive genetic correlation (+0.483) between those two traits in Brown Tsaiya ducks at 40 weeks of age. On the contrary, Blanco et al. (2014) estimated negative and undesired genetic correlations between EW and BS (from −0.19 to −0.36 according to the lines) as well as for the phenotypic correlations (from −0.05 to −0.19 according to the lines). The positive phenotypic and genetic correlations between STE and BS (+0.52 and +0.537 ± 0.190, respectively) indicate that egg shell thickness is an important factor affecting breaking strength; the eggs with thicker shells being stronger. The BS and SI were also positively correlated, both genetically (+0.713 ± 0.229) and phenotypically (+0.19). Longer, less wide eggs are therefore more resistant to breakage than rounder eggs. This result was original since opposite genetic correlations between SI and BS have been observed in hens. Indeed, in hens, either BS and SI were found to be genetically independent or the eggshell was more resistant when the egg was rounder (Zhang et al., 2005; Blanco et al., 2014). As shown in Table 5, no significant genetic correlations were evidenced between NE210, NE280, and NE300 and the egg quality traits. Except for the egg length, the egg quality traits were not genetically linked to egg weights or body weights, whatever the animals’ age. These results demonstrate that the laying ability and egg shell quality traits of Shan Ma ducks are genetically independent.
Fujian Longyan Honglong Poultry Industrial Company limited, Longyan, 364000 China; and † GenPhySE, INRA, INPT, INP-ENVT, Universit´e de Toulouse, 31076 Castanet Tolosan, France (ranging from 0.38 to 0.43), and low for the age at first egg (0.13). Heritability’s for egg shell quality traits varied from 0.20 for the breaking strength to 0.44 for egg length, with in-between values of 0.28 for shell thickness and 0.34 for the shape index. The number of eggs laid was not genetically correlated with the age at first egg or egg weight, but was correlated with body weight (rg = +0.54 ± 0.23). High positive correlations were found between egg weight and body weight traits, and both of these traits (except egg weight at first egg) were highly and positively correlated with egg length and width. Breaking strength was genetically correlated with egg shell thickness (rg = +0.54 ± 0.19) and the shape index (rg = +0.71 ± 0.23). These results suggest that an efficient selection strategy could be implemented to improve the egg production of the pure Shan Ma duck line.
Key words: egg quality, laying duck, genetic parameter 2016 Poultry Science 0:1–6 http://dx.doi.org/10.3382/ps/pew222
INTRODUCTION
estimating the genetic parameters for such economically important traits is to better understand the genetic variation of these traits and to define an optimized breeding program leading to genetic improvement of the breed. As yet, very few studies have focused on estimating the genetic parameters of egg production and egg shell quality in laying ducks, except in Brown Tsaiya ducks (Tai et al., 1989; Cheng et al., 1995). The purpose of this study was to estimate and discuss the genetic parameters for body weight, egg production, and egg shell quality traits of the Chinese Shan Ma duck.
Duck egg production is an important economic activity in China because duck eggs represent approximately 15% of all eggs produced for human consumption (Pingel, 2009). The Shan Ma duck (Anas Platyrhynchos) is one of the main Chinese indigenous egg laying duck breeds mentioned in the photograph album of China indigenous poultry breeds (Xu and Chen, 2003). In a first study, in order to obtain homogeneous plumage color phenotypes, Shan Ma ducks were crossbred with two other Chinese laying duck breeds, the Putian White and the Putian Black, and its plumage color inheritance was established (Lin et al., 2014). Nevertheless, the genetic variation of the quantitative traits related to egg production and egg shell quality remained unknown for Shan Ma ducks. The aim of
MATERIALS AND METHODS The present study was carried out in agreement with the guidelines on live animals research approved by the US Institutional Animal Care and Use Committee (IACUC).
C 2016 Poultry Science Association Inc. Received January 20, 2016. Accepted May 25, 2016. 1 Corresponding author: [email protected] 2 Current address: Institut National de la Recherche Agronomique, UMR GenPhySE, B.P. 52627, 31326 Castanet-Tolosan, Tel: (+33) 5 61 28 51 93 , Fax: (+33) 5 61 28 53 53.
Ducks A total of 304 female laying Shan Ma ducks were hatched from 11 sire families. More specifically, each of 1
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ABSTRACT Three hundred and four female ducks of the Chinese indigenous Shan Ma breed, progeny of 11 sires and 104 dams, were used to study laying traits. Among them, 264 ducks were used to study the egg shell quality traits of eggs laid at 300 days of age. The mean age at first egg was 109 days with an average egg weight of 49.6 ± 3.7 g. Between 210 and 300 days of age, egg weight increased from 65.0 ± 3.9 g to 67.0 ± 4.2 g and the mean of the number of eggs laid up to 300 days was 161 ± 15.0. Egg length was 59.57 ± 3.01 mm and egg width was 45.02 ± 1.98 mm, leading to a shape index of 1.32 ± 0.08. Egg shell thickness was about 0.31 mm whatever the shell region, and the breaking strength was 28.80 ± 8.29 N. The heritability’s estimated using restricted maximum likelihood (REML) methodology were high for egg weights (ranging from 0.43 to 0.61), intermediate for the number of eggs laid
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Traits Measured The individual body weights and egg laying traits were measured for 269 to 304 ducks, depending on the trait. Body weights were measured at 110 days of age (BW110) and 300 days of age (BW300). The age at first egg (A1EGG), the averaged weights of the 10 first eggs laid (EW1ST), the average weights of the 5 consecutive eggs laid from 210, 280, and 300 days of age (EW210, EW280, EW300), and the number of eggs laid up to 210, 280, and 300 days of age (NE210, NE280, NE300) were recorded. The egg shell quality traits were measured for eggs laid on 3 consecutive days starting at 300 days of age: 3, 2, and 1 eggs were measured for 243, 16, and 5 female ducks, respectively, leading to a total of 766 eggs. The following external traits were recorded for each egg: egg weight (EW), egg length or vertical diameter (LE), egg width or horizontal diameter (WE), shape index (SI) which was defined as the ratio of the length on the width measured to the nearest 0.1 mm, egg shell breaking strength (BS), egg shell thickness at the blunt region (STB), equatorial region (STE), and sharp region (STS), and the average of these 3 thicknesses (STA). Broken eggs were not used. Egg weight was measured to the nearest 0.01 g while the shell thickness was measured with a precision of 0.01 mm using a Vernier caliper. Breaking strength was measured by pole-to-pole pressing of the egg with a digital concrete compression testing machine with capacity range of 0 N to 500 N.
Statistical Analysis The normal distribution of the traits was tested using the Univariate procedure of the SAS software package (SAS Institute, 2009). The hypothesis of normal distribution was accepted except for A1EGG, NE210, NE280, NE300, and WE. In order to achieve normality, the number of eggs laid up to 210, 280, and 300 days of age were transformed using log (N-number of eggs)
with N = 96, N = 165, and N = 185 respectively at 210, 280, and 300 days of age. Because these transformations change the sign of the correlations, they have been reversed in the Tables 2 and 5 to match the biological results. The same transformation, with different parameters, was used by Dunn et al. (2005) for egg production traits in domestic hens. The means and phenotypic standard deviations of the traits were computed with the Means procedure of the SAS software package, while the “pen” fixed effect was tested with the GLM procedure of SAS. No significant within-sire pen effect was observed on body weight or egg production traits except for BW110 in family 1. The phenotypic correlations between traits were obtained using the CORR procedure of SAS. To estimate the genetic parameters, an animal model was constructed as follows: Yij = μ + ai + eij Where Yij is the ijth phenotypic record of a trait, μ the common mean, ai the ith individual breeding value, and eij the error. The restricted maximum likelihood (REML) procedure was applied to estimate heritability’s and genetic correlations using the VCE 6.0 software package (Neumaier and Groeneveld, 1998). Heritability’s were estimated using single-trait analysis, while genetic correlations between traits were estimated using 2-trait analysis. A multitrait REML procedure was also performed on a reduced number of egg shell quality traits, in order to obtain more accurate estimates while achieving convergence. The two data sets for egg production traits and egg shell quality traits were first analyzed separately, then genetic correlations between the traits of the two sets were estimated.
RESULTS AND DISCUSSION Body Weight and Egg Laying Traits Table 1 shows the means, standard deviations, and coefficients of variation for the body weight and egg laying traits. Duck body weights increased by more than 100 g from 110 days of age (1,269 ± 110 g) to 300 days of age (1,381 ± 117 g). On average, animals laid their first egg at 109.5 days of age, with a very small coefficient of variation (1.7%). The means and standard deviations for the NE210, NE280, and NE 300 were respectively 82 ± 8.5, 143 ± 13.6, and 161 ± 15.0 eggs, and the EW210, EW280, and EW300 were 65.0 ± 3.9, 65.9 ± 4.6, and 67.0 ± 4.2 g, respectively. The body weights for Shan Ma ducks are similar to those published by Tai et al. (1989), who reported body weights of 1,270 ± 136 g at 16 weeks of age and 1,407 ± 133 g at 40 weeks of age in Brown Tsaiya ducks. As regards to laying traits, our results are close to those reported in Brown Tsaiya ducks with 139 ± 15 eggs laid up to 280 days of age, and egg weights of 64.2 ± 4.3 g
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the 11 Shan Ma drakes was mated to 8 to 10 Shan Ma female ducks producing a progeny of 25 to 29 daughter ducks per sire family. The 11 sires and the 104 dams, parents of the study set of 304 female ducks, were selected at random in a large population and were assumed not to be related. All ducks in the study set were individually identified. In all, 22 pens were used for breeding the whole study population: progenies of each of the 11 drakes were raised into 2 separate pens, taking care that the full sisters of each sire family were well split into these 2 pens. Individual egg production was measured by caging each duck in the evening, taking it out of the cage early in the morning and recording the characteristics of the eggs laid. Animals were fed ad libitum with standard pellets and watered with a nipple drinker.
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GENETICS OF SHELL QUALITY IN DUCKS Table 1. Statistical parameters for body weights and egg laying traits. Unit
Sample size (N)
Mean
Standard deviation
Coefficient of variation (%)
BW110 BW300 A1EGG EW1ST EW210 EW280 EW300 NE210 NE280 NE300
g g day g g g g egg egg egg
304 304 304 304 295 292 269 304 298 298
1,269 1,381 109.5 49.6 65.0 65.9 67.0 82 143 161
110 117 1.85 3.7 3.9 4.6 4.2 8.5 13.6 15.0
8.7 8.5 1.7 7.5 6.0 7.0 6.3 10.4 9.5 9.3
N: number of ducks. BW110 and BW300: body weights at 110 days and 300 days of age. A1EGG: age at first egg. EW1ST: mean weight of the 10 first eggs. EW210, EW280, and EW300: mean weights of 5 eggs at 210, 280 and 300 days of age. NE210, NE280, and NE300: number of eggs laid up to 210, 280 and 300 days of age.
and 67.8 ± 4.3 g at 210 and 280 days of age, respectively. The age at first egg was earlier and less variable in Shan Ma than in Brown Tsaiya ducks (109.5 days for Shan Ma versus 126 days for Brown Tsaiya, coefficient of variation of 1.7% versus 8.7% respectively). Table 2 shows the heritability, the genetic correlation estimates and the phenotypic correlations. The heritability values for the body weights were medium to high, with values of 0.345 ± 0.117 for BW110 and 0.540 ± 0.142 for BW300. Tai et al. (1989) found similar heritability values for Brown Tsaiya ducks, with value of 0.47 ± 0.09 for both body weights at 16 weeks and at 40 weeks of age. The heritability estimates for the number of eggs laid were high with average values of 0.425 ± 0.139, 0.428 ± 0.152, and 0.376 ± 0.147, for the number of eggs laid up to 210, 280, and 300 days of age, respectively. These estimates were higher than those found in Brown Tsaiya ducks by both Tai et al. (1989) and Cheng et al. (1995) who reported heritability values for the number of eggs laid up to 280 days of age of 0.15 and 0.16, respectively. However, Pingel (1990) reported higher values in Pekin ducks with a heritability for the number of eggs laid ranging from 0.23 to 0.32. The phenotypic and genetic correlations between these three egg laying traits (NE210, NE280, and NE300) were extremely high, with a genetic correlation of 0.997 ± 0.004 between NE280 and NE300 so the number of eggs laid up to 280 days and up to 300 days of age seem to be the same trait. A1EGG showed a low heritability value (0.128 ± 0.076), compared to those published by Cheng et al. (1995) in Brown Tsaiya (0.191 ± 0.004) and Brun and Larzul (2003) in common ducks (0.47 ± 0.04). A1EGG did not seem to be correlated with the other traits, except for EW280 (+0.618 ± 0.299) but the standard error for this estimate was high. The heritability’s for egg weights were high with values of 0.426 ± 0.108, 0.468 ± 0.131, 0.507 ± 0.128, and 0.614 ± 0.148 respectively for the EW1ST, EW210, EW280, and EW300. These heritability values were higher than those described by Pingel (1990) who reported values ranging from 0.23 to 0.47
in Pekin ducks, and seemed to increase with the age of duck. The phenotypic correlations between body weight measurements and egg weights were low to moderate, ranging from +0.17 to +0.36. The phenotypic correlation between egg weights at two successive ages increased as the duck got older, with values of +0.36 between EW1ST and EW210, +0.56 between EW210 and EW280, and +0.72 between EW280 and EW300. Regarding the number of eggs laid, the phenotypic correlations at successive ages increased from +0.75 (between NE210 and NE280) to +0.97 (between NE280 and NE300). EW280 and EW300 were demonstrated to be the same trait with a genetic correlation estimate of +1 ± 0.001. The egg weights were highly genetically correlated with the body weights − for instance the genetic correlation between EW300 and BW300 was +0.816 ± 0.101 - but they were not correlated with the numbers of eggs laid since the genetic correlation between NE300 and EW300 of +0.112 ± 0.259 was not significantly different from 0. The genetic correlation between NE300 and BW300 was found to be significant although the standard error of the estimate was high (+0.545 ± 0.227), indicating a tendency for larger ducks to produce more eggs. Genetic correlation patterns between the three biological traits of economic importance, NE300, EW300, and BW300, were quite different from those observed in Brown Tsaiya ducks (Cheng et al., 1995) for which the genetic correlations, estimated on a large data set, between the number of eggs laid and the egg weight were found to be negative (−0.354 for the number of eggs laid up to 40 weeks of age and −0.323 for the number of eggs laid up to 52 weeks of age), and the genetic correlations between the number of eggs laid up to 40 weeks or 52 weeks of age and the body weight were null. Both at 40 weeks of age and at 52 weeks of age, there was a positive genetic correlation between the egg weight and the body weight. Unlike for laying hens, very little data is available on the genetic parameters of laying duck traits and apart
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Traits
4 0.287 0.227 0.370 0.240 0.264 0.263 0.259 0.087 0.004 0.147 ± ± ± ± ± ± ± ± ± ± +0.410 +0.545 +0.045 +0.191 +0.091 − 0.162 +0.112 +0.840 +0.997 0.376 0.290 0.237 0.380 0.228 0.256 0.285 0.255 0.062 0.152 0.152 0.189 0.336 0.163 0.131
+0.700 +0.780 +0.618 +0.551 +0.861 0.507 +0.72 +0.05 +0.14 +0.19
± ± ± ± ± ±
0.156 0.089 0.299 0.177 0.095 0.128
+0.798 +0.816 +0.471 +0.680 +0.995 +1.000 0.614 +0.05 +0.08 +0.11
± ± ± ± ± ± ±
0.127 0.101 0.328 0.145 0.058 0.001 0.148
+0.318 +0.186 − 0.351 +0.189 +0.092 − 0.144 − 0.065 0.425 +0.75 +0.69
± ± ± ± ± ± ± ±
0.275 0.272 0.359 0.228 0.240 0.249 0.229 0.139
+0.364 +0.427 − 0.044 +0.142 +0.020 − 0.165 +0.047 +0.888 0.428 +0.97
± ± ± ± ± ± ± ± ±
Egg Shell Quality Traits
BW110 and BW300: body weights at 110 days and 300 days of age. A1EGG: age at first egg. EW1ST: mean weight of the 10 first eggs. EW210, EW280 and EW300: mean weights of 5 eggs at 210, 280 and 300 days of age. NE210, NE280, and NE300: number of eggs laid up to 210, 280 and 300 days of age.
± ± ± ± ± +0.879 +0.664 +0.221 +0.757 0.468 +0.56 +0.53 +0.13 +0.11 +0.12 0.193 0.194 0.286 0.108 ± ± ± ± +0.502 +0.483 − 0.144 0.426 +0.36 +0.29 +0.32 +0.02 +0.10 +0.10 +0.808 ± 0.099 0.540 ± 0.142 − 0.05 +0.26 +0.32 +0.34 +0.36 +0.13 +0.09 +0.09 0.345 ± 0.117 +0.68 − 0.07 +0.27 +0.21 +0.24 +0.17 +0.06 +0.05 +0.06 BW110 BW300 A1EGG EW1ST EW210 EW280 EW300 NE210 NE280 NE300
− 0.166 ± 0.332 +0.491 ± 0.297 0.128 ± 0.076 − 0.02 +0.03 +0.02 +0.06 − 0.11 − 0.03 +0.01
NE300 NE280 NE210 EW300 EW280 EW210 EW1ST BW300 BW110 Traits
A1EGG
from the Brown Tsaiya duck, there was no other data with which to compare our Shan Ma estimates. These results show that a selection program could be implemented in Shan Ma ducks to increase NE300 without a detrimental effect on egg weight and while maintaining body weight.
Table 3 shows the means, standard deviations, coefficients of variation, and repeatability estimates for the 9 egg shell quality traits. The heritability’s and genetic/phenotypic correlations are provided in the Table 4. The genetic correlations between egg quality traits and body weights and egg production traits are shown in Table 5. The average egg weight of the subset of 264 Shan Ma ducks (67.3 g) is not different from the average egg weight (67.0 g) in the total population (n = 304) studied for body weights and laying traits. For all traits, the coefficients of variation were lower than 11.50% except for BS which was highly variable (coefficient of variation of 28.78%) and showed the lowest repeatability (0.23). LE, WE, and SI, for which the mean values were 59.57 mm, 45.02 mm, and 1.32 respectively, presented low coefficients of variation indicating homogeneity of these traits. Although the repeatability of LE was moderate (0.53), the estimated repeatability of WE (Table 3) was low (0.28). The difference between the mean values of STB and STS indicated that egg shells were thicker at the sharp end than at the blunt end of the eggs (Table 3). The STE was of an intermediate value. The average value for BS was 28.80 N, which could be converted to 2.88 kg/cm2 . In Brown Tsaiya ducks, Cheng et al. (1995) found that the egg shell strength at 40 weeks of age was lower than that at 30 weeks of age (3.5 kg/cm2 vs. 3.8 kg/cm2 ). Such a decrease in shell strength as the ducks get older could explain, at least partly, the value observed for the Shan Ma ducks at 300 days of age. The heritability of egg weight (0.652 ± 0.093) was similar to that computed with the entire population of 304 ducks at 300 days of age (Table 2). The heritability’s for the LE (0.443 ± 0.090) and SI (0.342 ± 0.146) were moderate, while the heritability’s for the BS and STE were lower with values of 0.204 ± 0.106 and 0.280 ± 0.097, respectively. In Brown Tsaiya ducks, Tai et al. (1989) found an average shell thickness of 0.37 mm and reported a heritability of 0.13 ± 0.08 for the egg shell strength at 30 weeks of age and a heritability of 0.25 ± 0.09 for the egg shell thickness. In a large population of Brown Tsaiya ducks, the heritability values for egg shell strength at 30 weeks and 40 weeks of age reported by Cheng et al. (1995) were quite similar (0.107 and 0.094, respectively). As far as we know, no other studies are available on the egg shell quality traits of ducks, and our results on the SI are the first to be reported. Conversely, numerous studies have
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Table 2. Heritability (diagonal), genetic correlations (above the main diagonal), and phenotypic correlations (below the diagonal) for body weights and egg production traits.
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GENETICS OF SHELL QUALITY IN DUCKS Table 3. Statistical parameters (mean, standard deviation, coefficient of variation) and repeatability of egg shell quality traits. Unit
EW LE WE SI BS STB STE STS STA
g mm mm N mm mm mm mm
Sample size (n)
Mean
Standard deviation
Coefficient of variation (%)
Repeatability
766 766 766 766 766 766 766 766 766
67.30 59.57 45.02 1.32 28.80 0.309 0.311 0.313 0.311
5.23 3.01 1.98 0.08 8.29 0.033 0.033 0.036 0.030
7.8 5.1 4.4 6.1 28.8 10.7 10.6 11.5 9.6
0.66 0.53 0.28 0.57 0.23 0.32 0.37 0.39 0.37
EW: egg weight. LE: egg length (vertical diameter). WE: egg width (horizontal diameter). SI: shape index (egg length/egg width). BS: breaking strength. STB: egg shell thickness at blunt region. STE: egg shell thickness at equatorial region. STS: egg shell thickness at sharp region. STA: average egg shell thickness.
Table 4. Heritability’s (diagonal), genetic correlations (above the diagonal), and phenotypic correlations (below the diagonal) for egg quality traits.
EW LE SI BS STE
EW
LE
SI
0.652 ± 0.093 +0.62 +0.15 +0.10 +0.15
+0.737 ± 0.097 0.443 ± 0.090 +0.79 +0.16 +0.16
+0.137 ± 0.155 +0.712 ± 0.118 0.342 ± 0.146 +0.19 +0.20
BS +0.125 +0.499 +0.713 0.204 +0.52
± ± ± ±
STE 0.163 0.176 0.229 0.106
+0.071 +0.253 +0.390 +0.537 0.280
± ± ± ± ±
0.173 0.191 0.239 0.190 0.097
EW: egg weight. LE: egg length (vertical diameter). SI: shape index (egg length/egg width). BS: breaking strength. STE: egg shell thickness at equatorial region.
Table 5. Genetic correlations between egg quality traits and body weight and egg production traits. LE BW110 BW300 EW1ST EW210 EW280 EW300 NE210 NE280 NE300
+0.660 +0.625 +0.372 +0.637 +0.900 +0.833 +0.090 +0.159 +0.151
± ± ± ± ± ± ± ± ±
SI 0.202 0.181 0.242 0.213 0.114 0.109 0.258 0.277 0.274
+0.215 +0.375 +0.063 −0.055 +0.190 +0.255 +0.442 +0.422 +0.341
± ± ± ± ± ± ± ± ±
BS 0.325 0.298 0.284 0.310 0.285 0.265 0.312 0.309 0.322
+0.054 +0.038 −0.191 −0.113 +0.104 +0.261 +0.369 +0.405 +0.391
± ± ± ± ± ± ± ± ±
STE 0.389 0.362 0.377 0.368 0.338 0.310 0.424 0.402 0.421
−0.040 +0.374 −0.087 −0.079 −0.136 +0.029 +0.543 +0.193 +0.130
± ± ± ± ± ± ± ± ±
0.327 0.252 0.290 0.126 0.311 0.287 0.349 0.327 0.328
LE: egg length (vertical diameter). SI: shape index (egg length/egg width). BS: breaking strength. STE: egg shell thickness at equatorial region. BW110 and BW300: body weights at 110 days and 300 days of age. EW1ST: mean weight of the 10 first eggs. EW210, EW280 and EW300: mean weights of 5 eggs at 210, 280 and 300 days of age. NE210, NE280 and NE300: number of eggs laid up to 210, 280 and 300 days of age.
been carried out in hens. In different pedigrees of laying hens, Blanco et al. (2014) found heritability estimates ranging from 0.23 to 0.35 for BS and from 0.27 to 0.44 for STE. Heritability levels for SI defined as the ratio width/length, i.e., the inverse of our SI, were moderate in some lines and showed higher heritability values
in other lines (ranging from 0.35 to 0.58). In brownegg dwarf layers, Zhang et al. (2005) found heritability values of 0.40 for the shape index (defined as the ratio width/length), 0.24 for BS and 0.34 for egg shell thickness. In domestic hens, Dunn et al. (2005) reported heritability values of 0.30 for the shape index (defined
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Traits
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CONCLUSION On the whole, the heritability’s of egg shell quality traits were moderate and no unfavorable genetic
correlations with egg production traits could be demonstrated. Although results needed to be confirm on a larger data set, it seemed possible to improve egg shell quality by selection. However, to implement their selection, breeders must have information about the heritability’s and genetic correlations between the traits of interest in their own breed. This study has evidenced genetic variations which should allow breeders to design efficient genetic selection strategies for the Shan Ma duck aimed at improving both egg production traits and egg shell quality traits.
REFERENCES Blanco, A. E., W. Icken, D. Ould-Ali, D. Cavero, and M. Schmutz. 2014. Genetic parameters of egg quality traits on different pedigree layers with special focus on dynamic stiffness. Poult. Sci. 93:2457–2463. Brun, J.-M., and C. Larzul. 2003. Inheritance of reproductive traits of female common ducks (Anas platyrhynchos) in pure breeding and in inter-generic crossbreeding with muscovy ducks (Cairina moschata). Br. Poult. Sci. 44:40–45. Cheng, Y. S., R. Rouvier, J. P. Poivey, and C. Tai. 1995. Genetic parameters of body weight, egg production and shell quality traits in the Brown Tsaiya laying duck. Genet. Sel. Evol. 27: 459–472. Dunn, I. C., M. Bain, A. Edmond, P. W. Wilson, N. Joseph, S. Solomon, B. De Ketelaere, J. De Baerdemaeker, M. Schmutz, R. Preisinger, and D. Waddington. 2005. Heritability and genetic correlation of measurements derived from acoustic resonance frequency analysis; a novel method of determining eggshell quality in domestic hens. Brit. Poult. Sci. 46:280–286. Lin, R. L., H. P. Chen, R. Rouvier, and J. P. Poivey. 2014. Selection and Crossbreeding in Relation to Plumage Color Inheritance in three Chinese Egg Type Duck Breeds (Anas Platyrhynchos). Asian Austr. J. Anim. Sci. 27:1069–1074. Neumaier, A., and E. Groeneveld. 1998. Restricted maximum likelihood estimation of covariances in sparse linear models. Genet. Sel. Evol. 30:3–26. Pingel, H. 2009. Waterfowl Production for Food Security. Conference at the 4th world waterfowl conference, Thrissur, India, 6p. Pingel, H. 1990. Genetics of egg production and reproduction in waterfowl. In: Poultry Breeding and Genetics, R. D. Crawford ed. Elsevier, Amsterdam, 771–780. SAS Institute, 2009. SAS/STAT Software Release 9.3. SAS Institute Inc., Cary, NC, USA. Tai, C., R. Rouvier, and J. P. Poivey. 1989. Genetic parameters of some growth and egg production traits in laying Brown Tsaiya (Anas platyrynchos). Genet. Sel. Evol. 21:377–384. Xu, G. F., and K. W. Chen. 2003. Photograph Album of China Indigeneous Poultry Breeds. Beijing, China Agricultural Press. Zhang, L. C., Z. H. Ning, G. Y. Xu, Z. C. Hou, and N. Yang. 2005. Heritabilities and genetic and phenotypic correlations of egg quality traits in brown-egg dwarf layers. Poult Sci. 84: 1209–1213.
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as our ratio) and 0.18 for breaking strength. These values were similar to the results we describe in ducks. Egg weight was not genetically correlated with the shell quality traits (Table 4) − except LE − and phenotypic correlations were low, inferring that heavier eggs were not more breakable than lighter ones. In particular, genetic correlation between BS and EW (+0.125 ± 0.163) was not significantly different from zero, while phenotypic correlation was +0.10. Zhang et al. (2005) concluded that both phenotypic and genetic correlations between EW and egg shell strength were low (−0.05 and −0.19 ± 0.20, respectively), inferring that larger eggs were not weaker than smaller ones. Cheng et al. (1995) reported a positive genetic correlation (+0.483) between those two traits in Brown Tsaiya ducks at 40 weeks of age. On the contrary, Blanco et al. (2014) estimated negative and undesired genetic correlations between EW and BS (from −0.19 to −0.36 according to the lines) as well as for the phenotypic correlations (from −0.05 to −0.19 according to the lines). The positive phenotypic and genetic correlations between STE and BS (+0.52 and +0.537 ± 0.190, respectively) indicate that egg shell thickness is an important factor affecting breaking strength; the eggs with thicker shells being stronger. The BS and SI were also positively correlated, both genetically (+0.713 ± 0.229) and phenotypically (+0.19). Longer, less wide eggs are therefore more resistant to breakage than rounder eggs. This result was original since opposite genetic correlations between SI and BS have been observed in hens. Indeed, in hens, either BS and SI were found to be genetically independent or the eggshell was more resistant when the egg was rounder (Zhang et al., 2005; Blanco et al., 2014). As shown in Table 5, no significant genetic correlations were evidenced between NE210, NE280, and NE300 and the egg quality traits. Except for the egg length, the egg quality traits were not genetically linked to egg weights or body weights, whatever the animals’ age. These results demonstrate that the laying ability and egg shell quality traits of Shan Ma ducks are genetically independent.