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Genetic parameters for performance and meat quality traits of crossbred pigs housed in two test environments
Livestock Science 121 (2009) 275–280
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Livestock Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / l i v s c i
Genetic parameters for performance and meat quality traits of crossbred pigs housed in two test environments D. Habier a,b,⁎, K.-U. Götz b, L. Dempfle a a b
Technical University of Munich-Weihenstephan, Department of Animal Science, Alte Akademie 12, 85354 Freising, Germany Bavarian Institute of Agriculture, Institute of Animal Breeding, Prof.-Dürrwaechter-Platz 1, 85586 Poing-Grub, Germany
a r t i c l e
i n f o
Article history: Received 12 April 2007 Received in revised form 20 April 2008 Accepted 27 June 2008 Keywords: Genetic parameters Test station Crossbred pigs Piétrain Genotype–environment interaction
a b s t r a c t Genetic parameters were estimated for crossbred progeny of Bavarian Piétrain sires housed in two test environments on the two Bavarian test stations. The data contained 13,980 pigs housed in traditional pens for 2 pigs and 3,454 pigs housed in big pens for 10–14 pigs with automatic feeding system recorded between 2000 and 2004. In total, 584 sires having progeny in both housing systems were available to estimate genetic correlations between the two test environments. The analysis showed that the housing of pigs in big pens is more demanding with respect to the test design than in 2-pig pens. Further, the results show differences in both phenotypic performance and genetic parameters between the two environments. Daily gain is lower and lean meat content is higher in big pens with automatic feeding system. Therefore, it is suspected that pigs develop slower in the new housing due to a different feed intake behavior in comparison to 2-pig pens. This might be the main reason for the moderate genetic correlations among fattening performance traits (0.5–0.7 ± 0.13), which result in re-rankings of selection candidates depending which kind of information is utilized. Genetic correlations of slaughter and meat quality traits, however, are close to 1. Differences between the variance components in the two test stations have been found and simple pooling of data is problematic with respect to the breeding value estimation. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Since 2001 the housing system on the Bavarian performance test stations is being converted from traditional pens for 2 pigs to big pens with automatic feeding system for 10–14 pigs. The aim is to have the conditions on the performance test stations more similar to the commercial production environment to avoid genotype–environment interactions. In the last 15 years, the final weight on Bavarian commercial farms increased from 105 to 117 kg, whereas the weight on performance test stations has remained at 105 kg. Hitherto, the adoption of the higher final weight was not possible due to limited pen space per test animal in 2-pig pens. Further, in ⁎ Corresponding author. Technical University of Munich-Weihenstephan, Department of Animal Science, Alte Akademie 12, 85354 Freising, Germany. Tel.: +49 515 294 2721; fax: +49 515 294 9150. E-mail address: [email protected] (D. Habier). 1871-1413/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2008.06.026
the commercial production virtually all fattening pigs are housed in big groups in which more behavioral interactions occur than in 2-pig pens. These interactions can affect performance characteristics just as well as the pen space per animal or the feeding techniques. Therefore, both housing systems on test stations have to be treated as different test environments. If genotype–environment interactions between these two systems exist, the ranking of selection candidates might change. An advantage of the automatic feeding system in big pens is that daily feed intake is recorded for every test animal which overcomes previous difficulties in the analysis of feed intake data. In addition, the new housing system enables further optimizations of the performance test. The objectives of this study were to estimate quantitativegenetic parameters for performance and meat quality traits of crossbred progeny housed in big pens with automatic feeding system, and to estimate genetic correlations between crossbred pigs housed in 2-pig pens and in big pens. These
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correlations are required to combine performances collected in the old and the new housing system in a single breeding value estimation.
βik γil
2. Materials and methods 2.1. Materials Data of female crossbred animals in both 2-pig pens and big pens were recorded on the two Bavarian test stations between January 2000 and August 2004. The crossbred animals from Piétrain sires were provided by piglet producing farms, with 75% originating from German Landrace sows and the rest from crossbred sows (Large White ⁎ Landrace). At the age of 25–30 days, piglets were collected in pairs of two from the same litter in the piglet producing farms and transported to quarantine stations. Six weeks later and about two weeks before the test on station started, the piglets were transferred into their pens on test stations. The performance test started with piglets weighing 30 kg and ended when they weighed 105 kg. Big pens had space for 10–14 test pigs, the temperature in both housing systems was 16–22 °C, the air humidity was 60–70%, and the food diet had an energy content of 13 MJME/kg dry matter (ALZ, 2003). The traits recorded for this study were daily gain from 30 to 105 kg (DG), feed conversion ratio (FCR), lean meat content of the carcass (LMC) and lean meat content in the belly (BMC) estimated via a standard multiple regression equation used in all German testing stations (ALZ, 2003), backfat thickness at the 13th rib (BF) and pH in m. long dorsi 45 min after slaughter (pH1). Table 1 presents a description of the data structure. 2.2. Model for performance in 2-pig pens The observation yijklmno on a crossbred animal in 2-pig pens was modeled by yijklmno
1 ¼ μ i þ bi xjklmno þ α ij þ βik þ γil þ Aim þ cijklmn 2 þ eijklmno ;
ð1Þ
where μi bi xjklmno
Mean of trait i, Regression coefficient of trait i on xjklmno, live weight at the end of fattening period,
Table 1 Distribution of the number of observations in housing systems, performance test stations, type of cross (2-way cross or 3-way cross), farms and sires as well as average number of progeny per sire System
Test station
No. of animals
Proportion of 2-way cross
No. of farms
No. of sires on station
Average no. of progeny/sire
Big pens
A B Total A B Total
1467 1987 3454 8856 5124 13,980
0.72 0.84 0.76 0.70 0.77 0.74
80 81 121 195 117 221
343 317 614 958 670 1332
4.2 6.3 5.6 9.2 7.7 10.5
2-pig pens
αij
No. of sires having progeny in both test environments: 584 (8.5 progeny/sire in 2-pig pens and 5.7 progeny/sire in big pens on average); there are 238 sires having more than 5 progeny within each test environment.
Aim cijklmn eijklmno
Effect of test station ⁎ slaughter week for carcass and meat quality traits, effect of test station ⁎ starting week for fattening traits (fixed), Effect of type of mother (fixed), Effect of farm-year where the piglet was born (random), Effect of breeding value of the sire (random), Effect of full-sib pair in one pen (random), residual effect.
The effects of this model are described in detail by Habier et al. (2007). 2.3. Model for fattening performance in big pens The observation yijklmnop on a crossbred animal in big pens is modeled by 1 yijklmnop ¼ μ i þ bi xjklmnop þ α ij þ βik þ γil þ δijm þ Ain þ cijklno 2 þ eijklmnop : The parameters μi, bi, xjklmnop, βik, γil, Ain and eijklmnop have the same meaning as in model (1). In contrast to the previous model, αij describes the fixed effect of the batch and δijm the random effect of the pen within batch. Batch was defined as fattening period ⁎ compartment. The batch effect corrects for seasonal influences affecting the contemporaries within a compartment (e.g., immunological status). The pen effect is nested within batch and accounts for differences between automatic feeding stations. Further note, that the effect of sib pairs, cijklno, does not include the pen effect in contrast to the model for performances in 2-pig pens. 2.4. Model for carcass and meat quality traits in big pens The model for carcass and meat quality traits is similar to the previous model but includes the fixed effect of test station ⁎ slaughter day, in, and these traits were not regressed on final weight. The model becomes 1 yijklmnopq ¼ μ i þ α ij þ βik þ γ il þ δijm þ in þ Aio þ cijkmop 2 þ eijklmnopq : Variance and covariance components were estimated by Restricted Maximum Likelihood (REML) using VCE 4.2.5 (Neumaier and Groeneveld, 1998). First, univariate estimations were carried out separately for the two test stations to check for heterogeneous variances, and then the pooled data were used to estimate parameters by bivariate models. 3. Results and discussion 3.1. Phenotypic differences between housing systems Table 2 summarizes means and raw standard deviations of performance traits of crossbred pigs in the two test environments. DG and BF of pigs housed in big pens are considerably lower and lean meat traits are about 1% point higher than for pigs housed in 2-pig pens. The difference in pH1 is significant, but negligible.
D. Habier et al. / Livestock Science 121 (2009) 275–280 Table 2 Means (x̄) and raw standard deviations (s) of crossbred performance in pens for two pigs (n = 13,980) and big pens (n = 3,454) Trait, unit
Abbreviation 2-pig pens x̄
Daily gain, g/day Feed conversion ratio, kg/kg Lean meat content of carcass, % Lean meat content of belly, % Backfat thickness, cm pH1 in m long dorsi a
DG FCR LMC
a
Big pens x̄ a
s
s
819.00 82.40 788.10 78.10 2.47 0.19 2.45 0.22 63.12 1.98 63.93 1.98
BMC BF pH1
62.00 1.96 6.36
2.68 0.30 0.26
62.96 1.86 6.32
2.51 0.27 0.24
All means are different (P b 0.01).
From the lower growth level and the leaner carcass, it can be inferred that pigs develop slower in big pens than in 2-pig pens. The main explanation might be the lower feed intake of about 93 g/day in big pens. Labroue et al. (1994) reported significant phenotypic correlations between daily feed intake (DFI) and the traits DG, FCR and BF of 0.65, 0.16 and 0.36, respectively. In addition, Labroue et al. (1997) found a high genetic correlation between DFI and growth rate of 0.8 and moderate genetic correlations with backfat thickness and lean percentage of 0.5 and −0.4, respectively. Similar genetic correlations were estimated by Von Felde et al. (1996). De Haer and Merks (1992) as well as Von Felde et al. (1996a) reported also lower feed intake values of 160 and 430 g/day, respectively, in group housing compared to single housing. The results of De Haer and Merks (1992) are more comparable to the present study, because gender and final weight, which affect feed intake pattern (De Haer et al., 1993; Labroue et al., 1994; Paulke and Scholz, 1999), were more similar. Explanations for the differences in DFI are given by De Haer and Merks (1992). They reported that due to competition, pigs in group housing eat faster and have a higher food intake per meal, but less meals and less eating time per day than pigs in
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single housing. An important figure with respect to competition might be the ratio of animals per feeding place which is 10–14:1 in big pens on Bavarian test stations. Pigs in 2-pig pens, in contrast, have always free admission to food, and they are most likely stimulated by the pen mate and other pigs in the batch. A pig in big pens might seldom be able to respond to stimuli of other pigs when the feeding station is occupied. Another study of De Haer et al. (1993) points to the connection between feed intake pattern and performance traits. They found that pigs showed higher digestibility when the number of short visits was higher. This would result in additional advantage for pigs in 2-pig pens. Differences between performance traits in 2-pig pens and big pens could decrease in the course of fattening, because feed intake pattern in group housing changes (Labroue et al., 1994; Paulke and Scholz, 1999). Both the frequency and the length of visits at the feeding station decrease, thus competition might decrease. At the same time, feed intake per meal and rate of intake, that have most favourable genetic correlations with daily gain, increase in the study of Labroue et al. (1997). However, Von Felde et al. (1996) found that only the length of time per day in the feeder showed a genetic correlation with daily gain (0.32), which is in agreement with the results of De Haer and Merks (1992) mentioned above. The differences between the two housing systems in this analysis for DG and BF are in contrast to the results of De Haer (1990) and Von Felde (1996). They found that DG was higher and BF lower in group housing than in single housing. These comparisons, however, are limited, because boars were housed individually and gilts in groups in the study of De Haer (1990), while the final weight was 120 kg in the study of Von Felde et al. (1996a). 3.2. Quantitative genetic parameters 3.2.1. Variance components and heritabilities Table 3 presents variance components and heritabilities for crossbred performances in big pens from univariate analyses
Table 3 Estimates of population parameters of performance traits of crossbred pigs in big pens with automatic feeding system Trait DG
FCR1)
LMC
BMC
BF1)
pH1) 1
Data set A B Total A B Total A B Total A B Total A B Total A B Total
x̄ a
781 792b 788 2.57a 2.37b 2.45 63.8a 64.1b 63.9 62.9a 62.9a 62.9 1.98a 1.77b 1.86 6.33a 6.31b 6.32
b
^ Δ
7.2 13.3 11.5 −0.001 −0.005 −0.003 −0.159 −0.106 −0.110 −0.098 −0.126 −0.099 0.019 0.012 0.013 – – –
−5.0 1.4 0.55 0.018 −0.007 0.002 0.59 0.79 0.73 0.27 0.65 0.50 −0.007 −0.073 −0.045 0.007 0.019 0.015
β
^ 2A σ
^ 2δ σ
^ 2γ σ
^ 2c σ
^ 2e σ
^ σ
1732 732 912 4.52 8.45 6.50 1.04 1.40 1.28 2.55 2.34 2.22 26.61 29.12 28.13 19.51 21.72 21.93
148 269 221 3.86 12.10 9.00 0.09 0.06 0.07 0.00 0.08 0.03 0.42 1.12 1.02 0.60 0.00 0.00
68 52 76 1.00 0.10 0.42 0.00 0.06 0.03 0.00 0.03 0.00 1.43 0.00 0.02 1.21 0.00 0.00
893 489 666 5.50 3.37 4.27 1.00 0.79 0.89 1.51 1.34 1.46 10.74 12.50 12.41 3.34 7.95 6.52
3564 2945 3263 22.80 19.81 21.10 2.10 2.17 2.14 3.53 3.53 3.53 44.81 46.70 45.94 47.69 33.74 39.62
5106 3938 4455 34.29 37.49 36.42 3.45 3.43 3.45 5.68 5.57 5.58 64.06 67.58 66.42 57.72 47.12 51.62
2 p
^ h 2 (s.e.) 0.34 (0.02) 0.19 (0.01) 0.21 (0.01) 0.13 (0.02) 0.23 (0.01) 0.18 (0.01) 0.30 (0.02) 0.41 (0.02) 0.37 (0.01) 0.45 (0.02) 0.42 (0.02) 0.40 (0.01) 0.42 (0.02) 0.43 (0.02) 0.42 (0.01) 0.34 (0.02) 0.46 (0.02) 0.43 (0.01)
1) Variance components multiplied by 103; statistical significance: a different from b with P b 0.01; b: regression coefficient on live weight at the end of the fattening ^ 2A: additive-genetic variance; σ ^ 2δ : variance between pen ⁎ date of housing; period; Δ^ β: GLS estimate of the contrast two way cross minus the three way cross; σ ^ 2γ: variance between farm-year effects; σ ^ 2c : variance between sib-pair effects; σ ^ 2e : residual variance; σ ^ 2p: phenotypic variance; ^h : heritability. σ
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utilizing the separate data sets of stations A and B as well as the pooled one. Furthermore, the contrast between two way and three way cross is depicted in Table 3, which is of immediate interest for the commercial production. The main result is a superiority of more than half a percent point in lean meat content in favour of the two way cross. Meat quality of the three way cross might be marginally better. These results are in agreement with findings in 2-pig pens (Habier et al., 2007). The comparison of additive-genetic variances estimated from the three data sets (A, B and pooled) shows that variances of the pooled records tend to be closer to the estimates of station B, because there are not only more observations but also a better data structure. This can be observed for BMC, pH1 and DG. The estimates of pH1 and BMC are not even within the range between the two separate estimates, which might have been caused by heterogeneous environmental variances being much higher on station A. This tendency carries over to the estimates of heritabilities. The data structure on station A was worse than on station B, because the former had more big pens with very few (one) progeny of the sire breed, since the other pen mates originate from dam breeds. This reduced the comparisons of sires within pens, and thus reduced accuracy of their estimated breeding values. The proportion of the phenotypic variance explained by the pen effect for the traits DG, FCR and BF is drastically higher on station B than on station A. This might be due to the fact that piglets on station B are sorted by initial weight. This sorting, however, bears the risk of falsely correcting for genetic effects. The influence of farm-year effects are low, being significant only for the fattening traits and backfat thickness. The c2-effect refers to the proportion of the variances explained by the sib-pair effect to the phenotypic variance and is 0.12 for feed conversion ration in group housing. The c2-effect of DG in big pens is only half as much as in 2-pig pens, whereas the c2-effect of the other traits hardly change. The main reason for the difference in DG is that the full-sib group means in 2-pig pens include batch and pen effects. The c2-effect affects the relative value of an observation for the breeding value estimation. Precision can be improved by testing just one piglet from a litter instead of two piglets, because crossbred performances are not utilized for estimating breeding values of dams kept by piglet producers. Similar as in 2-pig pens (Habier et al., 2007), the environmental variance components of DG and meat quality traits show large differences between the two test stations. In DG both σ2c and σ2e are increased on station A, whereas for pH1, σ2c is reduced and σ2e drastically increased on sta-
tion A. No plausible explanation could be found for these differences. The additive-genetic variances of fattening and lean meat traits of the pooled data set are lower than in 2-pig pens (Habier et al., 2007). However, considering the variances within test stations, this statement is not valid in general. Some traits show lower variances within big pens, others show higher variances than in 2-pig pens. Moreover, surprisingly, the test station having the higher additive-genetic variance can change from one to the other housing environment. This can be observed for feed conversion ratio and lean meat content. De Haer (1990), Knap and Van Der Steen (1994) as well as Von Felde et al. (1996a) reported higher phenotypic and additive-genetic variances in group housing. This was not found in this study. They ascribed this to an increased competition among the pigs in a pen, which might result from suppression by animals of higher rank. As a result of the lower additive-genetic variances within the pooled records in this study, the heritabilities of fattening traits and LMC are less in big pens than in 2-pig pens (Habier et al., 2007). The estimated values of DG and LMC are 0.28 and 0.44 in the old housing system and 0.21 and 0.37 in the new one, respectively. To compare the estimates of FCR, the heritability for big pens has to be related to full-sib means (Habier et al., 2007). In doing so, the heritabilities in 2-pig pens and big pens are 0.30 and 0.21, respectively. The heritability of backfat thickness, in contrast, is lower in 2-pig pens (0.34 vs. 0.42) due to a much higher residual variance and a slightly lower additive-genetic variance in 2-pig pens. The heritabilities of meat quality traits are higher in big pens. Comparing just the additive-genetic variances of the pooled data set in both housing systems for fattening and lean meat traits, one could assume the following hypothesis: The lower additive-genetic variances of pigs in big pens indicate that the growth capacity is not fully used and consequently, genetic differences show up less. However, the higher additive-genetic variance for backfat thickness and the estimated parameters for the separated data sets put this hypothesis into question. The parameters should be reestimated to check the statements after having improved standardization and design. Taking these parameters for granted, genetic progress of DG, FCR and LMC on test stations is expected to be lower in the future. However, whether genetic progress in the commercial production will be lower or higher is unknown, since little information is available to estimate the genetic correlations between test stations and commercial production environment. Furthermore, since crossbred pigs in big
Table 4 Genetic and phenotypic correlations (above and below the diagonal), heritabilities (diagonal) and c2-effects (c2 = σ2c /σ2p) of crossbred pigs in big pens
DG FCR LMC BMC BF pH1 c2
DG
FCR
LMC
BMC
BF
pH1
0.21 (0.01) − 0.31 (0.13) −0.09 (0.11) −0.10 (0.06) 0.13 (0.05) − 0.06 (0.11) 0.15 (0.01)
−0.14 (0.13) 0.18 (0.01) −0.35 (0.08) −0.38 (0.06) 0.35 (0.09) 0.11 (0.13) 0.12 (0.01)
−0.09 (0.11) −0.52 (0.08) 0.37 (0.01) 0.83 (0.02) −0.35 (0.07) −0.12 (0.07) 0.26 (0.02)
−0.00 (0.06) −0.76 (0.06) 0.82 (0.02) 0.40 (0.01) −0.58 (0.04) −0.05 (0.09) 0.26 (0.01)
0.09 (0.05) 0.71 (0.09) −0.39 (0.06) −0.79 (0.04) 0.42 (0.01) −0.02 (0.10) 0.19 (0.02)
−0.17 (0.11) 0.18 (0.13) −0.13 (0.07) 0.03 (0.09) −0.27 (0.10) 0.42 (0.01) 0.13 (0.02)
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Table 5 Genetic correlations (s.e.) between performance traits of crossbred pigs in 2-pig pens (2P) and in big pens (BP) DGBP DG2P FCR2P LMC2P BMC2P BF2P pH12P
0.52 −0.00 − 0.12 −0.19 0.09 −0.27
(0.13) (0.03) (0.06) (0.07) (0.06) (0.10)
FCRBP
LMCBP
BMCBP
BFBP
pH1BP
0.15 (0.11) 0.70 (0.13) −0.51 (0.06) −0.59 (0.11) 0.62 (0.11) 0.31 (0.12)
−0.25 (0.12) −0.24 (0.12) 1.00 (0.00) 0.86 (0.07) −0.60 (0.09) −0.45 (0.10)
−0.10 (0.09) −0.41 (0.11) 0.88 (0.06) 0.96 (0.06) −0.83 (0.07) − 0.37 (0.09)
0.07 (0.12) 0.30 (0.12) −0.41 (0.09) −0.67 (0.08) 0.98 (0.06) 0.12 (0.10)
−0.31 (0.53) −0.04 (0.13) −0.28 (0.08) −0.03 (0.07) −0.22 (0.08) 1.00 (0.00)
pens are suspected to develop slower, less information about the whole fattening period is recorded, as in the commercial production final weight is about 12 kg higher. It is desirable to adjust the final weight on station to the final weight in the commercial production. 3.2.2. Genetic correlations between performance traits in big pens Genetic and phenotypic correlations for crossbred traits in big pens estimated from the pooled data set can be found in Table 4. As expected, genetic correlations among lean meat traits and among meat quality traits are high. They correspond to correlations found in 2-pig pens (Habier et al., 2007). The correlations among meat quality traits are highly influenced by the Halothane locus, which is still segregating within the Bavarian Piétrain population. Furthermore, in contrast to the values found in the literature (Rothschild and Ruvinsky, 1998) and in 2-pig pens (Habier et al., 2007), there is no explanation for the genetic correlations between BF and meat quality traits, meaning that meat quality deteriorates with higher fat deposition (BF–pH1: ρ = −0.27). The very opposite direction was expected. Soon test pigs will be housed in big pens only, so that the new population parameters will determine future genetic progress. The antagonism between DG and LMC tends to be lower than in 2-pig pens (−0.09 vs. −0.18), whereas the antagonism between DG and BMC disappears totally (0 vs. −0.18). Moreover, with respect to the breeding goal (Habier et al., 2004), genetic correlations between FCR and lean meat traits are also more favourable. The correlation between FCR and LMC decreases from −0.32 to −0.52 and the correlation between FCR and BMC decreases from −0.39 to −0.76. The genetic correlation between DG and FCR of −0.14, in contrast, is less favourable in comparison to −0.40 in 2-pig pens (Habier et al., 2007). Since the genetic correlations between lean meat traits and FCR are higher, and the antagonism between DG and lean meat traits is reduced, pigs in big pens use a higher percentage of feed energy for protein deposition than pigs in 2-pig pens. This is reasonable when we expect that pigs in big pens develop slower. 3.2.3. Genetic correlations between performance traits of both test environments Table 5 summarizes the genetic correlations between performances in 2-pig pens and big pens. Genetic correlations between pigs in the two test environments are close to 1 or even 1 for backfat thickness, lean meat content and meat quality traits. However, the correlations of the fattening traits DG and FCR are just 0.52 and 0.7, respectively.
Von Felde (1996) reported similar values for LMC and DG of 1 and 0.46, respectively, whereas the genetic correlations for BF and FCR were 0.71 and 0.15, respectively. Thus, when breeding values of crossbred performance in big pens are used to derive the aggregate breeding value, re-rankings of selection candidates will occur. As mentioned, the consequences for the commercial production remain unknown. Most reciprocal correlations between performance traits of both environments (Table 5) are very similar, and within expectations. Exceptions are the correlations between BF in 2pig pens and meat quality traits in big pens. The reciprocal correlations between BF in big pens and meat quality in 2-pig pens, however, agree with correlations in 2-pig pens. Thus, in spite of the high genetic correlations between meat quality traits in both test environments, the meat quality traits in big pens behave differently regarding the genetic correlations to other traits. The correlations of meat quality traits with DG in 2-pig pens are another example. 4. Conclusions Housing of pigs in big pens is more demanding with respect to the test design than in 2-pig pens. To ensure an informative data structure for breeding value estimation, it should be attempted to standardize as much as possible and to follow very closely a proper experimental design and have conditions very similar to the commercial conditions. Due to substantial c2-effects, two crossbred pigs from different litters provide considerably more information to the breeding value estimation for the sire breed than two full-sibs from a single litter. The moderate genetic correlations of daily gain and feed conversion ratio between the two test environments will result in a re-ranking of selection candidates when using the breeding values of crossbred performance in big pens in the aggregate genotype instead of using breeding values of crossbred performance in 2-pig pens. The genetic progress on test stations is expected to be lower in the future, because the additive-genetic variances and the heritabilities of lean meat content as well as of fattening traits are lower in big pens than in 2-pig pens. For a more reliable prediction of future genetic progress in commercial farms, however, genetic correlations between performances on test stations and commercial farms should be estimated. For the same reason, final weight on test is to adjust to the final weight in the commercial level. References ALZ, 2003. Richtlinie für die Stationsprüfung auf Mastleistung, Schlachtkörper wert und Fleischbeschaffenheit beim Schwein vom 10.12.2003.
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housed Large White and French Landrace pigs. Genet. Sel. Evol. 29, 451–468. Neumaier, A., Groeneveld, E., 1998. Restricted maximum likelihood estimation of covariances in sparse linear models. Genet. Sel. Evol. 30, 3–26. Paulke, T., Scholz, A., 1999. Die Charakteristik von Merkmalen der Futteraufnahme unter ad libitum Bedingungen bei verschiedenen Schweinerassen und Rassenkom binationen. Züchtungskunde 71, 229–243. Rothschild, M.F., Ruvinsky, A., 1998. The Genetics of the Pig. CAB International, Wallingford UK. Von Felde, A., 1996. Genetische Analyse der Futteraufnahme-Informationen von Jungebern aus Gruppenprüfung mit automatischen Fütterungsanlagen. Schriftenreihe des Institutes für Tierzucht und Tierhaltung der Christian-Albrechts-Universität zu Kiel, Heft 90. Von Felde, A., Rhöhe, R., Kalm, E., 1996a. Genetische Analyse von Merkmalen der Mastleistung und des Schlachtkörpers stationsgeprüfter Jungeber in Einzel- und Gruppenhaltung mittels Gibbs-Sampling. Züchtungskunde 68, 305–318. Von Felde, A., Röhe, R., Looft, H., Kalm, E., 1996. Genetic association between feed intake and feed intake behaviour at different stages of growth of group housed boars. Livest. Prod. Sci. 47, 11–22.
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Livestock Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / l i v s c i
Genetic parameters for performance and meat quality traits of crossbred pigs housed in two test environments D. Habier a,b,⁎, K.-U. Götz b, L. Dempfle a a b
Technical University of Munich-Weihenstephan, Department of Animal Science, Alte Akademie 12, 85354 Freising, Germany Bavarian Institute of Agriculture, Institute of Animal Breeding, Prof.-Dürrwaechter-Platz 1, 85586 Poing-Grub, Germany
a r t i c l e
i n f o
Article history: Received 12 April 2007 Received in revised form 20 April 2008 Accepted 27 June 2008 Keywords: Genetic parameters Test station Crossbred pigs Piétrain Genotype–environment interaction
a b s t r a c t Genetic parameters were estimated for crossbred progeny of Bavarian Piétrain sires housed in two test environments on the two Bavarian test stations. The data contained 13,980 pigs housed in traditional pens for 2 pigs and 3,454 pigs housed in big pens for 10–14 pigs with automatic feeding system recorded between 2000 and 2004. In total, 584 sires having progeny in both housing systems were available to estimate genetic correlations between the two test environments. The analysis showed that the housing of pigs in big pens is more demanding with respect to the test design than in 2-pig pens. Further, the results show differences in both phenotypic performance and genetic parameters between the two environments. Daily gain is lower and lean meat content is higher in big pens with automatic feeding system. Therefore, it is suspected that pigs develop slower in the new housing due to a different feed intake behavior in comparison to 2-pig pens. This might be the main reason for the moderate genetic correlations among fattening performance traits (0.5–0.7 ± 0.13), which result in re-rankings of selection candidates depending which kind of information is utilized. Genetic correlations of slaughter and meat quality traits, however, are close to 1. Differences between the variance components in the two test stations have been found and simple pooling of data is problematic with respect to the breeding value estimation. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Since 2001 the housing system on the Bavarian performance test stations is being converted from traditional pens for 2 pigs to big pens with automatic feeding system for 10–14 pigs. The aim is to have the conditions on the performance test stations more similar to the commercial production environment to avoid genotype–environment interactions. In the last 15 years, the final weight on Bavarian commercial farms increased from 105 to 117 kg, whereas the weight on performance test stations has remained at 105 kg. Hitherto, the adoption of the higher final weight was not possible due to limited pen space per test animal in 2-pig pens. Further, in ⁎ Corresponding author. Technical University of Munich-Weihenstephan, Department of Animal Science, Alte Akademie 12, 85354 Freising, Germany. Tel.: +49 515 294 2721; fax: +49 515 294 9150. E-mail address: [email protected] (D. Habier). 1871-1413/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2008.06.026
the commercial production virtually all fattening pigs are housed in big groups in which more behavioral interactions occur than in 2-pig pens. These interactions can affect performance characteristics just as well as the pen space per animal or the feeding techniques. Therefore, both housing systems on test stations have to be treated as different test environments. If genotype–environment interactions between these two systems exist, the ranking of selection candidates might change. An advantage of the automatic feeding system in big pens is that daily feed intake is recorded for every test animal which overcomes previous difficulties in the analysis of feed intake data. In addition, the new housing system enables further optimizations of the performance test. The objectives of this study were to estimate quantitativegenetic parameters for performance and meat quality traits of crossbred progeny housed in big pens with automatic feeding system, and to estimate genetic correlations between crossbred pigs housed in 2-pig pens and in big pens. These
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correlations are required to combine performances collected in the old and the new housing system in a single breeding value estimation.
βik γil
2. Materials and methods 2.1. Materials Data of female crossbred animals in both 2-pig pens and big pens were recorded on the two Bavarian test stations between January 2000 and August 2004. The crossbred animals from Piétrain sires were provided by piglet producing farms, with 75% originating from German Landrace sows and the rest from crossbred sows (Large White ⁎ Landrace). At the age of 25–30 days, piglets were collected in pairs of two from the same litter in the piglet producing farms and transported to quarantine stations. Six weeks later and about two weeks before the test on station started, the piglets were transferred into their pens on test stations. The performance test started with piglets weighing 30 kg and ended when they weighed 105 kg. Big pens had space for 10–14 test pigs, the temperature in both housing systems was 16–22 °C, the air humidity was 60–70%, and the food diet had an energy content of 13 MJME/kg dry matter (ALZ, 2003). The traits recorded for this study were daily gain from 30 to 105 kg (DG), feed conversion ratio (FCR), lean meat content of the carcass (LMC) and lean meat content in the belly (BMC) estimated via a standard multiple regression equation used in all German testing stations (ALZ, 2003), backfat thickness at the 13th rib (BF) and pH in m. long dorsi 45 min after slaughter (pH1). Table 1 presents a description of the data structure. 2.2. Model for performance in 2-pig pens The observation yijklmno on a crossbred animal in 2-pig pens was modeled by yijklmno
1 ¼ μ i þ bi xjklmno þ α ij þ βik þ γil þ Aim þ cijklmn 2 þ eijklmno ;
ð1Þ
where μi bi xjklmno
Mean of trait i, Regression coefficient of trait i on xjklmno, live weight at the end of fattening period,
Table 1 Distribution of the number of observations in housing systems, performance test stations, type of cross (2-way cross or 3-way cross), farms and sires as well as average number of progeny per sire System
Test station
No. of animals
Proportion of 2-way cross
No. of farms
No. of sires on station
Average no. of progeny/sire
Big pens
A B Total A B Total
1467 1987 3454 8856 5124 13,980
0.72 0.84 0.76 0.70 0.77 0.74
80 81 121 195 117 221
343 317 614 958 670 1332
4.2 6.3 5.6 9.2 7.7 10.5
2-pig pens
αij
No. of sires having progeny in both test environments: 584 (8.5 progeny/sire in 2-pig pens and 5.7 progeny/sire in big pens on average); there are 238 sires having more than 5 progeny within each test environment.
Aim cijklmn eijklmno
Effect of test station ⁎ slaughter week for carcass and meat quality traits, effect of test station ⁎ starting week for fattening traits (fixed), Effect of type of mother (fixed), Effect of farm-year where the piglet was born (random), Effect of breeding value of the sire (random), Effect of full-sib pair in one pen (random), residual effect.
The effects of this model are described in detail by Habier et al. (2007). 2.3. Model for fattening performance in big pens The observation yijklmnop on a crossbred animal in big pens is modeled by 1 yijklmnop ¼ μ i þ bi xjklmnop þ α ij þ βik þ γil þ δijm þ Ain þ cijklno 2 þ eijklmnop : The parameters μi, bi, xjklmnop, βik, γil, Ain and eijklmnop have the same meaning as in model (1). In contrast to the previous model, αij describes the fixed effect of the batch and δijm the random effect of the pen within batch. Batch was defined as fattening period ⁎ compartment. The batch effect corrects for seasonal influences affecting the contemporaries within a compartment (e.g., immunological status). The pen effect is nested within batch and accounts for differences between automatic feeding stations. Further note, that the effect of sib pairs, cijklno, does not include the pen effect in contrast to the model for performances in 2-pig pens. 2.4. Model for carcass and meat quality traits in big pens The model for carcass and meat quality traits is similar to the previous model but includes the fixed effect of test station ⁎ slaughter day, in, and these traits were not regressed on final weight. The model becomes 1 yijklmnopq ¼ μ i þ α ij þ βik þ γ il þ δijm þ in þ Aio þ cijkmop 2 þ eijklmnopq : Variance and covariance components were estimated by Restricted Maximum Likelihood (REML) using VCE 4.2.5 (Neumaier and Groeneveld, 1998). First, univariate estimations were carried out separately for the two test stations to check for heterogeneous variances, and then the pooled data were used to estimate parameters by bivariate models. 3. Results and discussion 3.1. Phenotypic differences between housing systems Table 2 summarizes means and raw standard deviations of performance traits of crossbred pigs in the two test environments. DG and BF of pigs housed in big pens are considerably lower and lean meat traits are about 1% point higher than for pigs housed in 2-pig pens. The difference in pH1 is significant, but negligible.
D. Habier et al. / Livestock Science 121 (2009) 275–280 Table 2 Means (x̄) and raw standard deviations (s) of crossbred performance in pens for two pigs (n = 13,980) and big pens (n = 3,454) Trait, unit
Abbreviation 2-pig pens x̄
Daily gain, g/day Feed conversion ratio, kg/kg Lean meat content of carcass, % Lean meat content of belly, % Backfat thickness, cm pH1 in m long dorsi a
DG FCR LMC
a
Big pens x̄ a
s
s
819.00 82.40 788.10 78.10 2.47 0.19 2.45 0.22 63.12 1.98 63.93 1.98
BMC BF pH1
62.00 1.96 6.36
2.68 0.30 0.26
62.96 1.86 6.32
2.51 0.27 0.24
All means are different (P b 0.01).
From the lower growth level and the leaner carcass, it can be inferred that pigs develop slower in big pens than in 2-pig pens. The main explanation might be the lower feed intake of about 93 g/day in big pens. Labroue et al. (1994) reported significant phenotypic correlations between daily feed intake (DFI) and the traits DG, FCR and BF of 0.65, 0.16 and 0.36, respectively. In addition, Labroue et al. (1997) found a high genetic correlation between DFI and growth rate of 0.8 and moderate genetic correlations with backfat thickness and lean percentage of 0.5 and −0.4, respectively. Similar genetic correlations were estimated by Von Felde et al. (1996). De Haer and Merks (1992) as well as Von Felde et al. (1996a) reported also lower feed intake values of 160 and 430 g/day, respectively, in group housing compared to single housing. The results of De Haer and Merks (1992) are more comparable to the present study, because gender and final weight, which affect feed intake pattern (De Haer et al., 1993; Labroue et al., 1994; Paulke and Scholz, 1999), were more similar. Explanations for the differences in DFI are given by De Haer and Merks (1992). They reported that due to competition, pigs in group housing eat faster and have a higher food intake per meal, but less meals and less eating time per day than pigs in
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single housing. An important figure with respect to competition might be the ratio of animals per feeding place which is 10–14:1 in big pens on Bavarian test stations. Pigs in 2-pig pens, in contrast, have always free admission to food, and they are most likely stimulated by the pen mate and other pigs in the batch. A pig in big pens might seldom be able to respond to stimuli of other pigs when the feeding station is occupied. Another study of De Haer et al. (1993) points to the connection between feed intake pattern and performance traits. They found that pigs showed higher digestibility when the number of short visits was higher. This would result in additional advantage for pigs in 2-pig pens. Differences between performance traits in 2-pig pens and big pens could decrease in the course of fattening, because feed intake pattern in group housing changes (Labroue et al., 1994; Paulke and Scholz, 1999). Both the frequency and the length of visits at the feeding station decrease, thus competition might decrease. At the same time, feed intake per meal and rate of intake, that have most favourable genetic correlations with daily gain, increase in the study of Labroue et al. (1997). However, Von Felde et al. (1996) found that only the length of time per day in the feeder showed a genetic correlation with daily gain (0.32), which is in agreement with the results of De Haer and Merks (1992) mentioned above. The differences between the two housing systems in this analysis for DG and BF are in contrast to the results of De Haer (1990) and Von Felde (1996). They found that DG was higher and BF lower in group housing than in single housing. These comparisons, however, are limited, because boars were housed individually and gilts in groups in the study of De Haer (1990), while the final weight was 120 kg in the study of Von Felde et al. (1996a). 3.2. Quantitative genetic parameters 3.2.1. Variance components and heritabilities Table 3 presents variance components and heritabilities for crossbred performances in big pens from univariate analyses
Table 3 Estimates of population parameters of performance traits of crossbred pigs in big pens with automatic feeding system Trait DG
FCR1)
LMC
BMC
BF1)
pH1) 1
Data set A B Total A B Total A B Total A B Total A B Total A B Total
x̄ a
781 792b 788 2.57a 2.37b 2.45 63.8a 64.1b 63.9 62.9a 62.9a 62.9 1.98a 1.77b 1.86 6.33a 6.31b 6.32
b
^ Δ
7.2 13.3 11.5 −0.001 −0.005 −0.003 −0.159 −0.106 −0.110 −0.098 −0.126 −0.099 0.019 0.012 0.013 – – –
−5.0 1.4 0.55 0.018 −0.007 0.002 0.59 0.79 0.73 0.27 0.65 0.50 −0.007 −0.073 −0.045 0.007 0.019 0.015
β
^ 2A σ
^ 2δ σ
^ 2γ σ
^ 2c σ
^ 2e σ
^ σ
1732 732 912 4.52 8.45 6.50 1.04 1.40 1.28 2.55 2.34 2.22 26.61 29.12 28.13 19.51 21.72 21.93
148 269 221 3.86 12.10 9.00 0.09 0.06 0.07 0.00 0.08 0.03 0.42 1.12 1.02 0.60 0.00 0.00
68 52 76 1.00 0.10 0.42 0.00 0.06 0.03 0.00 0.03 0.00 1.43 0.00 0.02 1.21 0.00 0.00
893 489 666 5.50 3.37 4.27 1.00 0.79 0.89 1.51 1.34 1.46 10.74 12.50 12.41 3.34 7.95 6.52
3564 2945 3263 22.80 19.81 21.10 2.10 2.17 2.14 3.53 3.53 3.53 44.81 46.70 45.94 47.69 33.74 39.62
5106 3938 4455 34.29 37.49 36.42 3.45 3.43 3.45 5.68 5.57 5.58 64.06 67.58 66.42 57.72 47.12 51.62
2 p
^ h 2 (s.e.) 0.34 (0.02) 0.19 (0.01) 0.21 (0.01) 0.13 (0.02) 0.23 (0.01) 0.18 (0.01) 0.30 (0.02) 0.41 (0.02) 0.37 (0.01) 0.45 (0.02) 0.42 (0.02) 0.40 (0.01) 0.42 (0.02) 0.43 (0.02) 0.42 (0.01) 0.34 (0.02) 0.46 (0.02) 0.43 (0.01)
1) Variance components multiplied by 103; statistical significance: a different from b with P b 0.01; b: regression coefficient on live weight at the end of the fattening ^ 2A: additive-genetic variance; σ ^ 2δ : variance between pen ⁎ date of housing; period; Δ^ β: GLS estimate of the contrast two way cross minus the three way cross; σ ^ 2γ: variance between farm-year effects; σ ^ 2c : variance between sib-pair effects; σ ^ 2e : residual variance; σ ^ 2p: phenotypic variance; ^h : heritability. σ
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utilizing the separate data sets of stations A and B as well as the pooled one. Furthermore, the contrast between two way and three way cross is depicted in Table 3, which is of immediate interest for the commercial production. The main result is a superiority of more than half a percent point in lean meat content in favour of the two way cross. Meat quality of the three way cross might be marginally better. These results are in agreement with findings in 2-pig pens (Habier et al., 2007). The comparison of additive-genetic variances estimated from the three data sets (A, B and pooled) shows that variances of the pooled records tend to be closer to the estimates of station B, because there are not only more observations but also a better data structure. This can be observed for BMC, pH1 and DG. The estimates of pH1 and BMC are not even within the range between the two separate estimates, which might have been caused by heterogeneous environmental variances being much higher on station A. This tendency carries over to the estimates of heritabilities. The data structure on station A was worse than on station B, because the former had more big pens with very few (one) progeny of the sire breed, since the other pen mates originate from dam breeds. This reduced the comparisons of sires within pens, and thus reduced accuracy of their estimated breeding values. The proportion of the phenotypic variance explained by the pen effect for the traits DG, FCR and BF is drastically higher on station B than on station A. This might be due to the fact that piglets on station B are sorted by initial weight. This sorting, however, bears the risk of falsely correcting for genetic effects. The influence of farm-year effects are low, being significant only for the fattening traits and backfat thickness. The c2-effect refers to the proportion of the variances explained by the sib-pair effect to the phenotypic variance and is 0.12 for feed conversion ration in group housing. The c2-effect of DG in big pens is only half as much as in 2-pig pens, whereas the c2-effect of the other traits hardly change. The main reason for the difference in DG is that the full-sib group means in 2-pig pens include batch and pen effects. The c2-effect affects the relative value of an observation for the breeding value estimation. Precision can be improved by testing just one piglet from a litter instead of two piglets, because crossbred performances are not utilized for estimating breeding values of dams kept by piglet producers. Similar as in 2-pig pens (Habier et al., 2007), the environmental variance components of DG and meat quality traits show large differences between the two test stations. In DG both σ2c and σ2e are increased on station A, whereas for pH1, σ2c is reduced and σ2e drastically increased on sta-
tion A. No plausible explanation could be found for these differences. The additive-genetic variances of fattening and lean meat traits of the pooled data set are lower than in 2-pig pens (Habier et al., 2007). However, considering the variances within test stations, this statement is not valid in general. Some traits show lower variances within big pens, others show higher variances than in 2-pig pens. Moreover, surprisingly, the test station having the higher additive-genetic variance can change from one to the other housing environment. This can be observed for feed conversion ratio and lean meat content. De Haer (1990), Knap and Van Der Steen (1994) as well as Von Felde et al. (1996a) reported higher phenotypic and additive-genetic variances in group housing. This was not found in this study. They ascribed this to an increased competition among the pigs in a pen, which might result from suppression by animals of higher rank. As a result of the lower additive-genetic variances within the pooled records in this study, the heritabilities of fattening traits and LMC are less in big pens than in 2-pig pens (Habier et al., 2007). The estimated values of DG and LMC are 0.28 and 0.44 in the old housing system and 0.21 and 0.37 in the new one, respectively. To compare the estimates of FCR, the heritability for big pens has to be related to full-sib means (Habier et al., 2007). In doing so, the heritabilities in 2-pig pens and big pens are 0.30 and 0.21, respectively. The heritability of backfat thickness, in contrast, is lower in 2-pig pens (0.34 vs. 0.42) due to a much higher residual variance and a slightly lower additive-genetic variance in 2-pig pens. The heritabilities of meat quality traits are higher in big pens. Comparing just the additive-genetic variances of the pooled data set in both housing systems for fattening and lean meat traits, one could assume the following hypothesis: The lower additive-genetic variances of pigs in big pens indicate that the growth capacity is not fully used and consequently, genetic differences show up less. However, the higher additive-genetic variance for backfat thickness and the estimated parameters for the separated data sets put this hypothesis into question. The parameters should be reestimated to check the statements after having improved standardization and design. Taking these parameters for granted, genetic progress of DG, FCR and LMC on test stations is expected to be lower in the future. However, whether genetic progress in the commercial production will be lower or higher is unknown, since little information is available to estimate the genetic correlations between test stations and commercial production environment. Furthermore, since crossbred pigs in big
Table 4 Genetic and phenotypic correlations (above and below the diagonal), heritabilities (diagonal) and c2-effects (c2 = σ2c /σ2p) of crossbred pigs in big pens
DG FCR LMC BMC BF pH1 c2
DG
FCR
LMC
BMC
BF
pH1
0.21 (0.01) − 0.31 (0.13) −0.09 (0.11) −0.10 (0.06) 0.13 (0.05) − 0.06 (0.11) 0.15 (0.01)
−0.14 (0.13) 0.18 (0.01) −0.35 (0.08) −0.38 (0.06) 0.35 (0.09) 0.11 (0.13) 0.12 (0.01)
−0.09 (0.11) −0.52 (0.08) 0.37 (0.01) 0.83 (0.02) −0.35 (0.07) −0.12 (0.07) 0.26 (0.02)
−0.00 (0.06) −0.76 (0.06) 0.82 (0.02) 0.40 (0.01) −0.58 (0.04) −0.05 (0.09) 0.26 (0.01)
0.09 (0.05) 0.71 (0.09) −0.39 (0.06) −0.79 (0.04) 0.42 (0.01) −0.02 (0.10) 0.19 (0.02)
−0.17 (0.11) 0.18 (0.13) −0.13 (0.07) 0.03 (0.09) −0.27 (0.10) 0.42 (0.01) 0.13 (0.02)
D. Habier et al. / Livestock Science 121 (2009) 275–280
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Table 5 Genetic correlations (s.e.) between performance traits of crossbred pigs in 2-pig pens (2P) and in big pens (BP) DGBP DG2P FCR2P LMC2P BMC2P BF2P pH12P
0.52 −0.00 − 0.12 −0.19 0.09 −0.27
(0.13) (0.03) (0.06) (0.07) (0.06) (0.10)
FCRBP
LMCBP
BMCBP
BFBP
pH1BP
0.15 (0.11) 0.70 (0.13) −0.51 (0.06) −0.59 (0.11) 0.62 (0.11) 0.31 (0.12)
−0.25 (0.12) −0.24 (0.12) 1.00 (0.00) 0.86 (0.07) −0.60 (0.09) −0.45 (0.10)
−0.10 (0.09) −0.41 (0.11) 0.88 (0.06) 0.96 (0.06) −0.83 (0.07) − 0.37 (0.09)
0.07 (0.12) 0.30 (0.12) −0.41 (0.09) −0.67 (0.08) 0.98 (0.06) 0.12 (0.10)
−0.31 (0.53) −0.04 (0.13) −0.28 (0.08) −0.03 (0.07) −0.22 (0.08) 1.00 (0.00)
pens are suspected to develop slower, less information about the whole fattening period is recorded, as in the commercial production final weight is about 12 kg higher. It is desirable to adjust the final weight on station to the final weight in the commercial production. 3.2.2. Genetic correlations between performance traits in big pens Genetic and phenotypic correlations for crossbred traits in big pens estimated from the pooled data set can be found in Table 4. As expected, genetic correlations among lean meat traits and among meat quality traits are high. They correspond to correlations found in 2-pig pens (Habier et al., 2007). The correlations among meat quality traits are highly influenced by the Halothane locus, which is still segregating within the Bavarian Piétrain population. Furthermore, in contrast to the values found in the literature (Rothschild and Ruvinsky, 1998) and in 2-pig pens (Habier et al., 2007), there is no explanation for the genetic correlations between BF and meat quality traits, meaning that meat quality deteriorates with higher fat deposition (BF–pH1: ρ = −0.27). The very opposite direction was expected. Soon test pigs will be housed in big pens only, so that the new population parameters will determine future genetic progress. The antagonism between DG and LMC tends to be lower than in 2-pig pens (−0.09 vs. −0.18), whereas the antagonism between DG and BMC disappears totally (0 vs. −0.18). Moreover, with respect to the breeding goal (Habier et al., 2004), genetic correlations between FCR and lean meat traits are also more favourable. The correlation between FCR and LMC decreases from −0.32 to −0.52 and the correlation between FCR and BMC decreases from −0.39 to −0.76. The genetic correlation between DG and FCR of −0.14, in contrast, is less favourable in comparison to −0.40 in 2-pig pens (Habier et al., 2007). Since the genetic correlations between lean meat traits and FCR are higher, and the antagonism between DG and lean meat traits is reduced, pigs in big pens use a higher percentage of feed energy for protein deposition than pigs in 2-pig pens. This is reasonable when we expect that pigs in big pens develop slower. 3.2.3. Genetic correlations between performance traits of both test environments Table 5 summarizes the genetic correlations between performances in 2-pig pens and big pens. Genetic correlations between pigs in the two test environments are close to 1 or even 1 for backfat thickness, lean meat content and meat quality traits. However, the correlations of the fattening traits DG and FCR are just 0.52 and 0.7, respectively.
Von Felde (1996) reported similar values for LMC and DG of 1 and 0.46, respectively, whereas the genetic correlations for BF and FCR were 0.71 and 0.15, respectively. Thus, when breeding values of crossbred performance in big pens are used to derive the aggregate breeding value, re-rankings of selection candidates will occur. As mentioned, the consequences for the commercial production remain unknown. Most reciprocal correlations between performance traits of both environments (Table 5) are very similar, and within expectations. Exceptions are the correlations between BF in 2pig pens and meat quality traits in big pens. The reciprocal correlations between BF in big pens and meat quality in 2-pig pens, however, agree with correlations in 2-pig pens. Thus, in spite of the high genetic correlations between meat quality traits in both test environments, the meat quality traits in big pens behave differently regarding the genetic correlations to other traits. The correlations of meat quality traits with DG in 2-pig pens are another example. 4. Conclusions Housing of pigs in big pens is more demanding with respect to the test design than in 2-pig pens. To ensure an informative data structure for breeding value estimation, it should be attempted to standardize as much as possible and to follow very closely a proper experimental design and have conditions very similar to the commercial conditions. Due to substantial c2-effects, two crossbred pigs from different litters provide considerably more information to the breeding value estimation for the sire breed than two full-sibs from a single litter. The moderate genetic correlations of daily gain and feed conversion ratio between the two test environments will result in a re-ranking of selection candidates when using the breeding values of crossbred performance in big pens in the aggregate genotype instead of using breeding values of crossbred performance in 2-pig pens. The genetic progress on test stations is expected to be lower in the future, because the additive-genetic variances and the heritabilities of lean meat content as well as of fattening traits are lower in big pens than in 2-pig pens. For a more reliable prediction of future genetic progress in commercial farms, however, genetic correlations between performances on test stations and commercial farms should be estimated. For the same reason, final weight on test is to adjust to the final weight in the commercial level. References ALZ, 2003. Richtlinie für die Stationsprüfung auf Mastleistung, Schlachtkörper wert und Fleischbeschaffenheit beim Schwein vom 10.12.2003.
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