Estimation of genetic parameters and genotype effects for crossing constructions of Hungarian Pigs

During the last two decades the BLUP breeding value estimation became a wide-spread procedure in every animal breeding sector. The Hungarian pig breeding sector was no exception and after an extremely long transition period (more than 10 years) the BLUP procedure became official in 2009 (MGSZH, 2009). Since then the genetic merit of the Hungarian pig populations are obtained by means of BLUP evaluations that are based on the various performance test data (field and station tests). Generally the BLUP procedure was developed for purebred animals. An overview about the application of BLUP in the various breeding programs and about the various BLUP models was given by Komlósi (1999) and Szőke and Komlósi (2000). However applying crossing is one of the main characteristics of the pig breeding sector. In order to evaluate crossbreds one possibility is to use pooled datasets and pedigrees of all genotypes participating in a given cross. Although the genetic parameters of the Hungarian purebred pig populations were reported by several studies (Csató et al., 2002; Csató et al., 2004; Farkas, 2008; Nagy et al., 2009) no relevant literature is available about the genetic parameters of crossbreds or about the estimated genotype effects describing the efficiency of the different crosses. These were the objectives of this study. MATERIALS AND METHODS


INTRODUCTION
During the last two decades the BLUP breeding value estimation became a wide-spread procedure in every animal breeding sector.The Hungarian pig breeding sector was no exception and after an extremely long transition period (more than 10 years) the BLUP procedure became official in 2009 (MGSZH, 2009).Since then the genetic merit of the Hungarian pig populations are obtained by means of BLUP evaluations that are based on the various performance test data (field and station tests).Generally the BLUP procedure was developed for purebred animals.An overview about the application of BLUP in the various breeding programs and about the various BLUP models was given by Komlósi (1999) and Szőke and Komlósi (2000).However applying crossing is one of the main characteristics of the pig breeding sector.In order to evaluate crossbreds one possibility is to use pooled datasets and pedigrees of all genotypes participating in a given cross.Although the genetic parameters of the Hungarian purebred pig populations were reported by several studies (Csató et al., 2002;Csató et al., 2004;Farkas, 2008;Nagy et al., 2009) no relevant literature is available about the genetic parameters of crossbreds or about the estimated genotype effects describing the efficiency of the different crosses.These were the objectives of this study.

MATERIALS AND METHODS
Analyses were based on the field test data of Pietrain (Pi, 5717), Duroc (Du, 4868), Hampshire (Ha, 1157) pigs and their crosses (Pi × Ha,8210,Pi × Du,4728).Data was collected by the Agricultural Agency of Administration between 1998 and 2010 from 68 herds.Total number of animals in the pedigree files were 60926 (Pi, Du, Pi × Du) and 42004 (Pi, Ha, Pi × Ha), respectively.In the field test ultrasonic (SONOMARK 100) fat depth measurements were taken from boars and gilts between 80 and 110 kg between the 3 rd and 4th lumbar vertebrae (8 cm laterally from the spinal cord), between the 3 rd and 4 th ribs (6 cm laterally from the spinal cord) and the loin muscle area between the 3 rd and 4 th ribs (6 cm laterally from the spinal cord).Using these measurements lean meat percentage (LMP) can be calculated.This trait was used officially in the field test only from 2000 (MGSZH, 2000) but it was collected from 1998.(Age (AGE) and body weight (with an accuracy of 1 kg) of the animals were recorded at the same time from which their average daily gain (ADG) was also calculated.In order to have balanced data structure only those records were used where the animals had measurements for all traits.The regulations of animal housing and feeding conditions are defined in the Hungarian Pig Performance Testing Code (MGSZH, 2009).Descriptive statistics were calculated using SAS 9.1 (SAS Inst.Inc., Cary, NC).Genetic parameters of ADG, AGE and LMP were estimated by the REML method using bivariate animal models applying VCE6 (Groeneveld et al., 2008).The magnitude of the genotype effects were estimated by BLUP (using the PEST software) (Groeneveld, 1990) with the same model mentioned previously.
The structure of the applied animal model was the following: y = Xb + Za + Wc + e y = vector of observations, b = vector of fixed effects, a = vector of random animal effects, c = vector of common litter effect, e = vector of random residual effects, X, Z and W are incidence matrices relating records to fixed, random animal and common litter effects, respectively.
In the model year-month, sex, herd effects were treated as fixed effects, while additive genetic and common litter effects were considered as random effects.

RESULTS AND DISCUSSION
Descriptive statistics of the examined traits are provided in table 1 for each genotype.The Pietrain pigs showed the highest LMP values which finding was in accordance with the literature (Geysen et al., 2000;youssao et al., 2002;Klimas and Klimiené, 2009).On the contrary the ADG and AGE of the Pietrain pigs were lower and higher than that of Hampshire and Duroc pigs.Similar results were reported by Jasek et al. (2006) although they found larger differences between the Hampshire and Duroc pigs to the advantage of the latter breed.Wolf et al. (2006) however, reported lower ADG for Ha compared to Pietrain pigs.The estimated heritabilities of the examined traits were moderately low based on both datasets (Pi, Du, Pi × Du; Pi, Ha Pi × Ha) (table 2).Our results were in agreement with the findings of other studies (Lo et al., 1992;Serbán et al., 2000;Bühler and Postler, 2004;Nagy et al., 2008;Radnóczi et al., 2009).Other authors reported larger heritability estimates (0.40-0.64) for LMP (Knapp et al., 1997;Bühler and Postler 2004;Kanis et al., 2005;Stamer et al., 2007Stamer et al., , 2008) ) or for ADG (0.34-0.39) (Váradi et al., 1997).For ADG Váradi et al. (1997) did not use animal models which can be the reason of the higher estimates.However the high heritability estimates of the above mentioned authors were obtained by means of animal models which may suggest of the possibility of imprecise ultrasound scanning for our dataset.As Kövér et al. (2002) demonstrated the LMP estimation using ultrasound scanning on live animals is relatively imprecise compared to other procedures.The estimated genetic correlation coefficients among the examined traits were negligible (table 3).Using the dataset of the Pi, Ha and Pi × Ha genotypes the estimated genetic correlation coefficient were 0.01 and -0.01 between the ADG and LMP and between the AGE and LMP, respectively.Fort he other dataset (Pi, Du and Pi × Du) these values were -0.07 and 0.04, respectively.Similar genetic correlations were found among these traits for Hungarian Large White and Hungarian Landrace pigs (Nagy et al., 2008).On the contrary a moderate and negative genetic correlation (-0.42) was estimated between the ADG and LMP by Stege et al. (2010).

Estimated genetic correlation coefficients among the examined traits (standard errors are given in brackets)
Source: own edition Based on the (BLUP) estimates of the genotype effects it could be concluded that the LMP performances of the crossed genotypes practically did not exceed that of the parental breeds.This finding was however not surprising taking into account the exceptional LMP performance of the Pietrain pigs.Justifying our results Wolf et al. (2006) reported negative heterosis for LMP examining the same genotypes as in this study.AGE and ADG are equivalent traits showing opposite tendencies in numerical values.The heterosis estimates were substantial for AGE (table 4).

CONCLUSIONS
Based on the results it can be concluded that crossing was relatively inefficient for LMP.On the contrary the magnitudes of the observed heterosis were not negligible for AGE and ADG.The examined traits were affected most substantially by the herd effects suggesting that there are large technological differences.The relatively low LMP heritabilities may suggest an imprecise ultrasound scanning.

Table 2 . Heritability estimates of the examined traits (standard errors are given in brackets)
examined the Duroc, yorkshire, Landrace and Spotted breeds together with their crosses and observed 10.5% and 7.5% heterosis for ADG and AGE, respectively.Lower heterosis values