J. Estany

Estrogen receptor polymorphism in Landrace pigs and its association with litter size performance

Polymorphism at the estrogen receptor locus (ESR) and its association with reproductive performance in Landrace pig is reported. A total of 124 sows from a control line, and 163 sows from a line selected for litter size were genotyped. The traits studied were number born alive (NBA) and total number born (TNB). Prolificacy in first, second and third or later parities were considered as three different traits. A mixed model considering the ESR genotype as a fixed effect and polygenic background as a random effect, was carried out using Bayesian inference, implemented via the Gibbs sampling procedure. Two alternative statistical models, with and without ESR genotype by line interaction, were considered. Association of an additive ESR effect with NBA and TNB was not detected. Moreover, in third and further parities, a line by ESR genotype interaction was observed for both NBA and TNB. For third and further parities, allele B was associated with increasing litter size in selected animals, whereas the opposite was observed in control animals. These results suggest that a background genotype by ESR interaction exists, although a spurious association due to sampling or the possibility of different linkage phases between the ESR polymorphism and a putative QTL close by cannot be ruled out.

Estimates of genetic parameters for litter size at different parities in pigs

Abstract Different genetic models for litter size in pigs were compared. (Co)variance components at different parities were estimated by REML in two Landrace populations. Maternal genetic effects were also assessed. Data consisted of 34417 and 16750 litters records collected on each population. Different analyses for the number of pigs born in total and alive using an animal model were performed: univariate analyses with direct and maternal genetic effects (using a repeatability animal model when more than one parity was involved) and series of bivariate and multivariate analyses with each of first five parities treated as a different trait (without maternal genetic effects). The estimates of direct heritability obtained by a repeatability animal model ranged from 0.05 to 0.07. Maternal genetic effects were not significant in any populations, neither in the first parity nor in all parities. The estimates of direct heritability in each of the first five parities using series of bivariate or multivariate analyses were not different from each other within population. Nor were these estimates different from the heritability estimates obtained by a repeatability model. Estimates of genetic correlations between parities were not significantly different from unity, except for the estimate between the first and the third parity in one population ( r g = 0.5). These results confirmed the adequacy of a simple repeatability model without maternal effects in the selection for litter size in the populations analysed.

Expected genetic response for oleic acid content in pork

Intramuscular fat (IMF) and oleic acid (C18:1) content in pork are important issues for the pig industry and consumers. Data from a purebred Duroc line were used to i) estimate the genetic parameters of IMF and C18:1 and their genetic correlations with lean growth components, and ii) evaluate the opportunities for genetically improving C18:1 in IMF. The data set used for estimating genetic parameters consisted of 93,920 pigs, from which 85,194 had at least 1 record for BW or backfat thickness (BT) at 180 d and 943 for IMF and C18:1 at 205 d. Intramuscular fat content and C18:1, expressed as percentage of total fatty acids, were determined in the gluteus medius muscle by gas chromatography. Genetic parameters for C18:1 were estimated under a Bayesian 4-trait multivariate animal mixed model. Heritability of C18:1 was 0.50, with a probability of 95% of being greater than 0.37. Genetic correlations of C18:1 with BW, BT, and IMF were 0.11, 0.22, and 0.47, respectively (with a probability of 95% of being greater than -0.07, 0.04, and 0.27, respectively). Genetic responses were evaluated by deterministic simulation using a half-sib recording scheme for C18:1 and the previously estimated parameters. The C18:1 content is expected to exhibit only minor changes in selection programs directed at growth rate but to decrease in those focusing on lean content. Maximum expected response in C18:1 at no lean growth loss (i.e., at no change in BW and BT) was 0.44%, with a resulting correlated response in IMF of 0.15%. However, because lean growth is emphasized in the breeding goal, the resulting response scenarios are more constrained. We concluded that there is evidence to support the idea that C18:1 in IMF is genetically determined and defined selection strategies can lead to response scenarios in which C18:1, IMF, BT, and BW can be simultaneously improved. However, if adopted, the potential for lean growth would be reduced. The extent to which it is affordable relies on how much consumers are prepared to pay for high-C18:1 pork products.

Genetic correlations of intramuscular fat content and fatty acid composition among muscles and with subcutaneous fat in Duroc pigs.

There is an increasing interest in including intramuscular fat (IMF) content and fatty acid composition, particularly oleic acid (C18:1) content, in the selection objectives of pig lines for quality pork markets. These traits are costly and can be measured in more than 1 location, so knowing their correlation structure across muscles and with subcutaneous fat (SF) is necessary for developing optimum sampling and recording schemes. We analyzed the genetic and phenotypic correlations of IMF content and composition among 3 of the most relevant muscles (LM, gluteus medius muscle [GM], and semimembranosus muscle [SM]) and with the fatty acid composition of SF. All genetic correlations were positive but variable. For IMF, the genetic correlation between GM and LM was 0.68, and for fatty acids, the genetic correlation ranged from 0.62 for C18:1 to 0.82 for total PUFA. Genetic correlations of GM and LM with SM were much lower: 0.13 to 0.19 for IMF and 0.10 to 0.54 for fatty acids. Correlations for fatty acid composition in SF with GM and LM were moderate to high (0.29-0.53 and 0.43-0.75, respectively) but were null with SM. The expected responses for IMF in the 3 muscles and for C18:1 in each muscle and in SF to selection on records taken from only a single muscle or SF were estimated. Selection for IMF and C18:1 in GM is expected to lead to positive responses in IMF and C18:1 in LM and vice versa, although this can entail genetic lags of 20 to 45% in the muscle not directly selected for. Selection for C18:1 in SF is more effective for C18:1 in LM than in GM and of very limited value for IMF. In conclusion, the genetic correlations of IMF content and fatty acid composition among muscles and with SF, although positive, are variable enough to influence the genetic evaluation scheme for IMF and fat quality. They also indicate that GM and LM can be used alternatively for selection purposes.

Response to selection for decreased backfat thickness at restrained intramuscular fat content in Duroc pigs

Intramuscular fat (IMF) content is a relevant trait for the pig industry and consumers. However, selection for IMF has the undesired correlated effect of decreasing lean growth. A selection experiment was performed to investigate the effects of selection against backfat thickness (BT) at restrained IMF. Barrows from a purebred Duroc line were allocated into a selected (n = 165) or a control (n = 185) group based on their litter predicted EBV. Litters in the selected group were selected against BT at 180 d at restrained IMF in gluteus medius (GM) whereas those in the control group were chosen randomly. Realized selection intensities and genetic responses for BT, IMF in GM, and BW were estimated using a 3-trait multivariate animal mixed model under a Bayesian setting. Correlated responses for other traits were estimated similarly but using a 4-trait model, where other traits were added to the previous 3-trait model 1 at a time. Selected pigs had less BT than control pigs [-1.22 mm, with highest posterior density interval at 95% (HPD95; -2.47, -0.75)] with restrained decrease in IMF, both in GM [-0.16%; HPD95 (-0.36, +0.05)] and in LM [-0.15%; HPD95 (-0.37, +0.09)]. However, the realized selection intensity for IMF in GM denotes that the restriction on IMF was incomplete [-0.18; HPD95 (-0.36, +0.02)]. Selection decreased BW [-1.64 kg; HPD95 (-2.47, -0.75)] but increased carcass lean weight [+0.66 kg; HPD95 (+0.14, +1.22)], indicating that the response in BT offsets the unfavorable correlated response in BW. Selected pigs were shorter [-0.50 cm; HPD95 (-0.81, -0.20)] but with similar ham weight and loin depth. These results provide evidence that lean weight can be improved restraining the genetic change in IMF. However, they also stress that a complete restriction on IMF is difficult to achieve unless selection is practiced on a big population where IMF is accurately predicted.

Fast determination of oleic acid in pork by flow injection analysis/mass spectrometry

In some Mediterranean products such as olive oil or ham, oleic acid is the most abundant component of the total fat. Due to the large volume of trade in these products, it may be necessary to analyze oleic fatty acids in high numbers of samples in short periods of time. However, using classic lipid analysis techniques, it is not always possible to cope with these high demands. To solve this problem, a high-throughput analytical method for oleic fatty acid quantification in pork is presented. The purpose of the method is to avoid liquid chromatography processes using a flow injection analysis (FIA) system based on electrospray ionization mass spectrometry. The use of pentadecanoic fatty acid as an internal standard overcame matrix effects. The oleic FIA technique could be used as a suitable method for discriminating carcass samples for selection and labeling by oleic acid content when large numbers of pork samples must be processed in a short period of time.