Genomics of response to PRRSV in purebred and crossbred sows: antibody response and performance following natural infection versus vaccination

Abstract Antibody response, measured as sample-to-positive (S/P) ratio, to Porcine Reproductive and Respiratory Syndrome virus (PRRSV) following a PRRSV-outbreak (S/POutbreak) in a purebred nucleus and following a PRRSV-vaccination (S/PVx) in commercial crossbred herds have been proposed as genetic indicator traits for improved reproductive performance in PRRSV-infected purebred and PRRSV-vaccinated crossbred sows, respectively. In this study, we investigated the genetic relationships of S/POutbreak and S/PVx with performance at the commercial (vaccinated crossbred sows) and nucleus level (non-infected and PRRSV-infected purebred sows), respectively, and tested the effect of previously identified SNP for these indicator traits. Antibody response was measured on 541 Landrace sows approximately 54 days after the start of a PRRSV outbreak, and on 906 F1 (Landrace x Large White) gilts approximately 50 days after vaccination with a commercial PRRSV vaccine. Reproductive performance was recorded for 711 and 428 Landrace sows before and during the PRRSV outbreak, respectively, and for 811 vaccinated F1 animals. The estimate of the genetic correlation (rg) of S/POutbreak with S/PVx was 0.72±0.18. The estimates of rg of S/POutbreak with reproductive performance in vaccinated crossbred sows were low to moderate, ranging from 0.05±0.23 to 0.30±0.20. The estimate of rg of S/PVx with reproductive performance in non-infected purebred sows was moderate and favorable with number born alive (0.50±0.23) but low (0±0.23 to -0.11±0.23) with piglet mortality traits. The estimates of rg of S/PVx were moderate and negative (-0.38±0.21) with number of mummies in PRRSV-infected purebred sows and low with other traits (-0.30±0.18 to 0.05±0.18). Several significant associations (P0 > 0.90) of previously reported SNP for S/P ratio (ASGA0032063 and H3GA0020505) were identified for S/P ratio and performance in non-infected purebred and PRRSV-exposed purebred and crossbred sows. Genomic regions harboring the major histocompatibility complex class II region significantly contributed to the genetic correlation of antibody response to PRRSV with most of the traits analyzed. These results indicate that selection for antibody response in purebred sows following a PRRSV outbreak in the nucleus and for antibody response to PRRSV vaccination measured in commercial crossbred sows are expected to increase litter size in purebred and commercial sows.

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129 Genomic Relationship Between PRRSV Wild-type Infection and PRRSV Vaccination for Antibody Response and Reproductive Performance

Journal of Animal Science ◽

10.1093/jas/skab054.032 ◽

2021 ◽

Vol 99 (Supplement_1) ◽

pp. 18-18

Author(s):

Leticia P Sanglard ◽

Felipe Hickmann ◽

Yijian Huang ◽

Kent A Gray ◽

Daniel Linhares ◽

...

Keyword(s):

Antibody Response ◽

Reproductive Performance ◽

Genetic Correlations ◽

Clinical Signs ◽

Respiratory Syndrome Virus ◽

Wild Type ◽

Large White ◽

Selection For ◽

Indicator Trait ◽

Type Infection

Abstract Immunoglobulin G antibody response, measured as sample-to-positive (S/P) ratio, to Porcine Reproductive and Respiratory Syndrome virus (PRRSV) has been proposed as an indicator trait for improved reproductive performance in PRRSV-infected purebred sows and PRRSV-vaccinated crossbred gilts. In this study, we investigated the genetic correlations (rg) of S/P ratio following a PRRSV outbreak and PRRSV-vaccination with performance in non-exposed and PRRSV-exposed sows. PRRSV outbreak phase was defined based on previously described methodologies after the detection of typical clinical signs of PRRSV infection. 541 Landrace sows had S/P ratio measured at ~54 days after the beginning of the PRRSV outbreak (S/Poutbreak), and 906 Landrace x Large White naïve F1 gilts had S/P ratio measured at ~50 days after vaccination with a commercial modified live PRRSV vaccine (S/PVx). 711 and 428 Landrace sows had reproductive performance recorded before and during the PRRSV outbreak, respectively. 811 vaccinated F1 animals had farrowing performance for up to 3 parities. All animals were genotyped for ~28K SNPs. The estimate of rg of S/Poutbreakwith S/PVx was high (rg±SE = 0.72±0.18). Estimates of rg of S/Poutbreak with reproductive performance in F1 sows were low to moderate, ranging from 0.05±0.23 (number stillborn) to 0.30±0.20 (total number born). Estimates of rg of S/PVxwith reproductive performance in non-infected purebred sows were moderate and favorable with number born alive (0.50±0.23), but low (0 to -0.11±0.23) with litter mortality traits. Estimates of rg of S/PVx were moderate and negative (-0.47±0.18) with the number of mummies in PRRSV-infected purebred sows and low with other traits (-0.29±0.18 for total number born to 0.05±0.18 for number stillborn). These results indicate that selection for antibody response following a PRRSV outbreak collected in purebred sows and to PRRSV vaccination collected in commercial crossbred gilts may increase litter size of non-infected and PRRSV-exposed purebred and commercial crossbred sows.

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40 Novel Genomic Regions Associated with Igg Antibody Response to PRRSV Vaccination Revealed by Haplotype-based GWAS

Journal of Animal Science ◽

10.1093/jas/skab054.055 ◽

2021 ◽

Vol 99 (Supplement_1) ◽

pp. 31-32

Author(s):

Leticia P Sanglard ◽

Yijian Huang ◽

Kent A Gray ◽

Daniel Linhares ◽

Jack C Dekkers ◽

...

Keyword(s):

Antibody Response ◽

Candidate Genes ◽

Genetic Variance ◽

Genome Wide Association Study ◽

Chromosome 7 ◽

Respiratory Syndrome Virus ◽

Igg Antibody ◽

Large White ◽

Genomic Study ◽

Genomic Regions

Abstract Previous studies on genomics of antibody response, measured as sample-to-positive (S/P) ratio, to Porcine Reproductive and Respiratory Syndrome virus (PRRSV) have reported a major quantitative trait locus (QTL) on the major histocompatibility complex (MHC) on chromosome 7, explaining ~25% of the genetic variance of this trait. S/P ratio following modified live PRRSV vaccination in crossbred commercial gilts has been proposed as genetic indicator for reproductive performance in non-infected purebred sows and PRRSV-vaccinated crossbred sows. This motivated further genomic study for this trait by performing haplotype-based genome-wide association study (GWAS). 906 naïve F1 (Landrace x Large White) had blood samples taken at ~50d after vaccination for measuring PRRSV ELISA S/P ratio and genotyping. Haplotype-based GWAS identified 8 genomic regions on chromosomes 4 (108 Mb), 7 (15, 21, and 24–27 Mb), and 9 (33 Mb) that were associated (q-value < 0.07) with S/P ratio. From those, only the MHC region (chromosome 7; 24 – 26 Mb) had been identified in the SNP based GWAS. The main SNP identified in the SNP based GWAS (H3GA0020505) was not in LD with the haplotype; thus, we added this SNP to the haplotype model. We observed that the haplotype explained more of the genetic variance compared to the H3GA0020505 SNP, indicating that the MHC haplotype is in stronger LD with the QTL than the H3GA0020505 SNP. All the significant regions associated with S/P ratio included immune-related candidate genes, such as SLA-DOB, TAP2, TAPBP, TMIGD3, and ADORA. This study validated the QTL identified on the MHC region, narrowing the search for causal genes in this region, and identified new genomic regions, along with candidate genes associated with S/P ratio. Identifying novel genomic regions provides more resources for marker-assisted selection and genomic prediction of S/P ratio in purebred and commercial pig populations.

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ESTIMATES OF GENETIC CORRELATIONS AMONG CERTAIN CARCASS AND PERFORMANCE TRAITS IN SWINE

Canadian Journal of Animal Science ◽

10.4141/cjas68-001 ◽

1968 ◽

Vol 48 (1) ◽

pp. 1-6 ◽

Cited By ~ 5

Author(s):

G. L. Roy ◽

W. J. Boylan ◽

M. E. Seale

Keyword(s):

Birth Weight ◽

Genetic Correlation ◽

Genetic Relationships ◽

Carcass Traits ◽

Genetic Correlations ◽

Development Project ◽

Carcass Trait ◽

Selection For ◽

And Performance ◽

Daily Gain

Data from a swine breed development project provided estimates of the genetic correlation among six performance and carcass traits. The data from the new breed, called Managra, were obtained over a 7-year period. Most genetic relationships examined were such that selection for improvement of one trait would yield a favorable improvement in another. Both carcass backfat and live backfat probe were found to be negatively correlated with area of loin eye and length of carcass. A positive genetic correlation was found between post-weaning daily gain and loin eye area. A high positive genetic correlation was found between birth weight and loin eye area. An unfavorable association involved a positive genetic correlation between birth weight and backfat.Correction factors for effect of carcass weight on the magnitude of carcass trait measurements and differences in means between sexes were obtained.Heritability of the traits was estimated by paternal half-sib correlation. The estimates for carcass traits were moderately high and agree well with most other estimates reported in the literature.

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Further host-genomic characterization of total antibody response to PRRSV vaccination and its relationship with reproductive performance in commercial sows: genome-wide haplotype and zygosity analyses

Genetics Selection Evolution ◽

10.1186/s12711-021-00676-5 ◽

2021 ◽

Vol 53 (1) ◽

Author(s):

Leticia P. Sanglard ◽

Yijian Huang ◽

Kent A. Gray ◽

Daniel C. L. Linhares ◽

Jack C. M. Dekkers ◽

...

Keyword(s):

Antibody Response ◽

Reproductive Performance ◽

Genome Wide Association Study ◽

Reproductive Traits ◽

Chromosome 7 ◽

Potential Candidate ◽

Genome Wide ◽

Causal Genes ◽

Immune Related Genes ◽

Genomic Regions

Abstract Background The possibility of using antibody response (S/P ratio) to PRRSV vaccination measured in crossbred commercial gilts as a genetic indicator for reproductive performance in vaccinated crossbred sows has motivated further studies of the genomic basis of this trait. In this study, we investigated the association of haplotypes and runs of homozygosity (ROH) and heterozygosity (ROHet) with S/P ratio and their impact on reproductive performance. Results There was no association (P-value ≥ 0.18) of S/P ratio with the percentage of ROH or ROHet, or with the percentage of heterozygosity across the whole genome or in the major histocompatibility complex (MHC) region. However, specific ROH and ROHet regions were significantly associated (P-value ≤ 0.01) with S/P ratio on chromosomes 1, 4, 5, 7, 10, 11, 13, and 17 but not (P-value ≥ 0.10) with reproductive performance. With the haplotype-based genome-wide association study (GWAS), additional genomic regions associated with S/P ratio were identified on chromosomes 4, 7, and 9. These regions harbor immune-related genes, such as SLA-DOB, TAP2, TAPBP, TMIGD3, and ADORA. Four haplotypes at the identified region on chromosome 7 were also associated with multiple reproductive traits. A haplotype significantly associated with S/P ratio that is located in the MHC region may be in stronger linkage disequilibrium (LD) with the quantitative trait loci (QTL) than the previously identified single nucleotide polymorphism (SNP) (H3GA0020505) given the larger estimate of genetic variance explained by the haplotype than by the SNP. Conclusions Specific ROH and ROHet regions were significantly associated with S/P ratio. The haplotype-based GWAS identified novel QTL for S/P ratio on chromosomes 4, 7, and 9 and confirmed the presence of at least one QTL in the MHC region. The chromosome 7 region was also associated with reproductive performance. These results narrow the search for causal genes in this region and suggest SLA-DOB and TAP2 as potential candidate genes associated with S/P ratio on chromosome 7. These results provide additional opportunities for marker-assisted selection and genomic selection for S/P ratio as genetic indicator for litter size in commercial pig populations.

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Resilience Effects of SGK1 and TAP1 DNA Markers during PRRSV Outbreaks in Reproductive Sows

Animals ◽

10.3390/ani10050902 ◽

2020 ◽

Vol 10 (5) ◽

pp. 902

Author(s):

Marina Laplana ◽

Joan Estany ◽

Lorenzo José Fraile ◽

Ramona Natacha Pena

Keyword(s):

Candidate Genes ◽

Reproductive Performance ◽

Dna Markers ◽

Health Problems ◽

Respiratory Syndrome Virus ◽

Large White ◽

Genome Wide ◽

Stable Performance ◽

Potential Use

The porcine reproductive and respiratory syndrome virus (PRRSV) is a major infectious stressor that causes serious health problems and productivity drops. Based on previous genome-wide analyses, we selected SGK1 and TAP1 as candidate genes for resilience, and genotyped three mutations, including a 3′UTR variant SGK1_rs338508371 and two synonymous variants TAP1_rs1109026889 and TAP1_rs80928141 in 305 Landrace × Large White sows. All polymorphisms affected the reproductive performance in the outbreak, but not during the endemic phase, thereby indicating a potential use of these markers for resilience. Moreover, some genotypes were associated with a stable performance across PRRSV phases. Thus, in the outbreak, the SGK1_rs338508371 AA sows had less piglets born alive (p < 0.0001) and more stillborns (p < 0.05) while other sows were able to keep their productivity. During the outbreak, TAP1_rs80928141 GG sows had less piglets born alive (p < 0.05) and both TAP1 polymorphisms influenced the number of mummies in an additive manner (p < 0.05). Remarkably, TAP1_rs80928141 AA sows had around one mummy more than GG sows (p < 0.01). Resilience to PRRSV could be improved by including the SGK1 and TAP1 markers in crossbreeding and/or selection schemes, as they contribute to maintaining a stable number of piglets born alive and lost, particularly mummies, despite the outbreak.

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Genetics of leg weakness in performance-tested boars

Animal Science ◽

10.1017/s0003356100040010 ◽

1983 ◽

Vol 36 (1) ◽

pp. 117-130 ◽

Cited By ~ 23

Author(s):

A. J. Webb ◽

W. S. Russell ◽

D. I. Sales

Keyword(s):

Performance Index ◽

Genetic Relationships ◽

Genetic Correlations ◽

Live Weight ◽

Rapid Decline ◽

Large White ◽

Muscle Area ◽

Eye Muscle ◽

Leg Weakness ◽

And Performance

ABSTRACTGenetic relationships among leg and performance traits were estimated for 23 975 Large White and Landrace boars fed twice daily to appetite from 27 to 91 kg live weight at Meat and Livestock Commission testing stations between 1966 and 1972. For each boar, an overall leg score was derived as the sum of scores for 19 individual leg traits categorized as ‘absent’ (0), ‘slight’ (1) or ‘severe’ (2) at 91 kg. Heritabilities of leg score were 017 ± 0·03 in Large White and 0·19 ± 0·04 in Landrace. Genetic correlations with a visual ‘leg action’ score on a scale from 1 to 5 averaged 0·93 ± 0·02 over breeds. Genetic and phenotypic correlations between leg scores on the same boars at 27 and 91 kg averaged 0·50 ± 0·17 and 0·15 ± 0·01 respectively.Both breeds showed significant adverse genetic correlations ranging from 0·20 ± 0·10 to 0·40 ± 0·08 between leg score and boar ultrasonic backfat. From slaughtered littermates, leg scores showed favourable genetic correlations with eye-muscle area (0·30 ± 0·10) and killing-out proportion (0·35 ± 011) in Large White and unfavourable correlations with carcass length (0·31 ± 0·10), lean content (0·30 ± 0·14) and backfat (0·33 ± 0·11) in Landrace. There were no associations with growth rate, feed efficiency or the performance index on which boars are selected. The study indicates that leg condition and fatness are adversely genetically related, but that selection on the present national performance index would not be expected to cause a rapid decline in leg condition. Culling on leg score would be expected to reduce the frequency of leg weakness.

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Effects of dietary arginine supplementation on reproductive performance and immunity of sows

Czech Journal of Animal Science ◽

10.17221/6711-cjas ◽

2013 ◽

Vol 58 (No. 4) ◽

pp. 167-175 ◽

Cited By ~ 15

Author(s):

L. Che ◽

P. Yang ◽

Z. Fang ◽

Y. Lin ◽

D. Wu

Keyword(s):

Immune Response ◽

Fetal Growth ◽

Reproductive Performance ◽

Control Diet ◽

Late Gestation ◽

Respiratory Syndrome Virus ◽

Control Group ◽

Placental Development ◽

Large White ◽

Immunological Parameters

Arginine (Arg) is considered to have beneficial effects on placental development and function, as well as reproductive performance. The well-developed placenta is highly required in late gestation for rapid fetal growth, however, it is unknown if there is a crucial role of Arg in late gestation. Likewise, the immunological response of sows to Arg needs to be determined. Therefore, this study is designed to investigate the effects of dietary Arg supplementation on reproductive performance and immunity of sows. At day 30 of gestation, sixty sows (Landrace × Large White) were allocated to 3 groups receiving corn and soybean-based control diet (control group, n = 20), control diet supplemented with 1% l-arginine HCl until day 90 of gestation (Arg90 group, n = 20), and control diet supplemented with 1% l-arginine HCl until day 114 of gestation (Arg114 group, n = 20), respectively. Litter performance was recorded at parturition. Blood samples (n = 6) collected at days 30, 90, and 110 of gestation were measured for metabolic and immunological parameters. At parturition, total litter size was not affected by dietary Arg supplementation. As a result of less pigs born dead, however, sows in Arg114 group had more pigs born alive than sows in control group (+1.6 pigs, P < 0.05), total and live litter weights were increased (+1.6~2.1 kg, P < 0.05) in Arg114 group relative to both control and Arg90 groups. Compared with control group, dietary Arg supplementation increased (+12~110%, P < 0.05) plasma levels of ornithine, proline, and arginine at either day 90 (Arg90 and Arg110 groups) or day 110 of gestation (Arg110 group). Moreover, immune response was enhanced in Arg-supplemented sows, as indicated by the increased levels of serum immunoglobulin and porcine reproductive and respiratory syndrome virus (PRRSV) antibody. These findings indicate dietary Arg supplementation can improve litter performance and immune response, and the beneficial effect of Arg on fetal growth is evident in late gestation.

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Genetic relationships of reproduction with growth and with carcass traits in British pigs

Animal Science ◽

10.1017/s000335610003498x ◽

1975 ◽

Vol 20 (1) ◽

pp. 31-44 ◽

Cited By ~ 18

Author(s):

C. A. Morris

Keyword(s):

Reproductive Performance ◽

Genetic Relationships ◽

Selection Index ◽

Carcass Traits ◽

Genetic Correlations ◽

Progeny Testing ◽

Large White ◽

Young Females ◽

Combining Data ◽

The Matrix

SUMMARYData werfe analysed of litters from Large White and Landrace herds which were tested at central stations in Great Britain for growth and carcass traits. Information on reproductive performance of young females was combined with data on their relatives at central stations in order to calculate genetic relationships of reproduction with growth and with carcass traits. Progeny testing of boars for both sets of traits was the most efficient of the methods considered for this analysis.In general, the estimated genetic correlations of reproductive performance with growth and with carcass traits were alike in sign for the two breeds, and the signs of the matrix of values were internally consistent. For example, combining data for litter sizes in the Large White breed, genetic correlations were −0·15 (food conversion ratio), 0·06 (daily gain), −0·18 (average backfat depth), −0·63 (killing-out percentage) and −0·41 (hind quarter percentage). When the growth and carcass traits were combined as total points score in a selection index, the genetic correlation between this score and reproductive performance was very small, with a range from −0·04 to 0·02. Calculations showed that inclusion of reproductive performance in the index would increase the rate of genetic improvement by only 0·55%.

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27 Genomic relationship between antibody response to porcine reproductive and respiratory syndrome virus vaccination and reproductive performance in commercial sows

Journal of Animal Science ◽

10.1093/jas/skaa278.038 ◽

2020 ◽

Vol 98 (Supplement_4) ◽

pp. 20-21

Author(s):

Leticia P Sanglard ◽

Rohan Fernando ◽

Kent A Gray ◽

Daniel C Linhares ◽

Jack C Dekkers ◽

...

Keyword(s):

Antibody Response ◽

Reproductive Performance ◽

Association Studies ◽

Genetic Correlations ◽

Reproductive Traits ◽

Respiratory Syndrome Virus ◽

Genome Wide Association Studies ◽

Prrs Virus ◽

Positive Ratio ◽

Commercial Farms

Abstract Antibody response, measured as sample-to-positive ratio (S/P), to porcine reproductive and respiratory syndrome (PRRS) after PRRS outbreaks has been proposed as an indicator trait to improve reproductive performance in PRRS-infected sows. However, waiting for a PRRS outbreak to occur and having different relationships in healthy pigs may limit the use of this trait. Thus, we proposed to investigate if this relationship also occurs between S/P to PRRS vaccination and reproductive performance in sows without exposure to PRRS. Nine hundred six F1 replacement gilts (139□17 days old) from two commercial farms were vaccinated with a commercial modified live PRRS virus vaccine. Blood samples were collected at 52 days after vaccination to measure S/P to PRRS and SNP genotyping. Reproductive performance included: number born alive (NBA), number of piglets weaned, number born mummified (MUM), number stillborn (NSB), and pre-weaning mortality (PWM) at parities (P) 1 to 3. Average performance was calculated for each trait per sow per year (PSY). Farrowing rate and age at first service were also analyzed. BayesC0 was used to estimate genetic correlations between S/P and reproductive performance. Bivariate genome-wide association studies of antibody response and reproductive traits were performed using BayesB. High genetic correlations between S/P and farrowing performance were identified for NBA_P1 (0.61±0.16), PWM_P2 (-0.64±0.15), PWM_P2 (-0.63±0.20), NSB_P3 (-0.84±0.05), MUM_P3 (-0.83±0.11), and NSB_PSY (-0.90±0.05). A QTL was identified on chromosome 7 (MHC region) for these reproductive traits and for S/P, explaining from 1.2% (PWM_P2) to 22.4% (S/P) of the genetic variance. SNP H3GA0020505 explained most of the variance in this region for these traits. Heterozygote animals for this SNP had overall better performance: greater S/P (P = 0.001), greater (P = 0.06) NBA_P1, and lesser (P = 0.06) MUM_P3 than other genotypes. These results suggest that antibody response to PRRS vaccination may be used as a genetic indicator to improve reproductive performance in commercial pigs.

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127 Antibody Response as an Indicator Trait for Improved Reproductive Performance During a PRRSV Outbreak: Genetic Correlations of S/P Ratio with Reproductive Traits in Landrace and Duroc Sows

Journal of Animal Science ◽

10.1093/jas/skab054.034 ◽

2021 ◽

Vol 99 (Supplement_1) ◽

pp. 19-20

Author(s):

Felipe Hickmann ◽

José Braccini Neto ◽

Luke M Kramer ◽

Kent A Gray ◽

Yijian Huang ◽

...

Keyword(s):

Antibody Response ◽

Reproductive Performance ◽

Genetic Correlations ◽

Reproductive Traits ◽

Respiratory Syndrome Virus ◽

Potential Indicator ◽

Host Genetic ◽

Heritability Estimates ◽

Terminal Sire ◽

Indicator Trait

Abstract Previous studies proposed the use of antibody response to Porcine Reproductive and Respiratory Syndrome virus (PRRSV), measured as sample-to-positive (S/P) ratio, as a potential indicator trait to improve the reproductive performance of PRRSV-infected Landrace sows. However, this indicator trait has not yet been validated in Landrace sows or evaluated in a terminal sire line, such as Duroc. The main objective of this work was to perform host-genetic analyses of S/P ratio and reproductive traits during a PRRSV outbreak in maternal and terminal breeds. The data consisted of 690 Duroc and 541 Landrace multiparous sows (1.9±1.2 and 2.3±1.5, respectively) with S/P ratio collected at approximately 54 days after the predicted beginning of the outbreak. Of these, 644 Duroc and 528 Landrace sows also had reproductive data recorded during the PRRSV outbreak comprising number of piglets born alive (NBA), stillborn piglets (NSB), mummified piglets (NBM), number born dead (NBD; sum of NSB and NBM), total number born (TNB; sum of NBA and NBD), and number weaned (NW). All animals had genotype data on ~30K SNPs common across both breeds. Heritability estimates (± standard error) of S/P ratio during the PRRSV outbreak were moderate, with 0.33±0.06 for Duroc and 0.28±0.07 for Landrace. Reproductive traits during the PRRSV outbreak had overall low heritability estimates (≤0.18). Favorable genetic correlations of S/P ratio with NBA (0.65±0.33), in accordance with previous studies, and NBD (-0.33±0.28) were observed for Landrace sows only. Estimates of genetic correlation with other traits were -0.21±0.30 (NBM), -0.12±0.29 (NSB), 0.10±0.38 (NW), and 0.54±1.29 (TNB) for Landrace. For Duroc, these estimates were weaker: -0.33±0.40 (NBA), 0.26±0.27 (NBA), and 0.28±0.30 (NW), with convergence issues for mortality traits. These results further support the use of S/P ratio as an indicator trait for improved reproductive performance during a PRRSV outbreak in Landrace sows.

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