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Impact of porcine epidemic diarrhea virus infection at different periods of pregnancy on subsequent reproductive performance in gilts and sows

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					                                                     Animal Reproduction Science 122 (2010) 42–51



                                                     Contents lists available at ScienceDirect


                                              Animal Reproduction Science
                                       journal homepage: www.elsevier.com/locate/anireprosci




Impact of porcine epidemic diarrhea virus infection at different
periods of pregnancy on subsequent reproductive performance in gilts
and sows
Em-on Olanratmanee, Annop Kunavongkrit, Padet Tummaruk ∗
Department of Obstetrics, Gynaecology and Reproduction, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand




a r t i c l e        i n f o                        a b s t r a c t

Article history:                                    Reproductive performance of gilts and sows in a swine commercial herd following an out-
Received 22 January 2010                            break of porcine epidemic diarrhea virus (PEDV) were investigated. A PEDV outbreak was
Received in revised form 15 May 2010
                                                    observed in March 2008 in a swine herd in Thailand. The disease was diagnosed by clinical
Accepted 20 July 2010
                                                    symptoms, gross and histopathology and viral detection using reverse transcriptase-
Available online 27 July 2010
                                                    polymerase chain reaction assay. The intestines of the infected piglets were collected,
                                                    minced and fed to all of the gilts and sows within 2 weeks after the onset of the PEDV
Keywords:
                                                    outbreak. Reproductive data were collected during a period from January 2007 to July 2008
Pig
Porcine epidemic diarrhea                           and were retrospectively evaluated. The farrowing rate (FR), return rate (RR), abortion rate
Reproduction                                        (AR), number of total piglets born per litter (TB), number of piglets born alive per litter (BA),
Gestation                                           percentage of stillbirth piglets per litter (SB), percentage of mummified fetus per litter (MM)
                                                    and piglet’s birth weight (BW), before and after the PEDV outbreak were compared. It was
                                                    found that the impact of PEDV infection on the reproductive performance of gilts and sows
                                                    depended on the period of pregnancy when the females were exposed to the pathogen,
                                                    and parity number. The pregnant females infected with PEDV during the first 30 days of
                                                    pregnancy had a 12.6 percentage point decrease of FR (91.1% vs. 78.5%, P = 0.003), a 5.7 per-
                                                    centage point increase of RR (3.5% vs. 9.2%, P = 0.01), a 1.3 percentage point increase of AR
                                                    (2.1% vs. 3.4%, P = 0.01) and a 2.0 percentage point increase of MM (3.5% vs. 5.6%, P < 0.001).
                                                    SB increased in the pregnant females that were infected with PEDV during 91–120 days
                                                    of pregnancy (1.8 percentage points, 4.5% vs. 6.2%, P = 0.01). The impacts of PEDV infection
                                                    on subsequent reproductive performance were more severe in the pregnant gilts than the
                                                    pregnant sows. PEDV infection during the first 30 days of pregnancy resulted in a decrease
                                                    of TB by 1.4 (11.7 vs. 10.3 piglets/litter, P < 0.001) and a decrease of BA by 2.2 (10.7 vs. 8.5
                                                    piglets/litter, P < 0.001) in the gilts’ litters, while the influence of PEDV infection on TB and
                                                    BA was not significant in sows (P > 0.05). It was concluded that natural infection of PEDV in
                                                    the pregnant gilts and sows caused a reduction of subsequent reproductive performance.
                                                                                                              © 2010 Elsevier B.V. All rights reserved.




1. Introduction                                                                  and frequently leads to a high mortality rate in suck-
                                                                                 ling piglets (Dea et al., 1985; Pijpers et al., 1993; Hwang
   Porcine epidemic diarrhea (PED) is a highly conta-                            et al., 1994). PED is caused by the PED virus (PEDV), an
gious disease causing diarrhea in all age groups of pigs                         enveloped and single-strained RNA virus, in the family
                                                                                 Coronaviridae (Pensaert and DeBouck, 1978). Serological
                                                                                 examination of PEDV in swine herds has been reported and
 ∗ Corresponding author. Tel.: +66 2 2189644 5; fax: +66 2 2520738.              the virus has been isolated in most swine-raising coun-
   E-mail address: Padet.T@chula.ac.th (P. Tummaruk).                            tries in Europe, and in Korea, China and Japan (Debouck

0378-4320/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.anireprosci.2010.07.004
                                 E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51                           43


et al., 1982; Takahashi et al., 1983; Qinghua, 1992; Kweon              nant gilts and sows in a commercial swine herd in
et al., 1993). Under field conditions, outbreaks of PEDV                 Thailand.
are frequently observed during winter (Pensaert, 1999).
PEDV is normally transmitted through the ingestion of
                                                                        2. Materials and methods
feed stuff containing contaminated feces (Pensaert, 1999).
PEDV replicates in the cytoplasm of the enterocytes of
                                                                        2.1. Animals and general management
the small intestine (Debouck and Pensaert, 1980; Kim
et al., 1999) and results in a massive destruction of vil-
                                                                            The present study was conducted in a 3000-sow inven-
lous enterocytes, leading to villous atrophy and reduction
                                                                        tory commercial swine herd in the northeastern region of
of the intestinal epithelial surface (Kim and Chae, 2003;
                                                                        Thailand. The majority of the females were crossbred Lan-
Jung et al., 2006). The reduction of the enzymatic and
                                                                        drace × Yorkshire (LY) and some purebred Landrace (L) and
absorptive capacity in the small intestine after PEDV infec-
                                                                        Yorkshire (Y) breeds. The herd produced replacement gilts
tion causes maldigestive and malabsorptive diarrhea (Jung
                                                                        using their own grandparent (GP) stock. Gilts and sows
et al., 2006). The gross lesion of PEDV is characterized
                                                                        were housed in a conventional open-housing system facil-
by a thin wall of small intestine and missing milk vein
                                                                        itated with a water sprinkler and fan. The gilts and sows
(Pospischil et al., 2002). The histological lesions include
                                                                        were kept in individual stalls during gestation and in indi-
moderate to severe multi-focal villous atrophy in the
                                                                        vidual farrowing pens during lactation. The health of the
jejunum and the ileum of the small intestine (Kim et
                                                                        herds was monitored by the herd veterinarian. The vet-
al., 1999). The clinical signs of PEDV consist of 2 forms.
                                                                        erinarian recommended vaccinating the gilts/sows against
PEDV Type I is clinically characterized by acute diarrhea
                                                                        foot-and-mouth disease virus (FMDV), classical swine fever
in pigs of all ages except suckling piglets, and PEDV Type
                                                                        virus (CSFV), Aujeszky’s disease virus (ADV), porcine parvo
II is characterized by acute diarrhea in pigs of all age
                                                                        virus (PPV) and atrophic rhinitis, at between 22 and 30
groups (Wood, 1977). However, in Korea, it was found
                                                                        weeks of age in replacement gilts, and during late gesta-
that PEDV mainly affected unweaned piglets but was rel-
                                                                        tion (FMDV) and during lactation (SFV, PPV) in sows. Mass
atively uncommon among weaners and growers (Chae
                                                                        vaccination of ADV was conducted every 4 months. In gen-
et al., 2000). The infected piglets of up to 7 days old
                                                                        eral, the target of replacement rate of sows by gilts was 40%
often vomited and developed a severe watery fetid diar-
                                                                        annually. Culling due to old age was planned to be done
rhea, severe dehydration and death within 2–4 days. In
                                                                        after parity six. The gilts were mated at approximately 32
most cases, the clinical signs lasted for 3–5 weeks in
                                                                        weeks of age onwards with a body weight of at least 135 kg
the farrowing house (Kim and Chae, 2003). The infection
                                                                        at the second or later observed oestrus. Conventional arti-
of PEDV in the suckling piglets contributes to a mortal-
                                                                        ficial insemination (AI) was used in all pigs. The gilts and
ity rate of 30–80% (Sueyoshi et al., 1995). In the gilts
                                                                        sows received water up to ad libitum via water nipples. The
and sows, the clinical signs of PEDV infection include
                                                                        feed was provided twice a day (about 1.5–3.5 kg/day dur-
anorexia, depression, transient inappetence, watery diar-
                                                                        ing gestation and 5.0–7.0 kg/day during lactation). The feed
rhea and agalactia (Pijpers et al., 1993; Sueyoshi et al.,
                                                                        was a rice–corn–soybean–fish base containing 18% crude
1995). It has been suspected that PEDV may cause abor-
                                                                        protein (CP), 3200 kcal/kg metabolisable energy (ME) and
tions during the acute phase of the epidemic (Pijpers
                                                                        1.0% lysine for lactating sows, replacement gilts and boars,
et al., 1993). In the fatteners, the mortality rate of the
                                                                        and 15% CP, 2800 kcal/kg ME and 0.8% lysine for gestating
PEDV-infected pigs varied between 1% and 3% (Pensaert,
                                                                        females.
1999).
    In Thailand, an outbreak of PEDV was reported in
1995 (Srinuntapunt et al., 1995). Since then, no further                2.2. Data
comprehensive studies on PEDV has been performed. In
2007–2008, an extensive spread of PEDV was observed                         Data were obtained from the computer recording sys-
and became a major problem in many swine com-                           tems of the herds during January 2007 to March 2009. Data
mercial herds in Thailand. The clinical signs of PEDV                   of 18,640 matings and 16,669 farrowings were obtained
infection in Thailand are, in most cases, similar to that               from the database. The collected data include the sow’s
observed and previously described in Korea (Chae et al.,                identities, mating date, weaning-to-service interval, par-
2000). During the acute phase of the outbreak, mor-                     ity number at service, number of inseminations, the boar’s
bidity of the infected piglets can approximately be 95%                 identities, mating result, number of days until the sows
in the farrowing house, and mortality may approach                      returned to estrus after mating, farrowing date, number of
100%. Under the field conditions, herd immunization is                   piglets born alive per litter (BA), number of stillborn piglets
practically performed by feeding all the pigs, including                per litter, number of mummified fetuses per litter, litters’
the pregnant gilts and sows, minced intestine and/or                    birth weight, piglets’ birth weight (BW) and parity num-
feces of the infected piglets or sows. To our knowl-                    ber at farrowing. The data were scrutinized for accuracy
edge, no study on the influence of the PEDV outbreak                     and completeness. Since a certain number of sows insemi-
and herd immunization (using minced-intestinal feed-                    nated between August 2008 and March 2009 did not farrow
ing) on the subsequent reproductive performance of the                  at the time of the study, the analyzed data set includes
pregnant gilts and sows has been documented. The objec-                 the females that were mated between January 2007 to July
tive of the present study was to investigate the effects                2008. The data analyses were based on 12,922 matings of
of a PEDV outbreak on reproductive traits of the preg-                  8147 females.
44                                       E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51




Fig. 1. Clinical signs of porcine epidemic diarrhea virus (PEDV)-infected sows with watery diarrhea (a) and PEDV-infected piglets with emaciation (b); the
minced intestine of PEDV-infected piglets (c); feeding of sows with approximately 15 ml of the minced intestine (d); the histological appearance of the
intestine of the infected piglet with thin wall, villous atrophy and flattened epithelial lining (e).


2.3. Outbreak of porcine epidemic diarrhea virus                                (11.3 ± 2.9 piglets per litter). Of these born alive piglets,
                                                                                3519 piglets (49.2%) died before weaning. Herd immuniza-
   During the end of 2007–2008, the outbreaks of PEDV                           tion was performed using natural exposure methods. The
occurred in many swine herds in Thailand. After the out-                        intestines of the infected piglets were obtained, ground
breaks, at least 33 isolates of PEDV from 24 herds have                         and mixed well (Fig. 1). The minced-intestine mix was
been identified genetically (Puranaveja et al., 2009). In most                   fed to the pregnant gilts and sows, weaned sows and
cases, the clinical signs and gross lesions were practically                    replacement gilts within 2 weeks after the onset of clini-
used for clinical diagnosis during the early phase of the                       cal signs. The minced-intestine mix (approximately 15 ml)
outbreak. In the present study, an outbreak of PEDV was                         was twice fed to the gilts and sows once a week (with a
observed in March 2008. During the first month of the                            1-week interval). A total of 100 intestines was obtained
PEDV outbreak, 633 females farrowed and 406 females                             from the infected piglets (1 piglet for 20 sows) and
(64.1%) stopped lactating before 3 weeks after farrow-                          was used for the minced-intestinal preparation. There-
ing. The number of piglets born alive was 7153 piglets                          fore, approximately 2000 gilts and sows were fed with
                                   E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51                          45


the minced intestine. After the intestinal feeding, over                  Abortion was defined as ‘0’ when the sows were mated and
80% of the sows showed clinical signs of diarrhea (Fig. 1).               no evidence of abortion occur within 110 days after mating,
Piglet mortality dramatically reduced within 4 weeks                      and defined as ‘1’ when the sows were mated resulting in
after the herd immunization. In addition, intensive clean-                abortion. The farrowing rate (FR), the proportion of females
ing, disinfection and early weaning programs were also                    returning to oestrus after mating (return rate, RR) and abor-
applied.                                                                  tion rate (AR) were calculated using frequency analysis.
                                                                          The period of pregnancy when the females were infected
2.4. Diagnosis of porcine epidemic diarrhea virus                         with PEDV was defined as the interval from insemination to
                                                                          the PEDV outbreak (March 3, 2008). The pregnant females
    The disease was diagnosed by clinical symptoms,                       inseminated from January 1 to December 3, 2007 were
gross and histopathology of the intestine of the infected                 defined as ‘non-infected females’. The females inseminated
piglets (Fig. 1) and viral detection using duplex reverse                 from December 4, 2007 to January 2, 2008 were defined
transcription-polymerase chain reaction (RT-PCR) assay                    as ‘being infected during 91–120 days of pregnancy’. The
(Veterinary Diagnostic Laboratory, Faculty of Veterinary                  females inseminated from January 3 to February 1, 2008
Science, Chulalongkorn University, Thailand). Intestinal                  were defined as ‘being infected during 61–90 days of preg-
samples from 5 infected piglets were collected and sub-                   nancy’. The females inseminated from February 2 to March
mitted to the laboratory to confirm the presence of                        2, 2008 were defined as ‘being infected during 31–60 days
PEDV before the herd immunization program was applied.                    of pregnancy’. The females inseminated from March 3 to
Briefly, the PEDV 651-bp partial S gene was determined                     April 1, 2008 were defined as ‘being infected during 0–30
by using previously published primer, i.e., forward primer,               days of pregnancy’.
5 -TCCTAGACTTCAACCTTACG-3 and reverse primer, 5 -
GGTGACAAGTGAAGCACAGA-3 (Park et al., 2008). The                           2.6. Statistical analyses
primer used to amplify the M gene was designed depend-
ing on the previous isolation of PEDV (Puranaveja et                          The statistical analyses were carried out by Statisti-
al., 2009). The size of the expected product was 715-                     cal Analysis System Version 9.0 (SAS, 2002). Analysis of
bp. Nucleotide and amino acid sequences of the PEDV in                    variance (PROC GLM) was used to analyze continuous
Thailand have been identified and reported (Puranaveja                     variables, i.e., TB, BA, SB, MM and BW. The statistical
et al., 2009). The clinical signs of PEDV include an acute                models included periods of PEDV infection (non-infected
watery diarrhea in the suckling piglets (Fig. 1) and a high               females and females infected during 0–30, 31–60, 61–90,
pre-weaning mortality rate in piglets below 7 days old.                   and 91–120 days of pregnancy), parity number (1, 2, 3–5,
Tissue samples of the small intestine of 5 infected piglets               and 6–12), farrowing month and interaction between par-
were collected and examined. The gross lesions of the                     ity number and the period when the pregnant females were
small intestine of infected piglets revealed a thin wall of               infected with PEDV. Discrete data including FR, RR, and
the small intestine with yellow fluid in the lumen. The                    AR were analyzed using generalized linear-mixed models
microscopic lesion showed severe diffuse villous atrophy                  (GLIMMIX). The statistical models included the periods of
(Fig. 1). Villi were fused and lacked an epithelial lin-                  PEDV infection, parity number at mating (0, 1, 2–4, 5–11),
ing or had a flattened epithelium. RT-PCR test was used                    mating month and interaction between parity number and
for differential diagnosis between TGEV, Rota virus and                   the period of PEDV infection. In the statistical models for RR
PEDV (Kim et al., 2001). RNA was extracted from the                       and AR, parity numbers ≥1 were pooled. All of the repro-
intestines and stool samples of the infected pigs. The results            ductive performance traits during the 4-month period of
of the RT-PCR were positive to PEDV and negative to                       the PEDV outbreak (March to June 2008) and a 4-month
TGEV and Rota virus in both the fecal and intestinal sam-                 period a year before (March to June 2007) were compared.
ples.                                                                     Five statistical models were constructed for TB, BA, SB,
                                                                          MM, BW using GLM, and three statistical models were con-
2.5. Definition                                                            structed for FR, RR and AR using GLIMMIX. The models
                                                                          included parity number, time period (March to June 2008
     The number of total piglets born per litter (TB) was                 or March to June 2007) and interaction between parity
defined as the sum of BA, the number of stillborn piglets                  number and period. Least-squares means were obtained
and the number of mummified fetuses. The percentage of                     and were compared using the Tukey–Kramer adjustment
stillborn piglets (SB) was defined as the number of stillborn              for multiple comparisons. P < 0.05 were considered to have
piglets divided by TB multiplied by 100. The percentage of                statistical significance.
mummified fetuses (MM) was defined as the number of
mummified fetuses divided by TB multiplied by 100. Far-                    3. Results
rowing female, return to oestrus after mating and abortion
were binomial traits (0, 1). Farrowing was defined as ‘0’                  3.1. Descriptive statistics
when the sows were mated resulting in abortion, culling,
not being pregnant or repeat mating, and were defined as ‘1’                  The reproductive performance of sows in the
when the mating resulted in farrowing. The mated female                   herds during periods before and after the PEDV
not return to oestrus after mating was given a null value of              outbreak is presented in Table 1. On average, the
‘0’. A value of ‘1’ was assigned if the gilts/sows were mated             number of gilts and sows inseminated monthly was
and with either a regular or irregular return to oestrus.                 672 ± 63 gilts/sows (range 565–858) and the num-
46                                            E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51




Fig. 2. Farrowing rate (%) of gilts (parity 0) and sow parities 1, 2–4 and 5–8 after infection with porcine epidemic diarrhea virus (PEDV) during different
periods of pregnancy compared to non-exposed females; a,b,c values without the same superscripts within line differed significantly (P < 0.05).

Table 1
Reproductive performance data including farrowing rate (FR), return rate (RR), abortion rate (AR) and least-squares means ± SEM of total number of piglets
born per litter (TB), number of piglets born alive per litter (BA), percentage of stillbirth piglets per litter (SB), percentage of mummified fetuses per litter
(MM) and average individual birth weight of the piglet (BW) during 1 year before the outbreak of porcine epidemic diarrhea virus (PEDV) and in different
periods of pregnancy when the females were infected with PEDV.

   Reproductive data                 Before PEDV outbreak              Days of pregnancy when the females were infected

                                                                       0–30                     31–60                    61–90                    91–120

   Number of matings                 7201                              642                      702                      678                      659
   FR (%)                            91.1a                             78.5b                    92.5a                    92.5a                    91.4ab
   RR (%)                            3.5a                              9.2b                     2.1a                     2.4a                     1.2a
   AR (%)                            2.1a                              3.4b                     2.6ab                    1.9ab                    3.2ab
   TB (piglets/litter)               12.1 ± 0.1a                       11.7 ± 0.2b              12.4 ± 0.2ac             12.8 ± 0.2c              12.9 ± 0.3c
   BA (piglets/litter)               11.1 ± 0.1a                       10.3 ± 0.2b              11.3 ± 0.2ac             11.6 ± 0.2c              11.7 ± 0.2c
   SB (%)                            4.5 ± 0.3a                        5.9 ± 0.6b               5.4 ± 0.5ab              5.2 ± 0.5ab              6.2 ± 0.7b
   MM (%)                            3.5 ± 0.3a                        5.6 ± 0.6b               3.4 ± 0.5a               3.3 ± 0.5a               3.5 ± 0.7a
   BW (kg)                           1.62 ± 0.01a                      1.65 ± 0.02a             1.62 ± 0.02a             1.62 ± 0.02a             1.59 ± 0.02a
a,b,c
        value without the same superscripts within rows differed significantly (P < 0.05).


ber of sows farrowed monthly was 628 ± 42 sows                                          3.2. Farrowing rate, proportion of females return to
(range 567–708). One year before the PEDV outbreak,                                     oestrus after mating and abortion rate
the FR, RR and AR of the herd were 91.1%, 3.5% and
2.1%, respectively, and the TB, BA, SB and MM were                                          A comparison of the reproductive performance of
12.1 piglets/litter, 11.1 piglets/litter, 4.5% and 3.5%,                                gilts/sows during the 4-month period of the PEDV outbreak
respectively (Table 1). The mean gestational period was                                 with reproductive performance during the same period
116.3 ± 1.5 days (range 109–122 days). In sows, the inter-                              in the previous year is presented in Table 2. As can be
val from weaning-to-first-service interval was 5.5 ± 4.8                                 seen from the table, the FR during the 4-month period
days.                                                                                   of the PEDV epidemic was lower than that 1 year earlier


Table 2
Comparison of the farrowing rate (FR), return rate (RR) and abortion rate (AR) and least-squares means ± SEM of the total number of piglets born per litter
(TB), number of piglets born alive per litter (BA), percentage of stillbirth piglets per litter (SB), percentage of mummified fetuses per litter (MM) and piglets’
birth weight (BW) during the 4-month period of the porcine epidemic diarrhea virus (PEDV) outbreak (March to June, 2008) with the same period in the
year before the outbreak (March to June, 2007).

   Reproductive data                    Periods before PEDV outbreak                  Periods during PEDV outbreak                Difference           P-value

   Number of matings                    2581                                          2956                                        –                     –
   FR (%)                               91.3                                          87.5                                       −3.8                   0.003
   RR (%)                               3.3                                           5.0                                        +1.7                   0.73
   AR (%)                               2.0                                           2.7                                        +0.7                   0.05
   Number of farrowing                  2353                                          2583                                        –                     –
   TB (piglets/litter)                  12.2 ± 0.07                                   12.5 ± 0.07                                +0.3                   0.006
   BA (piglets/litter)                  11.3 ± 0.07                                   11.2 ± 0.07                                −0.1                   0.38
   SB (%)                               4.3 ± 0.19                                    6.1 ± 0.19                                 +1.8                  <0.001
   MM (%)                               2.9 ± 0.20                                    4.0 ± 0.19                                 +1.1                  <0.001
   BW (kg)                              1.59 ± 0.01                                   1.61 ± 0.01                                +0.02                  0.02
                                  E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51                            47


(P = 0.003). The AR during the PEDV outbreak was slightly                taken into account, the influence of PEDV infection on TB,
higher than the AR during the same period of the previous                BA and MM was more pronounced in the Parity-1 sows
year (+0.7%, P = 0.05).                                                  than the higher-parity sows (Fig. 3). PEDV infection dur-
    Table 1 shows the FR, RR and AR of the pregnant females,             ing the first 30 days of pregnancy resulted in a decrease
classified by the time that the animals were infected with                of 1.4 TB (11.7 vs. 10.3 piglets/litter, P < 0.001) and 2.2 BA
PEDV compared to reproductive performance before PEDV                    (10.7 vs. 8.5 piglets/litter, P < 0.001) in the Parity-1 sows,
infection. After the PEDV outbreak, FR varied according to               while the influence of PEDV infection on TB and BA were
the period that the gilts/sows were infected with PEDV.                  not significant for higher parities (P > 0.05) (Fig. 3a and b).
Across parities, the females infected with PEDV during                   The pregnant gilts that were infected with PEDV during
0–30 days of pregnancy had a decreased FR from 91.1%                     early pregnancy had an increased MM from 3.9% to 11.8%
to 78.5% compared to the non-infected females (P = 0.003),               (P < 0.001), a decreased TB from 11.7 to 10.3 piglets/litter
while the females infected with PEDV at the later stages                 (P < 0.001), and a decreased BA from 10.7 to 8.5 piglets/litter
of pregnancy had FRs which varied from 91.4% to 92.5%                    (P < 0.001), compared to the period before infection (Fig. 3).
(P > 0.05) (Table 1). On average, the pregnant females                       Across parities, infection with PEDV during late preg-
infected with PEDV during 0–30 days of pregnancy had an                  nancy (91–120 days of pregnancy) resulted in an increased
increase in the RR of 5.7 percentage points (from 3.5% to                SB from 4.5% to 6.2% (P = 0.014) compared to the period
9.2%, P = 0.01) and an increase in the AR of 1.3 percentage              before the epidemic (Table 1). The impact of PEDV infection
points (from 2.1% to 3.4%, P = 0.01).                                    during late-term pregnancy on SB was similar among pari-
    The impact of PEDV on FR differed among parity groups                ties: from 4.1% to 5.4% (P = 0.1), from 3.7% to 5.8% (P = 0.04),
(Fig. 2). Compared with non-infected gilts, the pregnant                 from 4.5% to 6.6% (P = 0.009) and from 5.5% to 7.1% (P = 0.1)
gilts infected with PEDV during 0–30 days of pregnancy                   for parities 1, 2, 3–5 and 6–12, respectively.
had a 16.6 percentage point decrease in the FR (from 88.0%
to 71.4%; P < 0.001). For sows of parities 1, 2–4 and 5–8,
compared to non-infected females, PEDV infection during                  4. Discussion
0–30 days of pregnancy caused a decrease of 1.9 percentage
points (from 90.9% to 89.0%, P = 0.3), 5.4 percentage points                 The present study demonstrated that infection with
(from 92.4% to 87.0%, P = 0.004) and 3.9 percentage points               PEDV during pregnancy significantly influences a number
(from 92.5% to 88.6%, P = 0.2), respectively. Compared with              of reproductive indicators including the FR, RR, AR, MM,
non-infected females, PEDV infection was associated with                 SB, TB and BA. On average, the reproductive performance of
an increase of 7.0 percentage points in the RR in gilts (from            the study herd before the outbreak of PEDV was superior to
5.4% to 12.4%, P = 0.002) and a 2.1 percentage point increase            other swine commercial herds in Thailand (Suriyasomboon
in sows (from 2.9% to 5.0%, P = 0.13). Compared with the                 et al., 2006; Tummaruk et al., 2007), but still within the
non-infected females, incidence of abortion increased from               normal range, comparable to the results presented earlier
3.1% to 4.1% (P = 0.007) in gilts infected with PEDV during              for Thailand and other countries in Asia (Koketsu et al.,
0–30 days of pregnancy, and from 1.7% to 2.5% (P = 0.02) in              1999; Tantasuparuk et al., 2000; Tummaruk et al., 2004;
sows infected with PEDV during 0–30 days of pregnancy.                   Suriyasomboon et al., 2006). The present study found an
Natural infection of PEDV during the period later than 30                overall reduction of 3.8 percentage points in the FR and
days of pregnancy was not associated with an increase in                 an increase of 1.8 percentage points in the SB, and 1.1 per-
either RR or AR (P > 0.05).                                              centage points in the MM during a 4-month period after the
                                                                         onset of the clinical signs of PEDV infection. In the present
3.3. Litter size at birth                                                study, 2956 females were inseminated during this 4-month
                                                                         period, with a reduction in the FR of 3.8 percentage points,
    TB, BA, SB and MM before and after the outbreak of                   indicating that the number of sows farrowing during this
PEDV are shown in Tables 1 and 2. Regardless of the period               period was at least 112 females below the target. This num-
of pregnancy and parity number, BA during the 4-month                    ber of sows represented a reduction of approximately 1112
period after the onset of PEDV infection did not differ                  piglets born alive (i.e., the herd had, on average, 11.1 BA)
significantly compared to the same period of the previ-                   below the expected number.
ous year; slight increases in SB and MM were observed                        In the present study, when the analysis compared the
(Table 2). On the other hand, when the period of preg-                   period of pregnancy in which the females were infected
nancy and parity number were taken into consideration,                   with PEDV, the results revealed that the reduction of FR
PEDV infection significantly influenced litter size at birth               was most evident among the females that were infected
of sows at certain periods of pregnancy and in some parity               during the first month of pregnancy compared with those
groups. The data in Table 1 show that, when the pregnant                 infected during others durations of gestation. For instance,
females were infected with PEDV during early pregnancy                   a decrease in the FR of 12.6 percentage points was found
(0–30 days), both TB and BA of those litters significantly                in females that were infected with PEDV during the first
decreased and MM significantly increased. Regardless of                   month of pregnancy period, while the FR of the females
parity number of the sows, infection with PEDV during                    infected with PEDV during other periods was almost
early pregnancy led to a decrease of TB from 12.1 to 11.7                unchanged compared to the non-infected females. An
piglets/litter (P = 0.03), a decrease of BA from 11.1 to 10.3            explanation for the early pregnancy loss might be either
piglets/litter (P < 0.001) and an increase of MM from 3.5%               fertilization failure or early embryonic loss (Dial et al.,
to 5.6% (P < 0.001) (Table 1). In addition, when parity was              1992). In the present study, the number of gilts and sows
48                                        E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51




Fig. 3. Total number of piglets born per litter (a) and number of piglets born alive per litter (b) and percentage of mummified fetuses per litter (c) (least-
squares means ± SEM) in sow parities 1, 2, 3–5 and 6–9 after infection with porcine epidemic diarrhea virus (PEDV) during different periods of pregnancy
compared to non-infected females; a,b,c values without the same superscripts within line differed significantly (P < 0.05).



that returned to oestrus after mating increased from 3.5% to                      of the FR is unknown; this might be caused by an inflam-
9.2% among those that were infected with PEDV during the                          matory process resulting from the systemic viral infections.
first month of pregnancy. In fact, the mechanism by which                          To our knowledge, transplacental infection of PEDV has not
PEDV infection causes an increase of the RR and a decrease                        been documented.
                                   E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51                          49


    In the present study, it was also found that AR sig-                  ride, which could lead to malnutrition and subsequently
nificantly increased from 2.1% to 3.4% in the gilts and                    cause pregnancy failure and/or embryonic/fetal loss. There-
sows infected with PEDV during the first month of preg-                    fore, the influence of PEDV infection on pregnancy failure
nancy. It has been reported that infection of PEDV causes                 and fetal loss observed in the present study might be at
fever (39–40 ◦ C) (Dea et al., 1985) and this fever causes                least in part caused by suboptimal nutrient supply, which
an increase of prostaglandins E2 (Roth et al., 2009) and                  was caused by poor digestive and absorptive capacity of
prostaglandin F2- (Vannier, 1999), and this might subse-                  the small intestine of the pigs.
quently lead to an increase in uterine muscle contractions                    In the present study, factors that contributed to the
(Konturek and Pawlik, 1986). This mechanism might cause                   severity of the PEDV infection include period of pregnancy
placentation failure and lead to termination of pregnancy.                and parity number. For instance, it was found that the gilts
To our knowledge, only a few cases of abortion have been                  infected with PEDV during early pregnancy had a reducted
linked with PEDV. Pijpers et al. (1993) noted some aborted                FR of 16 percentage points, while sows infected with PEDV
sows during the first months of a PEDV outbreak. Until now                 during early pregnancy period had a reduction in the FR of
however, PEDV has not been considered as a direct cause                   1.9–5.4 percentage points. The reason for this might be that
of abortions.                                                             the gilts were still utilizing nutrients for both the growth
    The present study demonstrated that PEDV infection                    and maintenance of the reproductive function; therefore
caused fetal mortality as indicated by an increase of MM                  the reduction of digestive and absorptive capacity of the
and SB and a decrease of BA. In the present study, MM                     small intestine after PEDV infection might have led to nutri-
increased from 2.6% to 4.7% in the females infected with                  tional levels much below that demanded. Similarly, it has
PEDV during the first month of pregnancy, and SB increased                 been demonstrated that the seasonal influence on the lit-
from 4.7% to 7.1% in gilts and sows exposed to PEDV dur-                  ter size at birth was more pronounced in the gilts’ than
ing the last month of pregnancy. In addition, it was found                the sows’ litters. The exposure of high ambient temper-
that the effect of PEDV on the litter size at birth of sows               ature during early pregnancy in gilts caused a significant
was most evident in the gilts’ litters. To our knowledge,                 decrease in TB, while this effect was less evident in sows
this is the first report showing the influence of PEDV on                   (Tummaruk et al., 2004, 2010). Furthermore, an increase of
litter size at birth for gilts and sows. Furthermore, in pigs,            the weaning-to-first-service interval during summer was
it is known that the presence of at least 4 embryos during                more pronounced in primiparous than multiparous sows
the period of placentation is required to achieve complete                (Tummaruk et al., 2000). An earlier study has demon-
maternal recognition of pregnancy (Hunter, 1997). The loss                strated that the reproductive performance of gilts was also
of embryos might also cause pregnancy failure and lead to                 affected by an outbreak of acute proliferative enteropa-
an increase in RR and a decrease in FR as observed in the                 thy (caused by Lawsonia intracellularis) (Mauch and Bilkei,
present study. However, in the present study, it was found                2005). Although L. intracellularis only affects enterocytes,
that sows exposed to PEDV during 60–120 days of gestation                 the conception rate, FR, TB and BA of the sero-positive gilts
had a larger TB than an average TB during the year before                 were significantly lower than the sero-negative gilts. These
the PEDV outbreak. The reason might be due to the fact that               findings indicate that the gilts are the group of pigs that
the PEDV outbreak was observed in March and, thus, these                  have the highest risk of having pregnancy failure due to
sows could have been mated in the cool period (November                   stressful factors, including PEDV infection.
to January) before the PEDV outbreak. In Thailand, the aver-                  In the present study, the immunization of the sows
age temperature in the cool season is 3.1–3.5 ◦ C lower than              in the herd was performed by feeding the sows with the
in the hot and rainy seasons (Tummaruk et al., 2010). The                 minced intestine of the sick piglets. This implementation
gilts and sows mated in the cool season may have a slightly               was performed to increase the diffusion of natural infection
higher litter size at birth than those mated during hot and               within the herd in order to achieve the highest propor-
rainy seasons (Tummaruk et al., 2004, 2010). Nevertheless,                tion of sero-positive pigs within a short period of time.
some other factors such as the year effects (feed quality,                Immunized sows were then introduced to the farrowing
genetic progress, etc.), mating management, and the boar                  house. The piglets delivered from sero-positive sows may
effect might have been involved (Tummaruk et al., 2000,                   obtain passive immunity from their mother and, hence,
2010). For instance, in the present study, TB was slightly                experience reduced mortality if infected with PEDV (Song
improved during the year of the PEDV outbreak compared                    et al., 2007). Under field conditions, this stock manage-
to the previous year.                                                     ment approach is quite common, and is a practical method
    In general, PEDV infection is characterized by viral                  for rapidly enhancing the immunity of sows against PEDV.
replication in small intestinal villous enterocytes, with                 During the last decade, this strategy has often been rec-
subsequent cell lysis and villous atrophy (Kim and Chae,                  ommended in swine commercial herds in Thailand after
2003). The reduction of enzyme and absorptive capacity                    PEDV outbreaks. This is one way of preventing the trans-
of the small intestine causes a reduction in the diges-                   mission of PEDV to the suckling piglets. The infection of
tive and absorptive function of the pigs. It has also been                PEDV in the suckling piglets can cause 30–100% mortality
demonstrated that infection with PEDV reduces alkaline                    (Kweon et al., 1999). However, this immunization strategy
phosphatase activities and some other digestive enzyme,                   is not the best way of preventing PEDV, since it could also
such as leucine aminopeptidase N and disaccharidase in                    increase the risk of introducing other infectious diseases to
the brush border of the villi of the small intestine (Jung                the pregnant gilts and sows, e.g., porcine reproductive and
et al., 2006). This phenomenon might cause a reduction of                 respiratory syndrome (PRRS) and some pathogenic strains
digestion and absorption of fat, amino acid and disaccha-                 of enteric bacteria such as Escherichia coli and Salmonella
50                                E.-o. Olanratmanee et al. / Animal Reproduction Science 122 (2010) 42–51


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