<p>Porcine
reproductive and respiratory syndrome virus (PRRSV) is estimated to cost the US
swine industry $664 million in annual production losses. Therefore, the
objective of this project was to evaluate the effect of MCFA on PRRSV
replication using in vitro and in-vivo studies. The overarching hypothesis was
that MCFA would inhibit or reduce viral replication of PRRSV infection in vitro
and reduce viral load in-vivo. In the first experiment (Chapter 2), MARC-145
cells were used to determine the effects of individual MCFA (C6, C8, C10, and
C12) exposure at concentrations ranging from 1-1000 µg/mL prior to and following inoculation of North
American Type II (P-129) or European
Type I (Lelystad) PRRSV. Viral replication was determined using FITC labeled
IgG anti-PRRSV monoclonal antibody and TCID<sub>50 </sub>was calculated for
each concentration. Data were analyzed using
the Proc Mixed procedure of SAS. Incubation
of MARC-145 cells with caproic acid (C6) at concentrations of 1-1000 µg/mL prior to and after inoculation with
Type II North American (P129) or Type I European (Lelystad) PRRSV did not alter
viral replication (<i>P</i> > 0.10). However,
incubation of MARC-145 cells with caprylic (C8), capric (C10), and lauric (C12)
acid prior to and after inoculation with Type I and Type II PRRSV did reduce
viral replication at concentrations ranging from 100-1000 µg/mL. In general, the effective dose
required to reduce (<i>P </i>< 0.05)
viral replication (Log<sub>10</sub>TCID<sub> 50</sub>/mL)<sub> </sub>decreased
as MCFA chain length increased. In experiment 2 (Chapter 3), the use of
MCFA combinations (C8:C10; C8:C12; C10:C12; and C8:C10:C12) to reduce viral
replication of PRRSV in MARC-145 cells was investigated. The MCFA combinations were analyzed at six
different concentrations ranging from 50-500 µg/mL with North American Type II (P-129) and
European Type I (Lelystad) PRRSV. Viral replication was determined as described
in experiment 1 (Chapter 2) using FITC labeled IgG anti-PRRSV monoclonal
antibody and Log<sub>10</sub>TCID<sub>50</sub>/mL was calculated for each concentration.
Data were analyzed using the Proc Mixed procedure of SAS. Incubation
of MARC-145 cells with MCFA combinations prior to and after inoculation with
Type II North American (P129) and Type I European (Lelystad) PRRSV resulted in reduced
viral replication at MCFA concentrations of 200-500 µg/mL and was
concentration dependent. Reduction of viral replication with MCFA was further evaluated
by independently incubating MARC-145 cells or PRRSV. Results indicated that
viral replication was reduced when MARC-145 cells were incubated with MCFA and
not when PRRSV was incubated with MCFA. In experiment 3 (Chapter 4), 112 mixed
sex pigs (PIC 1050 females x PIC 359 sire), weaned at 21 d of age, weighing 7.5
± 0.68 kg, were
used in a 33d PRRSV challenge study. Pigs were blocked by body weight and sex
and randomly assigned to one of four treatments in a 2x2 factorial design with
pigs receiving 0 or 0.30% MCFA in the diet and placebo or PRRSV inoculation. Following
a 5 d adjustment to diets and rooms, pigs were inoculated with either a placebo
(sterile PBS) or Type II North American (P129) PRRSV (1 x 10<sup>5</sup>,<sup> </sup>TCID<sub>50</sub>/mL)
given in 1 mL each intranasal and IM injection. Each room contained 4 pens with
7 pigs per pen and an equal ratio of barrows to gilts within treatment. Diets
were formulated to meet or exceed all nutritional requirements (NRC, 2012) and
were fed in 4 nursery phases. Feed budgets by phase were 1.13 kg/pig in phase
1, 2.72 kg/pig in phase 2, 6.35 kg/pig in phase 3, and phase 4 fed until the
end of the experiment. MCFA (C8:C12) were mixed in a 1:1 ratio (wt:wt), and then
mixed with finely ground corn to prepare a premix added to diets at 0.60% to
provide 0.30% total MCFA. Control diets used soybean oil mixed with finely ground
corn at the same 0.60% inclusion to keep ME levels constant across treatments.
Body weights, feed intakes, blood samples, and temperatures were determined or
collected on d 0, 3, 7, 10, 14, 21, and 28 post inoculation. Sections of tonsil,
lung, and intestines were collected at d 10 post-inoculation from 1 pig per pen
and at d 28 from all remaining pigs. Data were analyzed using the PROC Mixed
procedure of SAS with pen as the experimental unit for growth and performance
measurements and pig as the experimental unit for viral load analysis. Serum
viral load confirmed PRRSV was only detectable in challenged pigs. Body weights
were not different (<i>P</i> > 0.05)
between treatments prior to d 14 post inoculation. Body weights from d 14 to 28
post inoculation were reduced (<i>P</i> < 0.05) in PRRSV infected pigs compared
to non-infected pigs. Overall ADG and ADFI were reduced (<i>P </i>< 0.05) for PRRSV infected pigs compared to non-infected pigs
by an average of 18 and 28%, respectively. Body temperatures were not different
between treatments. Viral load measured
in the lung was not different (<i>P </i>>
0.05) between PRRSV infected treatments. Tonsil viral load was not different (<i>P</i> > 0.10) between PRRSV treatments.
However, there was a trend (<i>P</i> ≤ 0.10) for an effect of
day post inoculation with control-fed, PRRSV-infected pigs having higher viral
loads at d 10 post inoculation compared to d 28 post inoculation. Overall, no
effects of MCFA on PRRSV viral load or performance were observed during the
in-vivo trial. MCFA was effective at reducing viral replication of PRRSV in
MARC-145 cells in vitro. However, the results could not be confirmed in the in-vivo
experiment. Porcine alveolar macrophages should be used to confirm the in vitro
inhibition of PRRSV replication observed in MARC-145 cells. In order to fully
understand the application of MCFA to inhibit PRRSV infection in pigs, more studies
should be conducted to evaluate the form of MCFA as well as viral inoculation
with field strains of PRRSV. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14511732 |
| Date | 29 April 2021 |
| Creators | Stacie Anne Crowder (10722867) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/THE_EFFECT_OF_MEDIUM_CHAIN_FATTY_ACIDS_ON_PORCINE_REPRODUCTIVE_AND_RESPIRATORY_SYNDROME_VIRUS/14511732 |
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