Vitamin E supplementation does not mitigate the acute morbidity effects of porcine reproductive and respiratory syndrome virus in nursery pigs1

Impact of viral disease hypophagia on pig jejunal function and integrity

Pathogen challenges are often accompanied by reductions in feed intake, making it difficult to differentiate impacts of reduced feed intake from impacts of pathogen on various response parameters. Therefore, the objective of this study was to determine the impact of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) and feed intake on parameters of jejunal function and integrity in growing pigs. Twenty-four pigs (11.34 ± 1.54 kg BW) were randomly selected and allotted to 1 of 3 treatments (n = 8 pigs/treatment): 1) PRRSV naïve, ad libitum fed (Ad), 2) PRRSV-inoculated, ad libitum fed (PRRS+), and 3) PRRSV naïve, pair-fed to the PRRS+ pigs' daily feed intake (PF). At 17 days post inoculation, all pigs were euthanized and the jejunum was collected for analysis. At days post inoculation 17, PRRS+ and PF pigs had decreased (P < 0.05) transepithelial resistance compared with Ad pigs; whereas fluorescein isothiocyanate-dextran 4 kDa permeability was not different among treatments. Active glucose transport was increased (P < 0.05) in PRRS+ and PF pigs compared with Ad pigs. Brush border carbohydrase activity was reduced in PRRS+ pigs compared with PF pigs for lactase (55%; P = 0.015), sucrase (37%; P = 0.002), and maltase (30%; P = 0.015). For all three carbohydrases, Ad pigs had activities intermediate that of PRRS+ and PF pigs. The mRNA abundance of the tight junction proteins claudin 2, claudin 3, claudin 4, occludin, and zonula occludens-1 were reduced in PRRS+ pigs compared with Ad pigs; however, neither the total protein abundance nor the cellular compartmentalization of these tight junction proteins differed among treatments. Taken together, this study demonstrates that the changes that occur to intestinal epithelium structure, function, and integrity during a systemic PRRSV challenge can be partially explained by reductions in feed intake. Further, long term adaptation to PRRSV challenge and caloric restriction does reduce intestinal transepithelial resistance but does not appear to reduce the integrity of tight junction protein complexes.

Effects of dietary soy isoflavones and soy protein source on response of weanling pigs to porcine reproductive and respiratory syndrome viral infection

Porcine reproductive and respiratory syndrome virus (PRRSV) is the most prevalent disease of swine globally. Infection of weanling pigs with PRRSV leads to a complex immune response resulting in significant disease and decreased growth performance. Previous experimental evidence suggests that increasing concentrations of soybean meal in the diet of young pigs confer benefits in terms of growth performance and immune parameters. The objective of this experiment was to identify potential modes of action for this benefit, specifically the ability for soy-derived isoflavones (ISF) to confer immunological benefits to young pigs infected with PRRSV. Four dietary treatments differing in soy protein source (soy protein concentrate vs. enzyme-treated soybean meal) and ISF supplementation (none vs. 1,500 mg total ISF/kg) were fed; the control diet (CON) contained soy protein concentrate and no supplemental ISF. Weanling pigs (60 barrows, 21 d of age, 5.71 ± 0.44 kg) from a naturally Mycoplasma hyopneumoniae (Mh)-infected source herd were individually housed in disease containment chambers and provided ad libitum access to experimental diets for 7 d before receiving either a sham inoculation or a 9.28 × 103 50% tissue culture infective dose of PRRSV at 28 d of age (0 d postinoculation). A total of 5 experimental treatments included an uninfected group receiving the CON diet, plus four infected groups each receiving a different dietary treatment. Growth performance and rectal temperatures were recorded throughout the study, and blood was collected for quantification of serum PRRSV load, presence of anti-PRRSV antibodies, differential complete blood counts, cytokine concentrations, and T-cell immunophenotyping. Data were analyzed as a 2-way or 3-way ANOVA for all treatments including PRRSV-infected pigs, in addition to a single degree of freedom contrast to compare uninfected and infected pigs receiving the CON diet. PRRSV-infection reduced growth rate and efficiency compared with noninfected controls with minimal influences by ISF. Supplemental ISF reduced PRRSV-induced band neutrophilia and improved cytotoxic-to-helper T-cell ratios. These results suggest that ISF contribute to activation of adaptive immune system pathways and could benefit recovery from and clearance of PRRSV infections.

Effects of heat stress during porcine reproductive and respiratory syndrome virus infection on metabolic responses in growing pigs

Heat stress (HS) and immune challenges negatively impact nutrient allocation and metabolism in swine, especially due to elevated heat load. In order to assess the effects of HS during Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection on metabolism, 9-wk old crossbred barrows were individually housed, fed ad libitum, divided into four treatments: thermo-neutral (TN), thermo-neutral PRRSV infected (TP), HS, and HS PRRSV infected (HP), and subjected to two experimental phases. Phase 1 occurred in TN conditions (22 °C) where half the animals were infected with PRRS virus (n = 12), while the other half (n = 11) remained uninfected. Phase 2 began, after 10 d with half of the uninfected (n = 6) and infected groups (n = 6) transported to heated rooms (35 °C) for 3 d of continuous heat, while the rest remained in TN conditions. Blood samples were collected prior to each phase and at trial completion before sacrifice. PPRS viral load indicated only infected animals were infected. Individual rectal temperature (Tr), respiration rates (RR), and feed intakes (FI) were determined daily. Pigs exposed to either challenge had an increased Tr, (P < 0.0001) whereas RR increased (P < 0.0001) with HS, compared to TN. ADG and BW decreased with challenges compared to TN, with the greatest loss to HP pigs. Markers of muscle degradation such as creatine kinase, creatinine, and urea nitrogen were elevated during challenges. Blood glucose levels tended to decrease in HS pigs. HS tended to decrease white blood cell (WBC) and lymphocytes and increase monocytes and eosinophils during HS. However, neutrophils were significantly increased (P < 0.01) during HP. Metabolic flexibility tended to decrease in PRRS infected pigs as well as HS pigs. Fatty acid oxidation measured by CO2 production decreased in HP pigs. Taken together, these data demonstrate the additive effects of the HP challenge compared to either PRRSV or HS alone.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): porcine reproductive and respiratory syndrome (PRRS)

Porcine reproductive and respiratory syndrome (PRRS) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of PRRS to be listed, Article 9 for the categorisation of PRRS according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to PRRS. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, PRRS can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The animal species to be listed for PRRS according to Article 8(3) criteria are domestic pigs and wild boar.

Effects of porcine reproductive and respiratory syndrome virus on pig growth, diet utilization efficiency, and gas release from stored manure

The objectives of this study were to examine the effects of porcine reproductive and respiratory syndrome virus (PRRSV) infection and vaccination on pig growth, dietary nutrient efficiency of utilization, manure output, and emissions of CO, CH, HS, NO, and NH gases from stored manure. Forty-eight pigs, aged 21 d at the start of the study, were subjected to 1 of 4 treatment combinations arranged in a 2 × 2 factorial design with main factors of PRRSV vaccination and PRRSV infection. Body weight, ADFI, manure output, and nutrient efficiency of utilization were assessed and gas emissions from stored manure were determined daily from 50 to 78 d of age and for 24 d after completion of the animal phase. Infection with PRRSV markedly reduced final BW, ADG, and ADFI ( < 0.01) and reduced efficiencies of ADF and ether extract utilization ( = 0.05 and = 0.02, respectively) regardless of vaccination status. No significant treatment effects were found on manure output, manure pH, efficiencies of lignin utilization, and N retention. Infecting pigs with PRRSV increased daily manure CO emission per pig ( = 0.01). There was an interaction between immunization and infection for NO per pig with manure from uninfected, vaccinated pigs producing as much as the manure from infected, vaccinated pigs whereas there was a difference by PRRSV infection state for nonvaccinated pigs. There were also interactions between treatments for HS and NO emissions per kilogram of manure volatile solids excreted ( = 0.01 and = 0.0001, respectively) with the same pattern as for NO per pig; that is, the vaccinated pigs had similar rates of emission regardless of infection state. Pigs infected with PRRSV increased NO nitrogen per kilogram of total N excreted compared with noninfected groups ( = 0.03). Collectively, these results indicated that PRRSV infection caused decreased growth rates and nutrient utilization efficiency and increased gas emissions from stored manure.

Effects of dietary soybean meal concentration on growth and immune response of pigs infected with porcine reproductive and respiratory syndrome virus

An experiment was conducted to determine the effects of dietary soybean meal (SBM) concentration on the growth performance and immune response of pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Four experimental treatments included a 2 × 2 factorial arrangement of 2 dietary SBM concentrations, 17.5% (LSBM) or 29% (HSBM), and 2 levels of PRRSV infection, uninfected sham or PRRSV infected. Sixty-four weanling pigs of split sex (21 d of age, 7.14 ± 0.54 kg) were individually housed in disease containment chambers. Pigs were provided a common diet for 1 wk postweaning before being equalized for BW and sex and allotted to 4 treatment groups with 16 replicate pigs per group. Pigs were fed experimental diets for 1 wk before receiving either a sham inoculation (sterile PBS) or a 1 × 10 50% tissue culture infective dose of PRRSV at 35 d of age (0 d postinoculation, DPI). Pig BW and feed intake were recorded weekly, and rectal temperatures were measured daily beginning on 0 DPI. Blood was collected on 0, 3, 7, and 14 DPI for determination of serum PRRSV load, differential complete blood cell counts, and haptoglobin and cytokine concentrations. Infection with PRRSV increased (P < 0.01) rectal temperatures of pigs throughout the infection period, with no influence of dietary SBM concentration. Pigs in the PRRSV-infected group had lower (P < 0.01) ADFI and G:F from 0 to 14 DPI compared with uninfected pigs. In the PRRSV-infected group, pigs fed HSBM tended to have improved ADG (P = 0.06) compared with pigs fed LSBM, whereas there was no influence of SBM concentration on growth of pigs in the uninfected group. At 14 DPI, PRRSV-infected pigs fed HSBM had a lower serum PRRSV load (P < 0.05), a higher (P = 0.02) hematocrit value, and a tendency for greater hemoglobin concentration (P = 0.09) compared with pigs fed LSBM. Serum haptoglobin and tumor necrosis factor-α concentrations of PRRSV-infected pigs were lower (P < 0.05) in pigs fed HSBM at 3 and 14 DPI, respectively, than in pigs fed LSBM. Overall, increasing the dietary SBM concentration modulated the immune response and tended to improve the growth of nursery pigs during a PRRSV infection.

Dietary plant extracts improve immune responses and growth efficiency of pigs experimentally infected with porcine reproductive and respiratory syndrome virus

A study was conducted to evaluate the effects of 3 different plant extracts on growth performance and immune responses of weaned pigs experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). A total of 64 weaned pigs (7.8 ± 0.3 kg BW), free of PRRSV, were randomly allotted to 1 of 8 treatments in a 2 × 4 factorial arrangement with a randomized complete block design. Pigs were blocked by initial BW. Sex and ancestry were equalized across treatments. The first factor was with or without PRRSV challenge (intranasal dose; 10(5) 50% tissue culture infective dose). The second factor was represented by 4 diets: a nursery basal diet (CON), 10 mg/kg capsicum oleoresin (CAP), garlic botanical (GAR), or turmeric oleoresin (TUR). Pigs were housed in disease containment chambers for 28 d [14 d before and after the inoculation (d 0)]. Blood was collected on d 0, 7, and 14 to measure the total and differential white blood cells (WBC), and serum was collected to measure viral load by quantitative PCR, PRRSV antibody titer, tumor necrosis factor-α (TNF-α), IL-1β, C-reactive protein (CRP), and haptoglobin (Hp) by ELISA. In the unchallenged group, all piglets were PRRSV negative during the overall period postinoculation. All data were analyzed using PROC MIXED of SAS. The PRRSV challenge decreased (P < 0.01) ADG, ADFI, and G:F from d 0 to 14. Feeding TUR improved G:F of the PRRSV-infected pigs from d 0 to 14. The numbers of WBC and neutrophils were decreased (P < 0.05) by PRRSV on d 7 but increased (P < 0.05) by PRRSV on d 14, indicating the PRRSV-infected pigs undergo a stage of weak immune responses. Feeding GAR increased (P < 0.05) B cells and CD8+ T cells of PRRSV-infected pigs compared with the CON. Furthermore, the PRRSV challenge increased (P < 0.05) serum viral load, TNF-α, and IL-1β on d 7 and serum viral load, CRP, and Hp on d 14, but feeding plant extracts to PRRSV-infected pigs reversed (P < 0.05) this increase. Infection with PRRSV increased (P < 0.05) rectal temperature of pigs on d 7, 9, and 11, but PRRSV-infected pigs fed plant extracts had lower rectal temperature (P < 0.05) than pigs fed the CON, indicating feeding plant extracts delayed the fever caused by PRRSV infection. In conclusion, results indicate that supplementation with plant extracts reduces the adverse effects of PRRSV by improving the immune responses of pigs, and the 3 plant extracts tested here show different effects. Supplementation with TUR improved feed efficiency of pigs challenged with PRRSV.

Blood antioxidant enzymes (SOD, GPX), biochemical and haematological parameters in pigs naturally infected with porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) has become one of the most economically important diseases for the swine industry worldwide. The objective of the study was to determine selected blood antioxidant enzymes (glutathione peroxidase (GPX), superoxide dismutase (SOD)), biochemical and haematological parameters in PRRS positive and negative pigs of three different categories, mainly to test oxidative stress hypothesis in pigs naturally infected with PRRS virus. Ninety PRRS positive and 90 PRRS negative pigs were included in the study. The presence of PRRS was confirmed by serological detection of antibodies against PRRS virus (PRRSV) and detection of PRRS viral RNA by RT-PCR. Pigs were further divided into three groups of 30: piglets just before weaning (weaners), fatteners and finishers. Blood samples for determining selected blood parameters were collected from the vena cava cranialis. Significantly (P < 0.05) higher activities of SOD in weaners and fatteners and of GPX in weaners were determined in PRRS positive pigs than in corresponding groups of PRRS negative pigs. In contrast, significantly (P < 0.05) lower GPX activity was observed in finishers of PRRS positive pigs than in the corresponding group of PRRS negative pigs. Concentrations of serum total protein in PRRS positive weaners and fatteners were significantly (P < 0.05) higher than those found in PRRS negative pigs. Leukopenia was observed in all three groups of PRRS positive pigs. It has been demonstrated, for the first time, that oxidative stress might be increased in PRRSV naturally infected pigs, especially in weaners.

Mannan oligosaccharide increases serum concentrations of antibodies and inflammatory mediators in weanling pigs experimentally infected with porcine reproductive and respiratory syndrome virus

Mannan-containing products are capable of modulating immune responses in animals. However, different products may have diverse immunomodulation. The experiment was conducted to examine effects of mannan oligosaccharide (Actigen; ACT) on growth performance and serum concentrations of antibodies and inflammatory mediators in weanling pigs (Sus scrofa) experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). A total of 32 PRRSV-negative pigs (3 wk old) were randomly assigned from within blocks to 1 of 4 treatments in a 2 by 2 factorial arrangement [2 types of diet: control (0%) and ACT addition (0.04%); and with and without PRRSV] in a randomized complete block design. Pigs were blocked by initial BW within sex. Ancestry was equalized across treatments. Pigs (8/treatment) were kept individually in each pen. After 2 wk of an 8-wk period of feeding the treatments, pigs received an intranasal inoculation of PRRSV or sham medium at 5 wk of age. Infection by PRRSV decreased ADG, ADFI, and G:F throughout the experiment (P < 0.01). Actigen did not affect ADG (P = 0.450), but decreased (P = 0.047) ADFI from 28 to 42 days postinoculation (DPI). During that time, ACT improved G:F in infected pigs but not in sham controls (interaction, P = 0.009). Dietary ACT did not affect viremia in infected pigs (P > 0.05), but increased PRRSV-specific antibody titer at 35 DPI (P = 0.042). Infection with PRRSV induced the febrile responses of pigs from 3 to 10 DPI (P < 0.001) with return to normal at 14 DPI. During the experimental period, the rectal temperature of pigs was found slightly elevated by ACT (P = 0.045). Infected pigs had greater serum concentrations of IL-1β, tumor necrosis factor (TNF)-α, IL-12, interferon (IFN)-γ, IL-10, and haptoglobin (Hp) than sham controls (P < 0.001). These results indicate that PRRSV stimulated secretion of cytokines involved in innate, T-helper 1, and T-regulatory immune responses. Actigen tended to decrease the serum TNF-α concentration regardless of PRRSV (P = 0.058). The ACT × PRRSV interaction was significant for IL-1β (P = 0.016), IL-12 (P = 0.026), and Hp (P = 0.047), suggesting that infected pigs fed ACT had greater serum concentrations of these mediators than those fed the control. The increases in IL-1β and IL-12 may favorably promote innate and T-cell immune functions in infected pigs fed ACT. Feeding ACT may be useful as ACT is related to increased PRRSV antibody titers and G:F in infected pigs at certain times during infection.

Mannan oligosaccharide improves immune responses and growth efficiency of nursery pigs experimentally infected with porcine reproductive and respiratory syndrome virus

This study was conducted to determine whether the ingestion of mannan oligosaccharide (MOS, Bio-Mos) alters the immune response of nursery pigs challenged with porcine reproductive and respiratory syndrome virus (PRRSV). A total of 64 pigs (3 wk old), free of PRRSV, were used in 2 separate but similar experiments conducted sequentially. Pigs were blocked by initial BW. Sex and ancestry were equalized across treatments. Pigs were randomly assigned from within blocks to 1 of 4 treatments in a 2 × 2 factorial arrangement [2 types of diet: control (0%) and MOS addition (0.2%); 2 levels of PRRSV: with and without]. There were 8 replicate chambers of 2 pigs each. After 2 wk of a 4-wk period of feeding the treatments, pigs were intranasally inoculated with PRRSV or a sterile medium at 5 wk of age. The PRRSV challenge decreased ADG, ADFI, and G:F throughout the experiment (P < 0.001). Feeding MOS improved G:F of the pigs during d 7 to 14 (P=0.041) postinfection (PI). Serum concentrations of tumor necrosis factor (TNF)-α, C-reactive protein, and haptoglobin were increased by PRRSV (P < 0.001). The MOS × PRRSV interaction was significant for TNF-α at d 14 PI (P=0.028), suggesting that infected pigs fed MOS had less TNF-α than those fed the control. Dietary MOS increased serum IL-10 at d 14 PI (P=0.036). Further, MOS-fed pigs had greater numbers of white blood cells (WBC) at d 3 (P=0.048) and 7 PI (P=0.042) and lymphocytes at d 7 PI (P=0.023) than control-fed pigs. In contrast, PRRSV decreased (P < 0.01) WBC numbers until d 14 PI. Dietary MOS appeared (P=0.060) to increase the neutrophils in PRRSV-infected pigs at d 3 PI, but no (P=0.202) MOS × PRRSV interaction was found. Infection with PRRSV increased rectal temperature (RT) of pigs at d 3 PI (P < 0.001) and continued to affect the infected pigs fed the control diet until d 14 PI. The MOS × PRRSV interaction for RT was found at d 7 (P < 0.01) and 10 (P=0.098) PI, indicating that the infected pigs fed MOS had a decreased RT compared with those fed the control. This could explain why feed efficiency was improved by MOS. No effect (P > 0.05) of treatments on viremia or PRRSV-specific antibody was observed. These results suggest that MOS is associated with rapidly increased numbers of WBC at the early stage of infection and alleviates PRRSV-induced effects on G:F and fever. The results also indicate that the reduced intensity of inflammation by MOS may be related to changes in inflammatory mediator levels at the end of the acute phase.

Heat and social rank impact behavior and physiology of PRRS-virus-infected pigs

Changes in thermal environment can invoke a stress response in pigs, which in turn can potentially impact their immune system and disease susceptibility. We investigated effects of heat stress and social rank on behavior, immune responsiveness, and performance of pigs challenged with porcine reproductive and respiratory syndrome (PRRS) virus. Sixty-four 7-week-old PRRS-naïve pigs were assigned to each of four experimental treatments consisting of a 2 x 2 factorial design: PRRS (PRRS- or PRRS+) and environmental temperature (24 degrees C or 32 degrees C). Blood samples were taken prior to and at days 7 and 14 post-inoculation, and alveolar macrophages were collected via bronchoalveolar lavage at day 14. Total white blood cell counts, natural killer cytotoxicity, macrophage numbers, macrophage subpopulations, and performance measures were all significantly affected by social rank, heat stress, and/or infection status of the pig. Heat stress and PRRS status also significantly influenced the amount of time pigs spent lying with or without contacting another animal. Cortisol and various immune measures were also affected by PRRS status. These results show not only that intranasal inoculation with PRRS virus affects physiological, behavioral, and performance measures in growing pigs, but that social rank influences pigs' immune responsiveness to PRRS as well. Moreover, heat stress does not have additive negative impact on physiological or performance traits in pigs challenged with PRRS virus.

Supplementing drinking water with Solutein did not mitigate acute morbidity effects of porcine reproductive and respiratory syndrome virus in nursery pigs

The objective of this study was to determine whether providing nursery pigs drinking water supplemented with spray-dried animal plasma (Solutein, American Protein Corporation Inc., Ankeny, IA) would reduce the detrimental impact of porcine reproductive and respiratory syndrome virus (PRRSV) infection. Sixty-four pigs were subjected to 1 of 4 treatment combinations (2 x 2 factorial arrangement) of Solutein [0 or 2.5% (wt/wt) in drinking water] and PRRSV (sterile medium or 5 mL of tissue culture infectious dose of high-virulence strain ATCC VR-2385). Pigs were provided the water treatments during a 1-wk period before inoculation as well as during a 2-wk period after inoculation. Growth performance was determined throughout the study, and several indicators of the immunological response to PRRSV and disease pathology were assessed in blood and tissue samples collected from pigs killed 7 or 14 d after inoculation. Before inoculation, pigs provided water supplemented with Solutein tended to eat less (P = 0.08) but tended to gain more BW (P = 0.13) than pigs provided tap water. Thus, Solutein markedly improved G:F (P < 0.01), after accounting for the DM provided by Solutein. Inoculation with PRRSV reduced ADG and ADFI (P < 0.01) irrespective of water treatment; however, the beneficial effects of Solutein on G:F persisted. Infection with PRRSV also reduced (P < 0.009) villus height and crypt depth in cranial, medial, and caudal segments of the small intestine and increased (P < 0.05) lung and spleen weight, the number of leukocytes in lung lavage fluid, and serum concentrations of interferon-gamma and IL-1beta regardless of water treatment. Collectively, these results indicate that supplementing water with spray-dried animal plasma improved feed efficiency but did not afford nursery pigs protection from the effects of PRRSV on growth and certain hematological traits.

Decreased protein accretion in pigs with viral and bacterial pneumonia is associated with increased myostatin expression in muscle

Chronic respiratory infections reduce growth in pigs but protein accretion (PA) during an ongoing multifactorial respiratory infection has not been determined, and the mechanisms underlying growth inhibition are largely unknown. The objectives of this study were to determine whether viral and bacterial pneumonia in young pigs decrease PA, increase serum IL-1beta and IL-6, and increase myostatin (MSTN) mRNA in biceps femoris and triceps muscles. Mycoplasma hyopneumoniae (Mh) or medium was given intratracheally at 4 wk of age, Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) or medium was given intranasally at 6 wk of age, and pigs were killed 7 or 14 d after PRRSV inoculation for body composition analysis. PRRSV but not Mh induced a marked increase (P < 0.01) in IL-1beta, IL-6, and MSTN mRNA and a decrease (P < 0.01) in food intake, daily weight gain, PA, and lipid accretion. PRRSV also reduced (P < 0.01) myofiber area in the biceps femoris. Food intake, weight gain, PA, and weight of biceps femoris and triceps muscles were negatively correlated (r = -0.4 to -0.8, P < 0.05) with serum IL-1beta and IL-6 and with MSTN mRNA in muscle. These results suggest that the magnitude of increases in inflammatory cytokines during a respiratory infection may be predictive of decreases in PA and growth. They further suggest that during infection growth of skeletal muscle is limited in part by myostatin.