Quantitative relationship of systemic virus concentration on growth and immune response in pigs.

Abstract

Ninety-six pigs from a herd naive for porcine reproductive and respiratory syndrome (PRRS) virus were weaned (10 +/- 3 d of age), penned individually in isolation rooms, and, at 29 +/- 4 d of age, oronasally inoculated with a 2-mL dose of 10(4.3) JA142 PRRS virus/ mL. Body weight; feed intake; and serum concentrations of PRRS virus, interferon, and alpha1-acylglycoprotein were determined for each pig every 4 d on d -8 to 24 postinoculation to quantify the effect of PRRS exposure on the immune response and growth of pigs. Another objective was to determine whether a quantitative relationship between a measure of systemic (serum) virus concentration and pig growth exists. Serum PRRS virus and interferon peaked at 10(5) virus/mL and 69% protection, respectively, at 4 d postinoculation and then declined steadily. Serum alpha1-acylglycoprotein concentration peaked at 12 d postinoculation. Pig weight gains and feed intake were reduced sharply in the initial 8 d postinoculation and to a lesser degree for 24 d postinoculation. The serum concentration of virus and to a lesser degree serum concentrations of interferon and alpha1-acylglycoprotein were quantitatively related to body weight gain and feed intake. The magnitude of the relationship was dependent on the stage of recovery from PRRS infection. Specifically, each log increase in serum virus concentration was associated with a reduction of 4-d pig gain and feed intake of .047 kg and .189 kg, respectively, in 5.5-kg pigs 4 d postinoculation and .085 kg and .036 kg, respectively, in 12.5-kg pigs at 20 d postinoculation. Based on these data, factors that minimize the systemic presence of a virus in pigs result in improvements in pig growth that are quantitatively related to the degree of systemic virus elimination or minimization.

Clinical and pathological responses of pigs from two genetically diverse commercial lines to porcine reproductive and respiratory syndrome virus infection1

“…For example, virus concentration in serum and BAL were significantly related at 21 dpi, but not at 10 dpi, where virus levels were substantially greater, suggesting different time trends for the virus dynamics at different locations. Indeed, viral loads in serum are reported to peak as early as 4 dpi (Greiner et al, 2000), whereas virus load in the lung peaks at 7 to 9 dpi (Labarque et al, 2003). However, Petry et al (2005) found moderately strong positive correlations between virus concentrations in blood, lung, and lymph nodes at 14 dpi.…”

“…Greiner et al (2000) and Petry et al (2005) both reported a negative relationship between serum PRRS virus concentration and BW growth. However, they also found that the strength of the relationship varied throughout the stage of infection, with the strongest correlation/greatest reduction in growth occurring at the later infection stages when systemic virus concentration was less.…”

“…Porcine reproductive and respiratory syndrome virus infection is commonly known to have a negative impact on growth, but the degree of the impact appears to vary between and within pig lines or breeds (Greiner et al, 2000;Petry et al, 2005Petry et al, , 2007 The underlying mechanisms for this relationship are still poorly understood. It can be envisaged that genetic resistance to PRRSV may influence performance in positive (e.g., less impact of the virus on the biological systems) and negative (e.g., the resistant animal diverts more resources and effort to the immune mechanisms rather than growth) ways.…”

Selection for lean growth and food intake leads to correlated changes in innate immune traits in Large White pigs

“…These pigs were housed on a farm with intermediate health status, hence would have been exposed to some environmental pathogens. As infection can reduce performance, an increase in immunity may be expected to improve performance Balaji et al, 2000;Greiner and Stahly, 2000), provided the benefits outweigh the costs of the increased immunity. For this set of high lean growth pigs, the high WBC may reflect an ability to mount a higher immune response, the benefits of which may lead to improved lean growth, particularly in the circumstances under which they were selected, i.e.…”

Use of thermal imaging for the early detection of signs of disease in pigs challenged orally with Salmonella typhimurium and Escherichia coli

“…Infections with enteric pathogens such as Salmonella or Escherichia coli are common during intensive pig production and are associated with poor performance and animal welfare (Pijpers et al, 1991;Greiner et al, 2000). Such infections may also pose a risk to human health and lead to expensive veterinarian intervention costs.…”