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Models of immune system stimulation in growing pigs: porcine reproductive and respiratory syndrome (PRRS) versus E.coli lipopolysaccharide (LPS)
In recent years, there has been debate on developing a practical model of disease for studying nutrient needs of pigs during immune system stimulation (ISS). A study was conducted to compare a non-pathogenic model of ISS with the PRRSv model. Forty PRRSv-negative gilts (BW 9.4 ± 0.9 kg) were blocked by time, housed in metabolism crates, and fed-restricted (550 g/d) a corn and SBM based diet (ME 14 MJ/kg, SID Lysine 11.5 g/kg). Repeated i.m. injection of increasing amounts of LPS (initial dose of 30 µg/kg; n=10), or i.m. injection of live field PRRSv (n = 20) were used to induce ISS. Control pigs (CON; n=10) received saline injections. Blood was collected via the jugular vein at time 0 and then every 48 h after start of ISS, and assayed for hematology, metabolites, and acid-base balance. Body temperature (BT) was monitored on a daily basis. N-balances were determined during a 3 d pre-ISS period and a 3 d ISS period. Apparent ileal digestibility of dietary N was determined using the slaughter technique. No differences were observed in BT, blood parameters, N-balance, and feed intake (FI) between CON and pre-ISS period of LPS and PRRSv-treated pigs (P > 0.05). BT was elevated in pigs on LPS and PRRSv, by 0.7 and 0.9 °C, respectively, relative to CON (37.5 °C; P < 0.01). Relative to CON, LPS did not reduce daily FI (P > 0.05). However, PRRSv-challenged pigs consumed only 55 % of their daily feed allowance (P < 0.05). Blood glucose concentration was lower in LPS and PRRSv-treated pigs (34 and 8 %, respectively, relative to 92.5 g/dl for CON; P < 0.05). Higher blood anion-gap (CON vs. PRRSv; 13 vs. 17 mEq/L) and lower hemoglobin (12 vs. 8 g/dl) were only observed in PRRSv-treated pigs (P < 0.01). Blood urea nitrogen levels and hematocrit were not affected by the treatments (P > 0.05). N retention was decreased in LPS and PRRSv-treated pigs (20 and 64 %, respectively, relative to 11 g/d for CON; P < 0.03). Ileal digestibility of protein was decreased by LPS and PRRSv (16 and 26 %, respectively, relative to 0.76 for CON; P < 0.01). These results suggest that LPS and PRRSv both reduce performance and alter metabolism of pigs. However, compared to LPS, PRRSv model elicits a more severe response with a more negative impact on performance of pigs. NPB number 13-082
Keywords: PRRS, LPS, pig