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Increased dietary soybean meal does not affect performance during a PRRSV-Mycoplasma hyopneumoniae challenge
Porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (MHP) are two significant respiratory pathogens in finishing pigs, often found in tandem. Recent anecdotes have implied that increasing soybean meal content of diets can be beneficial in pathogen-challenged pigs, while other reports suggest similar benefits by increasing the use of synthetic AA, specifically Trp. The objective of this study was to determine if increased synthetic Trp replacing a portion of SBM would impact performance of late finishing pigs dual-challenged with PRRSV and MHP. Ninety-six mixed sex pigs (120 ± 1.4 kg BW), were selected and randomly assigned to a high SBM (CON; 9 pens/trt) or synthetic Trp (SYN; 9 pens/trt) diet. Both diets were formulated to contain 0.70% TID Lys and were isocaloric; only crude protein was different between CON and SYN diets (15.9 vs 13.5%, respectively). After 96 days on test diets, all pigs were inoculated intratracheally with MHP and intramuscularly with a field strain of PRRSV. Growth performance and feed efficiency were determined until pigs reached market weight (~138 kg BW), after which, carcass data and lung lesion scores were assessed. During the 96 day pre-challenge period, no performance differences were detected between the two dietary treatments. As expected, antibody titers for PRRSV and MHP increased post inoculation. However, change in PRRSV antibody titers from 0 to 28 days post inoculation tended (P = 0.09) to be increased in SYN verses CON pigs. MHP antibody titers and lung lesion scores did not differ between treatments. For the 28 day post-challenge period, there was no difference in ADG, ADFI or G:F. There was also no difference in hot carcass weight, yield percentage or muscle depth (P > 0.10). However, the SYN pigs had an increase in carcass fat depth compared to the CON (P = 0.01). Conversely, there was a tendency (P = 0.09) for carcass lean percent to be increased in CON pigs (57.6 vs 57.1%, respectively). Altogether, these data indicate that diets with increased synthetic AA or decreased SBM do not alter pig performance during a late breaking respiratory health challenge.
Keywords: PRRSV, Soybean meal