Impact of Lawsonia Intracellularis-Mycoplasma Hyopneumoniae Dual Challenge on Growth Performance of Pigs Divergently Selected for Residual Feed Intake

The aim of this study was to compare the growth performance of pigs divergently selected for residual feed intake (RFI) when presented with a 21 day respiratory and enteric disease dual challenge. Using a 2 x 2 factorial design, 25 littermate pairs of barrows from the high RFI (n=50, low feed efficiency) and 25 from the low RFI (n=50, low feed efficiency) line from the RFI selection project at Iowa State University were selected. One pig from each pair was assigned to either challenge or non-challenge (control) rooms (n=25 barrows per line/treatment). Pigs were individually housed, fed a common corn-soybean diet, and allowed to acclimate for 3 weeks prior to inoculation. On day post inoculation (dpi) 0, challenge pigs were inoculated intra-gastrically with Lawsonia intracellularis and intra-tracheally with Mycoplasma hyopneumoniae. Feed intake, body weight, fecal, and serum samples were collected and recorded at dpi 0, 7, and 14. On dpi 7, challenge pigs were confirmed positive for Lawsonia intracellularis via qPCR on pooled fecal swabs and for Mycoplasma hyopneumoniae via serology. The 14 day challenge period data were analyzed using the Mixed Procedure of SAS using line, challenge, and line x challenge interaction as fixed effects, with age as a covariate and litter as a random effect. Line x challenge interactions were observed, as low RFI challenge pigs had a smaller reduction in ADFI (P<0.05), and tended to have a smaller decrease in ADG (P=0.06) from dpi 8-14, but not in overall performance. Irrespective of challenge, low RFI pigs had lower ADFI compared with high RFI pigs (2.4 vs. 2.8 kg/day; P<0.01), but similar ADG, leading to greater G:F (0.35 vs. 0.30; P<0.05). From dpi 0-7, a significant challenge effect was not detected. However, from dpi 8-14 and irrespective of line, challenge pigs had lower ADFI (2.4 vs. 2.8 kg/day; P<0.01), ADG (0.62 vs. 0.89 kg/day; P<0.01), and G:F (0.26 vs. 0.32 ; P<0.01). Overall (dpi 0-14), the challenge pigs had an reduction in ADFI (2.5 vs. 2.7 kg/day; P<0.05), ADG (0.75 vs. 0.89 kg/day P<0.01), and G:F (0.30 vs. 0.33; P<0.01) compared with non-challenged control pigs. These data show that pig performance can be reduced by 6-10% as a result of this dual enteric and respiratory pathogen challenge. Further, these results also suggest that selection for lower RFI does decrease the impact of a disease challenge. This work was supported by AFRI-NIFA grants #2011-68004-30336 and #2016-67017-2474.