Effect of a Dual Enteric and Respiratory Pathogen Challenge on Swine Growth Efficiency, Carcass Composition, and Pork Qualit

The objective of this study was to determine the influence a dual respiratory and enteric pathogen challenge on growth performance, carcass composition, and pork quality of high and low feed efficient pigs. It was hypothesized that pigs with greater feed efficiency would have a more negative response to an early growth period dual pathogen challenge than less feed efficient pigs. Pigs divergently selected for low and high residual feed intake (RFI, ~ 68 kg) from the 11th generation of Iowa State University RFI project were used to represent high and low feed efficiency. To elicit a dual pathogen challenge, half of the pigs (n = 12 / line) were inoculated with Mycoplasma hyopneumoniae (Mh) and Lawsonia intracellularis (MhLI) on days post inoculation (dpi) 0. Pigs in a separate room of the barn were not inoculated and were used as controls (n = 12 / RFI line). Pigs were weighed and feed intake was recorded to calculate ADG, ADFI, and G:F for the acclimation period (period 1: dpi --21--0), during peak infection (period 2: dpi 0--42), and during the remaining growth period to reach market weight (period 3: dpi 42--slaughter). At ~ 125 kg, pigs were slaughtered using standard commercial procedures. Carcasses were evaluated for composition (weight, fat free lean, loin eye area, 10th rib fat depth) and meat quality (pH decline, temperature decline, Hunter L, a, and b, subjective color and marbling, star probe, drip loss, cook loss, proximate composition, and desmin degradation). Challenged pigs had reduced ADFI during period 2 (P < 0.05). However, pigs from the MhLI group had greater ADG and G:F during period 3 (P < 0.05). Selection for feed efficiency did not result in a differential response to MhLI ( P > 0.05). Loin chops from the less feed efficient, high RFI pigs, had greater drip loss, greater cook loss, lesser % moisture, greater Hunter L values, and greater Hunter b values (P < 0.05) than chops from low RFI pigs. Infection status did not significantly affect carcass composition or pork quality traits (P > 0.05). Peak antibody response of Mh was correlated significantly with pH decline, temperature decline, color (Hunter L, a, and b), drip loss, cook loss, 10th rib back fat, % moisture, and % fat (P < 0.05). These results indicate that a MhLI challenge early in growth did not significantly impact ultimate carcass composition or meat quality traits. Further, selection for greater feed efficiency in pigs did not affect their response to pathogenic challenge. The antibody response correlations are indicative of a previously unrecognized relationship between a dual pathogen challenge early in growth and carcass composition and pork quality.