本研究的目的是，探讨呼吸道和肠道双重病原体对猪只生长性能、胴体组成和猪肉品质的影响。按照饲料剩余量（RFI）分开选择猪只（68 kg），分别代表高饲料转化率组和低饲料转化率组；在接种疫苗的当天（dpi 0）注射猪肺炎支原体（Mh）和细胞内劳森菌（MhLI）给一半的猪只（12头）进行双重病原体感染挑战试验，另外一半猪只（12头）放置在另外单独的房间作为对照组。
分别在适应阶段（阶段1：dpi -21～0）、注射感染高峰期（阶段2：dpi 0～42）和达到市场体重剩余期（阶段3：dpi 42～达到市场体重）对猪只进行称重，记录采食量，以此来计算ADG、ADFI和G：F。按照商业程序，猪只在125 kg时达到市场体重，对胴体（重量、无脂肪瘦肉和腰眼区第十肋骨脂肪深度）和肉质（pH值下降、温度下降和色度Hunter L、a、b，以及主观颜色、大理石纹、星探测器分析、滴水损失、烹调损失、相似成分和肌间线蛋白降解）进行评估。
试验数据表明，病毒试验组猪只，在阶段2时ADFI降低（P < 0.05），但是在阶段3时ADG和G：F增加（P < 0.05），同时，在试验组中，按照RFI饲料效率分开的猪只没有出现差异（P > 0.05）。与低RFI组相比，高RFI低饲料效率组猪只猪排滴水损失和烹饪损失增加，水分含量降低，色度Hunter L值升高，Hunter b值增加（P < 0.05）。总体来看，病原体的感染并没有对猪只胴体组成和肉质特征产生显著影响（P > 0.05）。
Effect of a dual enteric and respiratory pathogen challenge on swine growth, efficiency, carcass composition, and pork quality
The objective of this study was to determine the influence of a dual respiratory and enteric pathogen challenge on growth performance, carcass composition, and pork quality of high and low 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 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 – harvest). At ~ 125 kg, pigs were harvested using standard commercial procedures. Carcasses were evaluated f or 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 lesser ADFI than controls during period 2 (P < 0.05), but 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 content, greater Hunter L values, and greater Hunter b values (P < 0.05) than loin chops from low RFI pigs. Infection status did not significantly affect carcass composition or pork quality traits (P > 0.05). These results indicate that a MhLI challenge early in growth did not significantly impact ultimate carcass composition or meat quality traits. Selection for greater feed efficiency in pigs did not affect their response to pathogenic challenge.