Interpretive Summary: Impact of Mycoplasma hyopneumoniae and Lawsonia intracellularis on the performance of pigs divergently selected for feed efficiency
By: Megan LaFollette
In February 2018, Journal of Animal Science published an article investigating the impact of selecting pigs for feed efficiency on their response to disease. Currently, production pigs often have respiratory and gut diseases simultaneously leading to decreased pig performance and welfare as well as economic loss. Feed efficiency is an economically valuable trait, but there is a concern that selection for feed efficiency could make pigs more vulnerable to disease. Increased disease susceptibility could occur if selected pigs have a reduced ability to repartition nutrients from growth to recovery. Two specific pathogens of concern are Mycoplasma hyponeumoniae and Lawsonia intracellularis. The former pathogen compromises respiratory health; the latter compromises gut health. This study’s objective was to determine if pigs selected for high feed efficiency (based on residual feed intake) have reduced growth performance during a disease challenge as compared to pigs selected for low feed efficiency.
In this study, across 6 weeks, littermate pairs of Yorkshire barrows were split into four treatment groups of 25 pigs each: low feed efficiency challenge, high feed efficiency challenge, low feed efficiency control, and high feed efficiency control. The split between low and high feed efficiency was made from the 11th generation of divergently selected pigs. In these selected pigs, the high feed efficiency pigs consume 12-15% less feed per given amount of growth and back fat as pigs with low feed efficiency. The split between challenge and control was made by inoculating disease challenge pigs with both respiratory and gut pathogens (Mycoplasma hyponeumoniae and Lawsonia intracellularis, respectively), while the controls received a sham inoculation. Pigs were housed individually and fed the same ad libitum diet. Researchers measured feed intake, body weight, fecal swabs, blood samples, body composition, and tissue accretion.
Pigs selected for high feed efficiency did not have a greater reduction in overall growth performance as compared to pigs selected for low feed efficiency during a disease challenge. Rather, all disease challenge pigs – regardless of selection – experienced a 17% reduction in average daily gain (ADG), a 12% reduction in average daily feed intake (ADFI), and a 7% reduction in gain to feed ratio (G:F) compared to control pigs. Pigs selected for high feed efficiency had decreased ADFI and increased G:F, but did not have different ADG or tissue accretion compared to low feed efficiency pigs. In this study, disease inoculation was shown to be successful based on serum antibody levels, fecal shedding, gross lesions and pathogen immunohistochemistry staining. However, challenge pigs showed limited outward signs of infection with only 2 or 50 pigs having diarrhea during the entire 6 week period. Control pigs remained pathogen free.
Overall, this study demonstrates that genetic selection of pigs for high feed efficiency does not inhibit growth performance during an extended disease challenge. Instead, regardless of genetic selection, pigs experiencing a disease challenge with both respiratory and gut pathogens had decreased growth, feed efficiency, and tissue accretion. These results show that even a mild disease challenge (that does not result in pig death, the necessity for antimicrobial intervention, and few outward signs) impairs pig growth performance. This study recommends future research to on the impact of sub-clinical infections on growing pigs.
To view the full article " Impact of Mycoplasma hyopneumoniae and Lawsonia intracellularis on the performance of pigs divergently selected for feed efficiency, " visit Journal of Animal Science.