Rapid changes occur in feed efficiency after infection with Mycoplasma hyopneumoniae and Pasteurella multocida

Mycoplasma hyopneumoniae (Mhp) and Pasteurella multocida (Pm) are the agents most frequently isolated from lungs affected with enzootic pneumonia. Primary infection with Mhp predisposes pigs to opportunistic infection with Pm, causing increased lung damage and reduced weight gains and feed intake (Eamens et al. 2007). This study tested the hypothesis that infection with multiple pathogens (Mhp+Pm) would reduce feed efficiency compared to a single infection of either pathogen or uninfected pigs.

Data from a previous trial using 64 individually-housed hybrid (Landrace x Large White) gilts weighing 24.0 ± 0.53 kg (mean ± SE) challenged with Mhp, Pm, Mhp+Pm, or receiving no challenge, was reanalysed to investigate the effects of single or multiple respiratory pathogens on feed efficiency (Eamens et al. 2007). Each treatment group was housed in a separate room. Individual weight gain and feed intakes were calculated weekly for the 4 weeks following challenge. Feed efficiency was calculated as gain : feed (G : F), to allow the comparison of results on a unidirectional scale, as pigs suffered significant weight losses. Differences in G : F were analysed using unbalanced ANOVA (Genstat, 17th Edition; UK).

All challenged pigs developed pneumonia and four pigs (one ‘Pm’ and three ‘Mhp+Pm’) required treatment. Infection with Pm, either alone or with Mhp, caused negative G : F ratios which were significantly reduced (P < 0.001) in the first week after challenge (Fig. 1). In the absence of repeated challenge or environmental stressors, Pm infected pigs recovered rapidly, with no differences (P > 0.05) at 2 weeks and higher (P < 0.001) G : F in Mhp+Pm pigs at 3 weeks. Over 4 weeks, pigs challenged with Mhp+Pm had lower (P < 0.002) G : F than uninfected pigs or pigs challenged only with Mhp.

Fig. 1.  Gain to feed ratios (+SEM) of uninfected (), or infected with P. multocida (Pm) (), M. hyopneumoniae (Mhp) () or the combined infection (Mhp+Pm) () over 4 weeks after challenge. *** denotes significant difference between treatments.

The large reduction inG : F in Pm and Mhp+Pm treatments was associated with both reduced average daily feed intake (ADFI) (P < 0.001) and reduced average daily gain (ADG) (P < 0.001). The rapid recovery in G : F of the Mhp+Pm group was associated with higher ADG at week three (P < 0.001) relative to all other treatments, as there was no difference in ADFI between pigs with single or multiple pathogens at this time. Carcass composition measures (computed tomography) over this period showed significantly reduced proportions of body fat and increased muscle (by weight) in pigs infected with both Mhp+Pm (Eamens et al. 2007), suggesting that recovering pigs were largely depositing muscle when ADFI increased.

Calculating G : F ratio on a weekly basis quantified the acute impact of Pm infection and also the subsequent rapid recovery in feed efficiency. However, calculations over the total period still showed a negative impact of Pm on G : F, and this longer interval is of greater relevance to producers as it indicates the long-term production effects of untreated respiratory disease.