SIGNS OF INFECTIONS AND REDUCED IMMUNE FUNCTIONS AT WEANING OF CONVENTIONALLY REARED AND SPECIFIC PATHOGEN-FREE PIGS

The growth rate and several immune parameters were recorded to monitor the performance, health and immune status of 40 piglets in a conventi onal farrow to finish herd. In addition, effects of wearing on immune parameters were studied under minimal influence of infections in 20 sp ecific pathogen free (SPF) pigs. The growth rate of the conventionally reared pigs decreased after weaning and after allocation of pigs to n ew premises. Around weaning a considerable number of pigs displayed in terferon-alpha (IFN-alpha) in serum, indicating the spread of vital in fections. Bacterial infections were indicated by elevated numbers of c irculating neutrophilic granulocytes during the weaning period. Functi onal in vitro tests of peripheral blood mononuclear cells (PBMC) revea led that the Concanavalin A (CON A) induced proliferation decreased bo th after wearing and after transfer of the conventionally reared pigs to the finishing unit. The decreased proliferation observed after wean ing was accompanied by decreased interleukin-2 (IL-2) production in re sponse to the mitogen. A reduced IL-2 producing capacity after weaning was confined with PBMC obtained from the SPF pigs. Flow cytometric an alyses of these cells showed that the proportion of PBMC expressing IL -2 receptors (IL-2R(+)) was decreased 3 and 6 days after weaning when cultured in the absence of mitogen while the proportion of IL-2R(+) ce lls was unaltered in Con A simulated cultures. Thus indications of red uced immune function coincided in time with signs of infections, espec ially around weaning.