Natural Pig Plasma Immunoglobulins Have Anti-Bacterial Effects: Potential for Use as Feed Supplement for Treatment of Intestinal Infections in Pigs

Hedegaard, Chris J.; Strube, Mikael L.; Hansen, Marie B.; Lindved, Bodil K.; Lihme, Allan; Boye, Mette; Heegaard, Peter M. H.

Antibodies are major effector molecules of the vertebrate adaptive immune system. In mammals, circulating antibody isotypes are predominantly immunoglobulin (Ig) G, and to a lesser extent IgA and IgM [1] . Maternal IgG is provided to the offspring ensuring an adequate level of circulating antibodies in the neonate by different routes depending on the species. Thus, among mammals, primate neonates are born with circulating IgG obtained via the placenta in the foetal stage, whereas ruminants and piglets acquire IgG through colostrum perinatally through an intestinal transport mechanism specifically working in the first 24 hours after birth allowing entry of ingested maternal IgG from the gut to the circulation [2] . In addition, mother's milk provides all mammals in the suckling stage with oro-gastric protection (lactogenic immunity) against pathogens until the offspring matures and becomes able to produce antibodies both at mucosal surfaces and in the circulation [2] [3] [4] [5] . In intensive pig production, piglets are weaned early when still immunologically incompetent (3-4 weeks of age), and they are therefore susceptible to intestinal (mucosal) infections including enterotoxigenic Escherichia coli (ETEC) [6] and depend on maternal antibodies for protection against such infections. ETEC infections are major contributing factors to the multifactorial disease post weaning diarrhoea (PWD) demanding excessive antimicrobial use in husbandry [7, 8] resulting in increasing incidence of antimicrobial-resistant bacteria posing a great threat to human health [8] [9] [10] . Vaccines may provide protection against specific pathogens, however as diseases such as PWD often has a multifactorial aetiology [11] , generating vaccines against such diseases is a complicated matter. Furthermore, efficient mucosal immunity is not easily induced [12] . With the exception of one commercially available, orally delivered E. coli F4-specific vaccine against PWD used in Canada for a number of years [13] and recently approved by the European Medicines Agency in Europe [14] , no vaccines are available for use against PWD.