BackgroundDespite years of effort, the proportion of serologically Salmonella-conspicuous pig farms has not been significantly reduced. Incoming piglets are considered to be a significant source of Salmonella for feeder-to-finish-farms. Therefore it is important for farrow-to-feeder-farms to deliver Salmonella-inconspicuous piglets. The aim of the present study was to establish a possible link between an inadequate colostrum supply as a side effect of steadily increasing number of piglets born alive and weaned per sow and increasing Salmonella seroprevalence in piglet rearing on Salmonella-conspicuous farms.MethodsTwenty four farms in total were selected for this study. Half of the farms (n = 12) had been detected as Salmonella-conspicuous in previous serological tests on piglets (25 kg) and remaining farms (n = 12) had appeared Salmonella-inconspicuous. Every farm was visited once 24–28 h after the main day of farrowing. For sampling, four sows were randomly selected on each farm. The parity, the litter weight and the litter size were recorded. The sow and six of her piglets were selected for blood sampling (two light-weight, two medium-weight and two heavy-weight piglets respectively). In addition, the colostrum supply of newborn piglets was estimated by using the immunocrit.ResultsThe lightest piglets on Salmonella-inconspicuous and Salmonella-conspicuous farms showed a significant difference (p < 0.0339) in the colostrum supply (estimated by immunocrit). While light-weighted piglets in Salmonella-inconspicuous farms had an average immunocrit of 0.100 (±0.04) light-weighted piglets in Salmonella-conspicuous farms had an average immunocrit of 0.087 (±0.04). There was no significant difference (p > 0.05) in the factors body weight, litter weight, parity and litter size.ConclusionThe study provides preliminary evidence that when comparing Salmonella-inconspicuous farms with Salmonella-conspicuous ones, the colostrum supply may be a critical factor that needs to be considered. The fact that there is no difference in body weight between the two groups of farms suggests that there may be differences in farrowing management and especially colostrum management. Further studies are now required to investigate what causes the various colostrum supply on the respective farms and what long-term effects the individual colostrum supply might have on Salmonella prevalence at abattoir.

A commercial farm study investigated whether colostrum production and antibody transfer can be improved by extra feeding in late pregnancy sows, and whether such improvements have an influence on disease status (measured as Salmonella spp. seroprevalence) in piglets, using a rapid and cost effective, ELISA-based estimation method (IDEXX Swine Salmonella spp. Ab Test). Four farms with established high Salmonella spp. seroprevalence were selected, and 16 sows in each farrowing group were selected over six farrowing cycles for the feeding experiment (n=368). One half (n=184) of the sows were fed a conventional feed following official nutrient recommendations concerning energy, amino acids and minerals when they entered the farrowing pen. The other half (n=184) received 1.25 kg of a test feed daily containing fibre rich cereals (barley, oats), a fibre component (soy husks) and potassium diformate in addition to the conventional feed until two days post-partum. Blood samples were taken from two light and two heavy piglets aged 2 d in each litter (n=1,469) and at the end of rearing (approximately nine weeks old; average body weight of 25 kg; n=588). In the test-fed group, piglet immunocrit value (as a measure of immunoglobulin transfer) was significantly improved (P<0.0219; K:0.1226±0.0437; V: 0.1278±0.0406). A moderate correlation (r=0.40935; P<0.0001) was found between immunocrit value and Salmonella spp. antibodies at 2 d old. There was no correlation between immunocrit value and Salmonella spp. antibodies at the end of the rearing period (r=0.09914), when the pigs were around nine weeks of age. Despite better colostrum supply, the animals in the test group did not show a significantly lower prevalence of Salmonella spp. seroprevalence (test group optical density (OD) 9.8000±17.4954%; control group OD 8.9486±14.2426%; P<0.5344) at nine weeks of age. It could be shown that the colostrum supply can be optimised by providing sows with extra feed. The moderate correlation between immunocrit and Salmonella spp. antibodies on the second day of life suggests that measuring antibodies by rapid, cost effective ELISA could be a practical tool to for the estimation of colostrum supply and the corresponding health of piglets. A suspected effect of reduced colostrum supply on the Salmonella spp. seroprevalence at the end of piglet rearing was not detectable. Other effects (e.g. hygiene) seem to be more significant.

Due to the zoonotic potential of Salmonella, the high prevalence of Salmonella on pig farms deserves particular attention. Because there is limited precise data on piglet-producing farms, this survey evaluated the Salmonella status of 24 different pig farms that had previously been divided into 12 Salmonella-conspicuous (SC) and 12 Salmonella-inconspicuous (SI) farms on the basis of the serological status of their piglets (25 kg). The evaluation was based on 498 environmental samples and 2641 blood samples, as well as on a biosecurity screening. SC farms were subdivided into farms with sow vaccination against Salmonella (n = 3) and those without vaccination (n = 9). In accordance with the previous classification, both the highest Salmonella prevalence in the environment and the highest antibody titers of the examined piglets were determined on SC farms at both defined time points. Piglets from vaccinated sows showed the highest OD% values, before and after vaccination. On SC farms, most Salmonella-positive samples could be obtained in rearing areas (2017: 40.8%, 2019: 26.0%). The results of this study indicate that sow vaccination alone cannot influence Salmonella prevalence at the farm level. Above all, general infection pressure seems to play a major role for Salmonella prevalence in the environment and for high OD% values of related pigs.