Relationships between colostrum supply of suckling piglets and Salmonella prevalence in piglet rearing

Epidemiological Study on Salmonella Prevalence in Sow Herds Using Direct and Indirect Detection Methods

In piglet production, the beginning of pork production, Salmonella prevalence requires greater attention as having an impact on the subsequent production steps. The aim of this study was to investigate Salmonella prevalence in three sow herds with attached piglet rearing units. Salmonella prevalence was investigated either directly by boot swabs and feces or indirectly by serum samples taken during gilt integration, the peripartal period, and piglet rearing. Boot swabs and feces were analyzed by real-time PCR and subsequent microbiology. Results indicated that high biosecurity measures in sow husbandry do not necessarily result in a low Salmonella prevalence. Furthermore, the sow herds’ Salmonella prevalence should not be used to infer the situation in the associated piglet rearing. The proportion of positive boot swabs was 10.5, 3.6, and 21.3% for sows (gilts and peripartal) with an inverse situation in piglet rearing with 50.0, 63.3, and 5.8% positive swabs for farms A, B, and C, respectively. Boot swabs are suitable as a direct sampling method to gain an overview of Salmonella prevalence in both sows and piglets. Indirect serum antibody testing can be useful, although it should be evaluated considering age-dependent levels of antibody titres.

Influence of colostrum supply on Salmonella spp. seroprevalence in piglet rearing and possibilities to increase colostrum production by optimised feeding

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.

Prevalence of Salmonella by Serological and Direct Detection Methods in Piglets from Inconspicuous, Conspicuous, and Vaccinated Sow Herds

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.

Weaned piglets: another factor to be considered for the control of Salmonella infection in breeding pig farms

Field studies on Salmonella infection in suckling piglets are scarce due to the intrinsic difficulties of collecting proper samples (i.e. tonsils or mesenteric lymph nodes), and most of them rely on the analysis of rectal swabs that limit their accuracy. We used 495 slaughtered 4-weeks-old male piglets intended for human consumption from 5 Salmonella-seropositive breeding farms to collect gastrointestinal packages and perform a thorough detection of Salmonella on mesenteric lymph nodes and intestinal content. The overall prevalence of both infection and shedding was high (≈ 36%) indicating that piglets played an active role in Salmonella maintenance in the farms. Major serotypes found in piglets included 4,[5],12:i: (35.4%), Rissen (17.1%), Derby (10.9%) and Bovismorbificans (10.3%). In most of the infected animals (72.8%) the same serotype was found in mesenteric lymph nodes and feces. Significant higher ELISA OD% values were found in meat juice samples from non-infected piglets compared to infected ones (median OD% of 12.0 and 17.3, respectively; P = 0.002) suggesting some protective effect of sow's colostrum. Salmonella was also isolated from feces from weaned sows contemporary of the slaughtered piglets, and 89% of the serotypes identified in sows were also detected in piglets. Pulsed field gel electrophoresis analyses showed that 75% of the piglet isolates that were compared to those of sows were related to them, suggesting the circulation of Salmonella strains between sows and piglets. It appears that improving piglet colostrum intake along with the reduction of the shedding in sows may favor the control of Salmonella infection in breeding farms.