Effects of linseed and oat in antibiotic-free diets on the gut health , mucosal integrity and performance of piglets

The infection-preventive effects of 10% linseed meal (FM) and 15% hulled oat meal (HOM) in antibiotic-free diets for weaned piglets (n=48) were studied. Compared with controls, both plants improved (P<0.01) feed intake and growth rates up to day 6 post-weaning (before infection with E. coli). After E.coli infection, all piglets showed poorer performance, irrespective of the diet. The FM and HOM exerted no clear impact on faecal consistency, E.coli shedding or mucosal integrity, except for reduced (P=0.003) goblet cell and increased (P=0.04) leukocyte counts.


INTRODUCTION
In the search for substitutes for antibiotics now banned in feeds, linseed (Linum usitatissimum) and oat (Avena sativa) have received renewed scientific interest (Morris, 2001;Oomah, 2001;Liu et al., 2002).Since prehistoric times, both plants are known for possessing, in addition to protein and energy, some specific phytochemicals and bioactive compounds.They might act to improve feed intake, protect epithelial cells against pathogenic colonization, stimulate mucosal growth and immunity in the absence of antibiotics for prophylaxis after weaning of piglets.Therefore, the aim of this study was to test the influence of linseed meal (FM) and hulled oat meal (HOM) in an antibiotic-free diet on the clinical health, performance, feacal E. coli shedding, haematological indices and gut morphology of weaned piglets before and after exposure to a controlled infection with enterotoxigenic E. coli K88 (ETEC).

MATERIAL AND METHODS
Forty-eight crossbred piglets of 8 kg initial BW were studied during 19 days post-weaning (5 d pre-infection and 14 d post-infection with ETEC with a single oral dose of 5×10 9 CFU E. coli O149K91F4 K88ac).They were kept individually at an ambient temperature of 25 o C and allotted to 4 isonitrogenous and isoenergetic treatments: 1. basal, no ETEC infection (B); 2. B + ETEC infection (B+); 3. B+10% FM +ETEC infection (BF+); 4. B+15% HOM + ETEC infection (BO+).The antibiotic-free, basal diet contained wheat (32.6%), barley (30.0%) and soyabean meal (17.8%) as the primary ingredients.The contents of CP, ileal digestible lysine and NE f were 20.3%, 0.98%, and 10.0 MJ/kg, respectively.The FM and HOM were incorporated at the expense of wheat and soyabean meal.The diets and faeces were analysed for the contents of DM, ash, and N (AOAC, 1984).Also, dietary minerals were determined by using inductively coupled plasma atomic emission spectrometry (ICP-AES).Samples of faeces were taken daily directly from the rectum for: 1. enumeration of haemolytic E. coli on sheep blood agar plates (after incubation for 24 h at 37˚C); 2. faecal score index (FSI, scale 0 to 3).The body weight of piglets and feed intake were recorded on d 0 (weaning), 6 (before ETEC infection) and 19 (slaughter).On d 11 and 19 after weaning, blood samples from v. jugularis were taken to assay the haemogram and IgG titers using a CellDyn 4000 automated haematology analyser.Post-mortem examination encompassed intestinal size, weight and histology.Jejunal sections were stained with haematoxylin and eosin to measure villous/crypt shapes using light and scanning electron microscopy.Also, staining with high-iron diamin (HID) blue was performed to distinguish sialomucins and sulphomucins.pH and VFA contents were measured in the digest by HPLC.The data were subjected to ANOVA analysis of variance for a randomized block design, with treatments and E.coli infection as experimental factors.The significance of the differences between treatments was tested with Student's t-test at P<0.05 or 0.01.

RESULTS AND DISCUSSION
There were no clinical health problems or piglet mortality before the E. coli challenge (up to d 5 post-weaning), whereas 3 d after the challenge, two piglets died (one in BF+, and another in BO+) due to severe diarrhoea.Compared with controls (B), the piglets fed 10% FM and 15% HOM consumed more (P<0.01)feed and grew faster (P<0.01)before the E. coli challenge, but not afterwards (Table 1).The piglets challenged with ETEC K88 grew significantly slower than the control (B), non-challenged piglets.However, over the whole post-weaning period of 19 d, the ADG of piglets were similar (P=0.31),i.e. 392, 311, 363, and 340 g/d for B, B+, BF+, and BO+, respectively.Faecal shedding of haemolytic E. coli highly corresponded to the ETEC K88 infection, whereas the differences among the dietary treatments were less evident (Table 1).The FSI and DM contents in faeces were affected (P<0.05) by the E. coli challenge, but not by the diets.Neither the length nor weight of the duodenum differed among the treatments.However, the jejunum of piglets fed both plants was longer (P=0.04) and tended (P=0.08) to contain less NH 3 in digesta than in B+.Besides, their ileum tended (P=0.06) to be lighter, whereas the contents of VFA were similar among the treatments.Jejunal histology and HID-values were similar, except for the goblet cells and mucosal thickness (Table 2).Of the total haemogram, only leukocytes, basophiles (as % of leukocytes) and IgG-titers were significantly affected by the dietary treatments in the post-infection period (Table 3).

CONCLUSIONS
Adding 10% of linseed meal and 15% of hulled oat meal significantly improved feed intake and growth of weaned piglets before E. coli infection (up to 5 d post-weaning), but not afterwards.Based on all the response criteria, the anti-pathogenic potency of both plants in a weaner diet was less evident.

Table 1 .
Feed intake (FI), growth rates and post-infective shedding of haemolytic E. coli (lg CFU/g) in faeces of piglets as affected by the treatments

Table 2 .
Jejunal histology and digesta composition on day 13 post-infection in piglets

Table 3 .
Blood indices in weaned piglets as affected by the treatments and E.coli infection