Effects of purple prairie clover (Dalea purpurea Vent.) on feed intake, nutrient digestibility and faecal shedding of Escherichia coli O157:H7 in lambs

This study was conducted to assess the effects of purple prairie clover (PPC, Dalea purpurea Vent.) on feed intake, nutrient digestibility, faecal shedding of Escherichia coli O157:H7 and blood metabolites of lambs. A total of 18 lambs were divided into three groups and housed in individual pens and fed green chop (I) alfalfa (Alt), (2) a mixture of Alf and PPC in a ratio of 40:60 (DM basis; Mix) and (3) Mix supplemented with polyethylene glycol (Mix-P) for 45 d. A 333 g/L polyethylene glycol (PEG) solution applied at the rate of 250 mL/kg DM of Mix diet was included in the third treatment to neutralize the biological activity of condensed tannins (CT) in PPC. Total tract digestibility of the diets was determined using acid-insoluble ash (AIA) as an indigestible marker. Blood samples were collected to measure serum metabolites and to estimate the activity of antioxidant enzymes. All lambs were orally inoculated with a five strain mixture of E. coli O157:H7 after determination of diet digestibility and faecal samples were enumerated for E. coli O157:H7 after 1, 2, 3, 4, 7, 14,21 and 28 d of inoculation. Feed intake did not differ among lambs fed the three diets. Organic matter digestibility (P<0.05) and protein digestibility (P< 0.01) of Mix were lower than that of Alf. However, the three diets had similar neutral detergent fibre digestibility. Lambs fed Mix had lower levels (P< 0.05) of serum creatinine and urea nitrogen than Alf, but both Mix and Mix-P had higher (P< 0.05) levels of serum phosphorus. Mix fed lambs had greater (P< 0.05) serum total antioxidant capacity but lower (P<0.05) serum superoxide dismutase activity than lambs fed Alf. After inoculation, lambs fed Mix shed less E. coli O157:H7 than lambs fed Alf between d 1 and d 7 (P<0.05-0.006), and lambs fed Mix-P between d 1 and d 3 (P<0.05-0.012). Lambs fed Alf shed more E. coli O157:H7 than lambs fed Mix (P< 0.001) or Mix-P (P< 0.01) over the 28-d post-challenge period. Incoportaion of PPC in lamb diets at 60% of DM reduced faecal shedding in lambs challenged with E. coli O157:H7 as compared to Alf. The fact that shedding of E. coli O157:H7 was also reduced with Mix-P suggests that the anti-E. coli O157:H7 response of PPC is not solely due to CT. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.