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

• Purple prairie clover (PPC) at 600 g/kg dietary DM did not affect feed intake.
• PPC condensed tannins (CT) at 36 g/kg DM reduced protein digestibility.
• PPC CT at 36 g/kg DM did not affect organic matter and fibre digestibility.
• PPC at 600 g/kg dietary DM reduced fecal shedding of E. coli O157:H7 in lambs.
• Feeding PPC enhanced serum antioxidant capacity of 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 (1) alfalfa (Alf), (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.