Document Type : Research Paper
Authors
1 Department of Animal and Poultry Science, Faculty of Agricultural Technology, University of Tehran, Tehran, Iran
2 Department of Animal Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran
Abstract
Cattle are the major reservoirs of the pathogenic bacteria Escherichia coli O157:H7, and approximately 30% of feedlot cattle shed E. coli O157:H7. Feedlot calves are fed high concentrate diets in order to increase feed efficiency. It has been reported that populations of E. coli O157:H7 were higher in grain-fed than in forage-fed cattle, and when cattle were abruptly switched from a high concentrate diet to an all-forage diet, total E. coli populations declined 1000-fold. Therefore, strategies that decrease E. coli O157:H7 prior to slaughter will reduce human exposures to this virulent pathogen. However, a dietary switch to forage in feedlot calves is not advocated due to feasibility, weight loss and other logistical issues, other feedstuffs rich in phenolics such as essential oils (EO) could be a more feasible alternative strategy to reduce E. coli O157:H7 populations. Data available indicate a strong bactericidal activity of EO against pathogenic bacteria such as E. coli O157:H7. Among the EO, thyme (THY) and cinnamon (CIN) oil have attracted considerable attention in several literatures due to their potential antibacterial activity against ruminal microbes. The aim of the present research was to evaluate the effects of THY and CIN on E. coli O157:H7 population in the rumen and feces of feedlot calves fed high-concentrate diets. Twenty-four growing Holstein calves (214±16 kg initial BW) were used in a completely randomized design and received their respective dietary treatments for 45 d. Treatments were: 1-control (no additive), 2-THY (5 g/d/calf), 3-CIN (5 g/d/calf) and 4- forage (sudden switch from grain diet to forage diet in the last ten days of experiment; as positive control for relative abundance of E. coli O157:H7 in the rumen and feces). Calves were fed ad libitum diets consisting of 15% forage and 85% concentrate. Ruminal and fecal samples were collected from calves at the end of the experiment. Quantitative detection of E. coli O157:H7 in samples were done using specific primers and real-time PCR method.
The average dry matter intake (DMI) and daily weight gain (ADG) of feedlot calves from day 36 to day 70 of the experiment was not affected by the experimental treatments. However, DMI and ADG decreased, and feed conversion ratio increased in calves fed forage treatment from day 71 to 80 (P<0.05). Supplementation of THY or CIN decreased the relative abundances of E. coli strain O157:H7 (rbfE) in rumen contents (P<0.05), while they did not affect strain O157:H7 (iudA). But forage treatment decreased the population of both strains of E. coli O157:H7 in the rumen fluid of feedlot calves compared to the control treatment (P<0.05). The experimental treatments also reduced the relative abundances of both strains of E. coli O157:H7 in the rumen and feces of feedlot calves compared to the control treatment (P<0.05). The results obtained from present research showed that the use of thyme and cinnamon essential oil in feedlot calves diet can be a more suitable way compared to nutritional methods such as abruptly switched from a high grain diet to an all-forage diet to reduce the population of pathogenic bacteria Escherichia coli O157:H7 in the rumen and reduction of its shedding in feces.
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