Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2015
Publication Date: 3/13/2015
Publication URL: http://doi:10.2527/jas.2014-8568
Citation: Taylor, J.B., Smith, D.J. 2015. Continuous, low-dose oral exposure to sodium chlorate reduces fecal generic Enterobacteriaceae coliforms in sheep feces without inducing subclinical chlorate toxicosis. Journal of Animal Science. 93:1942-1951.
Interpretive Summary: Early in a lamb’s life, bacteria-induced diarrhea from pathogenic E. coli and sometimes Salmonella spp. can impair lamb vitality and growth. These bacteria are often picked up by the lamb from sampling the environment where feces have been shed, such as tasting the pen bedding or nursing from a soiled utter. In shed-lambing systems, lambs and ewes are in very close proximity to each other for 2 to 4 days. Such concentration of animals can increase contamination of the environment and the incidence of disease transfer among the newborns. We propose that adding chlorate salts to the drinking water of ewes during lambing will reduce the amount of Enterobacteriaceae organisms (such as pathogenic E. coli) that are shed in the lambing area. In turn, this may decrease the probability that lambs will contract diarrhea from sampling the environment. In a preslaughter setting, chlorate salts have been successfully added to the drinking water and diets of livestock and poultry to reduce shedding of pathogenic E. coli and Salmonella spp. during the slaughter process. Furthermore, risk of bacteria becoming resistant to chlorate salts is minimal to nonexistent. Therefore, we are interested in chlorate salts as a prophylactic tool to minimize occurrence of diarrhea disease in new born lambs. However, chlorate salts can be toxic to livestock, when consumed a high levels. So, before we can determine if our proposal is valid, we must first determine the minimal daily dose of chlorate salt that is safe for the ewe to consume, but will result in a significant reduction of E. coli shed in the feces. We established a safe dose of chlorate salt, that when fed to mature ewe for 5 days fecal shedding of E. coli was reduced by more than 99%. Based on this finding, we are currently developing a shed-lambing management strategy that will test the effectiveness of chlorate salts to reduce incidence of enteric diseases in a commercial-scale setting.
Technical Abstract: Our objectives were to determine a minimal daily dose of sodium chlorate, to be included in the drinking water for 5 days, that is safe yet maintains efficacy in reducing fecal shedding of Escherichia coli in mature ewes. In a complete randomized experimental design, 25 Targhee ewes (age = 18- to 20-mo-old; BW = 62.5 +/- 7.3 kg) were assigned randomly to 1 of 5 treatments, which were administered in the drinking water for 5 consecutive days. Treatments were control group (no sodium chlorate) and 4 targeted levels of sodium chlorate intake that was offered over a 5-day period: 150, 300, 450, and 600 mg/kg BW/5 days, which was equivalent to a daily offering of 30, 60, 90, and 120 mg/kg BW, respectively. Ad libitum water and sodium chlorate intake were monitored daily, body weight was measured at the beginning and 15 and 51 days after the 5-day treatment period. Serum chlorate, whole blood methemoglobin and packed-cell volume (PCV), and fecal generic E. coli and general Enterobacteriaceae coliforms were measured from corresponding samples collected at the end of the 5-day treatment period. Actual 5-day cumulative intake (+/- standard deviation) of sodium chlorate was 141.0 +/- 10.1, 273.7 +/- 15.9, 404.0 +/- 19.2, and 496.6 +/- 31.4 mg/kg BW for ewes offered 150, 300, 450, and 600 mg NaClO3/kg BW/5 days, respectively. Daily intake remained constant for all treatment groups except for ewes offered 600 mg NaClO3/kg BW/5 days, which fluctuated daily and decreased (quadratic; P = 0.04) over the course of the treatment period. Serum chlorate concentrations increased (quadratic; P < 0.001) with increasing sodium chlorate intake. Mean (least squares +/- standard error of the mean) serum chlorate concentrations for ewes offered 150, 300, 450, and 600 mg NaClO3/kg BW/5 days were 15.6 (14.1), 32.8 (15.8), 52.9 (14.1), and 90.3 (14.1) mg/L, respectively. Whole blood methemoglobin and PCV were similar among control and ewes offered sodium chlorate (P = 0.31 to 0.81). Likewise, body weight was not affected by sodium chlorate (P > 0.27). Ewes consuming 273.7+/- 15.9 mg NaClO3/kg BW/5 days and greater (i.e., ewes offered 300, 450, and 600 mg) had 1.4-log unit or greater reduction in fecal E. coli and Enterobacteriaceae coliforms compared with control ewes. We suggest that for a short-term daily dosing strategy, the minimal and safe oral dose of sodium chlorate for mature ewes, to achieve a >99.9% reduction in fecal shedding of generic E coli, is 273.7+/-15.9 mg NaClO3/kg BW for a 5-day or less exposure period.