Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract only
Publication Acceptance Date: 4/1/2013
Publication Date: 7/8/2013
Citation: Taylor, J.B., Dungan, R.S., Smith, D.J. 2013. Safety and efficacy of low-dose, subacute exposure of mature ewes to sodium chlorate. Journal of Animal Science Supplement. 91:(Suppl.2):218. Interpretive Summary: The overall goal is to minimize the incidence of diarrhea in newborn, neonatal lambs by reducing the load of some pathogenic bacteria in the lambing system. Recently, we have demonstrated the advantages single oral doses of chlorate salts to reduce E. coli in the colon of lactating ewes and neonatal lambs. However, this effect was short lived and theoretically too short to provide benefit to the lamb. The current experiment investigated the effects of continuous exposure of mature ewes to chlorate salts in the drinking water over a 5-day period on ewe health and fecal E. coli. Based on the results, ewes consuming low doses of chlorate salts in the drinking water shed significantly less fecal E. coli in after 5 days, and continuous exposure to chlorate salts did not impair the health of the ewe.
Technical Abstract: The objective was to determine the safety and efficacy of low-dose, subacute exposure of mature ewes to NaClO3 in the drinking water. Twenty-five ewes (BW = 62.5 ± 7.3 kg) were placed indoors in individual pens with ad libitum access to water and feed. After 7 d of adaptation, ewes were assigned randomly to 1 of 5 treatments: 0 (control), 30, 60, 90, or 120 mg NaClO3•kg BW-1•d-1. Treatments were delivered in the drinking water for 5 d (i.e., 120 h). Endpoints of subclinical toxicity were daily water intake, whole-blood methemoglobin percentage, and packed-cell-volume (PCV). Efficacy of treatments was based on fecal Escherichia coli concentrations. Based on water intakes and BW, actual daily NaClO3 exposures were 0 and 28, 56, 80, and 110 ± 2 mg•kg BW-1 for control and 30-, 60-, 90-, and 120-mg treatments, respectively. Such doses neither induced methemoglobin formation (0.310, 0.304, 0.382, 0.334, and 0.300 ± 0.053%, respectively) nor altered PCV (42.5, 44.2, 43.8, 41.4, and 42.9 ± 1.9%, respectively). Ewes that consumed ˜110 mg NaClO3•kg BW-1•d-1 drank ˜ 14% less (P < 0.05) total water on d 2 than did other treatment groups. By d 5, the comparative reduction in voluntary water intake was nearly 30% less, which was accompanied with a reduction in feed intake. This response indicated that subacute exposure to = 110 mg NaClO3•kg BW-1•d-1 may not be safe for mature ewes. Consumption of NaClO3 for 5 d reduced fecal E. coli in a dose-dependent fashion (P < 0.08). Using unlike letters (a, b, and c) to indicate differences (P < 0.10) in fecal E. coli concentrations, the result of treatment contrasts for ewes consuming 0, 28, 56, 80, and 110 mg NaClO3•kg BW-1•d-1 were a, a, b, bc, c, respectively. These data suggested that subacute exposure to = 28 mg NaClO3•kg BW-1•d-1 is not efficacious, with respect to fecal E. coli. At 22 d after treatments stopped, fecal E. coli in all NaClO3-treated ewes were similar to control ewes, which indicated that the effect of NaClO3 is rapidly reversible following subacute exposure. In summary, daily consumption of 56 to 80 mg NaClO3•kg BW-1 for 5 d was safe for targeted, short-term reduction of fecal E. coli in mature ewes.