Associations between drinking-water nitrate and the productivity and health of farrowing swine

Review of potential risks associated with supplemental dietary exposure to nitrate-containing compounds in swine-a paradox in light of emerging benefits

Calcium nitrate has been reported to benefit reproductive outcomes in sows and their offspring when administered via the feed (15 to 19 mg/kg-body weight [bw]/day) during the periparturient period. Traditionally, dietary nitrate had been considered a methemoglobinemia (MetHb) risk in swine. Similar hazard concerns have existed in humans, but a recent benefit/risk analysis established that nitrate levels associated with well-recognized health benefits outweigh potential risks. A similar benefit/risk perspective in swine was lacking and challenged by sparse published hazard data, often referenced within larger reviews related to all livestock. The objective of this review was to better characterize the potential for adverse health and performance effects reported in the literature for swine consuming nitrate and to provide metrics for evaluating the reliability of the studies reviewed. Supplemental exposure via feed or drinking water was considered for any life stage, dose, and exposure duration. More than 30 relevant studies, including case reports and reviews, examined calcium, potassium, sodium, or unspecified nitrate salts at doses up to 1,800 mg nitrate/kg-bw/day for exposures ranging from 1 to 105 d. The studies primarily evaluated weight gain, blood methemoglobin levels, or vitamin A homeostasis in sows or growing swine. An extensive review of the literature showed reports of adverse effects at low nitrate doses to be of low reliability. Conversely, reliable studies corroborate nitrate intake from feed or drinking water at levels equal to or greater than the European Food Safety Authority's no-observed-adverse-effect level (NOAEL) for swine of 410 mg nitrate/kg-bw/day, with no MetHb or other adverse effects on reproduction, growth, or vitamin A levels. Using a weight-of-evidence evaluation, we have moderate-to-high confidence that the NOAEL for nitrate supplementation in swine is likely between 600 and 800 mg/kg-bw/day. These levels are several-fold higher than dietary nitrate concentrations (19 mg/kg-bw/day) that are known to benefit birth outcomes in sows. This review elucidates the quality and reliability of the information sources historically used to characterize nitrate in swine feed as a contaminant of concern. Results from this evaluation can assist risk managers (e.g., regulatory officials and veterinarians) in consideration of proposed benefits as well as reassuring swine producers that low-level nitrate supplementation is not anticipated to be a concern.

Association between Drinking Water Nitrate and Adverse Reproductive Outcomes: A Systematic PRISMA Review

One in six couples experience fertility problems. Environmental factors may affect reproductive health; however, evidence is lacking regarding drinking water nitrates and outcomes of male and female fertility. The aim of this study was to investigate if exposure to nitrates in drinking water is associated with adverse reproductive outcomes in humans, and animals of fertile age. We conducted a systematic literature search and included case-control studies, cohort studies, and randomized control trials reporting on the association between drinking water nitrate exposure of men, women, or animals and adverse reproductive outcomes, specified as: Semen quality parameters, time to pregnancy (TTP), pregnancy rates, assisted reproductive technologies (ART), and spontaneous abortion. Findings were reported in a narrative synthesis. A total of 12 studies were included. The only human study included reported a decrease in spontaneous abortion at any detectable nitrate level. Overall, the 11 included animal studies support a potential negative effect on semen quality parameters but report equivocal results on TTP and number of offspring produced, and higher risk of spontaneous abortion. In conclusion, animal studies indicate possible effects on semen quality parameters and spontaneous abortion. However, with a few studies, including some with methodological limitations and small sample sizes, caution must be applied when interpreting these results.

Current knowledge of water quality and safety for livestock

Basic laboratory evaluation of water quality for livestock should include measurement of TDS, sulfate, nitrate-nitrite, and coliform bacteria. Supplementary water tests may include pH, sodium, iron, magnesium, chloride, calcium, potassium, manganese, and contaminants specific to the situation. Using the best-quality drinking water available contributes to the optimal production of livestock. Restricted quantity of drinking water or drinking water containing excessive levels of nitrate, TDS, sulfate, and other constituents can affect growth and production of all classes of animals. Drinking-water quality and availability should be evaluated as a cause of poor performance or nonspecific disease conditions in livestock. It is important that attempts to evaluate water quality include obtaining a thorough history, making astute observations, and asking intelligent questions. A thorough laboratory examination of animal specimens and water samples should be evaluated in view of existing standards for livestock drinking-water quality.