Effects of subacute nitrate toxicity on production, reproduction, and gene expression in Suffolk ewes

Ruminants consuming elevated dietary nitrate (NO3- ) vary in their ability to efficiently reduce excess nitrite (NO 2-) to ammonia. This leads to methemoglobin formation and ultimately NO3- toxicity signs. Signs associated with subacute NO3- toxicity include lethargy, head pressing, decreased feed efficiency, decreased immune function, and reproductive complications. Variation in individual tolerance to elevated dietary NO 3- can be partially attributed to rate and duration of exposure, rate of elimination, metabolism, species, and dose. This study was conducted to: (1) confirm and quantify variation in response to high dietary NO3-, (2) determine if ewes can be identified as more or less tolerant to high dietary NO3- based on production and plasma measures, (3) identify genes differentially expressed among ewes highly tolerant or lowly tolerant to elevated dietary NO3 -, and (4) determine if ovulation and maintenance of pregnancy is impaired by subacute levels of dietary NO3 - administered prior to breeding. It was determined that ewes more tolerant or less tolerant to elevated dietary NO3- cannot be identified based on production traits and plasma analytes alone. However, genes involved in stress and metabolism were identified as differentially expressed between lowly and highly tolerant ewes. Finally, estrus cycles and maintenance of pregnancy were not affected by high dietary NO3 -.