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Dietary nitrate and presence of protozoa increase nitrate and nitrite reduction in the rumen of sheep
Author(s) -
Villar María Laura,
Hegarty Roger Stephen,
Clay Jonathon William,
Smith Katherine Anne,
Godwin Ian Robert,
Nolan John Vivian
Publication year - 2020
Publication title -
journal of animal physiology and animal nutrition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.651
H-Index - 56
eISSN - 1439-0396
pISSN - 0931-2439
DOI - 10.1111/jpn.13365
Subject(s) - rumen , nitrite , methemoglobin , nitrate , zoology , protozoa , biology , in vivo , food science , ammonia , methanogenesis , digestion (alchemy) , chemistry , defaunation , biochemistry , bacteria , agronomy , microbiology and biotechnology , fermentation , hemoglobin , ecology , chromatography , genetics
Nitrate ( NO 3 - ) supplementation is an effective methane (CH 4 ) mitigation strategy for ruminants but may produce nitrite ( NO 2 - ) toxicity. It has been reported that rumen protozoa have greater ability for NO 3 - and NO 2 - reduction than bacteria. It was hypothesised that the absence of ruminal protozoa in sheep may lead to higher NO 2 - accumulation in the rumen and a higher blood methaemoglobin (MetHb) concentration. An in vivo experiment was conducted with defaunated (DEF) and faunated (FAU) sheep supplemented with 1.8% NO 3 - in DM. The effects of rumen protozoa on concentrations of plasma and ruminal NO 3 - and NO 2 - , blood MetHb, ruminal volatile fatty acid (VFA) and ruminal ammonia (NH 3 ) were investigated. Subsequently, two in vitro experiments were conducted to determine the contribution of protozoa to NO 3 - and NO 2 - reduction rates in DEF and FAU whole rumen digesta (WRD) and its liquid (LIQ) and solid (SOL) fractions, incubated alone (CON), with the addition of NO 3 - or with the addition of NO 2 - . The results from the in vivo experiment showed no differences in total VFA concentrations, although ruminal NH 3 was greater ( p < .01) in FAU sheep. Ruminal NO 3 - , NO 2 - and plasma NO 2 - concentrations tended to increase ( p < .10) 1.5 hr after feeding in FAU relative to DEF sheep. In vitro results showed that NO 3 - reduction to NH 3 was stimulated ( p < .01) by incoming NO 3 - in both DEF and FAU relative to CON digesta. However, adding NO 3 - increased ( p < .05) the rate of NO 2 - accumulation in the SOL fraction of DEF relative to both fractions of FAU digesta. Results observed in vivo and in vitro suggest that NO 3 - and NO 2 - are more rapidly metabolised in the presence of rumen protozoa. Defaunated sheep may have an increased risk of NO 2 - poisoning due to NO 2 - accumulation in the rumen.