Villar, Maria Laura; Hegarty, Roger Stephen; Clay, Jonathon William; Smith, Katherine Anne; Godwin, Ian Robert; Nolan, John Vivian

Author(s)

Villar, Maria Laura

Hegarty, Roger Stephen

Clay, Jonathon William

Smith, Katherine Anne

Godwin, Ian Robert

Nolan, John Vivian

Publication Date

2020-09

Abstract

Nitrate (NO3–) supplementation is an effective methane (CH4) mitigation strategy for ruminants but may produce nitrite (NO2–) toxicity. It has been reported that rumen protozoa have greater ability for NO3– and NO2– reduction than bacteria. It was hypothesised that the absence of ruminal protozoa in sheep may lead to higher NO2– 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% NO3– in DM. The effects of rumen protozoa on concentrations of plasma and ruminal NO3– and NO2–, blood MetHb, ruminal volatile fatty acid (VFA) and ruminal ammonia (NH3) were investigated. Subsequently, two in vitro experiments were conducted to determine the contribution of protozoa to NO3– and NO2– 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 NO3– or with the addition of NO2–. The results from the in vivo experiment showed no differences in total VFA concentrations, although ruminal NH3 was greater (p < .01) in FAU sheep. Ruminal NO3–, NO2– and plasma NO2– concentrations tended to increase (p < .10) 1.5 hr after feeding in FAU relative to DEF sheep. In vitro results showed that NO3– reduction to NH3 was stimulated (p < .01) by incoming NO3– in both DEF and FAU relative to CON digesta. However, adding NO3– increased (p < .05) the rate of NO2– accumulation in the SOL fraction of DEF relative to both fractions of FAU digesta. Results observed in vivo and in vitro suggest that NO3– and NO2– are more rapidly metabolised in the presence of rumen protozoa. Defaunated sheep may have an increased risk of NO2– poisoning due to NO2– accumulation in the rumen.

Citation

Journal of Animal Physiology and Animal Nutrition, 104(5), p. 1242-1255

ISSN

1439-0396

0931-2439

Pubmed ID

32333622

Link

https://hdl.handle.net/1959.11/29199

Publisher

Wiley-Blackwell Verlag GmbH

Title

Dietary nitrate and presence of protozoa increase nitrate and nitrite reduction in the rumen of sheep

Type of document

Journal Article

Entity Type

Publication

Author(s)	Villar, Maria Laura Hegarty, Roger Stephen Clay, Jonathon William Smith, Katherine Anne Godwin, Ian Robert Nolan, John Vivian
Publication Date	2020-09
Abstract	Nitrate (NO<sub>3</sub><sup>–</sup>) supplementation is an effective methane (CH<sub>4</sub>) mitigation strategy for ruminants but may produce nitrite (NO<sub>2</sub><sup>–</sup>) toxicity. It has been reported that rumen protozoa have greater ability for NO<sub>3</sub><sup>–</sup> and NO<sub>2</sub><sup>–</sup> reduction than bacteria. It was hypothesised that the absence of ruminal protozoa in sheep may lead to higher NO<sub>2</sub><sup>–</sup> 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<sub>3</sub><sup>–</sup> in DM. The effects of rumen protozoa on concentrations of plasma and ruminal NO<sub>3</sub><sup>–</sup> and NO<sub>2</sub><sup>–</sup>, blood MetHb, ruminal volatile fatty acid (VFA) and ruminal ammonia (NH<sub>3</sub>) were investigated. Subsequently, two in vitro experiments were conducted to determine the contribution of protozoa to NO<sub>3</sub><sup>–</sup> and NO<sub>2</sub><sup>–</sup> 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<sub>3</sub><sup>–</sup> or with the addition of NO<sub>2</sub><sup>–</sup>. The results from the in vivo experiment showed no differences in total VFA concentrations, although ruminal NH<sub>3</sub> was greater (<i>p</i> < .01) in FAU sheep. Ruminal NO<sub>3</sub><sup>–</sup>, NO<sub>2</sub><sup>–</sup> and plasma NO<sub>2</sub><sup>–</sup> concentrations tended to increase (<i>p</i> < .10) 1.5 hr after feeding in FAU relative to DEF sheep. In vitro results showed that NO<sub>3</sub><sup>–</sup> reduction to NH<sub>3</sub> was stimulated (<i>p</i> < .01) by incoming NO<sub>3</sub><sup>–</sup> in both DEF and FAU relative to CON digesta. However, adding NO<sub>3</sub><sup>–</sup> increased (<i>p</i> < .05) the rate of NO<sub>2</sub><sup>–</sup> accumulation in the SOL fraction of DEF relative to both fractions of FAU digesta. Results observed in vivo and in vitro suggest that NO<sub>3</sub><sup>–</sup> and NO<sub>2</sub><sup>–</sup> are more rapidly metabolised in the presence of rumen protozoa. Defaunated sheep may have an increased risk of NO<sub>2</sub><sup>–</sup> poisoning due to NO<sub>2</sub><sup>–</sup> accumulation in the rumen.
Citation	Journal of Animal Physiology and Animal Nutrition, 104(5), p. 1242-1255
ISSN	1439-0396 0931-2439
Pubmed ID	32333622
Link	https://hdl.handle.net/1959.11/29199
Publisher	Wiley-Blackwell Verlag GmbH
Title	Dietary nitrate and presence of protozoa increase nitrate and nitrite reduction in the rumen of sheep
Type of document	Journal Article
Entity Type	Publication

Dietary nitrate and presence of protozoa increase nitrate and nitrite reduction in the rumen of sheep

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