Effect of added dietary nitrate and elemental sulfur on wool growth and methane emission of Merino lambs

The effects of dietary nitrate (NO3) and elemental sulfur (S) on nutrient utilisation, productivity, and methane emission of Merino lambs were investigated. Forty-four lambs were randomly allocated to four groups (n = 11) fed isonitrogenous and isoenergetic diets. The basal feed was supplemented with 1% urea + 0.18% S (T1), 1.88% NO3 + 0% S (T2), 1.88% NO3 + 0.18% S (T3), or 1.88% NO3 + 0.40% S (T4). Retention of S was improved by increasing the content of elemental S in the NO3-containing diet (P < 0.001), yet the N retention (g/day) by the animal, and the N and S content of wool (%), were not altered by S supplementation (P > 0.05). Dry matter intake, liveweight gain, and feed conversion ratio did not differ (P > 0.05) between treatments. Replacing urea with NO3 improved the rate of clean wool growth by 37% (P < 0.001, T1 vs T3). Clean wool growth increased by 26% (P < 0.001) when the S content of the NO3-containing diet was increased from 0 to 0.18% (T2 vs T3). Methane production (g/day) and methane yield (g/kg DM intake) were reduced (P < 0.05) by 24% when urea was replaced by NO3 (T1 vs T3). The addition of 0.4% S to a diet containing 1.88% NO3 also reduced methane production (P = 0.021) and methane yield (P = 0.028). In conclusion, the addition of 1.88% NO3 and 0.18% elemental S to a total mixed diet increased clean wool production and reduced methane production. However, there was no evidence of inter-relationships between NO3 and S.