Effect of added dietary nitrate and elemental sulfur on wool growth and methane emission of Merino lambs L. Li A,B , C. I. Silveira A , J. V. Nolan A , I. R. Godwin A , R. A. Leng A and R. S. Hegarty A A School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia. B Corresponding author. Email: lli3@une.edu.au Abstract. The effects of dietary nitrate (NO 3 ) 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% NO 3 + 0% S (T2), 1.88% NO 3 + 0.18% S (T3), or 1.88% NO 3 + 0.40% S (T4). Retention of S was improved by increasing the content of elemental S in the NO 3 -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 NO 3 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 NO 3 -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 NO 3 (T1 vs T3). The addition of 0.4% S to a diet containing 1.88% NO 3 also reduced methane production (P = 0.021) and methane yield (P = 0.028). In conclusion, the addition of 1.88% NO 3 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 NO 3 and S. Additional keywords: liveweight gain, feed conversion ratio, wool growth rate. Received 15 July 2013, accepted 19 August 2013, published online 6 September 2013 Introduction The impact of animal production systems on air quality has been under increasing public and political scrutiny. There is an urgent need to identify practical feeding strategies to reduce methane emissions from sheep and cattle in intensive and extensive systems. The potential for using nitrate (NO 3 ) supplementation as a methane mitigation technology has been established (Leng 2010; Nolan et al. 2010; van Zijderveld et al. 2010; Li et al. 2012), and methane emissions from ruminants are consistently reduced when nitrate (NO 3 ) is present in concentrate-based diets (van Zijderveld et al. 2010; van Zijderveld et al. 2011; Li et al. 2012; Hegarty et al. 2013). On the other hand, there are strong indications that NO 3 inclusion in ruminant diets can reduce feed intake and liveweight gain (Weichenthal et al. 1963; Goodrich et al. 1964; Farra and Satter 1971; Hegarty et al. 2013). Farra and Satter (1971) suggested that the suppression of feed intake when NO 3 was included in ruminant diets was probably caused by poor palatability. Others have shown that excessive NO 3 intake can cause rumen metabolic imbalances (Marais 1988), vasodilation (Sakai et al. 2000; Pinder et al. 2009), reduced blood pressure (Whatman et al. 2013), and methaemoglobinaemia. It appears that reduced feed intake may be a protective mechanism that animals use to avoid metabolic post-ingestive effects of excessive NO 3 (Forbes and Mayes 2002). It has been suggested that the increased capillary-bed blood flow would enhance nutrient delivery to the wool follicle and, hence, wool growth (Sokolowski et al. 1969; Hales and Fawcett 1993). In theory, the cardiovascular effects of nitric oxide (NO) formed from the reduction of absorbed NO 2 (Sakai et al. 2000; Pinder et al. 2009) would increase capillary-bed blood flow and nutrient supply to the wool follicle, which should stimulate wool growth. In a study of growing, white-faced south-western lambs, which appears to be the only study of its type, wool growth tended to increase when NO 3 replaced urea in a concentrate-based diet (Sokolowski et al. 1969). In the same study by Sokolowski et al.(1969), addition of inorganic sulfur (S) to the NO 3 -containing diet improved the utilisation of NO 3 -N by the lambs and facilitated NO 3 and NO 2 reduction to NH 3 in the rumen, thereby reducing the likelihood of methaemoglobinaemia (Leng 2010). van Zijderveld et al. (2010) showed that the addition of sulfate (SO 4 )-S (0.85% total S in dry matter (DM)) to a diet containing NO 3 (2.6% NO 3 in DM) reduced methane production by ~21% compared with a diet containing NO 3 with no added sulfate. Despite these diets differing in their ingredients and also in their total NO 3 and S content, it is still reasonable to hypothesise that differences in dietary NO 3 : S ratio could alter nutrient utilisation, wool production, animal growth performance, and methane emissions. The current study was undertaken primarily to investigate CSIRO PUBLISHING Animal Production Science, 2013, 53, 1195–1201 http://dx.doi.org/10.1071/AN13222 Journal compilation Ó CSIRO 2013 www.publish.csiro.au/journals/an