Effects of ground corn and Acacia mearnsii tannin extract supplementation on nitrogen excretion and nitrous oxide emissions from sheep

The nitrogen (N) excreted by grazing animals is the main source of nitrous oxide (N₂O) emissions in livestock systems, and feeding strategies to mitigate N excretion should be further studied. The objective of this study was to evaluate the effects of ground corn and tannin extract supplementation on mitigating N₂O emissions from sheep excreta. The emissions factor (EF,% of N excreted, which was emitted as N₂ON) under the studied conditions were also measured. Two experiments were conducted. In the first one, six Lacaune lambs, with an average BW of 27 ± 3 kg, were distributed in a replicated 3 × 3 Latin square experimental design. The treatments included ad libitum access to ryegrass (Lolium multiflorum Lam.) silage, which contained 21.1 g N/kg DM and was supplemented with 60 g of soybean meal (S), 140 g of ground corn + 60 g of soybean meal (SC) or 140 g of ground corn + 60 g of soybean meal + 40 g/kg Acacia mearnsii tannin extract concentrate (SCT). The daily production of faeces and urine was measured, and samples were collected each day. In the second experiment, urine and faeces were applied to static chambers in the field to determine their N₂O emissions. Three replicates of type of excreta from each treatment were included. The nitrogen intake was similar between the treatments, with an average of 18 g/day. The faecal N excretion obtained with tannin extract supplementation was 16% higher (P < 0.01) than that obtained with the S and SC treatments. The daily urinary N excretion from the animals administered ground corn supplementation was 12% lower (P < 0.05) than that from the animals that received only soybean meal, whereas the inclusion of tannins did not effectively induce further decreases in urinary N excretion. The faecal EF of the different treatments was similar, with an average of 0.56 g N₂ON/100 g N. The EF of the urine samples averaged 4.8 g N₂ON/100 g N. Corn grain supplementation decreased urinary N excretion and N₂O emissions from sheep excreta, whereas Acacia mearnsii tannin extract did not effectively improve this response.