Faecal methane, nitrous oxide emissions and nitrogen excretion by grazing sheep: implications of grazing management strategies

FÉLIX DA SILVA NETO, GENTIL; NADIN, LAURA B. ; BAYER C.; M.E. PRIANO; MARCHI, DANIELA ELISA; SAVIAN, JEAN VÍCTOR ; TRÊS SCHONS, RADAEL MARINHO; DE FACCIO CARVALHO, PAULO CÉSAR

Foz do Iguaçu

Congreso; 54 Reunião Anual da Sociedade Brasileira de Zootecnia; 2017

It is known that the diet quality is the key factor which regulates the nitrogen excretion by ruminants. The higher the nitrogen intake, the higher is the faecal and urinary nitrogen excretion by animals, with a consequent increase greenhouse gas emission. In this context, the hypothesis proposed is that the new grazing management strategy based on animal behaviour (rotatinuous stocking - RN) with a greater herbage chemical composition, results in a greater amount of faeces and faecal nitrogen excretion and consequently greater faecal greenhouse gas emissions of grazing sheep compared to the traditional rotational stocking method - RT. The objective of this study was to evaluate the effect of different grazing management strategies on the amount of faeces production, nitrogen excretion and faecal greenhouse gas emissions (CH4 and N2O) from sheep grazing Italian ryegrass pastures under rotational stocking method. The experiment was carried out in 2014 and 2015, in the south of Brazil. The experimental design was a randomized complete block with four replicates and two grazing management targets; traditional rotational stocking method - RT with pre- and post-grazing sward heights of 25 and 5 cm, respectively and, rotatinuous stocking - RN with pre- and post-grazing sward heights of 18 and 11 cm, respectively. For measuring the total faeces production, harnesses and faeces collection bags were used in three test-animals during five consecutive days; three measurements per year. In 2015, faeces samples from the three test-animals were mixed to form a composite sample of 500 grams; each sample was collected and immediately deposited on the soil. During July, CH4 and N2O emission from nine PVC cylinders chambers were measured with the static chamber method. RN treatment presented a greater daily faecal excretion and nitrogen excretion per animal than RT treatment. However, faecal daily excretion andnitrogen excretion per hectare were lower for the RN than for the RT treatment. Faecal crude protein was greater for the RN than the RT treatment. The faecal CH4 emission was three times higher than the RT, with a mean of 0.233 g CH4 kg-1 of fresh faeces and 0.079 g CH4 kg-1 of fresh faeces, respectively. In the RN, the faecal N2O emissions presented values of 9.97 mg of N2O kg-1 of fresh faeces, four times higher than the RT treatment (mean 2.29 mg N2O kg-1 of fresh faeces). In addition, the mean of CH4 soil flow (control chambers, without faeces) was -2.17 g ha-1 day-1 and the mean of N2O soil flux was 1.32 g ha-1 day-1. Thus, in the RN treatment, faecal emissions (CH4 and N2O) per animal and hectare were higher than RT treatment. In conclusion, rotatinuous stocking - RN presented higher faecal chemical composition (more crude protein) than traditional rotational stocking method - RT, resulting in higher daily nitrogen excretion per animal and higher faecal greenhouse gas emissions (CH4 and N2O).