Methane emissions of grazing sheep in a silvopastoral system with different shades

In livestock sector, the majority of methane (CH₄)emission is from enteric origin and is associated with the low utilization of the productive potential of pastures. Thus, the aim of the study was to evaluate the CH₄ emission from sheep grazing massai grass pastures in silvopastoral system under intermittent stocking with different arrangements of eucalyptus trees. The treatments consisted of three different arboreal arrangements: no trees, spacing of 12 m between the rows of trees and spacing of 6 m between the rows of trees. Evaluations were made in March and July 2015 grazing cycles. The experimental design was completely randomized with three treatments and five replications. The grazing was compared by polynomial orthogonal contrasts and arboreal arrangements by Tukey test (P < 0.05). CH₄ emissions were estimated according to the methodology of the tracer gas SF6 and intake estimated by fecal production and indigestible neutral detergent fiber in 15 adult male sheep (22.5 kg initial BW). There was interaction (p < 0.05) between grazing cycles and arboreal arrangements. In March, the average CH₄ emissions were 19.79 and 17.19 gCH₄ / day in the treatments without trees and trees spaced of 12 m, respectively. Already in July the average CH₄ emission in these treatments were 26.70 and 22.78 gCH₄ / day, respectively, higher (P < 0.05) than those recorded in March. There was no difference between the means of CH₄ emissions / day, when they were compared in the different arboreal arrangements. In grazing of March massai grass was flowering that caused the blanching plant, probably reducing the nutritional value and intake, which led to lower (p < 0.05) CH₄ emission compared to July. The means of CH₄ emissions per kg dry matter intake, CH₄ emitted by gross energy intake (Mcal) and CH₄ emission by digestible energy intake (Mcal) were lower in July. The CH₄ emissions per unit of dry matter intake and energy in July (35.05 g) was lower than March (42.54 g) and denoted that the animal's intake greater amount of digestible energy in July, but with lower CH₄ emissions for digestible energy intake (14.6g) than March (22.03g). This highlights the importance of providing improved food quality for ruminants indicating the capacity of mitigating effect of CH₄ emissions.