Desempenho produtivo e emissão de metano entérico de vacas de leite em sistemas silvipastoris

Abstract

Livestock plays a crucial role in global food security but faces significant challenges related to environmental sustainability, with methane being one of the primary greenhouse gases emitted by ruminants. Enteric fermentation is the main source of these emissions, highlighting the need for strategies to reduce their environmental impact. Silvopastoral systems (SPSs), which integrate trees, pastures, and animals, emerge as a sustainable alternative by providing shade, improving forage quality, enhancing animal thermal comfort, and offering potential for carbon sequestration. In this study, we investigated the effects of four tree density arrangements in an SPS and the genotype of Girolando cattle (1/2, 5/8, and 3/4 Holstein x Gir) on the productive performance and enteric methane emission (EME) of lactating cows during the rainy and dry seasons in the Amazon-Cerrado transition biome. Additionally, we compared the measured EME values with those predicted by the IPCC Tier 1 and Tier 2 models (2013) and the NS Dairy Cattle model. The SPS was composed of Eucalyptus urograndis (clone H13) and the forage hybrid BRS RB331 Ipyporã, managed under intermittent grazing, with four treatments: SSP 1 – Double-row lateral shading, 260 trees/ha – B (Total area = 1.25 ha; 6 cows); SSP 2 – Double-row lateral shading, 130 trees/ha – D (Total area = 1.25 ha; 6 cows); SSP 3 – Intensive internal shading, triple row, 340 trees/ha – C (Total area = 1.25 ha; 6 cows); and SSP 4 – Moderate internal shading, single row, 130 trees/ha – E (Total area = 1.25 ha; 6 cows). Enteric methane emissions were directly measured using the SF6 tracer gas method. The tree arrangements and cow genotypes did not affect (P<0.05) pasture or total dry matter intake, nor the cows' gross energy intake during either season (rainy or dry). Consequently, EME per cow, emission yield (proportion of gross energy intake), and EME intensity (relative to milk production) were unaffected by the tree arrangements or cow genotypes. The observed annual methane emission of 76.8 ± 11.7 kg methane/cow/year (with an average milk production of approximately 3600 kg/cow/year) was similar to the fixed value estimated by the IPCC Tier 1 model (81 kg/cow/year for cows producing 2550 kg of milk annually), the IPCC Tier 2 model (Ym = 6.5% of gross energy intake), and the NS Dairy Cattle model (80.5 ± 2.3 kg methane/cow/year). However, the IPCC Tier 1 model for cows producing 4200 kg of milk per year overestimated enteric methane emissions from Girolando cows in silvopastoral systems by 30%, indicating that this model is not suitable for estimating EME in such milk production systems. This was the first study to measure enteric methane emissions in dairy cows in the state of Mato Grosso. The information obtained from our study will be useful for future research on emissions and carbon balance in dairy farming within silvopastoral systems in the Amazon and Amazon-Cerrado transition regions.