Características produtivas e qualitativas do pasto, desempenho e emissão de metano de vacas Holandês X Zebu em pastagem de capim-Marandu

Abstract

This study aimed to evaluate two grazing intervals (GI) in an intermittent stocking along three consecutive grazing periods on productivity and forage quality of Urochloa brizantha cv. Marandu, and its impact on food and water consumption, individual milk production per hectare and emission enteric methane (CH4). Grazing intervals were: (i) 30-day fixed grazing interval (30-GI) and (ii) when the canopy intercepted 95% photosynthetically active radiation (95-LI). Multiparous Holstein x Zebu cows (548 ± 61,0 kg BW) and 70 ± 18,1 days in milk (DIM) were used. The adjustment of carrying capacity per paddok was according to put-andtake technique, aiming to a post-grazing residue of 20 cm high. The grazing interval for fixed 30-GI treatment was approximately six days longer (P=0,01) than 95-IL and 2% longer light interception. The total forage mass, stem and dead mass per area were higher (P<0,01) for 30- GI compared to 95-LI. However, the stocking rate was 11,3% higher (P=0,02) for 95-LI treatment than 30-GI. In the pre-grazing period, the management of 95-LI had greater leaf proportion (P<0,01) and leaf / stem ratio. Daily milk production and its components were 16 and 28% higher (P<0,01) for 95-LI compared to 30-GI, respectively. In vitro digestible dry matter (DM) content and crude protein (CP) concentration in grazing extract was higher (P0,02) for 95-LI than for 30-GI. Acid detergent fiber (ADF) and neutral detergent fiber (NDF) in the grazing extract were higher for 30-GI (P<0,01) over 95-LI. The potential for gas production from non-fibrous carbohydrates was 9,4% higher for 30-GI. The degradable dry matter in 24h was higher (P=0,03) for 95-LI compared to 30-GI. The production of methane (CH4) expressed in g/kg of degradable DM was higher (P<0,01) for 30-IG compared to 95-LI. Forage supply was higher (P<0,01) for 30-GI compared to 95-LI. CP, milk, lactose and total solids production was higher (P<0,05) for 95-IL compared to 30-GI. However, the fat, protein and total solids content was higher for 30-GI compared to 95-LI. Enteric emissions of CH4 in vivo and water consumption were not influenced by management (P> 0,5), mean consumption was 58 kg of water/day. These results suggest that the management of 95-LI for the Marandu grass enabled reduction of the grazing interval, improve nutritive value of the forage and increased milk production and productivity in relation to the 30-GI. However, the reduction of methane production due to improved pasture management needs to be investigated.