Prediction of voluntary intake and enteric methane emission by dairy heifers in integrated systems.

To compare the predictions of dry matter intake (DMI) and enteric methane (CH4) emissions in integrated crop-livestock (ICL) and integrated crop-livestock-forestry (ICLF) systems, a 2 × 2 crossover trial was carried out with eight 25 ± 6.8-month-old Girolando heifers divided into two groups during two 30-day experimental periods. The DMI was predicted by relation between in vitro DM digestibility and fecal production estimated with LIPE®. The CH4 emission was predicted by non-linear equation. The daily means of total dry matter intake (9.66 and 8.44 kg day-1) and total enteric CH4 emission (9.99 and 8.79 MJ day-1; and 186.68 and 164.30 g day-1) were similar between ICL and ICLF, respectively. The CH4 emission expressed per unit of crude protein intake (CPI) was lower (P<0.001) in the ICLF (8.40 MJ kg CPI-1; 157.00 g kg CPI-1) than in the ICL (10.94 MJ kg CPI-1; 204.37 g kg CPI-1), but per intake unit of total digestible nutrient (TDNI) or non-fiber carbohydrate (NFCI) CH4 emission was higher (P<0.001) in the ICLF system. Significant correlations between forage digestibility and nutrient composition with CH4 emissions per unit of nutrient intake were observed. In conclusion, there is no difference between ICL and ICLF systems in terms of voluntary intake and methane emission. However, the methane emission per unit of CP ingested is higher in the system without trees; and, per unit of energy intake, it is higher in the pasture integrated with eucalyptus. [ABSTRACT FROM AUTHOR]