Predicting enteric methane production from cattle in the tropics.

Accurate estimates of methane (CH4) production by cattle in different contexts are essential to developing mitigation strategies in different regions. We aimed to: (i) compile a database of CH4 emissions from Brazilian cattle studies, (ii) evaluate prediction precision and accuracy of extant proposed equations for cattle and (iii) develop specialized equations for predicting CH4 emissions from cattle in tropical conditions. Data of nutrient intake, diet composition and CH4 emissions were compiled from in vivo studies using open-circuit respiratory chambers, SF6 technique or the GreenFeed® system. A final dataset containing intake, diet composition, digestibility and CH4 emissions (677 individual animal observations, 40 treatment means) obtained from 38 studies conducted in Brazil was used. The dataset was divided into three groups: all animals (GEN), lactating dairy cows (LAC) and growing cattle and non-lactating dairy cows (GCNL). A total of 54 prediction equations available in the literature were evaluated. A total of 96 multiple linear models were developed for predicting CH4 production (MJ/day). The predictor variables were DM intake (DMI), gross energy (GE) intake, BW, DMI as proportion of BW, NDF concentration, ether extract (EE) concentration, dietary proportion of concentrate and GE digestibility. Model selection criteria were significance (P < 0.05) and variance inflation factor lower than three for all predictors. Each model performance was evaluated by leave-one-out cross-validation. The Intergovernmental Panel on Climate Change (2006) Tier 2 method performed better for GEN and GCNL than LAC and overpredicted CH4 production for all datasets. Increasing complexity of the newly developed models resulted in greater performance. The GCNL had a greater number of equations with expanded possibilities to correct for diet characteristics such as EE and NDF concentrations and dietary proportion of concentrate. For the LAC dataset, equations based on intake and animal characteristics were developed. The equations developed in the present study can be useful for accurate and precise estimation of CH4 emissions from cattle in tropical conditions. These equations could improve accuracy of greenhouse gas inventories for tropical countries. The results provide a better understanding of the dietary and animal characteristics that influence the production of enteric CH4 in tropical production systems.

Degradabilidade in situ da cana-de-açúcar tratada ou não com óxido de cálcio, em novilhas leiteiras Holandês x Gir

In situ degradability of sugarcane in natura or added to different levels of calcium oxide (CaO) in fed diet, 0.0; 0.5; 1.0 and 2.0% for 24 h in five Holstein x Gyr heifers, fitted with a rumen cannula.The parameters of rumen degradation of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were estimated by adjusting non-linear model to data degradation, and used the parameters obtained in regression analysis, linear and quadratic performed according to the level of inclusion of calcium oxide in diets.The potential and effective degradability, as well as the degradation rates of DM and OM were lineraly enhanced with the increasing of the CaO levels in diet. The increasing levels of CaO in sugarcane diets offered to Holstein x Gyr dairy heifers lead to a linear enhancement of in situ degradability of DM and OM, but does not affect the in situ degradability of fiber fractions.

Avaliou-se a degradabilidade in situ da cana-de-açúcar in natura ou tratada por 24h com óxido de cálcio em diferentes porcentagens de inclusão na matéria natural da dieta, 0,0; 0,5; 1,0 e 2,0%, no rúmen de cinco novilhas Holandês x Gir. Os parâmetros de degradação ruminal da matéria seca (MS), matéria orgânica (MO), fibra em detergente neutro (FDN) e fibra em detergente ácido (FDA) foram estimados ajustando modelo não linear aos dados de degradabilidade, sendo os parâmetros obtidos utilizados em análises de regressão linear e quadrática realizadas em função da inclusão do óxido de cálcio nas dietas. As degradabilidades potencial e efetiva e as taxas de degradação da MS e da MO aumentaram linearmente com o aumento de inclusão de CaO. O aumento da porcentagem de inclusão de CaO em dietas à base de cana-de-açúcar aumentou linearmente a degradabilidade in situ da MS e da MO e não alterou a degradabilidade in situ das frações fibrosas.