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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.

The objective of the present study was to investigate the effects of dietary-induced insulin enhancement during the late luteal phase on subsequent fertility of gilts. Fifty-two littermate cyclic gilts were subjected to dietary treatments where two energy sources were tested: corn starch (T1) and soybean oil (T2). The experimental diets were supposed to provide similar amounts of dietary energy, but from different sources. Gilts were fed ad libitum, starting day 8 of the estrous cycle, until the next standing heat. Blood sampling was performed in a subgroup of 20 gilts on days 14 and 21 of the cycle for analyses of glucose and insulin, and after ovulation detection until 18 h after ovulation for progesterone. All gilts were slaughtered on day 28 of pregnancy and the reproductive tracts recovered for further analysis. T1 gilts showed higher postprandial insulin peak on days 14 and 21 and lower glucose levels 4 h after feeding on day 14 (P<0.05), however, there were no treatment effects on plasma progesterone concentrations. Dietary energy sources did not affect average daily feed intake, body weight and backfat on day 28 of pregnancy. Estrous cycle length, estrus duration and time of ovulation were not affected by previous nutritional treatments either. T1 gilts showed higher ovulation rates, number of embryos, embryo weight and placental weight (P<0.05). There were no treatment effects on pregnancy rate, embryo survival rate and volume of amniotic fluid. A positive correlation between progesterone concentration 18 h after ovulation and ovulation rate was observed (r=0.75; P<0.01). These results suggest that it is possible to manipulate dietary insulin response in cyclic gilts and, thus, improve reproductive efficiency when feeding starch as the main energy source during the late luteal and follicular phases of the cycle.