Neem cake (Azadirachta indica) is a versatile plant with potential benefits for ruminant animals due to its effects on rumen modulation. This study aimed to evaluate the effects of increasing levels of neem cake and monensin on in vitro ruminal fermentation in cattle diets. Six treatments were tested: neem cake at 0, 240, 480, 720, and 960 mg/kg dry matter (DM) and monensin at 30 mg/kg DM. The basal diet consisted of a diet with a 15:85 roughage-to-concentrate ratio. Parameters evaluated included gas production kinetics, CH₄ and CO₂ emissions, pH, volatile fatty acids (VFAs), ammonia-N (NH₃-N), and organic matter digestibility. Neem cake increased ruminal pH compared to monensin (p < 0.01). The total VFAs increased linearly with neem cake inclusion (p < 0.01). The acetate proportion increased quadratically (p = 0.06). Propionate decreased linearly (p = 0.02), while branched-chain VFAs (BCVFAs) increased linearly (p = 0.09). The neem cake addition increased the NH₃-N concentration quadratically (p < 0.01). CH₄ and CO₂ concentrations were higher with neem cake compared to monensin (p < 0.05). Neem cake shows potential to reduce rumen acidosis and enhance fiber digestion, making it useful during the adaptation period for finishing diets in feedlots and for grazing animals. However, it was not effective in reducing greenhouse gas emissions in this in vitro system.

The use of processing techniques to increase the rumen-undegradable protein (RUP) content of protein meals aims to enhance the nutritional performance of high-performance animals. This study evaluated the effects of various processing techniques applied to peanut and cottonseed meals on ruminal parameters using a dual-flow continuous culture system. These two feeds were individually analyzed in two experiments, each one using five fermenters (1297 ± 33 mL) in a 5 × 5 Latin square arrangement with five periods of 10 d each, with 7 d for diet adaptation and 3 d for sample collections. Five treatments were evaluated in each experiment: no processed meal (control); meal thermally treated in an autoclave with xylose (autoclave); meal thermally treated in a conventional oven with xylose (oven); meal thermally treated in a microwave with xylose (microwave); and meal treated with tannin (tannin). All diets contained 60% concentrate (corn, minerals, and processed meal). Fermenters were fed 55 g of dry matter per day, divided equally into two meals at 06:00 and 18:00 h. The solid and liquid dilution rates were adjusted daily to 5.5% and 11% per hour, respectively. On days 8, 9, and 10, 500 mL samples of solid and liquid digesta effluent were collected, mixed, homogenized, and stored at −20 °C. Subsamples of 10 mL were preserved with 0.2 mL of a 50% H₂SO₄ solution for later determination of NH₃-N and volatile fatty acids. Microbial biomass was isolated from the fermenters for chemical analysis at the end of each experimental period. Data were analyzed using the MIXED procedure in SAS with a significance level of α = 0.05. Regarding cottonseed meal, the tannin treatment tended to have a lower true digestibility of DM compared to the control, autoclave, and oven treatments (p = 0.09). Additionally, tannin fermenters exhibited a lower apparent digestibility of CP compared to all other treatments (p = 0.04). The tannin and microwave treatments resulted in the highest flow of dietary nitrogen and the lowest supply of RDP-N (p < 0.01). The control treatment had a greater flow of NH₃-N compared to other treatments (p < 0.01). Regarding peanut meal, the autoclave and tannin treatments exhibited the highest acetate concentration (p = 0.03) and the lowest apparent digestibility of CP (p < 0.01). The tannin treatment increased the RUP content without impairing ruminal fermentation and exhibited a greater supply of RDP-N compared to all other treatments (p = 0.02). No significant differences were observed for the other digestibility and fermentation parameters (p > 0.20). Our results indicate that tannin inclusion and microwave processing were the most effective methods for reducing the protein fraction available in the rumen for cottonseed meal. Additionally, tannin inclusion increased the RUP in peanut meal without negatively affecting ruminal fermentation.