We assessed and ranked different dietary strategies for mitigating methane (CH₄) emissions and other fermentation parameters, using an automated gas system in two in vitro experiments. In experiment 1, a wide range of dietary CH₄ mitigation strategies was tested. In experiment 2, the two most promising CH₄ inhibitory compounds from experiment 1 were tested in a dose-response study. In experiment 1, the chemical compounds 2-nitroethanol, nitrate, propynoic acid, p-coumaric acid, bromoform, and Asparagopsis taxiformis (AT) decreased predicted in vivo CH₄ production (1.30, 21.3, 13.9, 24.2, 2.00, and 0.20 mL/g DM, respectively) compared with the control diet (38.7 mL/g DM). The 2-nitroethanol and AT treatments had lower molar proportions of acetate and higher molar proportions of propionate and butyrate compared with the control diet. In experiment 2, predicted in vivo CH₄ production decreased curvilinearly, molar proportions of acetate decreased, and propionate and butyrate proportions increased curvilinearly with increased levels of AT and 2-nitroethanol. Thus 2-nitroethanol and AT were the most efficient strategies to reduce CH₄ emissions in vitro, and AT inclusion additionally showed a strong dose-dependent CH₄ mitigating effect, with the least impact on rumen fermentation parameters.

The study aimed to evaluate sugarcane bagasse as roughage in lactating cow on feed intake, digestibility, ingestive behavior, milk production and composition, and microbial protein synthesis. Ten Girolando cows at initial body weight of 450±25.6 kg and at 143.7±30.7 days in milk were assigned in two 5×5 Latin square designs. Five 21-day experimental periods were adopted (1° to 14-day: diets adaptation period; 15° to 21-day: data collection and sampling period). The diets consisted of four different levels of sugarcane bagasse (45%, 50%, 55%, and 60%) and a control diet, commonly adopted in the region, based on spineless cactus (25% sugarcane bagasse), formulated to meet 12 kg/d milk yield. The dry matter (DM), organic matter (OM), and total digestible nutrients intakes and DM and OM digestibilities observed for 45% and 50% bagasse inclusion were similar to control diet, while that 55% and 60% bagasse inclusion were lower. Cows fed control diet, and bagasse diets of 45%, and 50% levels had the nutritional requirements attended, that guaranteed 12 kg/d of milk yield. The crude protein intake and digestibility of cows fed 45%, 50%, and 55% of bagasse inclusion were similar to control diet. The neutral detergent fiber (NDF) intake and digestibility differ for all bagasse diets related to control diet, while the non-fiber carbohydrates intake and digestibility for cows fed 45% of bagasse were similar for control diet. The intakes and digestibilities of nutrients decreased linearly in function of bagasse inclusion; NDF and indigestible NDF intakes did not vary. The ruminating time, feeding and rumination efficiency, microbial protein synthesis and milk yield decreased linearly with sugarcane bagasse inclusion. Sugarcane bagasse decreases milk production; however, its inclusion level in between 45% to 50% associated to concentrate could replace diets based on spineless cactus for crossbred dairy cow's producing 12 kg/d of milk.

The aim of this research was to evaluate the effect of different concentrate levels in diets based on cactus Opuntia Stricta (Haw.) Haw cladodes over the performance of lactating Girolando cows. The experiment involved 10 Girolando multiparous dairy cows (512.6 kg of body weight and producing 13.2kg milk/day), allocated into two 5 x 5 Latin squares. The experimental treatments consisted of control diet composed by cactus Nopalea cochenillifera. Salm-Dyck. cladodes (Nopalea), forage sorghum silage and concentrate (20% at DM basis), and four concentrate levels diets (20, 24, 28 and 32%) plus cactus Opuntia stricta (Haw.) Haw. cladodes (Opuntia) and forage sorghum silage. Regarding cows fed control diet, the nutrients intake were greater than for cows fed with cactus Opuntia and concentrate. Regarding concentrate levels, intakes of dry matter (DM), organic matter (OM), crude protein (CP), non-fiber carbohydrates (NFC) and total digestible nutrients (TDN) of cows increased linearly. The OM, CP and NDF digestibilities were similar in between to control diet and cactus Opuntia-based diets. The digestibility of NFC increased linearly when the concentrate was inserted. The N balance was the same for control diet and cactus Opuntia-based diets, irrespective the concentrate levels. For cows producing 14 kg/day with 3.5% of fat, it is recommended 32% of concentrate inclusion in cactus Opuntia-based diets, and the increase in concentrate level promotes a linear increase in milk yield.

Background: the red macroalgae Asparagopsis taxiformis is a potent natural supplement for reducing methane production from cattle. A. taxiformis contains several anti-methanogenic compounds including bromoform that inhibits directly methanogenesis. The positive and adverse effects of A. taxiformis on the rumen microbiota are dose-dependent and operate in a dynamic fashion. It is therefore key to characterize the dynamic response of the rumen microbial fermentation for identifying optimal conditions on the use of A. taxiformis as a dietary supplement for methane mitigation. Accordingly, the objective of this work was to model the effect of A. taxiformis supplementation on the rumen microbial fermentation under in vitro conditions. We adapted a published mathematical model of rumen microbial fermentation to account for A. taxiformis supplementation. We modelled the impact of A. taxiformis on the fermentation and methane production by two mechanisms, namely (i) direct inhibition of the growth rate of methanogens by bromoform and (ii) hydrogen control on sugars utilization and on the flux allocation towards volatile fatty acids production. We calibrated our model using a multi-experiment estimation approach that integrated experimental data with six macroalgae supplementation levels from a published in vitro study assessing the dose-response impact of A. taxiformis on rumen fermentation. Results: our model captured satisfactorily the effect of A. taxiformis on the dynamic profile of rumen microbial fermentation for the six supplementation levels of A. taxiformis with an average determination coefficient of 0.88 and an average coefficient of variation of the root mean squared error of 15.2% for acetate, butyrate, propionate, ammonia and methane. Conclusions: our results indicated the potential of our model as prediction tool for assessing the impact of additives such as seaweeds on the rumen microbial fermentation and methane production in vitro. Additional dynamic data on hydrogen and bromoform are required to validate our model structure and look for model structure improvements. We expect this model development can be useful to help the design of sustainable nutritional strategies promoting healthy rumen function and low environmental footprint.

Resource use efficiency and economic initiatives point towards using less human‐edible input in ruminant food production. This could also promote the nutrient‐rich dairy products to consumers in comparison with alternative plant‐based drinks. The global population is growing and food production will need to increase to feed more people in the future. The Swedish government has launched a national food strategy, which aims to move Swedish food production towards self‐sufficiency and sustainability, and greater exports. Simultaneously, strong economic development has stimulated consumers to request more high‐value foods, such as meat and refined dairy products. At the same time, public opinion states that today's food production from ruminants is negative for the environment and contributes to climate change. This review assesses some aspects of dietary ingredient composition and feeding choices that can contribute to making Swedish dairy production more sustainable. Efficient dietary methane mitigating strategies can decrease emissions of greenhouse gases in line with European Union targets and avoid major changes in dietary consumption patterns of meat and milk from ruminants. Although feeding management seems to be the most important approach to decrease nitrogen losses, rational use of fertilizers and improved manure management practices on dairy farms should also be considered to decrease the impact of nitrogen losses to the environment.