Some examples of PUFAs are linolenic acid also known as omega-3 fatty acid and linoleic acid, omega-6 fatty acid . PUFAs are high energy dense feed source and are used to supplement high performing animals such as lactating cattle . Fats provide over two-times more energy than carbohydrates and protein sources. Some PUFAs have been reported to have antimicrobial activities by inhibiting or even cause cell death through cellular membrane interactions . Similar to the effects of terpenoids, membranes of microbes are altered, limiting their function or may even cause cell death from electron leakage. Biohydrogenation is seen in the rumen, in which microbes rapidly convert PUFAs to saturated fatty acids.In addition to their microbial cytotoxicity, PUFAs have been shown to decrease rumen fermentation, though this depends on the types of fatty acids present . Blueberry seeds may be pressed, and their oils may be extracted to be used as additives, as they contain high PUFAs and polyphenolic compounds . PUFAs make up over 76% of total fatty acids in blueberry seeds with linoleic acid being the most abundant followed by linolenic acid. Even at a low dosage of 500mg L-1 of rumen fluid, large square plant pots addition of blueberry seed oils resulted in a decrease in in-vitro CH4 production by 16% when compared to a diet without any oils supplemented .
Embaby et al. concluded that the compounds found in seed oils directly inhibit methanogens rather than altering feed digestibility and overall metabolism, as there were no changes in total VFA production, gas production and DM degradability. Avocadoes also contain high amounts of unsaturated fatty acids , which makes them a high-energy food . In an in-vitro study using three adult fistulated goats as donors, 400mg of avocado pulp and peel mixture were added into 48mL of rumen fluid resulted in a significant decrease in potential gas production alongside with CH4 production when compared to mango peels and pulp mixture . This is due to the inhibition of bacteria cellulolytic activity and the consequence overall reduction of substrates for downstream metabolic activity, such as methanogenesis . However, in the same study when avocadoes were supplied at a 15% inclusion rate in a multi-nutrient block , there were no observed differences in gas production parameters between avocadoes and mango multi-nutrient blocks. Since inhibiting fiber fermentation can negatively affect the energy available to the host, it is recommended that high producing animals should only be given a maximum of 6% dietary fats in their diets .Many agriculture byproducts have the potential to act as both animal feed and contain bio-active compounds that can reduce greenhouse gas emissions. However, the processing of these byproducts still requires standardization as their composition can heavily vary even between the same byproducts. This is due to the different environmental factors that these crops were grown in, differences in cultivar, and the maturity stage that the crops were harvested at. Storage of these byproducts post-harvest also plays a factor as their composition can rapidly change as some spoil faster than others. Animal hosts also play a large factor in fermentation results as microbiomes are greatly different between animals even if fed the same diet.
Furthermore, future studies will require a comparison of byproducts between different ruminant species as well.The United States generated over $433 billion dollars in animal and crop cash receipts in the year of 2021 with California as the lead contributor of over $51 billion dollars . There were 69,000 operating farms in California, using ~98,000 square kilometer of land, producing 99% or more of many crops, such as almonds, pistachios, walnuts, and grapes . With the production of these crops, there is also a large amount of biomass that is being generated and does not make it through the production process to the consumer. This biomass represents unharvested crops that were grown but left in the field due to overproduction or harvesting is no longer profitable due to declined market prices leading to a burden to the producer and often to the environment. A prominent example are sunflowers with over 294 tons left unharvested on the fields in California in 2021 . Unutilized biomass are crops that were harvested but due to abundance in supply were not incorporated into the food supply chain. It was also reported by CDFA in 2021 that there were over 3,200 tons of onions that were unutilized after harvest. California is also the largest wine producing state, producing over 2,368 million liters in 2021, making up over 81% of total wine production in the U.S. . Grape pomace is a major byproduct that is generated during the wine making process since it cannot be consumed by humans and alternative routes for its utilization are desirable by the wine industry. Many other byproducts, such as hulls, shells, and meals, are generated during the processing of nuts and oils and in most cases these waste products are sent to either compost facilities or landfills that can lead to the production of greenhouse gas emissions during anaerobic digestion and fermentation.
Recent policies that mandate the reduction of methane from the livestock industry have led to the growing interest of repurposing plant-based waste into livestock feed that is nutritious but also holds the potential to inhibit methanogenesis in the rumen to reduce environmental impacts. Livestock, especially ruminants, are an integral part of agriculture as they can consume plant biomass and convert them into high-quality animal products such as meat and milk. On a global scale, 86% of feed consumed by livestock is not edible for humans, making livestock an important portion of human nutrition, especially in places where growing plants for dietary purposes is challenging . California is the leading dairy producer with over 1.72 million dairy cows producing over 20 million tons of milk in 2021 and it is also home to approximately 680,000 heads of beef cattle, which are usually held on pasture where they can graze. Microorganisms that drive feed digestion in the rumen are also producing greenhouse gases such as CO2 and the even more potent CH4, with beef cows emitting between 240 to 396 g CH4/day and dairy cows producing 269 to 354 g CH4/day . With the >2 million heads of cows it is therefore not surprising that California’s livestock industry also represents a major producers of greenhouse gases. There has been an increased interest in plant-sourced byproducts as a feed additive to reduce methanogenesis in the rumen with a particular focus on essential oils , phenolic compounds or byproducts that has been chemically altered by silaging . On the other hand, little work has been performed on the effect on enteric methane production of plant-sourced byproducts from California agriculture and byproducts that have not undergone further resource extensive processing, such as the extraction of essential oils or phenolic compounds. The objective of the present study was to determine the effects of byproducts on rumen fermentation with a particular focus on methane production and without the need for prior extensive processing of the byproducts. We tested 10 byproducts that were generated from agriculture in California at various inclusion rates to take into consideration that the chemical components of the byproducts we tested might be bio-active at different concentrations. We also generated chemical profiles of byproducts that were tested to provide a foundation to better understand the chemical composition of the different byproducts and to identify and quantify likely compounds, such as organosulfur compounds or tannins, large square planting pots that might have antimicrobial properties and that might drive enteric methane inhibition. We hypothesize that several of the byproducts generated from the production of crops and vegetables have the potential to reduce methanogen activities and consequentially CH4 production in ruminants.Almond hulls, shells, and a mixture of hulls and shells , and sunflower meal samples obtained from a processing facility in Selma, California. Onion waste was obtained from a processing facility in Oxnard, CA. Agave Pencas were received from growers in Yolo County, California. Grape pomace from Pinot Noir was obtained from a winery in Modesto, CA and grape pomace of three grape varieties were collected locally from the UC Davis Robert Mondavi Institute Teaching and Research Winery immediately after pressing.
All samples were placed in 3.79-liter bags and stored in a – 20°C freezer until further analysis.Rumen contents were collected from three fistulated cows one hour after feeding and just prior to the start of the in-vitro rumen fermentation. Rumen fluid was collected in accordance with the Institution of Animal Care and Use Committee at UCD under protocol number 22753. Approximately 1,500 mL of rumen fluid were collected from each cow via a perforated PVC pipe, 500 mL syringe and Tygon tubing , passed through a strainer and into individually pre-warmed insulated thermos . Rumen solid was collected by hand from each cow directly after rumen fluid was collected and solids were placed in a sterile container apart from the rumen fluid. Temperature and pH of the rumen fluid were immediately measured once rumen fluid had been collected from each cow and transported back to the laboratory within 30 minutes.Byproducts were grounded up using an Oster 14-Speed blender and dried in a Fisher brand Gravity Oven at 55°C for 72 h. Total mixed ration was collected from the UCD Dairy Facility with all components mixed to represent the animals’ typical diet. A total of 1g of TMR were weighed into 100mL serum bottles with 0.5%, 1%, 5%, 10% and 20% of the TMR replaced with the byproduct under evaluation. Vessels with TMR only were used as negative controls. As positive control, 2% of the TMR were replaced with Asparagopsis taxiformis. Rumen fluid collected from at least two cows was combined in equal amounts to account for biological variation and the rumen fluid mixture was further mixed with artificial saliva buffer . Artificial saliva buffer was according to Oeztuerk et al. . All treatment groups had 5 replicates , totaling 35 serum bottles per experiment. Every vessel was flushed with high-purity nitrogen for 15 seconds and sealed with a rubber cork attached to a Tygon tube to connect to 1L gas bags . Vessels were placed into a shaking water bath at 39°C.Temperature and pH were measured from individual rumen fluid samples immediately after rumen fluid was collected, after individual rumen fluid samples were combined, after the artificial saliva buffer was added to the rumen fluid mixture, and after 24 h of fermentation. After fermentation contents of serum bottles representing a particular treatment were pooled before the pH was measured. Gas samples were collected after 24 h of fermentation from each serum bottle and gas analysis was performed within 24 h using gas chromatography.During enteric fermentation methane is produced under anaerobic conditions. To determine the potential of the various byproducts, in vitro methane production in the presence and absence of the byproducts was determined . As previously shown, inclusion of A. taxiformis resulted an almost complete shutdown of methanogenesis when compared to the negative control . This significant reduction was observed for all in-vitro runs that were performed as part of this study. No significant change of CH4 production was observed between any of the other byproducts with onion waste being the only exception with a trend to produce less methane compared to the negative control.Carbon dioxide production, commonly also used as an indicator for microbial growth, was also monitored and results suggested that none of the treatments had strong antimicrobial properties, which would result significant decreased CO2 production. Carbon dioxide production remained consistent across all treatment groups , with agave at 10% inclusion rate showing a trend of lower CO2 production being an exception and with A. taxiformis stimulating microbial fermentation .Agave has been of particular interest as a feed additive since it grows under very arid conditions and provides farmers in areas where rainfall is limited the opportunity to provide extra fiber at low or no cost to the animals. The leaves of the agave utilized in this study was notably fibrous but also contained relatively high levels of moisture which is similar to what was reported previously by Iñiguez-Covarrubias et al. who investigated the effect of agave bagasse which are the residual fibers after sugar extraction as a feed replacement on 36 male sheep. Detailed chemical analyses revealed that total fiber content of NDF only accounted for 28.9% of the leaves’ total DM.