Measuring methane emission of dairy cattle in restricted grazing experiments
Methane emission measurement in dairy cattle indoors is already challenging. Performing measurements outdoors is even more complicated. Research experiments in which indoor and outdoor housing of cows is combined within one trial add additional challenges to the trial and measurement set-up. The difficulties are a result of the high number of influencing factors in such experimental design: e.g. practicalities of the indoor/outdoor combination measurement, variations in grass growth, pasture organization and ration composition. Measurement equipment should be accessible for all cows at all times i.e. indoor and outdoor. Pasture rotation implies that the measurement equipment needs to be moved regularly. Secondly, GreenFeed systems can be used as an outdoor measurement system, but they need regular visits from the animals to estimate emissions correctly. This means that easy access on pasture is required. Ensuring sufficient visits per animal per time period can be challenging, especially when specific pasture plots and rotations are used. We therefore developed a method to organize emission measurements using the GreenFeed system in a strip grazing context where fresh grass is provided on a daily basis. The method consists of using a circular fence allowing the GreenFeed system and drinking through to remain in the same location for a number of days, thus avoiding practical issues concerning water supply and equipment location. Using these circles in a combination with a parcel rotation scheme allows for good grass management while still allowing execution of different experimental treatments combined with emission measurements.
Our method can easily be used by other research groups that face similar difficulties performing emission measurements in grazing cattle. It allows for an easier and more structured approach of performing emission measurements in grazing experiments and simultaneously reduces the labor time needed for correct execution of a trial. As the number of research experiments on restricted grazing using GreenFeed units described in scientific literature is still limited, this method may provide a basis for the development of other experimental setups where a high degree of labor efficiency is required. Evidently, the practical approach needs tailoring to the research needs and practical circumstances. Our method is an organizational innovation that helps improving the execution of research trials in this field. The set-up furthermore brings opportunities for companies developing methane mitigation strategies which they want to be tested on grazing herds or on herds where indoor housing is combined with restricted grazing.
Gathering high quality emission data from cows under farm conditions can be challenging. The GreenFeed performs measurements in a non-invasive way, but requires regular cow visits . This can be challenging in barns, but even more challenging on pasture. Cows need to be around the GreenFeed to remain triggered to visit it, whereas they may be distracted easily by fresh grass in the area. This often conflicts with the trial goals, which often implies maximizing grass intake and supply. A potential solution is strip grazing, implying that cows have daily access to a new strip of fresh grass to maximize grass intake. Labor and time restrictions, however, may make it impossible to move the GreenFeed and water supply daily, thus impairing the preferential experimental design of a grazing trial. Especially when different treatments are compared simultaneously, a high number of grass strips may be needed, and a lot of equipment relocating is necessary. Although the GreenFeed may be easily relocated when put on a trailer, moving the trailer once or several times a day would be time-consuming and potentially disturb the animals or damage the pasture. When combining different treatments with limited availability of measuring equipment (e.g. one GreenFeed indoor and one outdoor), it may be impossible to move the GreenFeed between pasturing periods from one strip to another, thus obstructing the goal of providing fresh, ungrazed strips of grass for each treatment. Additionally, when restricting grass intake it is needed to control the pasture surface and the amount of grass available to the cow. With normal strip grazing, this can be achieved by adjusting strip size daily based on the grass availability. When trying to limit relocation of the GreenFeed and water supply however, controlling the strip size and grass availability becomes difficult. We hence developed a way to combine feeding trials including highly-controlled grazing experiments with methane emission measurements.
Our way of trial execution provides a solution to the aforementioned problem. We succeeded to reduce labor and time requirements to execute emissions measurements in grazing trials, while still allowing a high degree of control over grass supply, intake and quality. More in detail, we reduced the need to move the measuring equipment with every new grass strip that is used in a strip grazing pasture management. In our approach, the drinking trough and GreenFeed system are located near a fence in the length of a parcel. The GreenFeed is placed on a custom made trailer equipped with the calibration gas tanks and solar panels, as well as an easy way to attach an electrical fence to the trailer to fence off the immediate area around the trailer for protection. A small semicircle of 15 m radius is fenced off, and an outer circle is formed maximizing the used surface area within the available pasture plot. Movable fences equipped with spins allow to fence off a circle sector between the inner and outer circle with minimal time and effort to form a fresh strip of grass. With this method, the GreenFeed and water supply can remain in their central location for several days or weeks depending on the parcel size and experimental setup. Even when comparing different grazing treatments, a new strip of grass can easily be fenced off for each treatment throughout the day, allowing an alternating use of the available pasture, thus providing a similar grass height and grass quality at the time of consumption to all treatments. This system hence minimizes variation in grass quality between treatments. Using semicircles, strip surface calculations combined with grass density measurements still allow for calculation of the needed strip size for treatments with a restricted grass intake. The calculated strip size can then easily be measured using circle chords. As such, our approach can be used in experiments where a high degree of control is required.
Other research groups could take up this method and further improve it for their research application. Our research method can be used as it is, but potentially improvements can be made. Although the GreenFeed unit is positioned central in the pasture strip provided to the animals and close to the drinking trough, measurements are not always successful for all animals. Some animals may not be willing to visit the GreenFeed voluntarily, or do not visit on a regular basis of several visits throughout the day. Further research could help to determine which influencing factors have an effect on animal behavior concerning the frequency of visits to the GreenFeed, and how these factors should be accounted for to construct measuring setups that provide successful data gathering. Such factors could for example be the surroundings of the measuring setup or the provided feed. More research could focus on verifying similarity of measurements performed indoors and outdoors, and between different GreenFeed units, since more than one GreenFeed unit is used in a trial using this method. Therefore, it would be interesting to develop a method to perform GreenFeed measurements based on the same input and compare the results. Aforementioned input could either be a group of cows receiving the same feed and amount of feed indoors and outdoors with no actual access to grass but with environmental influences such as wind or precipitation, or a system that can mimic gas emissions from a cow in a controllable and repeatable way.
