Pasture grazing for dairy cows can form an important part of sustainable milk production. In terms of productivity and cost effectiveness, it is a genuine alternative to other forms of farming.
Lush, fresh grass from the meadows – this is all cows need to produce excellent quality milk and meat. "Cows are essential for human nutrition, because they use biomass which we are unable to digest and turn it into a high value protein. On top of this, they do so at locations where arable farming is not possible," emphasized Dr Carsten Malisch from the Institute of Crop Science and Plant Breeding. He is an agricultural scientist who works in the Grass and Forage Science / Organic Agriculture department (headed by Professor Friedhelm Taube) and conducts research into how to optimise cow pasture grazing while also keeping the negative environmental consequences low at the same time. The greenhouse gas methane is a considerable aspect of research into cattle farming. According to Malisch, however, the important thing here is not to consider methane emissions on their own. This is where pasture grazing proves itself to be advantageous. "The feed is produced regionally, meaning it is not necessary to buy and transport extra soy concentrate from abroad where production may well be associated with cutting down rainforests. Plus grassland systems store a lot of carbon in the ground."
The European research project SusCatt, involving Kiel University as well as institutions from Norway, Sweden, Great Britain, Poland and Italy, has already proven that pasture feeding cows is competitive, also in terms of the amount of milk produced and its quality. The Kiel part of this joint project focused on the question as to whether the composition of pasture fodder made a difference to milk production and methane gas emission. To do so, two different seed mixtures for grassland were tested at the Lindhof ecological experimental farm: the standard grass/white clover mixture and a mixture containing eight different types of herb and legume. This diverse mixture also included species with a tannin content aimed at helping the animals' digestion and causing them to emit less methane. Lab tests confirmed that herbs containing tannin have the potential to do this, at least. Jersey dairy cows in Lindhof were divided into two groups and grazed on either the grass-clover meadow or the species-rich meadow. Throughout the course of one year, the milk produced by the cows was recorded and the methane amounts emitted were measured twice in two weeks.
A special technique was used to measure how much methane the cows emitted (see the info box). Cecilia Loza, who completed her doctoral degree in the Grass and Forage Science / Organic Agriculture department, already specialised in pasture grazing for dairy cows and methane emissions of grazing dairy cows during her Master's thesis at the Universidad de la República, Uruguay. In her doctoral thesis, she examined whether adding plants containing tannin to the feed improved milk production and could reduce methane emissions.
"It was actually the case that the cows which grazed on the species-rich meadow produced slightly more milk. But they ate more, too," explained Loza, who also documented how much the cows ate as well as the composition and quality of the fodder on the meadow. Contrary to expectations, however, a reduction in methane emissions was not proven. The slightly higher amount of milk produced on the species-rich meadow was associated with a slightly higher amount of methane.
"But with total emissions of eight to ten grammes of methane per kilogramme of standard milk, we are still at a very low level in comparison to the international literature," emphasized Malisch. He puts the fact that the tannin-rich species did not lead to the anticipated reduction in methane emissions down to the very small amounts of these plants. "The areas were intensively grazed, and they were simply unable to keep up in this system, because basically they don't grow fast enough." The agricultural scientist is proud of the very high amount of milk produced. "It was comparable with Jersey cows from another study, which consumed 61 percent concentrated feed in their ration at the same body weight." This is mostly the result of excellent feed quality and high amounts consumed on the meadow. "By rotating between areas, we ensured that the cows were always able to eat very new and easily-digestible pasture fodder."
Author: Kerstin Nees
Marker technique for measuring methane
The sulphur hexafluoride (SF6) marker technique was used in the SusCatt project to measure how much methane the dairy cows in the meadow produced. "This is one of the very few methods we are able to use in the meadow and which does not restrict the animals' movement, nor cause them any stress," explained the Kiel-based agricultural scientist, Dr Carsten Malisch. The other common way to measure is in the respiration chamber, where the animals are held in place in small spaces and where very accurate incoming and outgoing gases are measured, but this would not have been suitable for the project. A small capsule containing sulphur hexafluoride is placed in the forestomach system in the SF6 technique, which does not harm the animal in any way. "The gas is completely safe and is also used on people as a trace gas for X-rays. The advantage is that it does not react with the body at all, and is breathed out fully within a short time. We also clarified in advance with the Bioland association that we are allowed to use this technique in organic farming, because it has been completely proven that absolutely none of the gas ends up in the milk," emphasised Malisch. The test gas contained in the capsule is exhaled from the forestomach system at a steady rate. The measurements were conducted by fitting the cows with a rucksack holding two cylinders. The weight of this equipment was no problem for the animals. Tubes collected small amounts of breath from the animals' mouths. "As we know how much SF6 was emitted, we know the percentage of breath that was collected in the cylinders. We can then calculate how much methane the cow breathed out," explained the scientist. (ne)