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Nitrogen efficiency in feed

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My name’s Chris Reynolds and I’m professor of animal and dairy science at the University of Reading, and director of the Centre for Dairy Research, which is where we are now. At the Centre for Dairy Research, we have a very active programme, looking at how we can manage dairy cows and feed dairy cows to reduce their environmental impact. So what I’d like to tell you about is some of that research and how it relates to the interactions between dairy production systems and climate change. In this paddock, we’ve established a series of forages that have different compositions. And this project that this paddock has been established for is looking at the potential benefits of multi-species swards as alternative to monoculture ryegrass swards.
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One of those is through the inclusion of legumes in that mixture. And legumes are important because they fix nitrogen from the atmosphere. So we don’t have to use as much nitrogen fertiliser in our swards when we include legumes. And this reduces the potential negative impacts of nitrogen fertiliser use in terms of nitrous oxide emissions that occur. And of course nitrous oxide is a very potent greenhouse gas. And also nitrates that may enter our watercourses which can cause eutrophication. So for example, in this sward, well it includes a certain amount of weeds because we just established it. But it includes ryegrass, and includes forbs like plantain and chicory.
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Now plantain and chicory are good feed for dairy cows, and they also have certain anthelmintic properties so they can actually be very useful in reducing our requirements for anthelmintic drugs in the animals that are grazing these swards. Another big benefit that we think may occur through the use of these multi-species swards is a number of these species have very deep rooting characteristics. So we’ve got roots that for some species that are relatively short, and others that it can be very deep. And this can be very useful in terms of benefiting the soil structure. But it also means that they can extract nutrients from lower down in the soil.
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So again, it can be of potential benefit, in terms of capturing nitrogen, and certain trace minerals. One of our other projects that we’re conducting, it’s been funded by DEFRA. And it’s about looking at the long term effects of feeding lower protein diets to dairy cows. We know that in the future, there will be increasing pressures on reducing the amount of protein that we feed to our cows. We’re checking to see what the long term implications of those lower protein diets might be, both positive and negative. Because when we feed cows lower protein diets, there’s a risk that we’ll be feeding cows protein below their requirements. And we want to make sure that doesn’t have any negative effects.
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One easy way that we can improve the efficiency is just to feed less. The less we feed, the more efficiently the cows use it. And that’s one of the strategies that people are using. Our work on protein efficiency has in part evolved from previous trials that we’ve been conducting here at the Centre for Dairy Research, looking at different feeding strategies by which we can reduce methane emissions from cows. And we’ve done a lot of work comparing different types of forages in particular. And other work has been focused on different types of supplements that we can add to the cows’ diets that might reduce their methane emissions.
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And one thing we’ve found is that diets that are higher in maize silage, partly because of the type of carbohydrate in that diet, the fibre and the starch. When we feed a higher maize silage diet, we tend to get less methane emission. But we don’t tend to, we do get less methane emission per unit of feed that the cow consumes. So just looking at it in terms of what the cow eats and how much methane they produce, there is this benefit of a higher starch diet, and a diet that’s higher in maize silage compared to grass silage. Now that doesn’t consider the environmental impacts in terms of the whole farming system.
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And there’s a lot of concern about growing maize and its impact on soil structure, and soil erosion, and carbon release from ploughing, and issues like that. We have to consider these approaches on a whole system basis because there are issues that can occur when we’re growing maize silage compared to grass silage.

The University of Reading is investigating how to make the dairy production system more sustainable. In this video, Professor Chris Reynolds talks about research on dairy cow nutrition, currently carried out by the School of Agriculture, Policy and Development.

As you watch this video, you may find this drawing of the nitrogen cycle useful. Nitrogen is important for plant growth and therefore a component of fertilisers. Nitrogen is also an important component of animal feed, but not all the nitrogen an animal ingests can be digested, which means that there is nitrogen in the manure. Both the application of manure and fertiliser to the land can result in N2O emissions. Bacteria living in symbiosis with legumes are able to fix nitrogen from the atmosphere, thereby increasing the amount of nitrogen in the soil naturally.

Infographic detailing the nitrogen cycle. It shows nitrogen in soil and the atmosphere being absorbed by grass and plants which are eaten by a cow. Nitrogen is then passed on in the cow's manure which is then absorbed by the soil.

Figure 1: Nitrogen cycle (Click to expand) © University of Reading

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