WHILE University of Adelaide trials have shown byproduct feeds are not the magical, low-cost solution to reducing methane outputs in cattle while maintaining growth rates, they have shown they do have a valuable place within the feed structure if utilised properly.
University of Adelaide Animal Science professor Phil Hynd said there had been a worldwide search for feed additives which reduced methane output from cattle.
“The issue isn’t just that you produce methane, a very significant greenhouse gas, but it’s also a waste of energy, because 10 per cent of the feed energy gets lost as methane,” Prof Hynd said.
“If you can divert that energy away from methane into products the animal can use, then it’s a win-win because you get less greenhouse gas and you get more energy for the animal.”
That dilemma prompted researchers at the University of Adelaide to trial byproduct feeds such as grape marc – a waste product from the wine industry – at different percentages in a pasture-based diet to measure their impact on methane output, growth rates and feed cost.
“Producers often buy grape marc, it turns up in a truck and they dump it into a paddock,” Prof Hynd said.
“It’s wet and grows mould on the top, which is not a good thing because there’s potential for mycotoxins.”
University of Adelaide researcher Mariana Caetano said those moulds could also reduce the dry matter intake of the animals, meaning less energy was available to the herd.
Researchers said one alternative was to use dried grape marc, but that increased costs and made the feed unpalatable when fed as a supplement.
The researchers ensiled crimped grape marc, discovering it was a good product because of its long storage period and palatability.
Prof Hynd said grape marc was good as a slow growth, maintenance feed source during periods of low feed availability, but if producers had low protein it was not a great feed solution because tannins in the marc reduced protein availability.
“Our advice is these byproducts, particularly grape marc, can be included in rations but you’ve got to be careful how much you put in there – no more than 15pc – and you’ve got to be aware it’s not a great growth ration,” Prof Hynd said.
Researchers hope to finish another trial – evaluating the cost effectiveness of low, medium and high-inclusion of grape marc in beef cattle diets – in December and present their findings in January.
Prof Hynd said while feed additives that reduced methane output had a place in the feed structure, he urged producers to focus on fast growth as a way of reducing emissions.
